The alpha 5 beta 1 integrin supports survival of cells on fibronectin and up-regulates Bcl-2 expression

Bit-1 mediates integrin-dependent cell survival through activation of the NFkappaB pathway

Loss of properly regulated cell death and cell survival pathways can contribute to the development of cancer and cancer metastasis. Cell survival signals are modulated by many different receptors, including integrins. Bit-1 is an effector of anoikis (cell death due to loss of attachment) in suspended cells. The anoikis function of Bit-1 can be counteracted by integrin-mediated cell attachment. Here, we explored integrin regulation of Bit-1 in adherent cells. We show that knockdown of endogenous Bit-1 in adherent cells decreased cell survival and re-expression of Bit-1 abrogated this effect. Furthermore, reduction of Bit-1 promoted both staurosporine and serum-deprivation induced apoptosis. Indeed knockdown of Bit-1 in these cells led to increased apoptosis as determined by caspase-3 activation and positive TUNEL staining. Bit-1 expression protected cells from apoptosis by increasing phospho-IκB levels and subsequently bcl-2 gene transcription. Protection from apoptosis under serum-free conditions correlated with bcl-2 transcription and Bcl-2 protein expression. Finally, Bit-1-mediated regulation of bcl-2 was dependent on focal adhesion kinase, PI3K, and AKT. Thus, we have elucidated an integrin-controlled pathway in which Bit-1 is, in part, responsible for the survival effects of cell-ECM interactions.

TGF-beta i promotes islet beta-cell function and regeneration

TGF-βi is a secreted protein and is capable of binding to both extracellular matrix (ECM) and cells. It thus acts as a bifunctional molecule enhancing ECM and cell interactions, a lack of which results in dysfunction of many cell types. In this study, we investigated the role of TGF-βi in the function and survival of islets. Based on DNA microarray followed by quantitative PCR confirmation, TGFβi gene showed drastic increase in expression in islets after culture. We demonstrated that recombinant TGF-βi could preserve the integrity and enhance the function of cultured islets. Such a beneficial effect was mediated via signaling through FAK. Exogenous TGF-βi was capable of sustaining high-level FAK phosphorylation in isolated islets, and FAK knockdown by small interfering RNA in islets resulted in compromised islet function. TGF-βi transgenic (Tg) islets showed better integrity and insulin release after in vitro culture. In vivo, β-cell proliferation was detectable in Tg but not wild-type pancreata. At age above 12 mo, Tg pancreata contained giant islets. Tg mice displayed better glucose tolerance than that of the controls. Tg islets were more potent in lowering blood glucose when transplanted into syngeneic mice with streptozotocin-induced diabetes, and these transplanted islets also underwent regeneration. Our results indicate that TGF-βi is a vital trophic factor promoting islet survival, function, and regeneration. At least some of its beneficial effect was mediated by signaling through FAK.

Myofibroblasts protect myoblasts from intrinsic apoptosis associated with differentiation via β1 integrin-PI3K/Akt pathway

Skeletal myoblasts withdrawing from cell cycle is a prerequisite for myodifferentiation, while upon proliferation/differentiation transformation, a large portion of myoblasts will undergo apoptosis. Skeletal fibroblasts, residing in muscle tissue both during and post myogenesis, have been proofed to play pivotal roles in muscle development, while their effect on myoblast apoptosis being coincident with differentiation has not been reported. Using a membrane insert co-culture system, we studied it and found that the mitochondrial pathway played a crucial role in myoblast apoptosis during differentiation, and fibroblasts promoted not only cell cycle withdrawal but also myoblast survival in a paracrine fashion, which was coupled with upregulations of β1 integrin, phosphorylated Akt and anti-apoptotic protein Bcl2. To determine the effect of β1 integrin in the process, we transfected myoblasts with siRNA specific for β1 integrin before co-culture and found that β1 integrin knockdown abolished anti-apoptotic ability of myoblasts and inhibited Akt activation and Bcl2 expression. Blockage of PI3K/Akt pathway with wortmannin also seriously impaired the protective effect of fibroblasts on myoblasts and fibroblast-induced Bcl2 expression. The data demonstrated that fibroblasts protected myoblasts from intrinsic apoptosis associated with differentiation, and β1 integrin-PI3K/Akt pathway activation was required for the process.

Fibronectin growth factor-binding domains are required for fibroblast survival

Fibronectin (FN) is required for embryogenesis, morphogenesis, and wound repair, and its Arg-Gly-Asp-containing central cell-binding domain (CCBD) is essential for mesenchymal cell survival and growth. Here, we demonstrate that FN contains three growth factor-binding domains (FN-GFBDs) that bind platelet-derived growth factor-BB (PDGF-BB), a potent fibroblast survival and mitogenic factor. These sites bind PDGF-BB with dissociation constants of 10-100 nM. FN-null cells cultured on recombinant CCBD (FNIII(8-11)) without a FN-GFBD demonstrated minimal metabolism and underwent autophagy at 24 hours, followed by apoptosis at 72 hours, even in the presence of PDGF-BB. In contrast, FN-null cells plated on FNIII(8-11) contiguous with FN-GFBD survived without, and proliferated with, PDGF-BB. FN-null cell survival on FNIII(8-11) and noncontiguous arrays of FN-GFBDs required these domains to be adsorbed on the same surface, suggesting the existence of a mesenchymal cell-extracellular matrix synapse. Thus, fibroblast survival required GF stimulation in the presence of a FN-GFBD, as well as adhesion to FN through the CCBD. The findings that fibroblast survival is dependent on FN-GFBD underscore the critical importance of pericellular matrix for cell survival and have significant implications for cutaneous wound healing and regeneration.

Galectin-1 sensitizes carcinoma cells to anoikis via the fibronectin receptor α5β1-integrin

Anoikis resistance is a hallmark of transformed epithelial cells. Here, we show that treatment of anoikis-resistant carcinoma cell lines with the endogenous lectin galectin-1 (Gal-1) promoted apoptosis via interaction with the unligated fibronectin receptor α(5)β(1)-integrin. Gal-1 efficiency correlated with expression of α(5)β(1)-integrin, and transfection of the α(5)-subunit into deficient cell lines conferred Gal-1 binding and anoikis stimulation. Furthermore, Gal-1 and the α(5)- and β(1)-integrin subunits co-precipitated in Gal-1-stimulated cells undergoing anoikis. Other members of the galectin family failed to be active. The functional interaction between Gal-1 and α(5)β(1)-integrin was glycan dependent with α2,6-sialylation representing a switch-off signal. Desialylation of cell surface glycans resulted in increased electrophoretic mobility of α(5)β(1)-integrin and facilitated Gal-1 binding and anoikis stimulation. On the level of signaling, Gal-1-stimulated anoikis was prevented by filipin, which impaired the internalization of α(5)β(1)-integrin via cholesterol-enriched microdomains, and by pretreatment with a caspase-8 inhibitor. We propose that Gal-1/α(5)β(1)-integrin interaction participates in the control of epithelial integrity and integrin sialylation may enable carcinoma cells to evade this Gal-1-dependent control mechanism.

