Ephrin-B2 overexpression enhances integrin-mediated ECM-attachment and migration of B16 melanoma cells

Eph-receptor tyrosine kinases (Eph-RTKs) and their membrane-bound receptor-like ligands, the ephrins, represent a cell-cell signaling system that directs cellular migration during development. Differential expression in cancer suggests similar roles in tumor progression. We have previously shown that ephrin-B2 mRNA is overexpressed in advanced malignant melanomas (MM). In this study, immunohistochemistry revealed a most prominent expression of ephrin-B2 in the invasive front of advanced MM. Therefore, we addressed the question of whether ephrin-B2 signaling modulates MM cell migration and matrix interaction. Using a wild-type ephrin-B2-negative B16 mouse MM subclone we show that overexpression of ephrin-B2 leads to the formation of multiple lamellipodia, enhanced polymerisation of actin fibers, and induction of focal adhesion complexes with constitutive activation of focal adhesion kinase. Consequently, ephrin-B2-overexpressing B16 cells display a significant increase of beta1-integrin-mediated attachment to matrix components, preferentially laminin and fibronectin. As a further effect of ephrin-B2 overexpression, we observed an accelerated migration in both Boyden chamber invasion experiments as well as in in vitro scratch-wound assays. We conclude that ephrin-B2 can act as a major modulator of cell migration and matrix interactions of MM cells, which possibly contributes to the expansion and metastatic spread of MM in vivo.     

Clinging to life: cell to matrix adhesion and cell survival

Cell to matrix adhesion regulates cellular homeostasis in multiple ways. Integrin attachment to the extracellular matrix mediates this regulation through direct and indirect connections to the actin cytoskeleton, growth factor receptors, and intracellular signal transduction cascades. Disruption of this connection to the extracellular matrix has deleterious effects on cell survival. It leads to a specific type of apoptosis known as anoikis in most non-transformed cell types. Anchorage independent growth is a critical step in the tumorigenic transformation of cells. Thus, breaching the anoikis barrier disrupts the cell's defenses against transformation. This review examines recent investigations into the molecular mechanisms of anoikis to illustrate current understanding of this important process.     

Overexpression of LASP-1 mediates migration and proliferation of human ovarian cancer cells and influences zyxin localisation

LIM and SH3 protein 1 (LASP-1), initially identified from human breast cancer, is a specific focal adhesion protein involved in cell proliferation and migration. In the present work, we analysed the effect of LASP-1 on biology and function of human ovarian cancer cell line SKOV-3 using small interfering RNA technique (siRNA).Transfection with LASP-1-specific siRNA resulted in a reduced protein level of LASP-1 in SKOV-3 cells. The siRNA-treated cells were arrested in G(2)/M phase of the cell cycle and proliferation of the tumour cells was suppressed by 60-90% corresponding to around 70% of the cells being transfected successfully as seen by immunofluorescence. Moreover, transfected tumour cells showed a 40% reduced migration. LASP-1 silencing is accompanied by a reduced binding of the LASP-1-binding partner zyxin to focal contacts without changes in actin stress fibre and microtubule organisation or focal adhesion morphology as observed by immunofluorescence. In contrast, silencing of zyxin is not influencing cell migration and had neither influence on LASP-1 expression nor actin cytoskeleton and focal contact morphology suggesting that LASP-1 is necessary and sufficient for recruiting zyxin to focal contacts.The data provide evidence for an essential role of LASP-1 in tumour cell growth and migration, possibly through influencing zyxin localization.     

A mutant form of the rho protein can restore stress fibers and adhesion plaques in v-src transformed fibroblasts.

