Integrin-dependent translational control: Implication in cancer progression

ITGB1 alleviates osteoarthritis by inhibiting cartilage inflammation and apoptosis via activating cAMP pathway

OBJECTIVE

We aimed to screen novel biomarkers for osteoarthritis (OA) using bioinformatic methods and explore its regulatory mechanism in OA development.

METHODS

Differentially expressed genes were screened out from GSE98918 and GSE82107 datasets. Protein-protein interaction network and enrichment analysis were employed to search for hub gene and regulatory pathway. Hematoxylin-eosin, Safranin O-Fast green staining, and immunohistochemistry were performed to assess pathological damage. TNF-α, IL-1β, and IL-6 concentrations were determined by enzyme-linked immunosorbent assay. Real-time quantitative PCR was applied to verify expression of hub genes in OA model. The expression of key protein and pathway proteins was determined by western blot. Furthermore, Cell Counting Kit-8 and flow cytometry were conducted to explore the role of hub gene in chondrocytes.

RESULTS

We identified 6 hub genes of OA, including ITGB1, COL5A1, COL1A1, THBS2, LAMA1, and COL12A1, with high prediction value. ITGB1 was screened as a pivotal regulator of OA and cAMP pathway was selected as the key regulatory pathway. ITGB1 was down-regulated in OA model. ITGB1 overexpression attenuated pathological damage and apoptosis in OA rats with the reduced levels of TNF-α, IL-1β and IL-6. ITGB1 overexpression activated cAMP pathway in vivo and vitro models. In vitro model, ITGB1 overexpression promoted cell viability, while inhibited apoptosis. ITGB1 overexpression also caused a decrease of TNF-α, IL-1β, and IL-6 concentrations. cAMP pathway inhibitor reversed the positive effect of ITGB1 on OA cell model.

CONCLUSION

ITGB1 is a novel biomarker for OA, which inhibits OA development by activating the cAMP pathway.

Integrin β1 regulates the perineural invasion and radioresistance of oral squamous carcinoma cells by modulating cancer cell stemness

Perineural invasion and radioresistance are the main determinants of treatment outcomes in oral squamous cell carcinoma (OSCC), but the exact mechanism is still unknown. We conducted an in vitro experiment to evaluate the role of integrin β1 (ITGB1) in the perineural invasion, radioresistance, and tumor aggressiveness of OSCC. Two OSCC cell lines (SCC25, SCC15) and radiation-induced radioresistant OSCC cell lines were used in this study. The expression of ITGB1 was compared between control radiosensitive and radioresistant OSCC cell lines. ITGB1 was inhibited by small hairpin RNA, and then the adhesion to neuronal cells, responsiveness to radiation, and aggressiveness of both OSCC cell lines were evaluated. Expression of ITGB1 and adhesion to neuronal cells were increased in radioresistant OSCC compared with control radiosensitive OSCC, and increased ITGB1 expression was more prominent in cancer stem cell-like cells. When the expression of ITGB1 was inhibited, the adhesion to neuronal cells, resistance to radiation, and invasion and migration of radioresistant OSCC were significantly reduced. Moreover, the expression of cancer stem cell markers and size of spheroid formations were also significantly attenuated by inhibiting ITGB1. These findings suggest that ITGB1 may be a significant contributor to perineural invasion and the maintenance of radioresistance in OSCC cells, and is associated with cancer stem cell-like cells. Furthermore, our results suggest a possible relationship between perineural invasion and radioresistance of OSCC. More detailed research is warranted to evaluate the role of ITGB1 as a novel emerging therapeutic target for radioresistant OSCC.

Comprehensive Analysis of the Expression and Prognosis for ITGBs: Identification of ITGB5 as a Biomarker of Poor Prognosis and Correlated with Immune Infiltrates in Gastric Cancer

Background: Integrin β superfamily members (ITGBs) are documented to play important roles in various biological processes, and accumulating evidence suggests that ITGBs are associated with carcinogenic effects in several malignancies. Gastric cancer (GC) is a complicated and highly heterogeneous disease; however, the expression and prognostic values of eight ITGBs and potential mechanism in GC remain largely unclear.

Methods: The expression and prognostic significance of ITGBs in GC were systematically analyzed through Gene Expression Profiling Interactive Analysis, Human Protein Atlas, Kaplan–Meier Plotter, and cBioPortal databases. Then, the mRNA transcription data and corresponding clinical data of GC were downloaded from the Gene Expression Omnibus database as a testing cohort, and differentially expressed and prognostic genes were identified. The correlation between ITGB5 expression and overall survival and various clinical parameters were found by using univariate/multivariable Cox regression and Kaplan–Meier survival analysis. Additionally, differential analysis of gene expression profiles in low- and high-ITGB5 expression groups and pathway enrichment analysis was performed. Finally, the correlation of ITGB5 expression with immune infiltrates in GC was clarified.