Identification of subtilase cytotoxin (SubAB) receptors whose signaling, in association with SubAB-induced BiP cleavage, is responsible for apoptosis in HeLa cells

Subtilase cytotoxin (SubAB), which is produced by certain strains of Shiga-toxigenic Escherichia coli (STEC), causes the 78-kDa glucose-regulated protein (GRP78/BiP) cleavage, followed by induction of endoplasmic reticulum (ER) stress, leading to caspase-dependent apoptosis via mitochondrial membrane damage by Bax/Bak activation. The purpose of the present study was to identify SubAB receptors responsible for HeLa cell death. Four proteins, NG2, α2β1 integrin (ITG), L1 cell adhesion molecule (L1CAM), and hepatocyte growth factor receptor (Met), were identified to be SubAB-binding proteins by immunoprecipitation and purification, followed by liquid chromatography-tandem mass spectrometry analysis. SubAB-induced Bax conformational change, Bax/Bak complex formation, caspase activation, and cell death were decreased in β1 ITG, NG2, and L1CAM small interfering RNA-transfected cells, but unexpectedly, BiP cleavage was still observed. Pretreatment of cells with a function-blocking β1 ITG antibody (monoclonal antibody [MAb] P5D2) enhanced SubAB-induced caspase activation; MAb P5D2 alone had no effect on caspase activation. Furthermore, we found that SubAB induced focal adhesion kinase fragmentation, which was mediated by a proteasome-dependent pathway, and caspase activation was suppressed in the presence of proteasome inhibitor. Thus, β1 ITG serves as a SubAB-binding protein and may interact with SubAB-signaling pathways, leading to cell death. Our results raise the possibility that although BiP cleavage is necessary for SubAB-induced apoptotic cell death, signaling pathways associated with functional SubAB receptors may be required for activation of SubAB-dependent apoptotic pathways.

Bcl-2 and β1-integrin predict survival in a tissue microarray of small cell lung cancer

INTRODUCTION

Survival in small cell lung cancer (SCLC) is limited by the development of chemoresistance. Factors associated with chemoresistance in vitro have been difficult to validate in vivo. Both Bcl-2 and β(1)-integrin have been identified as in vitro chemoresistance factors in SCLC but their importance in patients remains uncertain. Tissue microarrays (TMAs) are useful to validate biomarkers but no large TMA exists for SCLC. We designed an SCLC TMA to study potential biomarkers of prognosis and then used it to clarify the role of both Bcl-2 and β(1)-integrin in SCLC.

METHODS

A TMA was constructed consisting of 184 cases of SCLC and stained for expression of Bcl-2 and β(1)-integrin. The slides were scored and the role of the proteins in survival was determined using Cox regression analysis. A meta-analysis of the role of Bcl-2 expression in SCLC prognosis was performed based on published results.

RESULTS

Both proteins were expressed at high levels in the SCLC cases. For Bcl-2 (n=140), the hazard ratio for death if the staining was weak in intensity was 0.55 (0.33-0.94, P=0.03) and for β(1)-integrin (n=151) was 0.60 (0.39-0.92, P=0.02). The meta-analysis showed an overall hazard ratio for low expression of Bcl-2 of 0.91(0.74-1.09).

CONCLUSIONS

Both Bcl-2 and β(1)-integrin are independent prognostic factors in SCLC in this cohort although further validation is required to confirm their importance. A TMA of SCLC cases is feasible but challenging and an important tool for biomarker validation.

Binding of the fibronectin-mimetic peptide, PR_b, to alpha5beta1 on pig islet cells increases fibronectin production and facilitates internalization of PR_b functionalized liposomes

Islet transplantation is a promising treatment for type 1 diabetes. Recent studies have demonstrated that human islet allografts can restore insulin independence to patients with this disease. As islet isolation and immunotherapeutic techniques improve, the demand for this cell-based therapy will dictate the need for other sources of islets. Pig islets could provide an unlimited supply for xenotransplantation and have shown promise as an alternative to human islet allografts. However, stresses imposed during islet isolation and transplantation decrease islet viability, leading to loss of graft function. In this study, we investigated the ability of a fibronectin-mimetic peptide, PR_b, which specifically binds to the alpha(5)beta(1) integrin, to re-establish lost extracellular matrix (ECM) around isolated pig islets and increase internalization of liposomes. Confocal microscopy and Western blotting were used to show the presence of the integrin alpha(5)beta(1) on the pig islets on day 0 (day of isolation) as well as on different days of islet culture. Islets cultured in medium supplemented with free PR_b for 48 h were found to have increased levels of ECM fibronectin secretion compared to islets in normal culture conditions. Using confocal microscopy and flow cytometry, we found that PR_b peptide-amphiphile functionalized liposomes delivered to the pig islets internalized into the cells in a PR_b concentration dependent manner and nonfunctionalized liposomes showed minimal internalization. These studies proved that the fibronectin-mimetic peptide, PR_b, is an appropriate peptide bullet for applications involving alpha(5)beta(1) expressing pig islet cells. Fibronectin production stimulated through alpha(5)beta(1) PR_b binding may decrease apoptosis and therefore increase islet viability in culture. In addition, PR_b peptide-amphiphile functionalized liposomes may be used for targeted delivery of different agents to pig islet cells.

Fibronectin and integrin alpha 5 play essential roles in the development of the cardiac neural crest

Cardiac neural crest (CNC) plays a requisite role during cardiovascular development and defects in the formation of CNC-derived structures underlie several common forms of human congenital birth defects. Migration of the CNC cells to their destinations as well as expansion and maintenance of these cells are important for the normal development of the cardiac outflow tract and aortic arch arteries; however, molecular mechanisms regulating these processes are not well-understood. Fibronectin (FN) protein is present along neural crest migration paths and neural crest cells migrate when plated on FN in vitro; therefore, we tested the role of FN during the development of the CNC in vivo. Our analysis of the fate of the neural crest shows that CNC cells reach their destinations in the branchial arches and the cardiac outflow tract in the absence of FN or its cellular receptor integrin α5β1. However, we found that FN and integrin α5 modulate CNC proliferation and survival, and are required for the presence of normal numbers of CNC cells at their destinations.

Ubiquitination of alpha 5 beta 1 integrin controls fibroblast migration through lysosomal degradation of fibronectin-integrin complexes

Cell migration requires endocytosis and recycling of integrins, but it is not known whether degradation of these membrane proteins is involved. Here we demonstrate that in migrating cells, a fraction of the endocytosed fibronectin receptor, alpha 5 beta 1 integrin, is sorted into multivesicular endosomes together with fibronectin and degraded in lysosomes. This sorting requires fibronectin-induced ubiquitination of the alpha 5 subunit, and the activity of the endosomal sorting complex required for transport (ESCRT) machinery, which interacts with alpha 5 beta 1 integrin. Importantly, we demonstrate that both alpha 5 ubiquitination and ESCRT functions are required for proper migration of fibroblasts. We propose that ligand-mediated degradation of alpha 5 beta 1 integrin via the ESCRT pathway is required in order to prevent endosomal accumulation of ligand-bound integrins that might otherwise form nonproductive adhesion sites. Fibronectin and alpha 5 beta 1 integrin therefore are trafficked to lysosomes in a similar way to growth factors and their receptors.