The organization of polymerized actin in the mammalian cell is regulated by several members of the rho family. Three rho proteins, cdc42, rac and rho act in a cascade to organize the intracellular actin cytoskeleton. Rho proteins are involved in the formation of actin stress fibers and adhesion plaques in fibroblasts. During transformation of mammalian cells by oncogenes the cytoskeleton is rearranged and stress fibers and adhesion plaques are disintegrated. In this paper we investigate the function of the rho protein in RR1022 rat fibroblasts transformed by the Rous sarcoma virus. Two activated mutants of the rho protein, rho G14V and rho Q63L, and a dominant negative mutant, rho N1171, were stably transfected into RR1022 cells. The resulting cell lines were analysed for the organization of polymerized actin and adhesion plaques. Cells expressing rho Q63L, but not rho wt, rho G14V or rho N1171, showed an altered morphology. These cells displayed a flat, fibroblast like shape when compared with the RR1022 ancestor cells. Immunofluorescence analyses revealed that actin stress fibers and adhesion plaques were rearranged in these cells. We conclude from these data that an active rho protein can restore elements of the actin cytoskeleton in transformed cells by overriding the tyrosine kinase phosphorylation induced by the pp60(v-src).     

EGF receptor mediates adhesion-dependent activation of the Rac GTPase: a role for phosphatidylinositol 3-kinase and Vav2

Organization of the actin cytoskeleton in eucaryotic cells is controlled by small GTPases of the Rho family. Rac becomes activated by growth factor stimulation and integrin-mediated cell adhesion to extracellular matrix and is known to have a crucial role in lamellipodia formation, cell spreading and migration. At present, the intracellular pathways that connect cell surface receptors to Rac activation are poorly characterized. It has been reported previously that integrin-mediated cell attachment induces activation of the EGF receptor (EGFR) in the absence of EGF. We demonstrate here that this activation is instrumental for integrin-dependent Rac activation. Thus, we found that cells in which EGFR activity had been inhibited failed to spread and form lamellipodia on fibronectin. Failure to spread coincided with inhibition of adhesion-induced GTP loading of Rac and also with inhibition of the phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Subsequent studies demonstrated that an activated form of PI 3-kinase restored Rac GTP loading in the presence of EGFR inhibition, while a dominant-negative form of PI 3-kinase blocked Rac GTP loading in fibronectin-adherent cells. Our further functional studies identified Vav2, a known exchange factor for Rac, as a crucial downstream component in EGFR- and PI 3-kinase-dependent Rac activation upon integrin-mediated cell adhesion. Our results provide a mechanistic insight into integrin-dependent Rac activation, and identify a novel role for EGFR, PI 3-kinase and Vav2 in this pathway.     

Malignant transformation alters intracellular trafficking of lysosomal cathepsin D in human breast epithelial cells

Increased expression and alteration of intracellular trafficking of lysosomal cathepsins have been reported in malignant tumors, or in cells transformed by the transfection with the ras oncogene. In the present study, immortal MCF-10A human breast epithelial cells were transformed with the mutated ras oncogene. Both cell lines were investigated for changes in the intracellular localization of lysosomal cathepsin D and lamp-1 (lysosome-associated membrane protein) employing specific antibodies and confocal immunofluorescence microscopy. The results revealed that staining for cathepsin D along with for lamp-1 was mostly localized in the perinuclear region of MCF-10A cells. In contrast, the staining for these proteins was found to be widely distributed throughout the cytoplasm and at the cell periphery in MCF-10AneoT cells. The organization of microtubules, but not actin, appeared to differ between MCF-10A cells and their oncogenic ras transfectants. When the microtubules were depoly-merized by treatment of MCF-10A cells with nocodazole, vesicles containing the lysosomal cathepsin D were dispersed in the cytoplasm and translocation of these vesicles to the cell periphery was observed. The intracellular localization of cathepsin D in the nocodazole-treated MCF-10A cells seemed to be similar to that observed in the oncogenic ras transfectants of these cells. When taxol, which inhibits microtubule depolymerization, was added to the culture medium of neoT cells, a polymerized microtubule network was observed, and the reclustering of cathepsin D and lamp-1 occurred in a unidirectional manner towards the perinuclear region. These findings support a model in which cytoskeletal microtubule organization is closely related to the trafficking of lysosomes/endodomes, and in which oncogenic ras interferes with such organization in human breast epithelial cells.     

