Selection of Potentially Metastatic Subpopulations Expressing c-erbB-2 from Breast Cancer Tissue by Use of an Extravasation Model

Overexpression of the c-erbB-2 gene-encoded p185^c-erbB-2 is correlated with early onset of metastasis in breast cancer patients. Furthermore, the detection of blood-borne epithelium-derived clustered cells expressing p185^c-erbB-2 was related to advanced stages in breast cancer. To further elucidate the receptor’s function in the metastatic process of human breast cancers, we analyzed disaggregated cells and cell clusters from freshly dissected breast cancer tissues. We studied whether their capability of extravasation is correlated with their expression of c-erbB-2. A model for the venular wall was constructed by growing human umbilical vein endothelial cells (HUVECs) on porous membranes coated with basement membrane extracellular matrix. In four control breast cancer cell lines (SK-BR-3, MCF-7, MDA-MB-468, and MDA-MB-468, the latter transfected with a full-length c-erbB-2 cDNA vector) producing different levels of the c-erbB-2 receptor, the expression level correlated positively with the invasiveness of the cells. The invasive, predominantly clustered cells from 14 of 23 tumors were positively stained for p185^c-erbB-2 by immunocytochemistry. Furthermore, we show that the invasive cell populations express the metastasis-associated proteins matrix metalloproteinase MMP-2, CD44, and integrins αvβ3 and α6. In this first study on the behavior of cells and cell clusters from disaggregated operated cancers in an extravasation model, we could demonstrate the presence of c-erbB-2-expressing cell subpopulations within the individual breast cancers that are presumably of high metastatic potential.     

Paracrine overexpression of insulin-like growth factor-1 enhances mammary tumorigenesis in vivo

Insulin-like growth factor-1 (IGF-1) stimulates proliferation, regulates tissue development, protects against apoptosis, and promotes the malignant phenotype in the breast and other organs. Some epidemiological studies have linked high circulating levels of IGF-1 with an increased risk of breast cancer. To study the role of IGF-1 in mammary tumorigenesis in vivo, we used transgenic mice in which overexpression of IGF-1 is under the control of the bovine keratin 5 (BK5) promoter and is directed to either the myoepithelial or basal cells in a variety of organs, including the mammary gland. This model closely recapitulates the paracrine exposure of breast epithelium to stromal IGF-1 seen in women. Histologically, mammary glands from transgenic mice were hyperplastic and highly vascularized. Mammary glands from prepubertal transgenic mice had significantly increased ductal proliferation compared with wild-type tissues, although this difference was not maintained after puberty. Transgenic mice also had increased susceptibility to mammary carcinogenesis, and 74% of the BK5.IGF-1 mice treated with 7,12-dimethylbenz[a]anthracene (20 μg/day) developed mammary tumors compared with 29% of the wild-type mice. Interestingly, 31% of the vehicle-treated BK5.IGF-1 animals, but none of the wild-type animals, spontaneously developed mammary cancer. The mammary tumors were moderately differentiated adenocarcinomas that expressed functional, nuclear estrogen receptor at both the protein and mRNA levels. These data support the hypothesis that tissue overexpression of IGF-1 stimulates mammary tumorigenesis.     

Activation of AMP-Activated Protein Kinase Prevents TGF-β1–Induced Epithelial-Mesenchymal Transition and Myofibroblast Activation