Breast cancer cells in three-dimensional culture display an enhanced radioresponse after coordinate targeting of integrin alpha5beta1 and fibronectin

Tactics to selectively enhance cancer radioresponse are of great interest. Cancer cells actively elaborate and remodel their extracellular matrix (ECM) to aid in survival and progression. Previous work has shown that beta1-integrin inhibitory antibodies can enhance the growth-inhibitory and apoptotic responses of human breast cancer cell lines to ionizing radiation, either when cells are cultured in three-dimensional laminin-rich ECM (3D lrECM) or grown as xenografts in mice. Here, we show that a specific alpha heterodimer of beta1-integrin preferentially mediates a prosurvival signal in human breast cancer cells that can be specifically targeted for therapy. 3D lrECM culture conditions were used to compare alpha-integrin heterodimer expression in malignant and nonmalignant cell lines. Under these conditions, we found that expression of alpha5beta1-integrin was upregulated in malignant cells compared with nonmalignant breast cells. Similarly, we found that normal and oncofetal splice variants of fibronectin, the primary ECM ligand of alpha5beta1-integrin, were also strikingly upregulated in malignant cell lines compared with nonmalignant acini. Cell treatment with a peptide that disrupts the interactions of alpha5beta1-integrin with fibronectin promoted apoptosis in malignant cells and further heightened the apoptotic effects of radiation. In support of these results, an analysis of gene expression array data from breast cancer patients revealed an association of high levels of alpha5-integrin expression with decreased survival. Our findings offer preclinical validation of fibronectin and alpha5beta1-integrin as targets for breast cancer therapy.

Ovarian cancer ascites protects from TRAIL-induced cell death through alphavbeta5 integrin-mediated focal adhesion kinase and Akt activation

Interactions between ovarian cancer cells and the surrounding tumor microenvironment are not well characterized. We have earlier shown that ovarian cancer ascites induces Akt activation and protect tumor cells from TRAIL-induced apoptosis. Here, we investigated the mechanism by which ascites activates Akt. The ability of ovarian cancer ascites to activate Akt and inhibit TRAIL-induced cell death and caspase activity was decreased by heat inactivation, but was retained in ascites fractions >5 kDa. The survival promoting activity of ascites was not affected by inhibitors of growth factor receptor including epidermal growth factor receptor (EGFR), VEGFR, FGFR, Her2/neu, and IGF-R1. However, this activity was inhibited by an alphavbeta5 integrin-blocking antibody, but not by blocking antibodies against alphavbeta3, beta1, or beta3 integrins. alphavbeta5 integrin-blocking antibodies also inhibited ascites-induced Akt phosphorylation and c-FLIPs up-regulation. Ovarian cancer ascites induced a rapid phosphorylation of focal adhesion kinase (FAK), which closely correlated with the phosphorylation of Akt overtime. FAK phosphorylation was strongly inhibited by alphavbeta5 integrin-blocking antibodies. Depletion of FAK content by RNA interference was also associated with inhibition of ascites-mediated Akt activation and survival. These results suggest that ovarian cancer ascites induces FAK and Akt activation in an alphavbeta5 integrin-dependent pathway, which confers protection from TRAIL-induced cell death and caspase activation.

Emerging anticancer therapeutic targets and the cardiovascular system: is there cause for concern?

The race for a cure to cancer continues, fueled by unprecedented discoveries of fundamental biology underlying carcinogenesis and tumorigenesis. The expansion of the target list and tools to approach them is moving the oncology community extraordinarily rapidly to clinical trials, bringing new hope for cancer patients. This effort is also propelling biological discoveries in cardiovascular research, because many of the targets being explored in cancer play fundamental roles in the heart and vasculature. The combined efforts of cardiovascular and cancer biologists, along with clinical investigators in these fields, will be needed to understand how to safely exploit these efforts. Here, we discuss a few of the many research foci in oncology where we believe such collaboration will be particularly important.

Kallikrein-related peptidase 7 promotes multicellular aggregation via the alpha(5)beta(1) integrin pathway and paclitaxel chemoresistance in serous epithelial ovarian carcinoma

Kallikrein-related peptidase 7 (KLK7) is upregulated in epithelial ovarian carcinoma (EOC) with high levels correlated with poor prognosis. However, the mechanisms underlying this relationship and the role of KLK7 in EOC progression are unknown. We report that two different KLK7 transcripts, KLK7-253 and KLK7-181, are simultaneously expressed in high-grade serous EOC. Multicellular aggregates (MCA), which promote cell survival and chemoresistance, were observed in SKOV-3 cells stably overexpressing KLK7-253 in particular. Importantly, these MCAs invade into a monolayer of mesothelial cells and form cancer cell foci. Blocking MCA using antibodies against KLK7 and alpha(5)beta(1) and beta(1) integrins confirmed the involvement of KLK7 and integrin-regulated cell adhesion. Increased levels of alpha(5)/beta(1) integrins and enhanced attachment to fibronectin and vitronectin, which was blocked with an anti-beta(1) integrin antibody, were also observed. Finally, Western blot and immunohistochemistry showed higher KLK7 and alpha(5)/beta(1) integrin levels in serous EOC cells from ascites and tumor samples from chemotherapy nonresponders with short postsurvival times. Additionally, both KLK7-253 and KLK7-181 clones were more resistant to paclitaxel treatment in vitro. These findings suggest a mechanism for the association of high KLK7 levels with chemoresistance and poor prognosis for serous EOC patients by promotion of peritoneal dissemination and reinvasion via increased MCA and alpha(5)beta(1) integrin-dependent cell adhesion.

Gene expression profiling of cholangiocarcinoma-derived fibroblast reveals alterations related to tumor progression and indicates periostin as a poor prognostic marker

Background

Fibroblasts play important roles in several cancers. It was hypothesized that cholangiocarcinoma (CCA)-associated fibroblasts (Cfs) differ from non-tumorigenic liver fibroblasts (Lfs) in their gene expression profiles resulting in the capability to promote cancer. Periostin (PN) is a multi-functional protein and has emerged as a promising marker for tumor progression. The role of PN in CCA, however, has not yet been explored.

Results

In this study, the gene expression profile of Cfs in comparison to Lfs was performed using oligonucleotide microarrays. The common- and unique-expressed genes in Cfs and the promising roles in cancer promotion and progression were determined. PN was markedly over-expressed in Cfs confirmed by real time RT-PCR and western blot analysis. Immunohistochemistry examination of a number of patients with intrahepatic CCA showed the expression of PN solely in stromal fibroblasts, but was expressed neither in cancer cells nor immune cells. Low to no expression of PN was observed in tissues of benign liver disease and hepatocellular carcinoma. CCA patients with high levels of PN had significantly shorter survival time than those with low levels (P = 0.026). Multivariate analysis revealed high levels of PN (P = 0.045) and presence of lymph node metastasis (P = 0.002) as independent poor prognostic factors. The in vitro study revealed that recombinant PN induced CCA cell proliferation and invasion. Interestingly, interference RNA against integrin α₅ significantly reduced the cellular response to PN-stimulated proliferation and invasion.

