Integrin β1 mediates epithelial growth factor-induced invasion in human ovarian cancer cells

Ascitic autotaxin as a potential prognostic, diagnostic, and therapeutic target for epithelial ovarian cancer

BACKGROUND

Malignant ascites contributes to the metastatic process by facilitating the multifocal dissemination of ovarian tumour cells onto the peritoneal surface. However, the prognostic and diagnostic relevance of ascitic fluid remains largely unknown. Herein, we investigated the potential clinical value and therapeutic utility of ascitic autotaxin (ATX) in epithelial ovarian cancer (EOC).

METHODS

ATX expression was assessed in clinical samples. Spheroid-forming assay, real-time PCR, western blot analysis, invadopodia assay, and adhesion assays were performed.

RESULTS

Ascitic ATX expression was highly elevated in patients with ovarian cancer compared to those with benign ascites and was associated with advanced stage, high grade, and a short disease-free period in patients with EOC. Combining the diagnostic ability of ascitic ATX and serum CA-125 levels significantly improved the area under the curve (AUC) value for EOC compared to serum CA125 level alone. This marker combination showed a large odds ratio for short disease-free period in high-risk EOC groups. Functional studies revealed that ascitic ATX was required for maintaining cancer stem cell-like characteristics and invadopodia formation.

CONCLUSION

Ascitic ATX levels may serve as a useful prognostic indicator for predicting aggressive behaviour in EOC. ATX-linked invadopodia are a potential target to prevent peritoneal dissemination in ovarian cancer.

Psoralidin inhibits osteosarcoma growth and metastasis by downregulating ITGB1 expression via the FAK and PI3K/Akt signaling pathways

BACKGROUND

Psoralea corylifolia is a medicinal leguminous plant that has long been used to treat various diseases. Psoralidin (PSO) is the main extract compound of P. corylifolia and exhibits antibacterial, antitumor, anti-inflammatory, antioxidant, and other pharmacological activities. PSO has demonstrated inhibitory effects in several cancers; however, its inhibitory effect on osteosarcoma has not been reported. This study aimed to evaluate the inhibitory effect of PSO on osteosarcoma and elucidate the underlying molecular mechanisms.

METHODS

Crystal violet, cell counting kit-8 (CCK8), and 5-Ethynyl-2'-deoxyuridine (EdU) staining assays were used to assess the inhibitory effect of PSO on the proliferation of 143B and MG63 osteosarcoma cells. Wound healing and Transwell assays were conducted to evaluate the effects of PSO on osteosarcoma cell migration and invasion. The cell cycle and apoptosis were analyzed using flow cytometry. To determine the possible molecular mechanisms, RNA-sequencing was performed and protein expression was analyzed by western blotting. The inhibitory effect of PSO on osteosarcoma in vivo was analyzed using a mouse model of orthotopic osteosarcoma and immunohistochemistry.

RESULTS

PSO inhibited osteosarcoma cell proliferation in a concentration-dependent manner, inhibited cell migration and invasion, and induced cell-cycle arrest and apoptosis. Mechanistically, PSO treatment significantly inhibited the focal adhesion kinase (FAK) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways by downregulating ITGB1 expression in both MG63 and 143B cells. Furthermore, we demonstrated that PSO restrained osteosarcoma growth in vivo.

CONCLUSION

PSO may suppress osteosarcoma via the FAK and PI3K/Akt signaling pathways by downregulating ITGB1 expression.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

P76RBE silencing inhibits ovarian cancer cell proliferation, migration, and invasion via suppressing the integrin β1/NF-κB pathway