Results: Compared with adjacent normal tissue, the results reveal that the mRNA levels of ITGB1-2 and ITGB4-8 are significantly higher in GC, and immunohistochemistry results show the consistency between RNA and protein expression levels. Cox regression and Kaplan–Meier survival analysis indicate that high ITGB5 expression contributes to a poor prognosis and could be an independent prognostic factor in GC patients. Besides this, gene functional enrichment analysis indicates that ITGB5 expression is significantly associated with extracellular matrix organization, cell-substrate adhesion, and ossification. The KEGG pathway analysis of ITGB5 shows a close association between ITGB5 and focal adhesion, ECM-receptor interaction, phagosome, and PI3K-Akt signaling pathway. Last, the infiltrating level of CD4⁺ T cells, macrophages, and dendritic cells are positively related to the expression of ITGB5, especially macrophages, and lower levels of macrophages predict a better prognosis in GC in our study.

Conclusion: Our findings investigate that ITGB5 may function as a valid biomarker of prognosis, and high expression of ITGB5 predicts poor prognosis for patients with GC. Besides this, it might be a potential target of precision therapy against GC.

LncRNA SOCS2-AS1 promotes the progression of glioma via regulating ITGB1 expression

BACKGROUND

Accumulating evidence has underscored the important role of long non-coding RNAs (lncRNAs) in the development and progression of glioma. However, the role of lncRNA SOCS2-AS1 in glioma is largely unknown.

METHODS

lncRNA SOCS2-AS1 silencing was achieved by specific siRNAs. Proliferation of glioma cell line after lncRNA SOCS2-AS1 silencing was examined by MTT assay, Transwell assay was used to confirm changes of invasion and migration of glioma cells, and study the molecular mechanism of lncRNA SOCS2-AS1 by RT-qPCR and bioinformatics analysis.

RESULTS

We identified that lncRNA SOCS2-AS1 was significantly upregulated in glioma, and its overexpression was closely related with malignant clinical features and poor prognosis. To explore the cellular function of SOCS2-AS1, we performed loss-of function assays in two glioma cells. We demonstrated that SOCS2-AS1 knockdown repressed glioma cell proliferation, migration and invasion. Mechanistically, SOCS2-AS1 expression was positively correlated with the expression levels of core factors ITGB1 of ECM-receptor interaction signaling pathway in glioma. Moreover, SOCS2-AS1 knockdown suppressed ITGB1 expression in glioma cells. Finally, rescue assays were carried out to determine that ITGB1 involved in SOCS2-AS1-mediated glioma cell proliferation, migration and invasion.

CONCLUSION

Our findings provided the first evidence suggested that SOCS2-AS1 promoted the progression of glioma via upregulating ITGB1 expression.

Translational control of stem cell function

Stem cells are characterized by their ability to self-renew and differentiate into many different cell types. Research has focused primarily on how these processes are regulated at a transcriptional level. However, recent studies have indicated that stem cell behaviour is strongly coupled to the regulation of protein synthesis by the ribosome. In this Review, we discuss how different translation mechanisms control the function of adult and embryonic stem cells. Stem cells are characterized by low global translation rates despite high levels of ribosome biogenesis. The maintenance of pluripotency, the commitment to a specific cell fate and the switch to cell differentiation depend on the tight regulation of protein synthesis and ribosome biogenesis. Translation regulatory mechanisms that impact on stem cell function include mTOR signalling, ribosome levels, and mRNA and tRNA features and amounts. Understanding these mechanisms important for stem cell self-renewal and differentiation may also guide our understanding of cancer grade and metastasis.

The ITGB6 gene: its role in experimental and clinical biology

Integrin αvβ6 is a membrane-spanning heterodimeric glycoprotein involved in wound healing and the pathogenesis of diseases including fibrosis and cancer. Therefore, it is of great clinical interest for us to understand the molecular mechanisms of its biology. As the limiting binding partner in the heterodimer, the β6 subunit controls αvβ6 expression and availability. Here we describe our understanding of the ITGB6 gene encoding the β6 subunit, including its structure, transcriptional and post-transcriptional regulation, the biological effects observed in ITGB6 deficient mice and clinical cases of ITGB6 mutations.

