Abnormal growth of smooth muscle-like cells in lymphangioleiomyomatosis: Role for tumor suppressor TSC2

The TSC1 and TSC2 proteins, which function as a TSC1/TSC2 tumor suppressor complex, are associated with lymphangioleiomyomatosis (LAM), a genetic disorder characterized by the abnormal growth of smooth muscle-like cells in the lungs. The precise molecular mechanisms that modulate LAM cell growth remain unknown. We demonstrate that TSC2 regulates LAM cell growth. Cells dissociated from LAM nodules from the lungs of five different patients with LAM have constitutively activated S6K1, hyperphosphorylated ribosomal protein S6, activated Erk, and increased DNA synthesis compared with normal cells from the same patients. These effects were augmented by PDGF stimulation. Akt activity was unchanged in LAM cells. Rapamycin, a specific S6K1 inhibitor, abolished increased LAM cell growth. The full-length TSC2 was necessary for inhibition of S6 hyperphosphorylation and DNA synthesis in LAM cells, as demonstrated by co-microinjection of the C-terminus, which contains the GTPase activating protein homology domain, and the N-terminus, which binds TSC1. Our data demonstrate that increased LAM cell growth is associated with constitutive S6K1 activation, which is extinguishable by TSC2 expression. Loss of TSC2 GAP activity or disruption of the TSC1/TSC2 complex dysregulates S6K1 activation, which leads to abnormal cell proliferation associated with LAM disease.     

Tissue-specific renin-angiotensin system in pulmonary lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease found in middle-aged women, is characterized by cystic lung destruction and abdominal tumors (e.g., angiomyolipomas, lymphangioleimyomas), resulting from proliferation of abnormal-appearing, smooth muscle-like cells (LAM cells). The LAM cells, in combination with other cells, form nodular structures within the lung interstitium and in the walls of the cysts. LAM cells contain mutations in the tuberous sclerosis complex TSC1 and/or TSC2 genes, which lead to dysregulation of the mammalian target of rapamycin, affecting cell growth and proliferation. Proliferation and migration of vascular smooth muscle cells and production of angiogenic factors are regulated, in part, by angiotensin II. To determine whether a LAM-specific renin-angiotensin system might play a role in the pathogenesis of LAM, we investigated the expression of genes and gene products of this system in LAM nodules. mRNA for angiotensinogen was present in RNA isolated by laser-captured microdissection from LAM nodules. Angiotensin I-converting enzyme and chymase-producing mast cells were present within the LAM nodules. We detected renin in LAM cells, as determined by the presence of mRNA and immunohistochemistry. Angiotensin II type 1 and type II receptors were identified in LAM cells by immunohistochemistry and immunoblotting of microdissected LAM nodules. Angiotensin II is localized in cells containing alpha-smooth muscle actin (LAM cells). A LAM-specific renin-angiotensin system appears to function within the LAM nodule as an autocrine system that could promote LAM cell proliferation and migration, and could represent a pharmacologic target.     

Renal angiomyolipomas from patients with sporadic lymphangiomyomatosis contain both neoplastic and non-neoplastic vascular structures

Renal angiomyolipomas are highly vascular tumors that occur sporadically, in women with pulmonary lymphangiomyomatosis (LAM), and in tuberous sclerosis complex (TSC). The goal of this study was to determine whether the distinctive vessels of angiomyolipomas are neoplastic or reactive. We studied angiomyolipomas with loss of heterozygosity (LOH) in the TSC2 region of chromosome 16p13 from patients with LAM. We found that angiomyolipomas contain five morphologically distinct vessel types: cellular, collagenous, hemangiopericytic, glomeruloid, and aneurysmatic. Using laser capture microdissection, we determined that four of the vessel types have TSC2 LOH and are therefore neoplastic. One vessel type, collagenous vessels, did not have LOH, and is presumably reactive. Recently, activation of S6 Kinase and its target S6 ribosomal protein (S6) was demonstrated in cells lacking TSC2 expression. We found that angiomyolipoma vessel types in which LOH were detected were immunoreactive with anti-phospho-S6 antibodies. Angiomyolipoma cells without LOH, including the endothelial component of the vessels, were not immunoreactive. To our knowledge, angiomyolipomas are the first benign vascular tumor in which the vascular cells, rather than the stromal cells, have been found to be neoplastic. Angiomyolipomas appear to reflect novel vascular mechanisms that may be the result of activation of cellular pathways involving S6 Kinase.     