Transforming growth factor (TGF)-β contributes to tubulointerstitial fibrosis. We investigated the mechanism by which TGF-β exerts its profibrotic effects and specifically the role of AMP-activated protein kinase (AMPK) in kidney tubular epithelial cells and interstitial fibroblasts. In proximal tubular epithelial cells, TGF-β1 treatment causes a decrease in AMPK phosphorylation and activation together with increased fibronectin and α-smooth muscle actin expression and decreased in E-cadherin. TGF-β1 causes similar changes in interstitial fibroblasts. Activation of AMPK with 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside, metformin, or overexpression of constitutively active AMPK markedly attenuated TGF-β1 functions. Conversely, inhibition of AMPK with adenine 9-β-d-arabinofuranoside or siRNA-mediated knockdown of AMPK (official name PRKAA1) mimicked the effect of TGF-β1 and enhanced basal and TGF-β1–induced phenotypic changes. Importantly, we found that tuberin contributed to the protective effects of AMPK and that TGF-β1 promoted cell injury by blocking AMPK-mediated tuberin phosphorylation and activation. In the kidney cortex of TGF-β transgenic mice, the significant decrease in AMPK phosphorylation and tuberin phosphorylation on its AMPK-dependent activating site was associated with an increase in mesenchymal markers and a decrease in E-cadherin. Collectively, the data indicate that TGF-β exerts its profibrotic action in vitro and in vivo via inactivation of AMPK. AMPK and tuberin activation prevent tubulointerstitial injury induced by TGF-β. Activators of AMPK provide potential therapeutic strategy to prevent kidney fibrosis and progressive kidney disease.Tubulointerstitial fibrosis is a prominent pathologic feature of progressive renal disease that culminates in loss of renal function. Inflammatory and metabolic insults result in kidney fibrosis in which transforming growth factor (TGF)-β plays a prominent role. Tubular epithelial cells and interstitial fibroblast contribute to this process by secreting and remodeling the extracellular matrix. In progressive fibrotic renal disease, TGF-β causes proximal tubular epithelial cells (PTECs) to acquire mesenchymal cell characteristics sometimes referred to as epithelial-mesenchymal transition (EMT).¹ In the presence of TGF-β, interstitial fibroblasts are also activated, differentiate to myofibroblasts, and contribute to the accumulation of extracellular matrix proteins. Accumulation of matrix proteins progressively destroys the normal kidney tissue architecture and disrupts blood flow and nephron function.² The increase in TGF-β1 levels is causally linked to the activation of profibrotic signaling pathways initiated by angiotensin, glucose, and oxidative stress.³ There is substantial evidence supporting a role for AMP-activated protein kinase (AMPK) in multiple diseases, including diabetes mellitus,^4,5 metabolic syndrome,^6–9 and cancer.^10,11 However, the role of AMPK in renal disease is underexplored. AMPK is a phylogenetically conserved serine/threonine kinase that regulates diverse cellular functions.¹² AMPK is heterotrimeric complex comprising a catalytic α (α1, α2) subunit and two regulatory subunits β (β1, β2) and γ (γ1, γ2, γ3). The activity and subunit composition of AMPK are expressed in a cell- and tissue-specific manner, with the α₁ and α₂ subunits expressed in the kidney, including tubular epithelial cells and glomerular cells.^13,14 AMPK activation leads to its phosphorylation at Thr172 in the catalytic domain of the α-subunit. AMPK can also be activated independent of changes in the AMP/ATP ratio.^15–17 On activation, AMPK turns on ATP-generating catabolic pathways and turns off ATP-consuming anabolic pathways.We investigated the role of AMPK in mediating the effect of TGF-β1 in human and murine PTECs, rat kidney interstitial fibroblast cells, and TGF-β1 transgenic mouse model. We provide strong evidence that TGF-β induces EMT phenotype through inactivation of AMPK and that activation of AMPK prevents the effects of TGF-β.     

β1C Integrin in Epithelial Cells Correlates with a Nonproliferative Phenotype : Forced Expression of β1C Inhibits Prostate Epithelial Cell Proliferation