Overexpression of the thymosin beta-4 gene is associated with malignant progression of SW480 colon cancer cells

Thymosin beta-4 (Tbeta-4), a small peptide originally isolated from calf thymus, modulates the formation of F-actin microfilaments by sequestering the monomeric G-actin. Recent studies have shown that overexpression of the Tbeta-4 gene occurs not only in many human carcinomas but also in the highly metastatic melanomas and fibrosarcomas. However, little is known about the specific growth advantages acquired by different tumors from this genetic abnormality. To address the above questions, Tbeta-4-overexpressing human colon carcinoma (SW480) cells were established by stable transfection and their phenotypic changes were monitored. We found that both the morphology and the cortical actin cytoskeleton of SW480 cells were altered by Tbeta-4 overexpression. Moreover, both cellular level and that distributed over the intercellular junctions of the E-cadherin were decreased in the Tbeta-4 overexpressers, which were accompanied by a twofold increase in their saturation densities. Meanwhile, these cells also exhibited an increased ability to form colonies in soft agar. Interestingly, a dramatic increase of growth rate was detected in the Tbeta-4 overexpressers, which might be attributed to an accelerated proliferation induced by c-Myc that was activated by nuclear beta-catenin. Finally, a motility increase of these cells was demonstrated by two independent migration assays, which was accompanied by an enhanced focal contact. Taken together, our data suggest that the drastic growth property and motility changes of the SW480 cells overexpressing Tbeta-4 gene are due mainly to a deregulated cell-cell adhesion arisen from the downregulation of E-cadherin, plus uncontrolled cell proliferation owing to the upregulation of beta-catenin, both resulted from a breakdown of actin microfilaments caused by the overexpression of this G-actin sequestering peptide.     

Opioids increase bladder cancer cell migration via bradykinin B2 receptors

Data relating opioid treatment and modification of cancer cell migration (a prerequisite of metastasis) both in vitro and in vivo are diverging. In the present report we show that opioids increase the migratory activity of bladder cancer cells (T24 and EJ) and we provide a new mechanistic insight, explaining (at least partially) their action: we report that the enhanced opioid-related cell migration is controlled (in the absence of opioid receptors) through their interaction with bradykinin B2 receptors. Indeed, in these cell lines, opioids increase migration, adhesion, spreading and invasion by re-arranging actin cytoskeleton, increasing MMP-2 and -9 secretion and triggering specific intracellular signaling cascades in a non-opioid receptor mediated manner. An interaction, albeit with low affinity, of opioids with the bradykinin B2 receptor is reported, resulting in the increase of migration, while B2 antagonists revert this action. A systematic assay of different human epithelial cancer cell lines confirmed that only the B2-positive/opioid receptor-negative bladder cancer cells present this opioid-related increased migration/invasive phenotype. We suggest that opioid administration in cancer patients should be re-evaluated, keeping in mind that they may have other beneficial (protection) or adverse effects (spreading of cancer cells), in spite of their unique role in pain relief.     

The cytoskeleton and cancer

Cancer is a disease in which many of the characteristics of normal cell behavior are lost or perturbed. Uncontrolled cell proliferation and inappropriate cell survival are common features of all cancers, but in addition defects in cellular morphogenesis that lead to tissue disruption, the acquisition of inappropriate migratory and invasive characteristics and the generation of genomic instability through defects in mitosis also accompany progression of the disease. This volume is focused on the actin and microtubule cytoskeletons, key players that underpin these cellular processes. Actin and tubulin form highly versatile, dynamic polymers that are capable of organizing cytoplasmic organelles and intracellular compartments, defining cell polarity and generating both pushing and contractile forces. In the cell cycle, these two cytoskeletal structures drive chromosomal separation and cell division. During morphogenesis, they determine cell shape and polarity, and promote stable cell-cell and cell-matrix adhesions through their interactions with cadherins and integrins, respectively. Finally, during cell migration they generate protrusive forces at the front and retraction forces at the rear. These are all aspects of cell behavior than often go awry in cancer. This volume brings together those interested in understanding the contribution of the actin and microtubule cytoskeletons to the cell biology of cancer.     