Rhophilin Rho GTPase binding protein 2 (P76RBE) belongs to rhophilin family of Rho-GTPase-binding proteins and is found to contribute to the development of diverse cancers. Data in Oncomine and Kaplan-Meier Plotter databases showed that P76RBE was upregulated in ovarian cancer tissues compared with normal tissues, and patients with high P76RBE expression had worse overall survival, which indicated P76RBE may be associated with the pathogenesis of ovarian cancer. This study aimed to investigate the role of P76RBE in ovarian cancer and to reveal the possible underlying mechanisms. The results demonstrated that P76RBE was highly expressed in ovarian cancer tissues and ovarian cancer cell lines. Functionally, silencing of P76RBE suppressed the proliferation, induced cell cycle arrest, and inhibited migration and invasion in OVCAR-3 and OV-90 cells, while overexpression of P76RBE showed opposite effects on A2780 cells. Mechanically, P76RBE silencing resulted in downregulation of integrin β1, accompanying the reduced NF-κB p65 phosphorylation and nuclear translocation. Importantly, integrin β1 knockdown effectively rescued the effects of P76RBE overexpression on ovarian cancer cells with suppressed proliferation, migration, and invasion. Additionally, in the xenograft tumors derived from OVCAR-3 and OV-90 cell lines, P76RBE knockdown inhibited tumor growth. Meanwhile, the expression of integrin β1 and NF-κB p65 phosphorylation was decreased. In summary, our findings indicate that P76RBE contributes to the progression of ovarian cancer through regulating the integrin β1/NF-κB signaling, and it may be a promising target for ovarian cancer therapy.

The Overexpression of Acyl-CoA Medium-Chain Synthetase-3 (ACSM3) Suppresses the Ovarian Cancer Progression via the Inhibition of Integrin β1/AKT Signaling Pathway

Ovarian cancer is considered as one of the most fatal gynecologic malignancies. This work aimed to explore the effects and regulatory mechanism of Acyl-CoA medium-chain synthetase-3 (ACSM3, a subunit of CoA ligases) in ovarian cancer progression. As well as employing CCK-8 assay, clone formation assay, and cell cycle analysis were carried out to investigate cell proliferation ability. Wound healing assay and transwell assay were subsequently used to assess cell migration and invasion. Mice xenografts were then conducted to measure the effects of ACSM3 on tumor development in vivo. Our bioinformatics analysis suggested that the expression of ACSM3 was down-regulated in ovarian cancer tissues, and the low expression level of ACSM3 might related with poorer overall survival than high mRNA expression of ACSM3 in ovarian cancer patients. We artificially regulated the expression of ACSM3 to evaluate its effects on ovarian cancer malignant phenotypes. Our data revealed that the overexpression of ACSM3 inhibited cell proliferation, migration, and invasion of ovarian cancer cells. In contrast, the knock-down of ACSM3 received the opposite results. Our western blot results showed that the Integrin β1/AKT signaling pathway was negatively regulated by ACSM3 expression. Moreover, ACSM3 overexpression-induced suppression of cell migration and invasion activities were abolished by the overexpression of ITG β1 (Integrin β1). Additionally, the growth of ovarian cancer xenograft tumors was also repressed by the overexpression of ACSM3. And ACSM3 interference obtained the contrary effects in vivo. In summary, ACSM3 acts as a tumor suppressor gene and may be a potential therapeutic target of ovarian cancer.

Novel Long Noncoding RNA 005620 Induces Epirubicin Resistance in Triple-Negative Breast Cancer by Regulating ITGB1 Expression

Triple-negative breast cancer (TNBC) is often treated with anthracyclines (e.g., epirubicin or doxorubicin), but very little is known about anthracycline resistance, especially epirubicin resistance in TNBC. To identify novel long noncoding RNAs (lncRNAs) involved in epirubicin resistance in TNBC, we established a new TNBC MDA-MB-231 cell line that was resistant to epirubicin (Epi-R). A total of 12 differentially expressed lncRNAs were identified using RNA sequencing analysis of Epi-R cells. Among these lncRNAs, we found a novel intronic lncRNA, lnc005620, was highly expressed in Epi-R cells and human TNBC tissues. Further gain- and loss-of-function studies demonstrated that lnc005620 played an oncogenic role and partially abrogated the effects of epirubicin on TNBC cells. Using iTRAQ proteomics analysis, we found that three members of the integrin family, integrin β4, integrin β1 and integrin α6, were all upregulated in Epi-R MDA-MB-231 cells. Integrin β1, encoded by the ITGB1 gene, was validated to be a downstream target of lnc005620 in Epi-R MDA-MB-231 cells. Our study demonstrates that novel lnc005620 promotes TNBC progression and chemoresistance to epirubicin via integrin β1 both in vitro and in vivo and provides a promising therapeutic target for TNBC patients in terms of enhancing the benefits of epirubicin treatment.