Pathogenesis of multifocal micronodular pneumocyte hyperplasia and lymphangioleiomyomatosis in tuberous sclerosis and association with tuberous sclerosis genes TSC1 and TSC2

Tuberous sclerosis (TSC) is a rare, genetically determined disorder / familial tumor syndrome, currently diagnosed using specific clinical criteria proposed by Gomez, including the presence of multiorgan hamartomas. Pulmonary involvement in TSC is well known as pulmonary lymphangioleiomyomatosis (LAM), which has an incidence of 1-2.3% in TSC patients. LAM has immunohistochemical expression of both smooth-muscle actin and a monoclonal antibody specific for human melanoma, HMB-45. It has recently been reported that multifocal micronodular pneumocyte hyperplasia (MMPH) associated with TSC should be considered as a distinct type of lung lesion, whether it occurs with or without LAM. Two predisposing genes have been found in families affected by TSC; approximately half of the families show linkage to TSC1 at 9q34.3, and the other half show linkage to TSC2 at 16p13.3. TSC genes are considered to be tumor suppressor genes, and mutations in them may lead to abnormal differentiation and proliferation of cells. Tuberin, the TSC2 gene product, has recently been found to be expressed in LAM and MMPH. In this article we discuss the histogenesis and genetic abnormalities of neoplastic lesions associated with TSC, and we review the current understanding of the pathogenesis of pulmonary hamartomatous lesions such as LAM and MMPH in TSC.     

Metastasis of benign tumor cells in tuberous sclerosis complex

Lymphangiomyomatosis (LAM) is a life-threatening lung disease affecting almost exclusively young women. Histologically, LAM is characterized by the diffuse, bilateral proliferation of abnormal smooth muscle cells and cystic degeneration of the lung parenchyma. LAM can occur as an isolated disorder (sporadic LAM), or in women with tuberous sclerosis complex (TSC-LAM). Patients with both sporadic LAM and TSC-LAM often have benign renal angiomyolipomas. The smooth muscle cells within the angiomyolipomas are very similar to the smooth muscle cells in pulmonary LAM. Genetic data suggest that pulmonary LAM is the result of a highly unusual disease mechanism: the metastasis of benign cells. If LAM is the result of metastasis, it is remarkable that the metastasis occurs in women, but not in men. In this review, I discuss the genetic data supporting this metastatic model for LAM. The implications of the model for the functions of the TSC1 and TSC2 gene products, hamartin and tuberin, respectively, will also be considered. Hamartin and tuberin may play functional roles in the suppression of cell migration and/or metastasis, possibly through their regulation of the small GTPase Rho.     

p27Kip1 modulates cell migration through the regulation of RhoA activation

The tumor suppressor p27(Kip1) is an inhibitor of cyclin/cyclin-dependent kinase (CDK) complexes and plays a crucial role in cell cycle regulation. However, p27(Kip1) also has cell cycle-independent functions. Indeed, we find that p27(Kip1) regulates cell migration, as p27(Kip1)-null fibroblasts exhibit a dramatic decrease in motility compared with wild-type cells. The regulation of motility by p27(Kip1) is independent of its cell-cycle regulatory functions, as re-expression of both wild-type p27(Kip1) and a mutant p27(Kip1) (p27CK(-)) that cannot bind to cyclins and CDKs rescues migration of p27(-/-) cells. p27(-/-) cells have increased numbers of actin stress fibers and focal adhesions. This is reminiscent of cells in which the Rho pathway is activated. Indeed, active RhoA levels were increased in cells lacking p27(Kip1). Moreover, inhibition of ROCK, a downstream effector of Rho, was able to rescue the migration defect of p27(-/-) cells in response to growth factors. Finally, we found that p27(Kip1) binds to RhoA, thereby inhibiting RhoA activation by interfering with the interaction between RhoA and its activators, the guanine-nucleotide exchange factors (GEFs). Together, the data suggest a novel role for p27(Kip1) in regulating cell migration via modulation of the Rho pathway.     

Osteoprotegerin Contributes to the Metastatic Potential of Cells with a Dysfunctional TSC2 Tumor-Suppressor Gene