The expression of the β_1C integrin, an alternatively spliced variant of the β₁ subunit, was investigated in human adult and fetal tissues. In the adult, β_1C immunoreactivity was found in nonproliferative, differentiated simple, and/or pseudostratified epithelia in prostate glands and liver bile ducts. In contrast, β_1C was undetectable in stratified squamous epithelium of the epidermis and/or in hepatocytes. Luminal prostate epithelial cells expressed β_1C in vivo and in vitro, but no β_1C was seen in basal cells, which are proliferating cells. Fetal prostate expressed β_1C in differentiated glands that had a defined lumen, but not in budding glands, indicating that β_1C is a marker of prostate epithelium differentiation. The β_1C and the common β_1A variants are differentially distributed: β_1A was found in luminal and basal epithelial as well as in stromal cells in the prostate. In the liver, β_1C and β_1A were coexpressed in biliary epithelium, whereas vascular cells expressed only β_1A. Because we found β_1C in nonproliferative and differentiated epithelium, we investigated whether β_1C could have a causal role in inhibiting epithelial cell proliferation. The results showed that exogenous expression of a β_1C, but not of a β_1A, cytoplasmic domain chimeric construct, completely inhibited thymidine incorporation in response to serum by prostate cancer epithelial cells. Consistent with these in vitro results, β_1C appeared to be downregulated in prostate glands that exhibit regenerative features in benign hyperplastic epithelium. These data show that the presence of β_1C integrins in epithelial cells correlates with a nonproliferative, differentiated phenotype and is growth inhibitory to prostate epithelial cells in vitro. These findings indicate a novel pathophysiological role for this integrin variant in epithelial cell proliferation.     

Accumulation of Extracellular Matrix and Developmental Dysregulation in the Pancreas by Transgenic Production of Transforming Growth Factor-β1

Transgenic mice expressing transforming growth factor-β1 (TGF-β1) in the pancreatic β-islet cells directed by human insulin promoter were produced to study in vivo effects of TGF-β1. Fibroblast proliferation and abnormal deposition of extracellular matrix were observed from birth onward, finally replacing almost all the exocrine pancreas. Cellular infiltrates comprising macrophages and neutrophils were also observed. Plasminogen activator inhibitor was induced in the transgenic pancreas as well as fibronectin and laminin, partly explaining accumulation of extracellular matrix. TGF-β1 inhibited proliferation of acinar cells in vivo as evidenced by decreased bromodeoxyuridine incorporation. Development of pancreatic islets was dysregulated, resulting in small islet cell clusters without formation of normal adult islets; however, the overall islet cell mass was not signfifcantly diminished. Additional transgenic lines with less pronounced phenotypes had less expression of TGF-β1 transgene. These findings suggest that TGF-β1 might be a mediator of diseases associated with extracellular matrix deposition such as chronic pancreatitis, and this mouse model will be useful for further analysis of the in vivo effects of TGF-β1, including its potential for immunosuppression.     

Transforming growth factor-beta 1 (TGF-β1)-mediated inhibition of glial cell proliferation and down-regulation of intercellular adhesion molecule-1 (ICAM-1) are interrupted by interferon-gamma (IFN-γ)

We utilized a model of myelin basic protein (MBP) activation in vivo and MBP-stimulated cultures in vitro to study the influence of TGF-β1 on glial cell proliferation and ICAM-1/leucocyte function-associated antigen-1 (LFA-1) expression, and to observe the antagonistic effects of TGF-β1 and IFN-γ. TGF-β1 inhibited MBP-stimulated and MBP-activated glial cell proliferation, especially in MBP-stimulated separated microglia and astrocytes, and down-regulated the expression of ICAM-1 on MBP-stimulated glial cells and separated microglia. ICAM-1 expression on MBP-activated glial cells was intensely suppressed, whereas its expression on MBP-stimulated astrocytes was not influenced. TGF-β1 had no effect on LFA-1 expression. In contrast, IFN-γ up-regulated ICAM-1 expression, but inhibited proliferative response on MBP-stimulated glial cells when cultured without TGF-β1. Examination of TGF-β1 and IFN-γ interactions revealed that TGF-β1-mediated inhibition of proliferation and down-regulation of ICAM-1 on glial cells were prevented by IFN-γ. The suppressive effect was re-established with high doses of TGF-β1 in cultures, indicating that biological effects of TGF-β1 vary depending on nitric oxide (NO) production, its concentration in the microenvironment and regulation of the cytokine network.     