Conclusion

The gene expression profile of fibroblasts in CCA is apparently explored for the first time and has determined the genes involving in induction of this cancer progression. High PN can be used to distinguish CCA from other related liver diseases and is proposed as a prognostic factor of poor survival. Regulation of fibroblast-derived PN in CCA proliferation and invasion may be considered as an alternative therapeutic approach.

Gene expression profiling of cholangiocarcinoma-derived fibroblast reveals alterations related to tumor progression and indicates periostin as a poor prognostic marker

BACKGROUND

Fibroblasts play important roles in several cancers. It was hypothesized that cholangiocarcinoma (CCA)-associated fibroblasts (Cfs) differ from non-tumorigenic liver fibroblasts (Lfs) in their gene expression profiles resulting in the capability to promote cancer. Periostin (PN) is a multi-functional protein and has emerged as a promising marker for tumor progression. The role of PN in CCA, however, has not yet been explored.

RESULTS

In this study, the gene expression profile of Cfs in comparison to Lfs was performed using oligonucleotide microarrays. The common- and unique-expressed genes in Cfs and the promising roles in cancer promotion and progression were determined. PN was markedly over-expressed in Cfs confirmed by real time RT-PCR and western blot analysis. Immunohistochemistry examination of a number of patients with intrahepatic CCA showed the expression of PN solely in stromal fibroblasts, but was expressed neither in cancer cells nor immune cells. Low to no expression of PN was observed in tissues of benign liver disease and hepatocellular carcinoma. CCA patients with high levels of PN had significantly shorter survival time than those with low levels (P = 0.026). Multivariate analysis revealed high levels of PN (P = 0.045) and presence of lymph node metastasis (P = 0.002) as independent poor prognostic factors. The in vitro study revealed that recombinant PN induced CCA cell proliferation and invasion. Interestingly, interference RNA against integrin alpha 5 significantly reduced the cellular response to PN-stimulated proliferation and invasion.

CONCLUSION

The gene expression profile of fibroblasts in CCA is apparently explored for the first time and has determined the genes involving in induction of this cancer progression. High PN can be used to distinguish CCA from other related liver diseases and is proposed as a prognostic factor of poor survival. Regulation of fibroblast-derived PN in CCA proliferation and invasion may be considered as an alternative therapeutic approach.

Priming integrin alpha5 promotes human mesenchymal stromal cell osteoblast differentiation and osteogenesis

Adult human mesenchymal stromal cells (hMSCs) have the potential to differentiate into chondrogenic, adipogenic, or osteogenic lineages, providing a potential source for tissue regeneration. An important issue for efficient bone regeneration is to identify factors that can be targeted to promote the osteogenic potential of hMSCs. Using transcriptome analysis, we found that integrin alpha5 (ITGA5) expression is up-regulated during dexamethasone-induced osteoblast differentiation of hMSCs. Gain-of-function studies showed that ITGA5 promotes the expression of osteoblast phenotypic markers and in vitro osteogenesis of hMSCs. Down-regulation of endogenous ITGA5 using specific shRNAs blunted osteoblast marker gene expression and osteogenic differentiation. Molecular analyses showed that the enhanced osteoblast differentiation induced by ITGA5 was mediated by activation of focal adhesion kinase/ERK1/2-MAPKs and PI3K signaling pathways. Remarkably, activation of endogenous ITGA5 using agonists such as a specific antibody that primes the integrin or a peptide that specifically activates ITGA5 was sufficient to enhance ERK1/2-MAPKs and PI3K signaling and to promote osteoblast differentiation and osteogenic capacity of hMSCs. Importantly, we demonstrated that hMSCs engineered to overexpress ITGA5 exhibited a marked increase in their osteogenic potential in vivo. Taken together, these findings not only reveal that ITGA5 is required for osteoblast differentiation of adult hMSCs but also provide a targeted strategy using ITGA5 agonists to promote the osteogenic capacity of hMSCs. This may be used for tissue regeneration in bone disorders where the recruitment or capacity of hMSCs is compromised.

An in-vitro tumour microenvironment model using adhesion to type I collagen reveals Akt-dependent radiation resistance in renal cancer cells

BACKGROUND

Renal cell carcinoma (RCC) is considered resistant to ionizing radiation. Recently, the extracellular matrix (ECM) has been shown to play a role in both drug resistance and radiation resistance (RR). While fibronectin has been extensively investigated in the context of RR, the role of type I collagen [col(I)], a principal constituent of the ECM in tumour metastases, in RR of RCC is unknown.

METHODS

RCC cell adhesion to matrix was studied via pre-coating a variety of ECM glycoproteins onto plates. Cancer cell apoptosis and cell cycle were evaluated with flow cytometry using annexin V and propidium iodide stains, respectively. Activation of cellular survival signalling was analysed with western blots, and specific molecular inhibitors were correspondingly employed to block signalling. Hypoxia (<1%) was induced via N(2)/CO(2) gas flow in a specialized chamber.

RESULTS

While adherence to col(I) enhanced RCC cell proliferation in general, col(I) and fibronectin, but not fibrinogen, could confer specific anti-apoptotic RR to RCC cells. The radioprotective effect of col(I) was maintained during both hypoxia/reoxygenation and normoxia conditions. In contrast to intact col(I), micronized col(I), lacking the natural fibrillar structure, was not radioprotective. The effect of col(I) in RCC cells is mediated via attenuation of apoptosis rather than cell cycle redistribution, involving the PI3 kinase/Akt pathway but not the MAP kinase pathway.

CONCLUSIONS

Adherence to col(I) appears to be a relevant environmental cue enhancing RR in RCC cells, Akt dependently. Our results support inhibition of the PI3-kinase/Akt pathway as a radiosensitizing approach.

Transforming growth factor-beta1-induced satellite cell apoptosis in chickens is associated with beta1 integrin-mediated focal adhesion kinase activation

Transforming growth factor-beta1 (TGF-beta1) induces apoptosis in many types of cells. The cell adhesion receptor, beta1 integrin subunit, prevents apoptosis and may be involved in TGF-beta1-induced muscle cell apoptosis. In the current study, chicken primary satellite cells, myogenic precursors, were used to investigate the apoptotic effect of TGF-beta1 on muscle cells. The data from the current study showed that the addition of exogenous TGF-beta1 reduced beta1 integrin expression and altered its localization. Treatment of the satellite cells with TGF-beta1 increased the number of apoptotic cells indicated by annexin-V using flow cytometry. The number of caspase-positive cells was increased in the TGF-beta1-treated immunostained cells, which supported that TGF-beta1 induced satellite cell apoptosis. It has been shown that beta1 integrin is involved in muscle cell survival. In response to the activation of beta1 integrin, focal adhesion kinase (FAK) phosphorylates tyrosine at residue 397 and activates cell survival signal transduction. The phosphorylation of FAK was significantly reduced from 30 min to 4 h after TGF-beta1 treatment during both satellite cell proliferation and differentiation. These data suggested that the apoptotic effect of TGF-beta1 on satellite cells is likely associated with a beta1 integrin-mediated FAK signaling pathway during satellite cell proliferation and differentiation.