In addition to its effects on bone metabolism, osteoprotegerin (OPG), a soluble member of the tumor necrosis factor family of receptors, promotes smooth muscle cell proliferation and migration and may act as a survival factor for tumor cells. We hypothesized that these cellular mechanisms of OPG may be involved in the growth and proliferation of lymphangioleiomyomatosis (LAM) cells, abnormal smooth muscle-like cells with mutations in one of the tuberous sclerosis complex tumor-suppressor genes (TSC1/TSC2) that cause LAM, a multisystem disease characterized by cystic lung destruction, lymphatic infiltration, and abdominal tumors. Herein, we show that OPG stimulated proliferation of cells cultured from explanted LAM lungs, and selectively induced migration of LAM cells identified by the loss of heterozygosity for TSC2. Consistent with these observations, cells with TSC2 loss of heterozygosity expressed the OPG receptors, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules showed reactivities to antibodies to tumor necrosis factor–related apoptosis-inducing ligand, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules also produced OPG, as shown by expression of OPG mRNA and colocalization of reactivities to anti-OPG and anti-gp100 (HMB45) antibodies in LAM lung nodules. Serum OPG was significantly higher in LAM patients than in normal volunteers. Based on these data, it appears that OPG may have tumor-promoting roles in the pathogenesis of lymphangioleiomyomatosis, perhaps acting as both autocrine and paracrine factors.Osteoprotegerin (OPG; TNFRSF11B), a soluble member of the tumor necrosis factor (TNF) receptor family, is best known as a regulator of bone metabolism that promotes bone formation by inhibiting osteoclast development, thus protecting against osteoporosis.^1,2 OPG, acting as a decoy receptor, binds to receptor activator of NF-κB ligand (RANKL), preventing the interaction of RANKL with its receptor RANK, resulting in the inhibition of osteoclast activation and bone resorption. Polymorphisms in the OPG gene have been linked to development of osteoporosis.^3–6 Patients with juvenile Paget disease, a rare inherited disease affecting children, show increased bone turnover, leading to skeletal deformity. Mutations in the OPG gene determine the severity of the juvenile Paget disease phenotype,⁷ with the loss of the entire gene or mutations leading to the loss of OPG structure resulting in a severe phenotype.More recently, the role of OPG in vascular cell biological characteristics has been studied. OPG knockout mice have both severe osteoporosis and significant arterial calcification,⁸ suggesting that OPG plays a protective role against arterial calcification in mice. OPG serum levels are associated with the severity of cardiovascular disease in humans.^9–11 OPG levels may be higher either directly, through a proatherosclerotic effect, or indirectly, because of an incomplete compensatory mechanism in which increases in serum OPG levels are seen as a response to RANKL activity.^9–11 This compensatory effect may also be invoked to explain high serum levels of OPG, sometimes seen in subjects with osteoporosis.¹²Vascular smooth muscle cells express OPG, and aortic smooth muscle cells proliferate in response to OPG.¹³ OPG induced both the proliferation and migration of pulmonary artery smooth muscle cells¹⁴ and human microvascular endothelial cells.¹⁵ The effects of OPG on human microvascular endothelial cells were mediated through integrins α_Vβ₃ and α_Vβ₅ and the extracellular signal–regulated kinase 1/2. OPG can also stimulate monocyte migration; this effect was shown to involve syndecans and phosphatidylinositol-3-OH kinase/Akt, protein kinase C, and tyrosine kinases.¹⁶OPG also has roles in tumor development and metastasis.^17,18 OPG can bind TNF-related apoptosis-inducing ligand (TRAIL), blocking TRAIL’s apoptotic effects on cancer cells.^19–23 Serum OPG levels may be higher in cancer patients compared with healthy controls, and levels may correlate with cancer stage.^24–27 Tumor growth and metastasis are also supported by OPG’s promotion of endothelial cell survival and angiogenesis.^28,29 Interestingly, some malignant breast cancer tumors show endothelial OPG expression, whereas neighboring normal endothelium does not express high levels of the protein.²⁹Lymphangioleiomyomatosis (LAM) cells are abnormal neoplastic smooth muscle-like cells, with mutations in one of two tuberous sclerosis complex tumor-suppressor genes (TSC1 or TSC2). TSC1 (encoding hamartin) and TSC2 (tuberin) form a complex that regulates the serine/threonine kinase, mammalian target of rapamycin.³⁰ Mutations in TSC1/TSC2 lead to uncontrolled mammalian target of rapamycin activity, resulting in increased cell proliferation and size.³⁰ These LAM cells form nodules covered with type II pneumocytes, with surrounding areas of cystic destruction in the lungs of patients with LAM. In addition to the cystic destruction of lung parenchyma, LAM, a rare multisystem disease affecting women,³¹ is characterized by lymphatic abnormalities and abdominal tumors (eg, angiomyolipomas). LAM cells can metastasize, as LAM cells from lung lesions and angiomyolipomas in the same patient have the same TSC2 mutation.³² Consistent with their migratory behavior, LAM cells have been isolated from blood and other body fluids of patients with LAM.^33,34 LAM cells have characteristics of both smooth muscle cells, such as reactivity with antibodies to smooth muscle actin and desmin, and of melanocytes, with reactivity with HMB45,³⁵ an antibody recognizing gp100, a melanosomal protein.^36–38In this study, we investigated the effect of OPG on the neoplastic smooth muscle cell-like LAM cells. OPG promoted proliferation of cells grown from explanted LAM lungs and specifically induced LAM cell migration. Three OPG receptors, RANKL, syndecan-1, and syndecan-2, were detected on LAM cells and LAM lung nodules. Furthermore, LAM cells produced OPG, and OPG levels were elevated in serum from patients with LAM compared with healthy volunteers, suggesting both autocrine and paracrine effects of OPG in LAM.     