Characterization of the prognostic and oncologic values of ITGB superfamily members in pancreatic cancer

Integrin β (ITGB) superfamily members have been reported to play important roles in multiple biological functions in various cancers. However, the prognostic and oncologic values of ITGB superfamily members have not been systematically investigated in pancreatic cancer (PC). In this study, the mRNA expression and biological functions of ITGB superfamily members in PC were evaluated by bioinformatic analysis. Our results demonstrated that ITGB1, ITGB4, ITGB5 and ITGB6 overexpressions were significantly associated with advanced AJCC stage and histologic grade, and worse prognosis in PC. A prognostic signature based on ITGB1, ITGB4, ITGB5 and ITGB6 showed a reliable predictive performance. Furthermore, one CpGs (cg20545410) in promoter region of ITGB1, four (cg18709893, cg15700850, cg20667796 and cg18326022) of ITGB4, two (cg10977398 and cg03518058) of ITGB5 and one (cg23008083) of ITGB6 were negatively associated with their corresponding mRNA expression, and positively associated with prognosis in PC. We also identified TFAP2A as the potential transcription factor for ITGB4, SP1 for ITGB1 and ITGB6, and FHL2 for ITGB5 and ITGB6. ITGB1, ITGB4, ITGB5 and ITGB6 overexpressions were all significantly involved in focal adhesion signalling pathway. ITGB1 and ITGB5 overexpressions also associated with up-regulation of TGF-β and WNT signalling pathway, whereas ITGB4 and ITGB6 overexpressions associated with up-regulation of Notch signalling pathway. Besides, ITGB1, ITGB5 and ITGB6 overexpressions significantly correlated with immunosuppression in PC. In summary, our study investigated the multilevel prognostic and biological values of ITGB superfamily members in PC.

Cyanidin-3-glucoside binds to talin and modulates colon cancer cell adhesions and 3D growth

Cyanidin-3-glucoside (C3G) is a natural pigment, found in many colorful fruits and vegetables. It has many health benefits, including anti-inflammation, cancer prevention, and anti-diabetes. Although C3G is assumed to be an antioxidant, it has been reported to affect cell-matrix adhesions. However, the underlying molecular mechanism is unknown. Here, we show that the expression of talin1, a key regulator of integrins and cell adhesions, negatively correlated with the survival rate of colon cancer patients and that depletion of talin1 inhibited 3D spheroid growth in colon cancer cells. Interestingly, C3G bound to talin and promoted the interaction of talin with β1A-integrin. Molecular docking analysis shows that C3G binds to the interface of the talin-β-integrin complex, acting as an allosteric regulator and altering the interaction between talin and integrin. Moreover, C3G promoted colon cancer cell attachment to fibronectin. While C3G had no significant effect on colon cancer cell proliferation, it significantly inhibited 3D spheroid growth in fibrin gel assays. Since C3G has no or very low toxicity, it could be potentially used for colon cancer prevention or therapy.

Adding Nanotechnology to the Metastasis Treatment Arsenal

Metastasis is a major cause of cancer-related mortality, accounting for 90% of cancer deaths. The explosive growth of cancer biology research has revealed new mechanistic network information and pathways that promote metastasis. Consequently, a large number of antitumor agents have been developed and tested for their antimetastatic efficacy. Despite their exciting cytotoxic effects on tumor cells in vitro and antitumor activities in preclinical studies in vivo, only a few have shown potent antimetastatic activities in clinical trials. In this review, we provide a brief overview of current antimetastatic strategies that show clinical efficacy and review nanotechnology-based approaches that are currently being incorporated into these therapies to mitigate challenges associated with treating cancer metastasis.

Prognostic value of increased integrin-beta 1 expression in solid cancers: a meta-analysis