Activin A increases human trophoblast invasion by upregulating integrin β1 through ALK4

Activin A promotes human trophoblast invasion during the first trimester of pregnancy and is associated with preeclampsia and pregnancy-induced hypertension (PE/PIH) in naturally conceived pregnancies. However, whether integrin β1 mediates activin A-increased trophoblast invasion remains unknown and the evidence is limited regarding the predictive value of activin A for PE/PIH in women receiving in vitro fertilization (IVF) treatment. Here, we studied the role and underlying molecular mechanisms of integrin β1 in activin A-promoted invasion in immortalized (HTR8/SVneo) and primary human extravillous trophoblast (EVT) cells. A nest case-control study was designed to investigate the predictive/diagnostic value of activin A in IVF pregnancies. Results showed that integrin β1 expression increased after activin A treatment and knockdown of integrin β1 significantly decreased both basal and activin A-increased HTR8/SVneo cell invasion. SB431542 (TGF-β type I receptors inhibitor) abolished activin A-induced SMAD2/SMAD3 phosphorylation and integrin β1 overexpression. Activin A-upregulated integrin β1 expression was attenuated after the depletion of ALK4 or SMAD4 in both HTR8/SVneo and primary EVT cells. Furthermore, we found similar first-trimester activin A levels in IVF patients with or without subsequent PE/PIH. These results reveal that integrin β1 mediates activin A-promoted trophoblast invasion through ALK4-activated SMAD2/3-SMAD4 pathway, and the predictive/diagnostic value of first-trimester maternal serum activin A for hypertensive disorders of pregnancy might be different in IVF population.

Integrin subunit β1 and laminin γ1 chain expression: a potential prognostic biomarker in cervical cancer

Aim: The aim of this study was to analyze the prognostic value of integrin subunit β1 and laminin γ1 chain in patients with cervical cancer (CC). Materials & methods: The study included 96 samples. Cytological diagnosis, human papillomavirus (HPV) genotyping, HPV integration status and integrin subunit β1 and laminin γ1 chain expressions were performed or determined using Papanicolaou smear, INNO-LiPA^® Genotyping Extra Kit, in situ hybridization, and immunocytochemistry, respectively. The association between variables was calculated using chi-squared and Fisher's exact test; logistic regression analysis was performed to calculate odds ratios and CI at 95%. Results: Our results show that integrin subunit β1 and laminin γ1 chain expressions increase according to tumor progression. Integrin subunit β1 and laminin γ1 chain expressions are associated with cytological diagnosis (p < 0.001 and p = 0.001, respectively) and laminin γ1 chain expression with the integration status of HPV (p < 0.001). Moderate/high expressions of integrin subunit β1 and laminin γ1 chain were correlated with overall survival and increased risk of CC (6.86 and 3.75, respectively), the odds ratio was 12.91 when the moderate/high expression of integrin subunit β1 and laminin γ1 chain were combined. Conclusion: Our results suggest that integrin subunit β1 and laminin γ1 chain expressions could be a prognostic biomarker in CC.