Mutation analysis of the TSC1 and TSC2 genes in Japanese patients with pulmonary lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is a destructive lung disease characterized by a diffuse hamartomatous proliferation of smooth muscle cells (LAM cells) in the lungs. Pulmonary LAM can occur as an isolated form (sporadic LAM) or in association with tuberous sclerosis complex (TSC) (TSC-LAM), a genetic disorder with autosomal dominant inheritance with various expressivity resulting from mutations of either the TSC1 or TSC2 gene. We examined mutations of both TSC genes in 6 Japanese patients with TSC-LAM and 22 patients with sporadic LAM and identified six unique and novel mutations. TSC2 germline mutations were detected in 2 (33.3%) of 6 patients with TSC-LAM and TSC1 germline mutation in 1 (4.5%) of 22 sporadic LAM patients. In accordance with the tumor-suppressor model, loss of heterozygosity (LOH) was detected in LAM cells from 3 of 4 patients with TSC-LAM and from 4 of 8 patients with sporadic LAM. Furthermore, an identical LOH or two identical somatic mutations were demonstrated in LAM cells microdissected from several tissues, suggesting LAM cells can spread from one lesion to another. Our results from Japanese patients with LAM confirmed the current concept of pathogenesis of LAM: TSC-LAM has a germline mutation but sporadic LAM does not; sporadic LAM is a TSC2 disease with two somatic mutations; and a variety of TSC mutations causes LAM. However, our study indicates that a fraction of sporadic LAM can be a TSC1 disease; therefore, both TSC genes should be examined, even for patients with sporadic LAM. Received: August 30, 2001 / Accepted: November 2, 2001     

Mutational analysis of the tuberous sclerosis gene TSC2 in patients with pulmonary lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is a rare disorder limited almost exclusively to women of reproductive age. LAM affects about 5% of women with tuberous sclerosis complex (TSC). LAM also occurs in women who do not have TSC (sporadic LAM). TSC is a tumour suppressor gene syndrome characterised by seizures, mental retardation, and tumours in the brain, heart, and kidney. Angiomyolipomas, which are benign tumours with smooth muscle, fat, and dysplastic vascular components, are the most common renal tumour in TSC. Renal angiomyolipomas also occur in 63% of sporadic LAM patients. We recently found that 54% of these angiomyolipomas have TSC2 loss of heterozygosity, leading to the hypothesis that sporadic LAM is genetically related to TSC. In this study, we screened DNA from 21 women with sporadic LAM for mutations in all 41 exons of TSC2. Twelve of the patients had known renal angiomyolipomas. No TSC2 mutations were detected. We did find three silent TSC2 polymorphisms. We conclude that patients with sporadic LAM, including those with renal angiomyolipomas, do not have a high frequency of germline mutations in the coding region of TSC2.     

Development of a Lymphangioleiomyomatosis Model by Endonasal Administration of Human TSC2(-/-) Smooth Muscle Cells in Mice

Lymphangioleiomyomatosis (LAM) is an interstitial lung disease characterized by invasion and proliferation of abnormal smooth muscle (ASM) cells in lung parenchyma and axial lymphatics. LAM cells bear mutations in tuberous sclerosis (TSC) genes. TSC2(-/-) ASM cells, derived from a human renal angiomyolipoma, require epidermal growth factor (EGF) for proliferation. Blockade of EGF receptors (EGFR) causes cell death. TSC2(-/-) ASM cells, previously labeled with PKH26-GL dye, were endonasally administered to 5-week-old immunodeficient female nude mice, and 4 or 26 weeks later anti-EGFR antibody or rapamycin was administered twice a week for 4 consecutive weeks. TSC2(-/-) ASM cells infiltrated lymph nodes and alveolar lung walls, causing progressive destruction of parenchyma. Parenchymal destruction was efficiently reversed by anti-EGFR treatment and partially by rapamycin treatment. Following TSC2(-/-) ASM cell administration, lymphangiogenesis increased in lungs as indicated by more diffuse LYVE1 expression and high murine VEGF levels. Anti-EGFR antibody and rapamycin blocked the increase in lymphatic vessels. This study shows that TSC2(-/-) ASM cells can migrate and invade lungs and lymph nodes, and anti-EGFR antibody is more effective than rapamycin in promoting lung repair and reducing lymphangiogenesis. The development of a model to study metastasis by TSC cells will also help to explain how they invade different tissues and metastasize to the lung.     

Multifocal micronodular pneumocyte hyperplasia and lymphangioleiomyomatosis in tuberous sclerosis with a TSC2 gene.