Elevated c-Src is linked to altered cell-matrix adhesion rather than proliferation in KM12C human colorectal cancer cells

Elevated expression and/or activity of c-Src, the prototype of the Src family of protein tyrosine kinases, is associated with the development of human colon cancer. However, despite the known pleiotropic effects of these kinases in promoting (a) cell growth downstream of growth factor receptors, and (b) the dynamic regulation of integrin adhesions in fibroblast model systems, their precise role in epithelial cancer cells is unknown. Here we addressed whether elevated expression and activity of cellular Src alters cell proliferation and/or cell-matrix adhesion in cancer cells from the Fidler model of colorectal metastasis. Although elevated Src correlates with ability to metastasise to the liver after intrasplenic injection, we found that this was not linked to enhanced growth, either in vitro or in vivo as sub-cutaneous tumours. However, elevated Src was associated with enhanced attachment to extracellular matrix. In addition, adhesion to fibronectin, was suppressed by agents that inhibited Src activity, while enforced elevation of Src in non-metastatic cells was sufficient to stimulate adhesion to fibronectin and enhanced assembly of adhesion complexes, without influencing cell growth. Thus, we conclude that one role of elevated Src in human colon cancer cells is to modulate integrin-dependent cell-matrix attachment and formation of adhesion structures, which may, in turn, influence cell motility and integrin-dependent cellular responses.     

Lack of correlation between induction of chemotactic peptide receptors and stimulus-induced actin polymerization in HL-60 cells treated with dibutyryl cyclic adenosine monophosphate or retinoic acid

We used the promyelocytic leukemic cell line HL-60 to explore the molecular mechanisms regulating stimulus-induced actin polymerization in myeloid cells. HL-60 cells express very few chemotactic peptide receptors in their undifferentiated state and fail to undergo actin polymerization when stimulated with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP). However, when the cells were induced to differentiate with dibutyryl cyclic AMP (dbcAMP) or retinoic acid, they acquired the ability to undergo actin polymerization on stimulation with FMLP or phorbol myristate acetate. Kinetic experiments revealed that in the first 48 h of retinoic acid treatment there was no increase in the chemotactic peptide receptors on HL-60 cells, but the cells were capable of undergoing actin polymerization on stimulation with FMLP. Similarly, treatment with dbcAMP showed no increase in chemotactic peptide receptors until 24 h but stimulus-induced actin polymerization was demonstrable as early as 4 h after the treatment. In addition, with dbcAMP-treated cells the magnitude of stimulus-induced actin polymerization showed large variation depending on the duration of exposure to the drug. Dual-label studies using propidium iodide to measure DNA content and NBD-phallacidin to measure the F-actin content revealed that these variations were not related to the stages of cell cycle. Cells in all stages of the cell cycle responded to stimulus-induced actin polymerization, but the magnitude of the response appeared to be more in cells in G2/M phase. The observations reported here indicate that the small number of chemotactic peptide receptors present on HL-60 cells are adequate to mount an actin polymerization response, provided the required intracellular mechanisms exist. Differentiation-inducing agents, therefore, must cause changes within the cell, such as induction of actin-binding proteins, to cause actin polymerization following FMLP stimulation. The HL-60 system serves as a useful model for studying the molecular mechanisms regulating stimulus-induced actin polymerization in human neutrophils.     