Relationship of TLR2, TLR4 and tissue remodeling in chronic rhinosinusitis

In order to explore the role of innate immunity in the remodeling of CRS (chronic rhinosinusitis), we investigated the correlation between TLR2, TLR4 and remodeling involved cytokines and histopathological features. Immunohistochemical staining was applied to detect the expression of TLR2, TLR4 and TGF-β1. Masson staining was used for observing the collagen deposition. The other histopathologic features of remodeling were observed by hemotoxylin and eosin (HE) staining. Nasal epithelial cell culture was used to elucidate the effect of TLR2, TLR4 agonists and inhibitors on the expression of TGF-β1 and MMP-9. The association study showed that the significantly higher expression of TLR2, TLR4, TGF-β1 and collagen appeared in CRSsNP (chronic rhinosinusitis without nasal polyps) patients compared with CRSwNP (chronic rhinosinusitis with nasal polyps) patients. In CRSsNP, patients with a severe epithelial damage (score 3) had a significantly higher expression of TLR2 than patients with mild epithelial damage (score ≤ 2) (P < 0.05). Moreover the expression of TLR2 correlated negatively with squamous hyperplasia in CRSsNP, and positively with gland hyperplasia in CRSwNP. The expression of TLR2 and TLR4 was closely related to neutrophil infiltration in CRSsNP (P < 0.01). TGF-β1 was downregulated by TLR2 agonist in CRSwNP and upregulated by TLR4 agonist in CRSsNP (P < 0.05). MMP-9 was upregulated by TLR4 agonist in CRSwNP (P < 0.05). TLR2 and TLR4 had close relationship with TGF-β1 and the histologic features of remodeling, especially collagen deposition and neutrophil infiltration in CRSsNP. The innate immunity could influence the histologic characteristics and involved cytokines through TLR2 and TLR4 in the remodeling of CRS.     

Mechanisms of binding of cutaneous lymphocyte-associated antigen-positive and αeβ7-positive lymphocytes to oral and skin keratinocytes

Intraepithelial lymphocytes (IEL) utilize the integrin αeβ7 on their surface to bind to E-cadherin on epithelial cells in the gut and breast. In oral mucosa and skin IEL express αeβ7 and the cutaneous lymphocyte-associated antigen (CLA) but the mechanisms of adhesion of these subsets to keratinocytes are unknown. Levels of αeβ7 and CLA were up-regulated on peripheral blood lymphocytes (PBL) by transforming growth factor-β (TGF-β) and interleukin-12 (IL-12), respectively, and both groups of lymphocytes adhered onto oral and skin keratinocytes. Adhesion of IL-12-activated PBL was totally abolished by anti-lymphocyte-associated function antigen type 1 (anti-LFA-1) antibodies but was unaffected by anti-αeβ7 antibodies indicating that adhesion of the CLA-positive subset is mediated via LFA-1 interaction with intercellular adhesion molecule-1 (ICAM-1). Adhesion of TGF-β-activated PBL to E-cadherin-positive oral and skin keratinocytes was partially inhibited by anti-αeβ7 antibodies but was unaffected by the blocking antibody E4.6 against E-cadherin which detects the binding site for αeβ7-positive lymphocytes in breast and gut epithelium. TGF-β-activated PBL also bound to an E-cadherin-negative oral keratinocyte cell line and adhesion was inhibited by anti-αeβ7 antibodies. These results strongly suggest that in oral epithelium and epidermis αeβ7-positive lymphocytes do not bind to E-cadherin and there may be a novel second ligand for the αeβ7 integrin.     