A 45-year-old woman with a long-standing diagnosis of tuberous sclerosis (TSC) is presented. She has multifocal micronodular pneumocyte hyperplasia (MMPH) and lymphangioleiomyomatosis (LAM) of the lung, together with the detection of TSC2 gene mutation. During surgery for spontaneous pneumothorax, an open-lung biopsy was performed. Micronodules were well defined, measuring approximately 4 mm in diameter. These MMPHs were histologically composed of papillary proliferation of Type II pneumocytes, with positive immunoreactivity of keratin and surfactant apoprotein. The cystlike spaces, with dilatation and destruction of air spaces, were diffusely formed, and the walls were composed of the spindle cells. Such LAM showed positive immunoreactivity for HMB-45 (a monoclonal antibody specific for human melanoma) and tuberin (the gene product of TSC2). On germline mutation analysis using leukocytes of the present patient, a TSC2 gene mutation was confirmed as a deletion of G (or g) on Exon 9 by polymerase chain reaction-single-strand conformational polymorphism. However, no mutation was detected in her son. With microdissection analysis using paraffin-embedding lung tissues, LOH of the TSC2 gene preliminarily was detected in a LAM lesion but not in MMPH. It is suggested that MMPH, in addition to LAM, could be another pulmonary lesion in TSC patients and that the detection of TSC2 and/or TSC1 gene could essentially be useful for the pathogenesis of MMPH and LAM in TSC patients.     

Matrix proteoglycans and remodelling of interstitial lung tissue in lymphangioleiomyomatosis

The interstitial lung disease lymphangioleiomyomatosis (LAM) is characterized by diffuse proliferation of smooth muscle cells (SMCs), which in many patients show TSC2 (tuberin) gene mutations, in addition to thickening of interstitial tissues, loss of alveoli, and the development of cystic spaces. While SMC proliferation is the defining feature of LAM, a significant proportion of LAM lung tissue consists of expanded interstitial connective tissue that is negative for smooth muscle actin and TSC2 mutations. The importance of this actin-negative interstitial tissue to the pathophysiology of LAM is not clear. The present study has determined the contribution of this interstitial tissue to LAM lung volume by morphometric analysis and has examined its cell and matrix proteoglycan composition by immunohistochemistry. Lung tissue from nine LAM patients and four control subjects was examined. LAM lung contained twice as much interstitial tissue as control lung (27% versus 13% of total lung volume), with SMCs accounting for less than 25% of the interstitial volume. Areas of interstitial tissue stained strongly for the matrix proteoglycans versican and biglycan. Decorin was prominent in association with collagen bundles. SMCs did not stain, or stained lightly, for proteoglycans. Versican and biglycan deposits were closely associated with actin-negative interstitial fibroblasts identified by prolyl 4-hydroxylase immuno-staining. Comparatively normal alveolar walls in LAM lung also stained strongly for versican and had a reduced elastin content. Thickened interstitial regions contained significant amounts of elastin (approximately 13% of interstitial volume) but with fibres in disorganized patterns. Elastic fibres were absent from areas that stained strongly for versican and biglycan. These areas also showed weak staining for elastin binding protein (EBP), consistent with proteoglycan-induced shedding of EBP and inhibition of elastic fibre formation. These findings point to a significant contribution from matrix proteoglycans to the expanded and remodelled interstitial lung tissue of LAM patients.     

Selected case from the Arkadi M. Rywlin International Pathology Slide Seminar: Sporadic lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a systemic, progressive, and fatal condition affecting almost exclusively women in their reproductive years. LAM most often occurs as a sporadic disease, but also occurs in women with tuberous sclerosis complex (TSC) (syndromic LAM). There are no pathologic differences between sporadic and syndromic LAM. Sporadic LAM is a rare disease with prevalence of approximately 1 to 2 cases per million women in the United States and among populations of white descent, and is even rarer among Asian and African individuals. Syndromic LAM affects 4% to 5% of women with TSC. Sporadic LAM is often found also in association with renal angiomyolipoma, the most common sign of TSC, but LAM associated with angiomyolipoma does not define TSC. Although LAM is not diagnostic for TSC either in isolation or in association with angiomyolipoma, still it is considered by some researchers as an incomplete expression (forme fruste) of TSC. LAM may involve the lungs and the axial lymphatics and lymph nodes of the thorax and retroperitoneum. In sporadic LAM, thoracic, intraabdominal, and cervical lymph nodes can be involved with or without lung involvement. The diagnosis of LAM is often delayed. A case of LAM in a young lady, which was complicated with pleural and peritoneal chylous effusions, is presented. The diagnosis was first made on a retroperitoneal lymph node biopsy. The patient had a prolonged prior history of respiratory problems owing to lung involvement, and eventually died 2 years after diagnosis. Focus on the clinicopathologic diagnosis of TSC is also made.     