Integrated Analysis of Prognostic and Immune Associated Integrin Family in Ovarian Cancer

Human integrin receptors are important for cell-cell and cell-matrix adhesion in normal epithelial cells. Emerging evidences have indicated integrin members are involved in cancer development and progression as well. However, the expression patterns and clinical significance of the whole integrin family in ovarian cancer (OC) have not yet been well understood. In the present study, we utilized the public datasets including GEPIA, GEO, ONCOMINE, cBioPortal, Kaplan-Meier Plotter, TIMER databases, to analyze the expression and prognostic value of integrin members in OC. We found ITGA3/B4/B6/B7/B8 were abnormally overexpressed in OC; ITGA6 was good prognosis predictor in OC; ITGA3/ B4/B8 were poor prognosis predictor specially in advanced OC patients; elevated ITGA3/B4 might promote metastasis and elevated ITGA3/B8 might promote platinum resistance of OC; ITGA3 and ITGB4 might synergistically or independently regulate cell adhesion and proliferation; ITGA4/AL/AM/AX/B2/B7 showed strong correlations with various tumor immune infiltrates (TILs), especially with pro-tumor immunes cell types like monocyte, M2 macrophage and exhaustion T cells infiltration; ITGAL/AM/B2/B7 and residing memory CD8+ T cells marker ITGAE were specially associated with early OC patients outcome. Our results implied that ITGA3/B4 were important prognostic markers of advanced OC, ITGAL/AM/ B2/B7 were immune associated prognosis markers of early OC, together they might render important therapeutic targets for OC.

Hsa_circ_CSPP1/MiR-361-5p/ITGB1 Regulates Proliferation and Migration of Cervical Cancer (CC) by Modulating the PI3K-Akt Signaling Pathway

This study aimed to investigate the regulatory mechanism of circular RNA CSPP1 (hsa_circ_CSPP1) in cervical cancer. Based on GEO database, differentially expressed circRNAs and mRNAs related to cervical cancer were screened out by R software. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology (GO) term analysis were performed to analyze the functional and pathway enrichment of identified DEGs. In addition, Cytoscape software was used to build interaction network of DEGs. The mRNA expressions were examined by qRT-PCR. Western blot was conducted to view the expression of proteins. Cell proliferation and apoptosis were respectively evaluated using CCK-8 assay and flow cytometry, whereas cell migration abilities were detected by Transwell assay. The relationship among factors was validated by dual-luciferase reporter gene assay. The influence in cervical tumor growth was further verified through nude mouse model in vivo. Hsa_circ_CSPP1 and ITGB1 were high-expressed in cervical cancer, while miR-361-5p was low-expressed. Hsa_circ_CSPP1 knockdown or miR-361-5p overexpression could suppress cervical cancer cell proliferation and migration, whereas promoted cell apoptosis. In addition, further experiments demonstrated that both hsa_circ_CSPP1 and ITGB1 mRNA were targets of miR-361-5p. Repressing hsa_circ_CSPP1 restrained cell viability and mobility and induced apoptosis through sponging miR-361-5p. Meanwhile, miR-361-5p also inhibited cervical cancer tumorigenesis via downregulation of ITGB1. Knockdown of hsa_circ_CSPP1 impeded tumor growth through suppressing the expression of downstream gene ITGB1, PI3K, and Akt. Circular RNA hsa_circ_CSPP1 regulates cell migration and proliferation in cervical cancer through miR-361-5p/ITGB1 in PI3K-Akt signaling pathway.

Deregulation of miR-183 promotes melanoma development via lncRNA MALAT1 regulation and ITGB1 signal activation

Dysregulation of miR-183 has been recently elucidated in several carcinomas. However, the expression patterns and mechanisms of miR-183 involved in malignant melanoma remain unidentified. Here, we found down-regulation of miR-183 in melanoma tissues and cells. Decreased level of miR-183 was relevant to poor overall survival, while miR-183 up-regulation resulted in a marked suppression of cell growth in vitro and in vivo. We further found that the expression and function of miR-183 were suppressed by MALAT1. Integrin β1 (ITGB1) was then speculated and confirmed as a direct target of miR-183. We also illustrated that MALAT1 may function as a sponge competitive endogenous RNA (ceRNA) for miR-183, and thus regulate the molecular expression of ITGB1. Collectively, we found a new signaling pathway promoting melanoma development by MALAT1-miR-183-ITGB1 axis, which may be clinically valuable as new targets for malignant melanoma therapy.