Salinomycin suppresses TGF-β1-induced EMT by down-regulating MMP-2 and MMP-9 via the AMPK/SIRT1 pathway in non-small cell lung cancer

Salinomycin (Sal) is a recently identified anti-tumor drug for treating several types of solid tumor; however, its effects on the migratory and invasive properties of non-small cell lung cancer (NSCLC) remain unclear. This study investigated the inhibitory effect underlying mechanisms of Salon transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) and cell migration. Sal solidly blocked cell migration and invasion enhancement by TGF-β1-induced EMT, through recovering E-cadherin loss and suppressing mesenchymal markers induction, as well as TGF-β1-mediated AMPK/SIRT signaling activity upregulation. The pharmacologic inhibition or knockdown of AMPK or SIRT1 can act synergistically with Sal to inhibit TGF-β1-induced MMP-2 and MMP-9. In contrast, AMPK or SIRT1 upregulation can protect against TGF-β1-induced MMP-2 and MMP-9 inhibition by Sal. Next we demonstrated that the MMP-2 and MMP-9 knockdown can act synergistically with Sal to inhibit TGF-β1-induced EMT. Moreover, treatment of PMA of MMP activator increased TGF-β1-induced MMP-2 and MMP-9, even with Sal. Our results demonstrate that Sal suppresses TGF-β1-induced EMT by downregulating MMP-2 and MMP-9 through the AMPK/SIRT pathway, thereby inhibiting lung cancer cell migration and invasion.     

Inhibition of Mycobacterium bovis BCG-Induced Tumor Necrosis Factor Alpha Secretion in Human Cells by Transforming Growth Factor β

The effect of exogenous transforming growth factor β (TGF-β) on Mycobacterium bovis BCG-induced tumor necrosis factor alpha (TNF-α) production by human mononuclear cells was studied. It was found that TNF-α production by human cells stimulated with BCG was significantly inhibited by TGF-β. The specificity of the observed inhibition was demonstrated, since the addition of an anti-TGF-β neutralizing monoclonal antibody completely reversed the inhibitory effect. Furthermore, the suppressive effect of TGF-β on TNF-α secretion in this system was not due to a direct cytotoxic effect, since cell viability was comparable in the presence or absence of TGF-β. Interestingly, our results demonstrated comparative suppressive effects of TGF-β and interleukin-10 on BCG-induced TNF-α secretion. Together, the data demonstrate, for the first time, that TGF-β inhibits BCG-induced TNF-α secretion by human cells.     

Contribution of Hepatic Parenchymal and Nonparenchymal Cells to Hepatic Fibrogenesis in Biliary Atresia

Extrahepatic biliary atresia is a severe neonatal liver disease resulting from a sclerosing cholangiopathy of unknown etiology. Although biliary obstruction may be surgically corrected by a “Kasai” hepatoportoenterostomy, most patients still develop progressive hepatic fibrosis, although the source of increased collagen deposition is unclear. This study examined the role of hepatic stellate cells (HSCs) and assessed the source of transforming growth factor-β (TGF-β) production in hepatic fibrogenesis in patients with biliary atresia. Liver biopsies from 18 biliary atresia patients (including 5 pre- and post-Kasai) were subjected to immunohistochemistry for α-smooth muscle actin and in situ hybridization for either procollagen α₁ (I) mRNA or TGF-β₁ mRNA. Sections were also subjected to immunohistochemistry for active TGF-β₁ protein. The role of Kupffer cells in TGF-β₁ production was assessed by immunohistochemistry for CD68. Procollagen α₁ (I) mRNA was colocalized to α-smooth muscle actin-positive HSCs within the region of increased collagen protein deposition in fibrotic septa and surrounding hyperplastic bile ducts. The number of activated HSCs was decreased in only one post-Kasai biopsy. TGF-β₁ mRNA expression was demonstrated in bile duct epithelial cells and activated HSCs and in hepatocytes in close proximity to fibrotic septa. Active TGF-β₁ protein was demonstrated in bile duct epithelial cells and activated HSCs. This study provides evidence that activated HSCs are responsible for increased collagen production in patients with biliary atresia and therefore play a definitive role in the fibrogenic process. We have also shown that bile duct epithelial cells, HSCs, and hepatocytes are all involved in the production of the profibrogenic cytokine, TGF-β₁.     