Arylsulfatase B regulates colonic epithelial cell migration by effects on MMP9 expression and RhoA activation

Arylsulfatase B (ASB; N-acetylgalactosamine-4-sulfatase; 4-sulfatase; ARSB) is the enzyme that removes 4-sulfate groups from N-acetylgalactosamine 4-sulfate, which combines with glucuronate to form the disaccharide unit of chondroitin-4-sulfate (C4S). In this study, we report how variation in expression of ASB affected the migration of human colonic epithelial cells. In the T84 cell line, derived from lung metastasis of malignant colonic epithelial cells, the activity of ASB, as well as steroid sulfatase, arylsulfatase A, and galactose-6-sulfatase, were significantly less than in normal, primary colonic epithelial cells and in the NCM460 cell line which was derived from normal colonocytes. In the T84 cells, matrix metalloproteinase 9 (MMP9), activated RhoA, and cell migration, as well as C4S content, were significantly more than in the NCM460 cells. Silencing and overexpression of ASB had inverse effects on MMP9, activated RhoA, and cell migration, as well as the C4S content, in the NCM460 and T84 cells. When ASB expression was silenced by siRNA in the NCM460 cells, MMP9 secretion increased to over 3 times the basal level, activated RhoA increased ~85%, and cell migration increased ~52%. Following overexpression of ASB, MMP9 declined 51%, activated RhoA declined ~51%, and cell migration decreased ~37%. These findings demonstrate marked effects of ASB expression on the migratory activity of colonic epithelial cells, activated RhoA, and MMP9, and suggest a potential vital role of ASB, due to its impact on chondroitin sulfation, on determination of the invasive phenotype of colonic epithelial cells.     

BTG2 suppresses cancer cell migration through inhibition of Src-FAK signaling by downregulation of reactive oxygen species generation in mitochondria

BTG2 is a tumor suppressor gene. It is frequently downregulated in human cancer tissues, and its loss is associated with cancer cell metastasis, suggesting that the suppression of BTG2 plays a critical role in cancer cell migration and invasion. Here, we report that re-expression of BTG2 decreased cell migration and invasion in A549 and PC3 cancer cells. Furthermore, BTG2 expression was correlated with downregulation of focal adhesion kinase (FAK) Tyr576 and Tyr925 residues phosphorylation, while Tyr397 which is the autophosphorylation site was not influenced by BTG2 expression. c-Src phosphorylation which is the upstream of FAK was not influenced, whereas c-Src kinase activity was significantly decreased by BTG2 expression. BTG2 overexpression increased Src reduction state and inhibited reactive oxygen species (ROS) generation by being localized in mitochondria. Mitochondria-target BTG2 also inhibited cell migration via downregulation of Src-FAK signaling. In conclusion, our study reveals that BTG2 negatively regulated cancer cell migration by inhibiting Src activity through downregulation of ROS generation in mitochondria.     

Tuberin Regulates E-Cadherin Localization: Implications in Epithelial-Mesenchymal Transition