The translational blocking of α5 and α6 integrin subunits affects migration and invasion, and increases sensitivity to carboplatin of SKOV-3 ovarian cancer cell line

Epithelial ovarian cancer is the most lethal gynecologic malignancy. Integrins, overexpressed in cancer, are involved in various processes that favor the development of the disease. This study focused on determining the degree of involvement of α5, α6 and β3 integrin subunits in the establishment/development of epithelial ovarian cancer (EOC), such as proliferation, migration, invasion, and response to carboplatin. The translation of the α5, α6 and β3 integrins was blocked using morpholines, generating morphant cells for these proteins, which were corroborated by immunofluorescence assays. WST-1 proliferation assay showed that silencing of α5, α6, and β3 integrins does not affect the survival of morphants. Wound healing and transwell chamber assays showed that blocking α5 and α6 integrins decrease, in lesser and greater level respectively, the migratory and the invasive capacity of SKOV-3 cells. Finally, blocking α5 and α6 integrins partially sensitized the cells response to carboplatin, while blocking integrin β3 generated resistance to this drug. Statistical analyses were performed with the GraphPad Prism 5.0 software employing one way and two-way ANOVA tests; data are shown as average±SD. Results suggest that α5 and α6 integrins could become good candidates for chemotherapy targets in EOC.

Lysine-specific demethylase 1 mediates epidermal growth factor signaling to promote cell migration in ovarian cancer cells

Epigenetic abnormalities play a vital role in the progression of ovarian cancer. Lysine-specific demethylase 1 (LSD1/KDM1A) acts as an epigenetic regulator and is overexpressed in ovarian tumors. However, the upstream regulator of LSD1 expression in this cancer remains elusive. Here, we show that epidermal growth factor (EGF) signaling upregulates LSD1 protein levels in SKOV3 and HO8910 ovarian cancer cells overexpressing both LSD1 and the EGF receptor. This effect is correlated with a decrease in the dimethylation of H3K4, a major substrate of LSD1, in an LSD1-dependent manner. We also show that inhibition of PI3K/AKT, but not MEK, abolishes the EGF-induced upregulation of LSD1 and cell migration, indicating that the PI3K/PDK1/AKT pathway mediates the EGF-induced expression of LSD1 and cell migration. Significantly, LSD1 knockdown or inhibition of LSD1 activity impairs both intrinsic and EGF-induced cell migration in SKOV3 and HO8910 cells. These results highlight a novel mechanism regulating LSD1 expression and identify LSD1 as a promising therapeutic target for treating metastatic ovarian cancer driven by EGF signaling.

Inhibition of integrin β1 decreases the malignancy of ovarian cancer cells and potentiates anticancer therapy via the FAK/STAT1 signaling pathway

Integrin β1 (ITGB1) is frequently upregulated in ovarian cancer, and promotes ovarian tumorigenesis and cancer progression. However, the effects of ITGB1 inhibition on ovarian cancer progression and anticancer therapy remain to be elucidated. The results of the present study indicated that ITGB1 was upregulated in HO-8910 and HO-8910PM ovarian cancer cell lines, and knockdown of ITGB1 using short hairpin RNA markedly increased tumor cell apoptosis, decreased tumor cell adhesion and migration, and reduced tumor cell invasion by suppressing matrix metalloproteinase (MMP)-2 and MMP-9 expression. Furthermore, the results of the present study provided evidence regarding the role of ITGB1 inhibition in bevacizumab anticancer therapy. The activation of signal transducer and activator of transcription 1 (STAT1) by focal adhesion kinase (FAK) is involved in integrin-mediated cell migration and adhesion. In the present study, the expression levels of FAK were markedly upregulated in ovarian cancer. The adherence and migratory potentials of ovarian cancer cells were significantly reduced when the FAK/STAT1 signaling pathway was inhibited by fludarabine. The results of the present study demonstrated that ITGB1 inhibition effectively reduced tumorigenesis and disease exacerbation, and contributed to bevacizumab anticancer therapy via the FAK/STAT1 signaling pathway, suggesting that inhibition of ITGB1 is a potential novel therapeutic strategy for ovarian carcinogenesis.