Extracellular matrix in bone marrow can mediate drug resistance in myeloma

Glucocorticoids such as dexamethasone, frequently used for the treatment of multiple myeloma (MM), produce a rapid reduction in tumor mass. However, despite frequent initial complete remission, prolonged dexamethasone treatment results in the appearance of chemoresistant tumor cells and most patients with MM ultimately present relapse of the underlying disease. Accumulating data suggest that bone marrow components such as cytokines, extracellular matrix (ECM) and adjacent stroma cells could cooperate to provide a sanctuary to malignant plasma cells that allow their survival after initial drug exposure. This review focuses on the two major components of the bone marrow ECM that have been identified as mediators for innate or acquired drug resistance in MM, hyaluronan and fibronectin. These two ECM molecules are thought to play a crucial role in the pathogenesis of MM, combining their protective activities to promote optimal conditions for the long life of plasma cells and contribute to de novo drug resistance. They represent promising targets for the development of innovative treatments in order to prevent interactions between tumor cells and their microenvironment and to sensitize cancer cells to chemotherapy before the emergence of acquired mechanisms of chemoresistance.

Cell adhesion to fibronectin induces mitomycin C resistance in bladder cancer cells

OBJECTIVE

To investigate whether cell adhesion to fibronectin induces drug resistance in human bladder cancer cells, and to study the survival signalling pathway in cell adhesion to fibronectin-mediated chemotherapy resistance in vitro.

MATERIALS AND METHODS

T24 cells (human bladder cancer cell lines) were pre-coated with fibronectin, and treated with mitomycin C (MMC) and the specific phosphoinositide-3 kinase (PI3-K) inhibitor LY294002. The apoptosis and cell cycles were analysed. The activity of the caspase-8, -9 and apoptosis-inducing factor (AIF) apoptosis pathways were assessed using colorimetric assay, immunofluorescence, Western blot and flow cytometry. The expression of glycogen synthase kinase-3beta (GSK-3beta) and cyclin D1, as the key regulator of G1/S phase transition, were determined by Western blot. The expression of PI3-K, Akt, phospho-Akt and beta1-integrin were also examined by Western blot.

RESULTS

Apoptosis induced by MMC was significantly resisted by fibronectin adhesion in T24 cells, and this effect was through inhibition of the caspase-9 and AIF apoptosis pathways, but not the caspase-8 pathway. Fibronectin antagonized MMC-induced G0/G1-phase arrest by inactivating GSK-3beta to stabilize cyclin D1 expression in T24 cells. Furthermore, fibronectin-mediated protection of T24 cells was dependent on the activity of the PI3-K/Akt signalling pathway, and the protection could be abolished by the PI3-K inhibitor LY294002.

CONCLUSIONS

Fibronectin-mediated PI3-K/Akt activation protects T24 cells from MMC-induced cell death through inhibition of both caspase-9 and AIF-mediated apoptosis and GSK-3beta/cyclin D1 involved G0/G1-phase arrest.

PKCepsilon regulation of an alpha5 integrin-ZO-1 complex controls lamellae formation in migrating cancer cells

Disruption of intercellular adhesions, increased abundance of alpha(5)beta(1) integrin, and activation of protein kinase Cepsilon (PKCepsilon) correlate with invasion and unfavorable prognosis in lung cancer. However, it remains elusive how these distinct factors contribute to the invasive behavior of cancer cells. Persistent cell motility requires the formation of stable lamellae at the leading edge of a migrating cell. Here, we report that the tight junction protein zonula occludens-1 (ZO-1) preferentially interacts with alpha(5)beta(1) integrin at the lamellae of migrating cells. Disruption of ZO-1 binding to an internal PDZ-binding motif in the alpha(5) cytoplasmic tail prevented the polarized localization of ZO-1 and alpha(5) at the leading edge. Furthermore, silencing of alpha(5) integrin inhibited migration and invasion of lung cancer cells, and silencing of ZO-1 resulted in increased Rac activity and reduced directional cell motility. The formation of the alpha(5)-ZO-1 complex was dependent on PKCepsilon: Phosphorylation of ZO-1 at serine-168 regulated the subcellular localization of ZO-1 and thus controlled its association with alpha(5) integrin. In conclusion, PKCepsilon activation drives the formation of a spatially restricted, promigratory alpha(5)-ZO-1 complex at the leading edge of lung cancer cells.

WWOX gene expression abolishes ovarian cancer tumorigenicity in vivo and decreases attachment to fibronectin via integrin alpha3

The WW domain-containing oxidoreductase (WWOX) gene is located at FRA16D, a common fragile site involved in human cancer. Targeted deletion of Wwox in mice causes increased spontaneous tumor incidence, confirming that WWOX is a bona fide tumor suppressor gene. We show that stable transfection of WWOX into human PEO1 ovarian cancer cells, containing homozygous WWOX deletion, abolishes in vivo tumorigenicity, but this does not correlate with alteration of in vitro growth. Rather, WWOX restoration in PEO1, or WWOX overexpression in SKOV3 ovarian cancer cells, results in reduced attachment and migration on fibronectin, an extracellular matrix component linked to peritoneal metastasis. Conversely, siRNA-mediated knockdown of endogenous WWOX in A2780 ovarian cancer cells increases adhesion to fibronectin. In addition, whereas there is no WWOX-dependent difference in cell death in adherent cells, WWOX-transfected cells in suspension culture display a proapoptotic phenotype. We further show that WWOX expression reduces membranous integrin alpha(3) protein but not integrin alpha(3) mRNA levels, and that adhesion of PEO1 cells to fibronectin is predominantly mediated through integrin alpha(3). We therefore propose that WWOX acts as an ovarian tumor suppressor by modulating the interaction between tumor cells and the extracellular matrix and by inducing apoptosis in detached cells. Consistent with this, the suppression of PEO1 tumorigenicity by WWOX can be partially overcome by implanting these tumor cells in Matrigel. These data suggest a possible role for the loss of WWOX in the peritoneal dissemination of human ovarian cancer cells.

Proapoptotic function of integrin beta(3) in human hepatocellular carcinoma cells

PURPOSE

This study evaluates the proapoptotic function of integrin beta(3) in human hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

The expression of integrin beta(3) in 67 HCC specimens paired with corresponding neighboring nontumorous tissue was studied by quantitative real-time PCR and Western blot. The proapoptotic function of integrin beta(3) in SMMC-7721 human hepatoma cells overexpressing ITGB3 (gene coding integrin beta(3)) was determined through colony formation, serum starvation, and anoikis assay.

RESULTS

Compared with neighboring pathologically normal liver tissue, approximately 60% of the HCC specimens showed a significant down-regulated level of integrin beta(3) expression. Transient expression of integrin beta(3) in SMMC-7721 resulted in an enhanced level of apoptosis and suppression of colony formation. Cell growth inhibition on serum/ligand deprivation and incidences of anoikis were remarkably increased in SMMC-7721 with stable expression of integrin beta(3) in comparison with vector control transfectants. In addition, expression of fibrinogen and vitronectin, two native ligands for integrin alpha(v)beta(3) in liver, was inhibited, which was correlated with the decreased integrin beta(3) expression. Replenishing these ligands to the starved SMMC-7721 stable transfectants effectively restored the proapoptotic function of integrin beta(3).

CONCLUSIONS

Down-regulation of integrin beta(3) and its ligands in liver is related to the aggressive growth of HCC. Thus, reconstitution of integrin beta(3) in HCC may be a potential therapeutic approach to inhibit aggressive growth of liver cancer.