A variant actin (βm) reduces metastasis of mouse B16 melanoma

We recently reported an acidic actin co-expressed with β and γ actin in mouse B16 melanoma, whose expression was inversely correlated with the metastatic potential. The cDNA for this actin is slightly different from the hitherto recognized mouse β actin cDNA, and we designated it βm actin. In order to directly investigate the effects of βm actin on metastasis, we transfected the βm actin cDNA into a re-cloned B16-BL6 cell line which is more invasive than the highly metastatic cell line, B16-F10; we have already reported the suppressive effect of pm actin on the invasiveness of B16 F10. Here we report on the decline in the metastatic ability of βm-transfected cells. In the pm-transfected B16-BL6 cell line, we observed an increase in the organization of actin stress fibers, accompanied by a decrease in metastasis to the lung, in the invasion of collagen gels, in In vivo invasive-ness, and in cell migration on a glass plate covered with colloidal gold particles. We observed no correlation of pm actin expression either with cell attachment to Matrigel, or with type-IV collagenase expression. These results suggest that βm actin can play a role in reducing the invasiveness of mouse B16 melanoma, most probably through decreasing cell motility, which may thus result in suppression of the metastatic ability of cells.     

Antimitotic chemotherapeutics promote adhesive responses in detached and circulating tumor cells

In the clinical treatment of breast cancer, antimitotic cytotoxic agents are one of the most commonly employed chemotherapies, owing largely to their antiproliferative effects on the growth and survival of adherent cells in studies that model primary tumor growth. Importantly, the manner in which these chemotherapeutics impact the metastatic process remains unclear. Furthermore, since dissemination of tumor cells through the systemic circulation and lymphatics necessitates periods of detached survival, it is equally important to consider how circulating tumor cells respond to such compounds. To address this question, we exposed both nontumorigenic and tumor-derived epithelial cell lines to two antitumor compounds, jasplakinolide and paclitaxel (Taxol), in a series of attached and detached states. We report here that jasplakinolide promoted the extension of microtubule-based projections and microtentacle protrusions in adherent and suspended cells, respectively. These protrusions were specifically enriched by upregulation of a stable post-translationally modified form of α-tubulin, and this occurred prior to, and independently of any reductions in cellular viability. Microtubule stabilization with Taxol significantly enhanced these effects. Additionally, Taxol promoted the attachment and spreading of suspended tumor cell populations on extracellular matrix. While the antiproliferative effects of these compounds are well recognized and clinically valuable, our findings that microfilament and microtubule binding chemotherapeutics rapidly increase the mechanisms that promote endothelial adhesion of circulating tumor cells warrant caution to avoid inadvertently enhancing metastatic potential, while targeting cell division.     

2-deoxy-D-Glucose Synergizes with Doxorubicin or L-Buthionine Sulfoximine to Reduce Adhesion and Migration of Breast Cancer Cells

Background: Cancer metastasis depends on cell motility which is driven by cycles of actin polymerizationand depolymerization. Reactive oxygen species (ROS) and metabolic oxidative stress have long been associatedwith cancer. ROS play a vital role in regulating actin dynamics that are sensitive to oxidative modification. Thecurrent work aimed at studying the effects of sub-lethal metabolic oxidative stress on actin cytoskeleton, focaladhesion and cell migration. Materials and Methods: T47D human breast cancer cells were treated with 2-deoxy-D-glucose (2DG), L-buthionine sulfoximine (BSO), or doxorubicin (DOX), individually or in combination, andchanges in intracellular total glutathione and malondialdehyde (MDA) levels were measured. The expressionof three major antioxidant enzymes was studied by immunoblotting, and cells were stained with fluorescentphalloidinto evaluate changes in F-actin organization. In addition, cell adhesion and degradation ability weremeasured. Cell migration was studied using wound healing and transwell migration assays. Results: Our resultsshow that treating T47D human breast cancer cells with drug combinations (2DG/BSO, 2DG/DOX, or BSO/DOX)decreased intracellular total glutathione and increased oxidized glutathione, lipid peroxidation, and cytotoxicity.In addition, the drug combinations caused a reduction in cell area and mitotic index, prophase arrest and adecreased ability to form invadopodia. The formation of F-actin aggregates was increased in treated T47D cells.Moreover, combination therapy reduced cell adhesion and the rate of cell migration. Conclusions: Our resultssuggest that exposure of T47D breast cancer cells to combination therapy reduces cell migration via effects onmetabolic oxidative stress.     