Colon carcinoma cell lines stimulate monocytes and lamina propria mononuclear cells to produce IL-10

Cytokines released from tumour cells may have function as signals to neighbouring immune and inflammatory cells. Several studies have shown that the immunoregulatory cytokines IL-10 and transforming growth factor-beta 1 (TGF-β1) as well as prostaglandin-E₂ (PGE₂) play an important role in tumour-induced immunosuppression. The aim of the study was to investigate the effect of colon carcinoma cell lines on IL-10 production in peripheral monocytes (PBMC) and lamina propria mononuclear cells (LPMC). We examined four colon carcinoma cell lines (HT-29, Caco-2, Colo-320 and HCT-116) and determined their production of TGF-β1, IL-10 and PGE₂. Peripheral monocytes were isolated by density gradient centrifugation and LPMC were isolated from surgical specimens using a collagenase digestion method. Monocytes and LPMC were cultured with colon carcinoma cell conditioned medium or in co-culture with colon carcinoma cells. Supernatants were then determined for the production of IL-10 by ELISA assays. All colon carcinoma cell lines stimulated peripheral monocytes as well as LPMC to produce markedly increased levels of IL-10. Colon cancer cells secreted negligible levels of IL-10, but high amounts of TGF-β1 and PGE₂. Neutralization of TGF-β1 by administration of anti-TGF-β as well as neutralization of PGE₂ with anti-PGE₂ antisera reduced the IL-10 production of monocytes markedly, indicating that tumour cell-derived TGF-β1 and PGE₂ are major factors for IL-10 stimulation. In vitro stimulation of monocytes with TGF-β1 and PGE₂ could confirm that TGF-β1 as well as PGF₂ at picogram concentrations were able to prime monocytes for enhanced IL-10 production. Our results demonstrate that colon carcinoma cell lines enhance the ability of monocytes and intestinal macrophages to produce IL-10. The stimulation of monocyte IL-10 by colon cancer cell-derived TGF-β1 and PGE₂ may act as a tumour-protecting mechanism by impairing the activation of anti-tumour cytokines.     

Prolonged NF-κB Activation by a Macrophage Inhibitory Cytokine 1-Linked Signal in Enteropathogenic Escherichia coli-Infected Epithelial Cells

Intestinal epithelial activation of nuclear factor kappa B (NF-κB) exerts both detrimental and beneficial functions in response to various luminal insults, including ones associated with mucosa-associated pathogens. Gastrointestinal infection with enteropathogenic Escherichia coli (EPEC) causes severe injuries in epithelial integrity and leads to watery diarrhea. The present study was conducted to investigate the prolonged epithelial responses to persistent EPEC infection via NF-κB activation. EPEC infection led to sustained activation of NF-κB signal in mouse intestinal epithelial cells in vivo and in vitro, which was positively associated with a type III secretion system, whereas early NF-κB is regulated. Moreover, prolonged NF-κB activation was found to be a part of macrophage inhibitory cytokine 1 (MIC-1)-mediated signaling activation, a novel link between NF-κB signaling and infection-associated epithelial stress. EPEC infection induced gene expression of MIC-1, a member of the transforming growth factor β (TGF-β) superfamily, which then activated TGF-β-activated kinase 1 and consequently led to NF-κB activation. Functionally, both EPEC-induced MIC-1 and NF-κB signaling mediated epithelial survival by enhancing the expression of cyclin D1, a target of NF-κB. In summary, the results of the present study suggest that MIC-1 serves as a mediator of prolonged NF-κB activation, which is critical in maintaining gut epithelial integrity in response to infection-induced injuries.     