From mechanotransduction to extracellular matrix gene expression in fibroblasts

Tissue mechanics provide an important context for tissue growth, maintenance and function. On the level of organs, external mechanical forces largely influence the control of tissue homeostasis by endo- and paracrine factors. On the cellular level, it is well known that most normal cell types depend on physical interactions with their extracellular matrix in order to respond efficiently to growth factors. Fibroblasts and other adherent cells sense changes in physical parameters in their extracellular matrix environment, transduce mechanical into chemical information, and integrate these signals with growth factor derived stimuli to achieve specific changes in gene expression. For connective tissue cells, production of the extracellular matrix is a prominent response to changes in mechanical load. We will review the evidence that integrin-containing cell-matrix adhesion contacts are essential for force transmission from the extracellular matrix to the cytoskeleton, and describe novel experiments indicating that mechanotransduction in fibroblasts depends on focal adhesion adaptor proteins that might function as molecular springs. We will stress the importance of the contractile actin cytoskeleton in balancing external with internal forces, and describe new results linking force-controlled actin dynamics directly to the expression of specific genes, among them the extracellular matrix protein tenascin-C. As assembly lines for diverse signaling pathways, matrix adhesion contacts are now recognized as the major sites of crosstalk between mechanical and chemical stimuli, with important consequences for cell growth and differentiation.

Cell survival, activation and apoptosis of hepatic stellate cells: modulation by extracellular matrix proteins

AIM

Cytokines and growth factors released by various hepatic cells exert both paracrine and autocrine effects on hepatic stellate cell (HSC) activation during liver injury. The aim of the present study was to examine whether the surrounding extracellular matrix (ECM) influences the activation, transdifferentiation and survival of HSCs.

METHODS

An in vitro model system of isolated HSCs maintained in culture on different matrix protein substrata was employed.

RESULTS

The rate of loss of HSC-specific retinol uptake activity and gain of myofibroblast-like activity such as (35)[S] proteoglycan synthesis varied in cells maintained on different matrix proteins and was in the order collagen I > collagen IV >/= laminin. (3)[H]-thymidine incorporation by HSCs maintained on different matrix proteins varied and was in the order collagen I > collagen IV > laminin. MTT assay revealed that the growth inhibition in response to curcumin was significantly low in cells maintained on collagen I. Apoptotic marker activities such as DNA fragmentation, 4',6'-diamidino-2-phenylindole dihydrochloride (DAPI) staining, annexin staining and caspase-3 activities showed that cells maintained on collagen I showed minimal apoptosis than those maintained on collagen IV, laminin and polylysine, showing the influence of ECM on HSC apoptosis. Experiments using blocking antibodies showed that the collagen I effect was mediated through alpha(2)beta(1) integrin.

CONCLUSIONS

These results indicate that ECM influences activation, transdifferentiation and survival of HSCs, and suggest that apart from diffusible factors, the surrounding ECM also influences HSC behavior critical in both the progression of the fibrosis and the restitution of the liver during recovery after hepatic injury.

Hematopoietic niche and bone meet

PURPOSE OF REVIEW

To provide an overview of the hematopoietic stem cell (HSC) niche in the bone marrow. In addition to highlighting recent advances in the field, we will also discuss components of the niche that may contribute to the development of cancer, or cancer metastases to the bone.

RECENT FINDINGS

Much progress has been very recently made in the understanding of the cellular and molecular interactions in the HSC microenvironment. These recent findings point out the extraordinary complexity of the HSC microenvironment. Emerging data also suggest convergence of signals important for HSC and for leukemia or metastatic disease support.

SUMMARY

The HSC niche comprises complex interactions between multiple cell types and molecules requiring cell-cell signaling as well as local secretion. These components can be thought of as therapeutic targets not only for HSC expansion, but also to modify behavior of hematopoietic malignancies and cancer metastases to the bone.

A novel dynamic matrix detachment model reveals a shift from apoptosis to necrosis in melanoma cells

Anchorage-independence is a hallmark of invasive cancer. The setback of the classical poly-HEMA static matrix detachment (SMD) anoikis model is the absence of dynamic fluid circulation, resulting in cell aggregates. We addressed this problem by developing a novel 3D cell culture dynamic matrix detachment (DMD) model with a turbulent-free laminar flow, yielding a very low shear stress. In this study, we focused on melanoma cells where apoptosis was evaluated both via annexin V flow cytometry and caspase cleavage. The DMD model was superior to SMD in the induction of melanoma cell death and in revealing a shift from apoptosis to necrotic cell death, as evident by failure to activate caspase 9 and a decrease in annexin V stain. Combination of DMD with cisplatin could further accentuate necrotic cell death in cisplatin-resistant melanoma cells. Thus, the DMD model may be a useful matrix deprivation model to identify necrotic vs. apoptotic cell death pathways.

Clinical and biological significance of tissue transglutaminase in ovarian carcinoma

Tissue type transglutaminase (TG2) is a unique multifunctional protein that plays a role in many steps in the cancer metastatic cascade. Here, we examined the clinical (n = 93 epithelial ovarian cancers) and biological (in vitro adhesion, invasion, and survival and in vivo therapeutic targeting) significance of TG2 in ovarian cancer. The overexpression of TG2 was associated with significantly worse overall patient survival in both univariate and multivariate analyses. Transfection of TG2 into SKOV3ip1 cells promoted attachment and spreading on fibronectin-coated surfaces and increased the in vitro invasive potential of these cells. Conversely, TG2 silencing with small interfering RNA (siRNA) of HeyA8 cells significantly decreased the invasive potential of the cells and also increased docetaxel-induced cell death. In vivo therapy experiments using chemotherapy-sensitive (HeyA8) and chemotherapy-resistant (HeyA8-MDR and RMG2) models showed significant antitumor activity both with TG2 siRNA-1,2-dioleoyl-sn-glycero-3-phosphatidylcholine alone and in combination with docetaxel chemotherapy. This antitumor activity was related to decreased proliferation and angiogenesis and increased tumor cell apoptosis in vivo. Taken together, these findings indicate that TG2 overexpression is an adverse prognostic factor in ovarian carcinoma and TG2 targeting may be an attractive therapeutic approach.

Elimination of interfering activity in serum samples in the Chinese hamster ovary pertussis serology assay

An interfering substance in various frozen serum samples was observed to inhibit the adhesion of Chinese hamster ovary (CHO) cells to microplate surfaces during a CHO pertussis neutralization test, resulting in wells that lacked cells or wells with dead cells after 2 days of incubation. The interfering activity in the serum could be eliminated by (i) transferring cells to other wells after their initial incubation, (ii) adding fetal calf serum (FCS) to the sample dilution buffer, (iii) precoating microplates with FCS, or (iv) preincubating the samples at 4 degrees C for 5 days. Preincubating the samples at 4 degrees C for 5 days reduced the interfering activity in only some of the samples. Adding serum to the sample dilution buffer or precoating the microplates with serum did not influence the antibody titers in the serum samples. The method described may be used for routine applications.