Discoidin Domain Receptor-1a (DDR1a) Promotes Glioma Cell Invasion and Adhesion in Association with Matrix Metalloproteinase-2

Summary Invasion of glioma cells involves the attachment of invading tumor cells to extracellular matrix (ECM), disruption of ECM components, and subsequent cell penetration into adjacent brain structures. Discoidin domain receptor 1 (DDR1) tyrosine kinases constitute a novel family of receptors characterized by a unique structure in the ectodomain (discoidin-I domain). These cell surface receptors bind to several collagens and facilitate cell adhesion. Little is known about DDR1 expression and function in glioblastoma multiforme. In this study we demonstrate that DDR1 is overexpressed in glioma tissues using cDNA arrays, immunohistochemistry and Western blot analysis. Functional comparison of two splice variants of DDR1 (DDR1a and DDR1b) reveal novel differences in cell based glioma models. Overexpression of either DDR1a or DDR1b caused increased cell attachment. However, glioma cells overexpressing DDR1a display enhanced invasion and migration. We also detect increased levels of matrix metalloproteinase-2 in DDR1a overexpressing cells as measured by zymography. Inhibition of MMP activity using MMP inhibitor suppressed DDR1a stimulated cell-invasion. Similarly, an antibody against DDR1 reduced DDR1a mediated invasion as well as the enhanced adhesion of DDR1a and DDR1b overexpressing cells. These results suggest that DDR1a plays a critical role in inducing tumor cell adhesion and invasion, and this invasive phenotype is caused by activation of matrix metalloproteinase-2.     

Senescent stromal cells induce cancer cell migration via inhibition of RhoA/ROCK/myosin-based cell contractility

Cells induced into senescence exhibit a marked increase in the secretion of pro-inflammatory cytokines termed senescence-associated secretory phenotype (SASP). Here we report that SASP from senescent stromal fibroblasts promote spontaneous morphological changes accompanied by an aggressive migratory behavior in originally non-motile human breast cancer cells. This phenotypic switch is coordinated, in space and time, by a dramatic reorganization of the actin and microtubule filament networks, a discrete polarization of EB1 comets, and an unconventional front-to-back inversion of nucleus-MTOC polarity. SASP-induced morphological/migratory changes are critically dependent on microtubule integrity and dynamics, and are coordinated by the inhibition of RhoA and cell contractility. RhoA/ROCK inhibition reduces focal adhesions and traction forces, while promoting a novel gliding mode of migration.     

Expression of alpha-catenin in alpha-catenin-deficient cells results in a reduced proliferation in three-dimensional multicellular spheroids but not in two-dimensional monolayer cultures

alpha-Catenin is an intracellular protein that associates with the carboxy-terminal region of cadherin, a cell adhesion molecule, via beta-catenin or gamma-catenin (plakoglobin). Linkage of cadherin to the cytoskeleton by catenins is required for full cadherin activity. Following transfection of an alpha-catenin-deficient colon carcinoma cell line with a series of alpha-catenin constructs, we discovered that the restoration of alpha-catenin expression results in reduced proliferation in three-dimensional multicellular spheroids, but not in two-dimensional monolayer cultures. The cellular function of alpha-catenin has not been compared between cells in three- and two-dimensional culture; this is the first evidence that growth regulation in three-dimensional cultures requires signaling mediated by alpha-catenin. Two classes of constructs, containing deletions in either the central segment or the COOH terminus of the molecule, both induced morphological changes, including cell compaction, and suppressed cell growth in three-dimensional cultures. In alpha-catenin-expressing cells, inhibition of cadherin cell adhesion by treatment with anti-E-cadherin antibodies resulted in a similar phenotype as that observed following the loss of alpha-catenin. Therefore, both the homophilic interaction of the cadherin extracellular domain and the linkage of the cadherin cytoplasmic domain to the actin cytoskeleton by alpha-catenin are necessary for growth control in three-dimensional culture.     