The ZNF304-integrin axis protects against anoikis in cancer

Ovarian cancer (OC) is a highly metastatic disease, but no effective strategies to target this process are currently available. Here, an integrative computational analysis of the Cancer Genome Atlas OC data set and experimental validation identifies a zinc finger transcription factor ZNF304 associated with OC metastasis. High tumoral ZNF304 expression is associated with poor overall survival in OC patients. Through reverse phase protein array analysis, we demonstrate that ZNF304 promotes multiple proto-oncogenic pathways important for cell survival, migration and invasion. ZNF304 transcriptionally regulates β1 integrin, which subsequently regulates Src/focal adhesion kinase and paxillin and prevents anoikis. In vivo delivery of ZNF304 siRNA by a dual assembly nanoparticle leads to sustained gene silencing for 14 days, increased anoikis and reduced tumour growth in orthotopic mouse models of OC. Taken together, ZNF304 is a transcriptional regulator of β1 integrin, promotes cancer cell survival and protects against anoikis in OC.

The novel estrogen receptor GPER regulates the migration and invasion of ovarian cancer cells

G protein-coupled estrogen receptor (GPER) was identified as a new member of the estrogen receptor family in recent years. It has become apparent that GPER mediates the non-genomic signaling of 17β-estradiol (E2) in a variety of estrogen-related cancers. Our previous study has found that GPER was overexpressed in human epithelial ovarian cancer and was positively correlated with the expression of matrix metalloproteinase 9 (MMP-9), which suggested GPER might promote the metastasis of ovarian cancer. However, the mechanisms underlying GPER-dependent metastasis of ovarian cancer are still not clear. In the present study, estrogen receptor α (ERα)-negative/GPER-positive OVCAR5 ovarian cancer cell line was used to investigate the role of GPER in the migration and invasion of ovarian cancer. Wound healing assay and transwell matrigel invasion assay were performed to determine the potentials of cell migration and invasion, respectively. The production and activity of MMP-9 in OVCAR5 cells were examined by Western blot and gelatin zymography analysis. The results showed that E2 and selective GPER agonist G-1 increased cell motility and invasiveness, and upregulated the production and proteolytic activity of MMP-9 in OVCAR5 cells. Small interfering RNA (siRNA) targeting GPER and G protein inhibitor pertussin toxin (PTX) inhibited the migration and invasion of OVCAR5 cells, and also reduced the expression and activity of MMP-9. Our data suggested that GPER promoted the migration and invasion of ovarian cancer cells by increasing the expression and activity of MMP-9. GPER might play an important role in the progression of ovarian cancer.

HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix interactions and intercellular adhesions

Restitution is a critical form of intestinal epithelial cell (IEC) healing. We have previously shown that heparin-binding epidermal-like growth factor (HB-EGF) is necessary for IEC restitution; however, the mechanisms by which HB-EGF promotes restitution remain poorly understood. This study was designed to investigate whether HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix (ECM) interactions and intercellular adhesions. The effect of HB-EGF administration was examined in a murine necrotizing enterocolitis (NEC) model in vivo and an IEC line scrape-wound healing model in vitro. We evaluated the effect of HB-EGF on the expression of integrins, E-cadherin/β-catenin, and integrin α5β1-dependent cell-ECM interactions. We found that HB-EGF promoted intestinal restitution and the expression of integrin α5β1. HB-EGF promoted integrin α5β1-dependent cell adhesion and spreading. In addition, HB-EGF decreased the expression E-cadherin/β-catenin, via the activation of v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB-1). We conclude that HB-EGF promotes intestinal restitution by affecting integrin-ECM interactions and intercellular adhesions.