Transforming growth factor-beta prevents osteoblast apoptosis induced by skeletal unloading via PI3K/Akt, Bcl-2, and phospho-Bad signaling

Loss of mechanical loading induces rapid bone loss resulting from reduced osteoblastogenesis and decreased bone formation. The signaling mechanisms involved in this deleterious effect on skeletal metabolism remain poorly understood. We have previously shown that hindlimb suspension in rats increases osteoblast apoptosis associated with decreased phosphatidylinositol 3-kinase (PI3K) signaling. In this study, we investigated whether transforming growth factor (TGF)-beta2 may prevent the altered signaling and osteoblast apoptosis induced by skeletal unloading in vivo. Hindlimb suspension-induced decreased bone volume was associated with reduced alpha(5)beta(1)-integrin protein levels and PI3K/Akt signaling in unloaded bone. Continuous administration of TGF-beta2 using osmotic minipumps prevented the decreased alpha(5)beta(1)-integrin expression and the reduced PI3K/Akt signaling in unloaded bone, resulting in the prevention of osteoblast apoptosis. We also show that TGF-beta2 prevented the decreased Bcl-2 levels induced by unloading, which suggests that TGF-beta2 targets Bcl-2 via PI3K/Akt to prevent osteoblast apoptosis in unloaded bone. Furthermore, we show that TGF-beta2 prevented the decrease in phosphorylated Bad, the inactive form of the proapoptotic protein Bad, induced by unloading. These results identify a protective role for TGF-beta2 in osteoblast apoptosis induced by mechanical unloading via the alpha(5)beta(1)/PI3K/Akt signaling cascade and downstream Bcl-2 and phospho-Bad survival proteins. We thus propose a novel role for TGF-beta2 in protection from unloading-induced apoptosis in vivo.

FAK-independent alphavbeta3 integrin-EGFR complexes rescue from anoikis matrix-defective fibroblasts

Extracellular matrix (ECM) binding to integrin receptors regulates cell cycle progression and survival. In adherent cells, ECM disassembly induces anoikis, the apoptotic pathway switched on by loss of adhesion. ECM-deficient Ehlers-Danlos syndrome (EDS) fibroblasts, to adhere to rare fibronectin (FN) fibrils, and to proliferate, only organize, as FN receptor, the alphavbeta3 integrin. We report that in EDS cells the alphavbeta3 integrin is bound to talin and vinculin, but not to tensin, and that actin cytoskeleton is disorganized. Furthermore, in EDS cells Bcl-2 is down-regulated and caspases are active. We provide evidence that the antibody-mediated alphavbeta3 integrin or the FN inhibition induces anoikis in EDS cells. The alphavbeta3 integrin transduces survival signals to pp60src-mediated tyrosine phosphorylated paxillin, instead than to FAK, and interacts with EGF receptor (EGFR). This complex, when activated by EGF and FN, signals for the rescue of EDS cells from anoikis. Therefore, EDS cells, through the alphavbeta3 integrin-EGFR complexes, engage a paxillin- but not FAK-mediated pathway of cell survival.

RGDS peptides immobilized on titanium alloy stimulate bone cell attachment, differentiation and confer resistance to apoptosis

A major cause of implant failure in skeletal tissues is failure of osseointegration, often due to lack of adhesion of cells to the titanium (Ti) alloy interface. Since arginine-glycine-aspartic acid (RGD)-containing peptides have been shown to regulate osteoblast adhesion, we tested the hypothesis that, bound to a Ti surface, these peptides would promote osteoblasts differentiation, while at the same time inhibit apoptosis. RGDS and RGES (control) peptides were covalently linked to Ti discs using an APTS linker. While the grafting of both RGDS and RGES significantly increased Ti surface roughness, contact angle analysis showed that APTS significantly increased the surface hydrophobicity; when the peptides were tethered to Ti, this was reduced. To evaluate attachment, MC3T3-E1 osteoblast cells were grown on these discs. Significantly more cells attached to the Ti-grafted RGDS then the Ti-grafted RGES control. Furthermore, expression of the osteoblasts phenotype was significantly enhanced on the Ti-grafted RGDS surface. When cells attached to the Ti-grafted RGDS were challenged with staurosporine, an apoptogen, there was significant inhibition of apoptosis; in contrast, osteoblasts adherent to the Ti-grafted RGES were killed. It is concluded that RGD-containing peptides covalently bonded to Ti promotes osteoblasts attachment and survival with minimal changes to the surface of the alloy. Therefore, such modifications to Ti would have the potential to promote osseointegration in vivo.

An altered fibronectin matrix induces anoikis of human squamous cell carcinoma cells by suppressing integrin alpha v levels and phosphorylation of FAK and ERK

Fibronectin regulates many cellular processes, including migration, proliferation, differentiation, and survival. Previously, we showed that squamous cell carcinoma (SCC) cell aggregates escape suspension-induced, p53-mediated anoikis by engaging in fibronectin-mediated survival signals through focal adhesion kinase (FAK). Here we report that an altered matrix, consisting of a mutated, nonfunctional high-affinity heparin-binding domain and the V region of fibronectin (V+H-), induced anoikis in human SCC cells; this response was blocked by inhibitors of caspase-8 and caspase-3. Anoikis was mediated by downregulation of integrin alpha v in a panel of SCC cells and was shown to be proteasome-dependent. Overexpression of integrin alpha v or FAK inhibited the increase in caspase-3 activation and apoptosis, whereas suppression of alpha v or FAK triggered a further significant increase in apoptosis, indicating that the apoptosis was mediated by suppression of integrin alpha v levels and dephosphorylation of FAK. Treatment with V+H- decreased the phosphorylation of extracellular signal-regulated kinase (ERK) 1 and 2, and direct activation of ERK by constitutively active MEK1, an ERK kinase, increased ERK1 and ERK2 phosphorylation and inhibited the increase in apoptosis induced by V+H-. ERK acted downstream from alpha v and FAK signals, since alpha v and FAK overexpression inhibited both the decrease in ERK phosphorylation and the increase in anoikis triggered by V+H-. These findings provide evidence that mutations in the high-affinity heparin-binding domain in association with the V region of fibronectin, or altered fibronectin matrices, induce anoikis in human SCC cells by modulating integrin alpha v-mediated phosphorylation of FAK and ERK.

Gastric cancer cells in collagen gel matrix: Three-dimensional growth and differential expression of adhesion molecules (CD44s, CD54, E-cadherin)

To characterize the growth of human gastric cancer cells in collagen gel matrix and adhesive status of the cells in comparison with conventional monolayer cells. Three kinds of human gastric cancer cell lines (BGC823, SGC7901, and MKN28) were cultured alone or co-cultured with normal human fibroblasts in collagen gel matrix, and their cell cycle, metabolic function, and the expression of adhesive molecules (CD44s, CD54, and E-cadherin) were analyzed by flow cytometry or other methods. Two of three cell lines (BGC823 and SGC7901) and their co-cultures showed multilayer growth in collagen gel matrix, and their growth and metabolism rate became slow and the cell adhesion molecules (CAMs) expression was down regulated. Gastric cancer cell alone or with fibroblasts in collagen gel matrix showed distinct growth feature when compared with monolayer cells, which represent two kinds of different experimental models. BGC823 and SGC7901 cells growing in three-dimension may recur some characteristics of their original solid tumor in vivo with the invasive or metastatic ability. According to different aims, it should pay great care in choice of experimental model to get more reasonable results.