The role of the cytoskeleton in differentially regulating pressure-mediated effects on malignant colonocyte focal adhesion signaling and cell adhesion

Increased extracellular pressure stimulates colon cancer cell adhesion by activating focal adhesion kinase (FAK) and Src. We investigated the role of the cytoskeleton in pressure-induced inside-out FAK and Src phosphorylation and pressure-stimulated adhesion. We perturbed actin polymerization with phalloidin, cytochalasin D and latrunculin B, and microtubule organization with colchicine and paclitaxol. We compared the effects of these agents on pressure-induced SW620 and human primary colon cancer cell adhesion and inside-out FAK/Src activation with outside-in adhesion-dependent FAK/Src activation. Cells pretreated with cytoskeletal inhibitors were subjected to 15 mmHg increased pressure and allowed to adhere to collagen I coated plates or prevented from adhesion to pacificated plates for 30 min. Phalloidin, cytochalasin D, latrunculin B and colchicine pretreatment completely prevented pressure-stimulated and significantly inhibited basal SW620 cell adhesion. Taxol did not inhibit pressure-induced colon cancer cell adhesion, but significantly lowered basal adhesion. Cytochalasin D and colchicine had similar effects in pressure-stimulated primary human malignant colonocytes. Phalloidin, cytochalasin D, latrunculin B and colchicine prevented pressure-induced SW620 FAK phosphorylation but not Src phosphorylation. FAK phosphorylation in response to collagen I adhesion was significantly attenuated but not completely prevented by these inhibitors. Although Src phosphorylation was not increased on adhesion, the cytoskeleton disrupting agents significantly lowered basal Src phosphorylation in adherent cells. These results suggest that both cytoskeleton-dependent FAK activation and cytoskeleton-independent Src activation may be required for extracellular pressure to stimulate colon cancer cell adhesion. Furthermore, the cytoskeleton plays a different role in pressure-activated FAK and Src signaling than in FAK and Src activation in adherent cells. We, therefore, hypothesize that cytoskeletal interactions with focal adhesion signals mediate the effects of extracellular pressure on colon cancer cell adhesion.     

Thyroid Hormone Controls Breast Cancer Cell Movement via Integrin αV/β3/SRC/FAK/PI3-Kinases

Thyroid hormones (TH) play a fundamental role in diverse processes, including cellular movement. Cell migration requires the integration of events that induce changes in cell structure towards the direction of migration. These actions are driven by actin remodeling and stabilized by the development of adhesion sites to extracellular matrix via transmembrane receptors linked to the actin cytoskeleton. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that promotes cell migration and invasion through the control of focal adhesion turnover. In this work, we demonstrate that the thyroid hormone triiodothyronine (T3) regulates actin remodeling and cell movement in breast cancer T-47D cells through the recruitment of FAK. T3 controls FAK phosphorylation and translocation at sites where focal adhesion complexes are assembled. This process is triggered via rapid signaling to integrin αV/β3, Src, phosphatidylinositol 3-OH kinase (PI3K), and FAK. In addition, we established a cellular model with different concentration of T3 levels: normal, absence, and excess in T-47D breast cancer cells. We found that the expression of Src, FAK, and PI3K remained at normal levels in the excess of T3 model, while it was significantly reduced in the absence model. In conclusion, these results suggest a novel role for T3 as an important modulator of cell migration, providing a starting point for the development of new therapeutic strategies for breast cancer treatment.