Integrin β1 regulates leiomyoma cytoskeletal integrity and growth

Uterine leiomyomas are characterized by an excessive extracellular matrix, increased mechanical stress, and increased active RhoA. Previously, we observed that mechanical signaling was attenuated in leiomyoma, but the mechanisms responsible remain unclear. Integrins, especially integrin β1, are transmembrane adhesion receptors that couple extracellular matrix stresses to the intracellular cytoskeleton to influence cell proliferation and differentiation. Here we characterized integrin and laminin to signaling in leiomyoma cells. We observed a 2.25±0.32 fold increased expression of integrin β1 in leiomyoma cells, compared to myometrial cells. Antibody-mediated inhibition of integrin β1 led to significant growth inhibition in leiomyoma cells and a loss of cytoskeletal integrity. Specifically, polymerization of actin filaments and formation of focal adhesions were reduced by inhibition of integrin β1. Inhibition of integrin β1 in leiomyoma cells led to 0.81±0.02 fold decrease in active RhoA, and resembled levels found in serum-starved cells. Likewise, inhibition of integrin β1 was accompanied by a decrease in phospho-ERK. Compared to myometrial cells, leiomyoma cells demonstrated increased expression of integrin α6 subunit to laminin receptor (1.91±0.11 fold), and increased expression of laminin 5α (1.52±0.02), laminin 5β (3.06±0.92), and laminin 5γ (1.66±0.06). Of note, leiomyoma cells grown on laminin matrix appear to realign themselves. Taken together, the findings reveal that the attenuated mechanical signaling in leiomyoma cells is accompanied by an increased expression and a dependence on integrin β1 signaling in leiomyoma cells, compared to myometrial cells.

Epidermal growth factor (EGF) regulates α5β1 integrin activation state in human cancer cell lines through the p90RSK-dependent phosphorylation of filamin A

BACKGROUND

Regulation of integrin activation has important implications for tumor cell invasion and metastasis.

RESULTS

EGF activates ERK/p90RSK and Rho/Rho kinase signaling in A431 and DiFi colon cancer cells, leading to phosphorylation of filamin A (FLNa) and inactivation of the α5β1 integrin receptor.

CONCLUSION

EGF promotes α5β1 inactivation through the p90RSK-dependent phosphorylation of FLNa.

SIGNIFICANCE

We have identified a novel EGF-dependent mechanism controlling the α5β1 integrin activation state. Cell adhesion, motility, and invasion are regulated by the ligand-binding activity of integrin receptors, transmembrane proteins that bind to the extracellular matrix. Integrins whose conformation allows for ligand binding and appropriate functional activity are said to be in an active state. Integrin activation and subsequent ligand binding are dynamically regulated by the association of cytoplasmic proteins with integrin intracellular domains. In this study, we evaluated the role of EGF in the regulation of the activation state of the α5β1 integrin receptor for fibronectin. The addition of EGF to either A431 squamous carcinoma cells or DiFi colon cancer cells resulted in loss of α5β1-dependent adhesion to fibronectin but no loss of integrin from the cell surface. EGF activated the EGF receptor/ERK/p90RSK and Rho/Rho kinase signaling pathways. Blocking either pathway inhibited EGF-mediated loss of adhesion, suggesting that they work in parallel to regulate integrin function. EGF treatment also resulted in phosphorylation of filamin A (FLNa), which binds and inactivates β1 integrins. EGF-mediated FLNa phosphorylation was completely blocked by an inhibitor of p90RSK and partially attenuated by an inhibitor of Rho kinase, suggesting that both pathways converge on FLNa to regulate integrin function. A431 clonal cell lines expressing non-phosphorylated dominant-negative FLNa were resistant to the inhibitory effects of EGF on integrin function, whereas clonal cell lines overexpressing wild-type FLNa were more sensitive to the inhibitory effect of EGF. These data suggest that EGF-dependent inactivation of α5β1 integrin is regulated through FLNa phosphorylation and cellular contractility.