The tuberous sclerosis complex 2 (TSC2) gene encodes the protein tuberin, which functions as a key negative regulator of both mammalian target of rapamycin (mTOR) C1-dependent cell growth and proliferation. Loss-of-function mutations of TSC2 result in mTORC1 hyperactivity and predispose individuals to both tuberous sclerosis and lymphangioleiomyomatosis. These overlapping diseases have in common the abnormal proliferation of smooth muscle-like cells. Although the origin of these cells is unknown, accumulating evidence suggests that a metastatic mechanism may be involved, but the means by which the mTOR pathway contributes to this disease process remain poorly understood. In this study, we show that tuberin regulates the localization of E-cadherin via an Akt/mTORC1/CLIP170-dependent, rapamycin-sensitive pathway. Consequently, Tsc2(−/−) epithelial cells display a loss of plasma membrane E-cadherin that leads to reduced cell-cell adhesion. Under confluent conditions, these cells detach, grow in suspension, and undergo epithelial-mesenchymal transition (EMT) that is marked by reduced expression levels of both E-cadherin and occludin and increased expression levels of both Snail and smooth muscle actin. Functionally, the Tsc2(−/−) cells demonstrate anchorage-independent growth, cell scattering, and anoikis resistance. Human renal angiomyolipomas and lymphangioleiomyomatosis also express markers of EMT and exhibit an invasive phenotype that can be interpreted as consistent with EMT. Together, these results suggest a novel relationship between TSC2/mTORC1 and the E-cadherin pathways and implicate EMT in the pathogenesis of tuberous sclerosis complex-related diseases.Mutation of the TSC2 gene gives rise to the autosomal dominant disorder, tuberous sclerosis complex (TSC), that is characterized by “hamartomas” in the brain, kidney, skin, heart, and lung.¹ Genetic and biochemical analyses have highlighted the role of the TSC2 protein, tuberin, in concert with its interacting partner, TSC1 (hamartin), in negatively regulating mammalian target of rapamycin (mTOR) C1 by promoting the hydrolysis of Rheb-GTP.² Multiple factors including growth factors, energy, and oxygen availability converge on the TSC1/TSC2 complex to modulate mTORC1 activity.³ The best characterized function of mTORC1 is the promotion of protein synthesis through its downstream targets, p70S6K and 4E-BP1. In turn, p70S6K mediates phosphorylation of IRS-1 to inhibit phosphatidylinositol 3-kinase/AKT signaling in a negative feedback mechanism.⁴ Consequently, the loss of TSC1 or TSC2 leads to an “overgrowth” phenotype with increased cell size and proliferation, characteristic of the hamartomas seen in tuberous sclerosis. However, many of the clinical and pathological features of TSC remain unexplained by our current understanding of the function of these genes.One such example is the lymphangioleiomyomatosis (LAM) that occurs in ∼40% of females diagnosed with TSC.⁵ The sporadic form of LAM is also associated with mutation of the TSC2 gene.⁶ LAM is a unique disease that affects women of childbearing age and is characterized by the infiltration of smooth muscle-like cells in the lung interstitium, which eventually leads to the progressive loss of pulmonary function and cystic destruction of the lung.⁷ Although LAM is not exclusive to the lungs and can involve the axial lymphatic system and other organs, mortality due to respiratory failure takes place within 8 to 15 years after diagnosis.⁸ LAM and angiomyolipoma (AML) are classified as perivascular epithelioid cell neoplasms), that is, defined as “mesenchymal tumors composed of histologically and immunohistochemically distinctive perivascular epithelioid cells.”⁹ These tumors are characterized histologically by their epithelioid appearance and their physical relationship to blood vessels.⁹ The abnormal cells display a distinct immunophenotype that includes the expression of melanocytic (eg, gp100) and smooth muscle markers (eg, smooth muscle actin) but not epithelial antigens. Because perivascular epithelioid cells have no normal anatomical counterpart, the origin of these tumors remains elusive.One current theory suggests that pulmonary LAM is the result of a metastatic process in which certain precursor cells migrate to the lung and invade the parenchyma.¹⁰ Indeed, primary LAM cells have been shown to be invasive in vitro,¹¹ and these cells have been identified in body fluids, including blood and urine, suggesting that LAM cells are capable of detaching from their primary sites and entering the circulation.¹² Further evidence in support of this hypothesis comes from the observations that pulmonary recurrences of LAM after lung transplant contain cells that originated from the organ recipients,^13,14 and common patterns of TSC2 mutation have been identified in LAM and lymph node disease from the same individual.¹⁵ Finally, the unique immunophenotype in LAM does not reflect an epithelial nor mesenchymal origin but rather a mixture of “epithelioid” and “spindle” cells that is suggestive of a variable differentiation pattern.¹⁶ Nonetheless, both populations of cells are believed to be clonally derived. The spindle cells are reported to be more proliferative and express smooth muscle actin, whereas the epithelioid cells express the melanocytic markers (eg, HMB-45) and are less mitotically active. Collectively, the observed behavior of LAM cells with respect to their infiltrative growth pattern, metastatic potential, and altered cell differentiation is reminiscent of cells undergoing epithelial-mesenchymal transition (EMT).^17,18 Here, we propose that LAM may be a manifestation of EMT and show that human AML and LAM do indeed express markers of EMT.One of the critical steps driving EMT is the repression of E-cadherin, resulting in loss of cell-cell adhesion. E-cadherin is expressed in most epithelial cells in which adherens junctions are formed to create the multicellular organization important for the formation and maintenance of bodily compartments. Structural studies highlight the essential role of calcium in the progressive cis-dimerization of the cadherin ectodomain, leading to the formation of a trans-dimer “zipper” between multiple cis-dimers to form cell adhesion.¹⁹ In this study, we provide evidence that E-cadherin membrane localization is regulated by the Akt/mTORC1 pathway such that the loss of TSC2 leads to significant reduction in membrane E-cadherin. Consequently, cells deficient in Tsc2 are less adhesive and more prone to detach and to undergo EMT. Our findings highlight a novel functional link between tuberin and E-cadherin activity that may contribute to the pathogenesis of TSC and related disorders.     