Integrin-beta 1 (ITGB1) is aberrantly overexpressed or downregulated in solid cancers; however, its prognostic value remains controversial. Therefore, we conducted a meta-analysis to explore whether ITGB1 expression is correlated with overall survival (OS) and the clinicopathological characteristics of patients with solid cancers. We systematically searched the PubMed, Embase, and Web of Science databases for eligible studies published up to June 1, 2017. In total, 22 studies involving 3,666 patients were included. A sensitivity analysis was performed to assess the validity and reliability of the pooled OS. Among the 22 studies, 7 focused on lung cancer, 3 focused on colorectal cancer, 6 focused on breast cancer, 3 involved melanoma, and 3 involved pancreatic cancer. The pooled results showed that high ITGB1 expression was significantly associated with worse OS in lung cancer (pooled hazard ratio [HR]=1.78, 95% CI: 1.19–2.65, p<0.05) and breast cancer (pooled HR=1.88, 95% CI: 1.46–2.42, p<0.01). In addition, a significant association was observed between high ITGB1 expression and disease-free survival in breast cancer (pooled HR=1.63, 95% CI: 1.17–2.25, p<0.001) and pancreatic cancer (pooled HR=2.49, 95% CI: 1.35–4.61, p<0.001). However, high ITGB1 expression was not related to OS in colorectal cancer, pancreatic cancer, or melanoma. The pooled HRs used to evaluate the prognostic value of increased ITGB1 expression in lung cancer, breast cancer, and pancreatic cancer were not significantly altered, which indicates that the pooled results were robust. The results of this study indicate that the prognostic value of decreased ITGB1 expression varies among solid cancers.

A gene expression-based comparison of cell adhesion to extracellular matrix and RGD-terminated monolayers

This work uses global gene expression analysis to compare the extent to which model substrates presenting peptide adhesion motifs mimic the use of conventional extracellular matrix protein coated substrates for cell culture. We compared the transcriptional activities of genes in cells that were cultured on matrix-coated substrates with those cultured on self-assembled monolayers presenting either a linear or cyclic RGD peptide. Cells adherent to cyclic RGD were most similar to those cultured on native ECM, while cells cultured on monolayers presenting the linear RGD peptide had transcriptional activities that were more similar to cells cultured on the uncoated substrates. This study suggests that biomaterials presenting the cyclic RGD peptide are substantially better mimics of extracellular matrix than are uncoated materials or materials presenting the common linear RGD peptide.

Integrin β6 can be translationally regulated by eukaryotic initiation factor 4E: Contributing to colonic tumor malignancy

It is well known that both eukaryotic initiation factor 4E (eIF4E) and integrin αvβ6 can contribute to malignant behavior of colon cancer. We have found that integrin αvβ6 and eIF4E were co-expressed and positively correlated in colon cancer tissues. Recently, deregulation of the protein synthesis apparatus has begun to gain attention as a major participant in cancer development and progression. However, the regulation of integrin β6 expression at translational level has never been investigated before. In present study, gene-silencing technique for eIF4E by small interfering RNA (siRNA) was used in all the subsequent experiments, in order to investigate whether eIF4E could translationally regulate expression of integrin β6 in colon cancer SW480 and HT-29 cell lines. Additionally, the subsequent effects of eIF4E knockdown on cellular malignant behavior were observed. siRNA in SW480 and HT-29 transfectants. Subsequently, protein expression of β6 was markedly suppressed, while mRNA expression of β6 showed no significant variation before and after eIF4E RNA interfering. Therefore, it could be seen that eIF4E could upregulate the expression of β6, without effect on β6 mRNA expression. More importantly, after treated with eIF4E siRNA, cellular migratory capacity on fibronectin of HT-29 and β6-transfected SW480 as well as their survival to 5-FU was decreased distinctly. Expression of integrin β6 could be translationally regulated by eIF4E, which subsequently contributed to tumor malignancy through enhancing cellular migration, survival, anti-apoptosis, and chemoresistance of colon cancer in vitro. Thus, targeting eIF4E in integrin αvβ6 expressing tumors can be a potential therapeutic strategy for patients with colon cancer.

α6-Integrin is required for the adhesion and vasculogenic potential of hemangioma stem cells

Infantile hemangioma (IH) is the most common tumor of infancy. Hemangioma stem cells (HemSC) are a mesenchymal subpopulation isolated from IH CD133+ cells. HemSC can differentiate into endothelial and pericyte/smooth muscle cells and form vascular networks when injected in immune-deficient mice. α6-Integrin subunit has been implicated in the tumorgenicity of glioblastoma stem cells and the homing properties of hematopoietic, endothelial, and mesenchymal progenitor cells. Therefore, we investigated the possible function(s) of α6-integrin in HemSC. We documented α6-integrin expression in IH tumor specimens and HemSC by RT-qPCR and flow cytometry. We examined the effect of blocking or silencing α6-integrin on the adhesive and proliferative properties of HemSC in vitro and the vasculogenic and homing properties of HemSC in vivo. Targeting α6-integrin in cultured HemSC inhibited adhesion to laminin but had no effect on proliferation. Vessel-forming ability in Matrigel implants and hepatic homing after i.v. delivery were significantly decreased in α6-integrin siRNA-transfected HemSC. In conclusion, α6-integrin is required for HemSC adherence to laminin, vessel formation in vivo, and for homing to the liver. Thus, we uncovered an important role for α6 integrin in the vasculogenic properties of HemSC. Our results suggest that α6-integrin expression on HemSC could be a new target for antihemangioma therapy.