Development of a KLD-12 polypeptide/TGF-β1-tissue scaffold promoting the differentiation of mesenchymal stem cell into nucleus pulposus-like cells for treatment of intervertebral disc degeneration

Objective: To develop tissue engineering scaffolds consisting of self-assembling KLD-12 polypeptide/TGF-β1 nanofiber gel, for the induction of mesenchymal stem cell (MSCs) differentiation into nucleus pulposus (NP)-like cells. Methods: The release of TGF-β1 from KLD-12 polypeptide gels containing varying TGF-β1 concentrations was detected by ELISA. MSCs were isolated with a density gradient method and their differentiation into NP-like cells was analyzed in KLD-12 polypeptide/TGF-β1- or KLD-12 polypeptide control nanofiber-gel 3D-cultures. The Alcianblue method, Real-time quantitative PCR (RT-qPCR), and immunocytochemistry were used to measure the expression of extracellular matrix (ECM) molecules, such as aggrecan, glycosaminoglycans (GAGs), and type II collagen. Results: ELISA results documented favorable time-dependent release characteristics of TGF-β1 in the KLD-12 polypeptide/TGF-β1 gel scaffolds. The results of CCK-8 cell proliferation assay showed the TGF-β1 containing scaffolds induced higher growth rate in MSCs compared to the control group. Calcein-AM/PI fluorescent staining showed: the cells in the gel grew well, maintaining the circular shape of cells, and the spindle and fusiform shape of cells on the gel edges. The cell viability displayed a survival rate of 89.14% ± 2.468 for the TGF-β1 group with no significant difference between the two groups at 14 d of culture. The production of ECM was monitored showing higher expression of GAGs in the TGF-β1 group (P < 0.01) with highest amounts at 10 d and 14 d compared to 4 d and 7 d (P < 0.05). Real-time PCR results revealed that the expression levels of collagen II and aggrecan mRNA were higher in the TGF-β1 group (P < 0.05). Finally, immunocytochemical staining of collagen II confirmed the higher expression levels. Conclusion: A scaffold containing a KLD-12 polypeptide/TGF-β1-nanofiber gel and MSCs differentiated into NP-like cells is able to produce ECM and has the potential to serve as a three-dimensional (3-D) support scaffold for the filling of early postoperative residual cavities and the treatment of intervertebral disc degeneration.     

MMTV promoter-regulated caveolin-1 overexpression yields defective parenchymal epithelia in multiple exocrine organs of transgenic mice

Caveolin-1 (Cav-1) is a major structural protein of caveolae, specialized plasma membrane invaginations that are involved in a cell-specific fashion in diverse cell activities such as molecular transport, cell adhesion, and signal transduction. In normal adult mammals, Cav-1 expression is abundant in mesenchyme-derived cells but relatively low in epithelial parenchyma. However, epithelial Cav-1 overexpression is associated with development and/or progression of many carcinomas. In this study, we generated and characterized a transgenic mouse model of Cav-1 overexpression under the control of a mouse mammary tumor virus (MMTV) long terminal-repeat promoter, which is predominantly expressed in specific epithelial cells. The MMTVcav-1⁺ transgenic mice were fertile, and females bore litters of normal size with no obvious developmental abnormalities. However, by age 11 months, the MMTVcav-1⁺ mice demonstrated overtly different phenotypes in multiple exocrine organs when compared with their nontransgenic MMTVcav-1⁻ littermates. Cav-1 overexpression in MMTVcav-1⁺ mice produced organ-specific abnormalities, including hypotrophy of mammary glandular epithelia, bronchiolar epithelial hyperplasia and atypia, mucous-cell hyperplasia in salivary glands, elongated hair follicles and dermal thickening in the skin, and reduced accumulation of enzymogen granules in pancreatic acinar cells. In addition, the MMTVcav-1⁺ transgenic mice tended to have a greater incidence of malignant tumors, including lung and liver carcinomas and lymphoma, than their MMTVcav-1⁻ littermates. Our results indicate that Cav-1 overexpression causes organ-specific, age-related epithelial disorders and suggest the potential for increased susceptibility to carcinogenesis.