Glutamine synthetase interpretation in hepatocellular adenoma

Lymphangioleiomyomatosis (LAM) of the lung is a rare low-grade malignancy affecting primarily women of childbearing age. LAM is characterized by the proliferation of SMA and HMB-45 positive spindle-shaped and epithelioid cells throughout the lung in the form of discrete lesions causing cystic destruction and ultimately respiratory insufficiency. LAM occurs sporadically or in patients with tuberous sclerosis complex (TSC) and is etiologically linked to mutations in the TSC1 and TSC2 genes. Although LAM cells are known to express estrogen and progesterone receptors (ER and PR, respectively), their respective expression level was never determined. Therefore, here we measured the immunohistochemical expression of ERs and PRs in a large series of pulmonary LAM cases using the Aperio Spectrum Analysis Platform. Our case series comprised open lung biopsy specimens from 20 LAM patients and lungs explanted during the course of lung transplant from 24 patients. All cases were positive for ER and PR. PR expression was statistically significantly higher than ER in 80 % of the biopsies while ER predominated only in one case. Specimens from explanted cases of LAM had relatively fewer PR-positive nuclei. As a result, PR expression was significantly higher than ER in 38 % of the cases, whereas ER predominated in 33 %. Overall, PR expression predominated in 57 % of cases and ER in 21 %. These data indicate that PR frequently prevails over ER in pulmonary LAM. LAM is unusual in its high PR/ER ratio; other female neoplasms show a definite prevalence of ER. Our findings therefore warrant further study of PR function in LAM.     

NGAL knockdown by siRNA in human cholangiocarcinoma cells suppressed invasion by reducing NGAL/MMP-9 complex formation

We studied the role of Neutrophil Gelatinase-associated Lipocalin (NGAL, lipocalin 2) in regulating the invasiveness of a cholangiocarcinoma cell line, RMCCA-1. RMCCA-1 cells expressed multiple forms of 25, 40, 75 and 115/135 kDa NGAL which were detected in the conditioned medium, whereas only the 25 kDa form was detected in the cell lysates. NGAL expression was induced by serum deprivation. NGAL downregulation by siRNA suppressed NGAL mRNA and protein expression by about 70–80%, concommittant with a significant reduction of in vitro invasiveness, migration and pro-MMP-9 activity, but not cell proliferation. Suppression of pro-MMP-9 activity paralleled a reduction of NGAL/MMP-9 complex in the conditioned medium, although MMP-9 mRNA expression was unaffected. Our data suggest that NGAL promotes the invasiveness of the cholangiocarcinoma cells by forming complex with MMP-9, stabilizing its activity and rendering the cancer cells to be more invasive.     

Molecular pathogenesis of lymphangioleiomyomatosis: lessons learned from orphans

Lymphangioleiomyomatosis (LAM) is a rare progressive cystic lung disease affecting young women. The pivotal observation that LAM occurs both spontaneously and as part of the tuberous sclerosis complex (TSC) led to the hypothesis that these disorders share common genetic and pathogenetic mechanisms. In this review we describe the evolution of our understanding of the molecular and cellular basis of LAM and TSC, beginning with the discovery of the TSC1 and TSC2 genes and the demonstration of their involvement in sporadic (non-TSC) LAM. This was followed by rapid delineation of the signaling pathways in Drosophila melanogaster with confirmation in mice and humans. This knowledge served as the foundation for novel therapeutic approaches that are currently being used in human clinical trials.     

Wiskott-Aldrich syndrome protein (WASp) and N-WASp are involved in the regulation of NK-cell migration upon NKG2D activation

NKG2D is a transmembrane receptor mainly expressed on CD8(+) T cells and NK cells. Engagement of NKG2D with its ligands can trigger a cytotoxic response. It has been shown that tumor cells deliver soluble NKG2D ligands as a mechanism of immune evasion through the downregulation of surface-expressed NKG2D. These ligands may be also secreted in microvesicles and regulate NK-cell function, but the existence of alternative mechanisms has not been explored. In this study, we describe that NKG2D activation inhibits NK-cell chemotaxis toward a CXCL12 gradient. Costimulation of the inhibitory receptor NKG2A rescues NK-cell migration rates. Thus, the balance of NKG2D/NKG2A activation may determine the migratory ability of NK cells. Furthermore, our data indicated that NKG2D cross-linking induces the activation of the Rho GTPases Rac1 and Cdc42, while RhoA activity is decreased. Pharmacological inhibition of the Cdc42 effectors Wiskott-Aldrich syndrome protein (WASp)/N-WASp, and the reduction of their levels using RNA interference partially abolished NKG2D-mediated impairment of cell migration, suggesting a pivotal role of Cdc42 in the regulation of NK-cell migration by NKG2D activation. Therefore, our results provide a new mechanism that may contribute to the immune response or evasion in tumors.