Spatiotemporal patterns of smooth muscle cell changes in ascending aortic dilatation with bicuspid and tricuspid aortic valve stenosis: focus on cell-matrix signaling

OBJECTIVE

The present study examined temporal and spatial patterns of extracellular matrix and smooth muscle cell changes in the ascending aorta with bicuspid and tricuspid aortic valve stenosis.

METHODS

Wall specimens were retrieved from both the greater and the lesser curvature ("convexity" and "concavity") of 14 nonaneurysmal and 12 aneurysmal aortas (aortic ratios 1.2 and 1.5, respectively) and from 3 heart donors (normal). Immunochemistry was performed for detection of apoptotic (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling [TUNEL]-positive) and proliferating (Ki-67-positive) smooth muscle cells and for semiquantification of matrix proteins (collagens, fibronectin, tenascin, laminin). Co-immunoprecipitation assessed the extent of Bcl-2-modifying factor binding to Bcl-2, indicating a matrix-derived cytoskeleton-mediated proapoptotic signaling. Polymerase chain reaction allowed for quantification of messenger RNA expression for Bcl-2.

RESULTS

In both bicuspid and tricuspid aneurysms, fibrillar collagens were reduced, whereas fibronectin and tenascin were increased compared with those in normal conditions. These matrix alterations were already evident in bicuspid nonaneurysmal aortas at the convexity, with significant elevation of apoptotic indexes (P = .02 bicuspid vs normal; P = .48 tricuspid vs normal). Apoptotic indexes correlated with aortic dimensions only in tricuspid aortas (P = .01). No significant increase in Ki-67 was found. Higher levels of Bcl-2-modifying factor-Bcl-2 binding were found in bicuspid nonaneurysmal aorta versus tricuspid (P = .03) and normal aortas (P = .01). Bcl-2 messenger RNA expression was reduced in the bicuspid aorta versus normal (P = .08).

CONCLUSIONS

Smooth muscle cell apoptosis with bicuspid aortic valve stenosis occurred before overt aortic dilation, mainly at the convexity, where wall stress is expectedly higher. In this setting, a matrix-dependent proapoptotic signaling was evidenced by increased Bcl-2-modifying factor-Bcl-2 binding. Stress-dependent bicuspid aortic valve matrix changes may trigger early apoptosis by inducing cytoskeletal rearrangement.

Fak/Src signaling in human intestinal epithelial cell survival and anoikis: differentiation state-specific uncoupling with the PI3-K/Akt-1 and MEK/Erk pathways

Human intestinal epithelial cell survival and anoikis are distinctively regulated according to the state of differentiation. In the present study, we analyzed the roles of focal adhesion kinase (Fak)/Src signaling to the PI3-K/Akt-1 and mitogen-activated protein kinase (MEK)/extracellular regulated kinases (Erk) pathways, within the context of such differentiation-state distinctions. Anoikis was induced by inhibition of beta1 integrins (antibody blocking), inhibition of Fak (pharmacologic inhibition or overexpression of dominant negative mutants), or by maintaining cells in suspension. Activation parameters of Fak, Src, Akt-1, and Erk1/2 were analyzed. Activities of Src, Akt-1, or Erk1/2 were also blocked by pharmacological inhibition or by overexpression of dominant-negative mutants. We report that: (1) the loss or inhibition of beta1 integrin binding activity causes anoikis and results in a down-activation of Fak, Src, Akt-1, and Erk1/2 in both undifferentiated, and differentiated cells; (2) the inhibition of Fak likewise causes anoikis and a down-activation of Src, Akt-1, and Erk1/2, regardless of the differentiation state; (3) Src, PI3-K/Akt-1, and MEK/Erk contribute to the survival of differentiated cells, whereas MEK/Erk does not play a role in the survival of undifferentiated ones; (4) the inhibition/loss of beta1 integrin binding and/or Fak activity results in a loss of Src engagement with Fak, regardless of the state of differentiation; and (5) Src contributes to the activation of both the PI3-K/Akt-1 and MEK/Erk pathways in undifferentiated cells, but does not influence PI3-K/Akt-1 in differentiated ones. Hence, Fak/Src signaling to the PI3-K/Akt-1 and MEK/Erk pathways undergoes a differentiation state-specific uncoupling which ultimately reflects upon the selective engagement of these same pathways in the mediation of intestinal epithelial cell survival.

Bone growth retardation in mouse embryos expressing human collagenase 1

Cellular growth and differentiation are readouts of multiple signaling pathways from the intercellular and/or extracellular milieu. The extracellular matrix through the activation of cellular receptors transmits these signals. Therefore, extracellular matrix proteolysis could affect cell fate in a variety of biological events. However, the biological consequence of inadequate extracellular matrix degradation in vivo is not clear. We developed a mouse model expressing human collagenase (matrix metalloproteinase-1, MMP-1) under the control of Col2a1 promoter. The mice showed significant growth retardation during embryogenesis and a loss of the demarcation of zonal structure and columnar array of the cartilage. Immunological examination revealed increased degradation of type II collagen and upregulation of fibronectin and alpha(5)-integrin subunit in the transgenic cartilage. The resting zone and proliferating zone of the growth plate cartilage exhibited a simultaneous increase in bromodeoxyuridine (BrdU)-incorporated proliferating cells and terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling-positive apoptotic cells, respectively. Chondrocyte differentiation was not disturbed in the transgenic mice as evidenced by normal expression of the Ihh and type X collagen expression. These data demonstrate that type II collagen proteolysis is an important determinant for the skeletal outgrowth through modulation of chondrocyte survival and cartilagenous growth.

Luteogenic hormones act through a vascular endothelial growth factor-dependent mechanism to up-regulate alpha 5 beta 1 and alpha v beta 3 integrins, promoting the migration and survival of human luteinized granulosa cells

The formation of the corpus luteum (CL) is critical for the establishment of a successful pregnancy. After ovulation, the CL develops from the remnants of the ovulated ovarian follicle. This process, which involves varying cell-matrix interactions, is poorly characterized. To understand the role and potential regulation of cell-matrix interactions in the formation of the CL, we investigated the expression and activity of the matrix protein fibronectin (FN) and several of its integrin receptors on luteinized granulosa cells (GCs). In situ, FN and several FN-binding integrins were detected around luteinizing GCs during the early luteal phase, although expression declined in the late luteal phase. In vitro, GCs released FN, and stimulation of these cells with human chorionic gonadotropin increased the surface expression of FN, alpha(5)beta(1), and alpha(v)beta(3). Up-regulation of these proteins on GCs was reproduced by stimulation with vascular endothelial growth factor (VEGF) and was inhibited by anti-VEGF antibody. Lastly, expression of alpha(5)beta(1) and alpha(v)beta(3) mediated adhesion to FN, facilitated migration, and prevented apoptosis. These data suggest that in vivo luteogenic hormones, in part through a VEGF-dependent mechanism, stimulate selected integrin-matrix adhesive interactions that promote the motility and survival of GCs and thus contribute to the formation and preservation of the CL.