Changes in the adhesion and migration ability of peripheral blood cells: potential biomarkers indicating exposure dose

The expression of adhesion molecules and their related functions of adhesion and migration were investigated in peripheral blood mononuclear cells (PBMCs) to identify radiation-related changes and dose-dependency. The authors screened new biomarkers as radiation exposure dose indicators. Heparinized human peripheral blood was irradiated in vitro with different doses of γ-rays. The expression levels of the CD11a, CD11b, CD18, CD29, CD49d, and CD54 molecules on the surface of PBMC cells were determined by flow cytometry at different time points post-irradiation. The adhesion ability of human PBMCs was determined using an enzyme-linked immunoassay kit, and the migration ability of rat PBMCs was evaluated using a transwell chamber assay. Compared with the unirradiated control group, a significant increase (p < 0.05) in human CD11b/CD13 double-positive cells was detected 6 h post 6 Gy irradiation in vitro. These results indicated that the decrease in human CD29/CD13 double-positive cells in the 6 Gy exposure group at 6, 12, and 24 h post-irradiation was significant (p < 0.01). The adhesion ability of irradiated human PBMCs to IgG substrate increased significantly (p < 0.05) at 6 h after irradiation of 2, 4, or 6 Gy compared with non-irradiated controls. The migration ability of the rat PBMCs toward the MIP-1α chemokine significantly decreased (p < 0.05) with increasing irradiation doses. These results suggest that the protein expression of cell surface molecules and their associated cellular functions might be potential biomarkers for identifying radiation exposure doses in an emergency radiation accident.

Oligophrenin-1 is associated with cell adhesion and migration in prostate cancer

OBJECTIVE

We performed Escherichia coli ampicillin secretion trap (CAST) analysis in prostate cancer (PCa) to identify novel biomarkers. We show here that OPHN1, which encodes oligophrenin-1 protein, is upregulated in PCa. OPHN1 was first determined to be one of the genes associated with X-linked mental retardation; however, neither the gene's function nor the link between its expression and survival of patients has been investigated.

METHODS

We investigate the expression of oligophrenin-1 in 141 PCa tissue samples by immunohistochemistry and perform functional analysis using RNA interference.

RESULTS

Immunohistochemical analysis of oligophrenin-1 demonstrated that 60 (43%) PCa cases were positive for oligophrenin-1. Positive oligophrenin-1 expression was significantly correlated with a high Gleason score (p = 0.0198). Furthermore, patients with oligophrenin-1-positive PCa had a worse biochemical recurrence-free survival rate than patients with oligophrenin-1-negative PCa (p = 0.0079). Cell adhesion to fibronectin was significantly reduced in OPHN1 small interfering (si)RNA-transfected LNCaP and PC3 cells in comparison to negative-control siRNA-transfected cells. Knockdown of OPHN1 reduced the expression of ITGA5 and stress fiber formation in LNCaP and PC3 cells.

CONCLUSION

These results suggest that oligophrenin-1 is involved in tumor progression in PCa.

Metastasis review: from bench to bedside

Cancer is the final result of uninhibited cell growth that involves an enormous group of associated diseases. One major aspect of cancer is when cells attack adjacent components of the body and spread to other organs, named metastasis, which is the major cause of cancer-related mortality. In developing this process, metastatic cells must successfully negotiate a series of complex steps, including dissociation, invasion, intravasation, extravasation, and dormancy regulated by various signaling pathways. In this review, we will focus on the recent studies and collect a comprehensive encyclopedia in molecular basis of metastasis, and then we will discuss some new potential therapeutics which target the metastasis pathways. Understanding the new aspects on molecular mechanisms and signaling pathways controlling tumor cell metastasis is critical for the development of therapeutic strategies for cancer patients that would be valuable for researchers in both fields of molecular and clinical oncology.

Protein expression of eIF4E and integrin αvβ6 in colon cancer can predict clinical significance, reveal their correlation and imply possible mechanism of interaction

Background

Both eukaryotic translation initiation factor 4E (eIF4E) and integrin αvβ6 play an important role in the development and progression of cancer. The aim of this study was to investigate the expression of eIF4E and Integrin αvβ6, their clinical significance as well as the two proteins’ correlation in colonic carcinoma tissues.

Results

The expression levels of eIF4E and integrin αvβ6 were analyzed in colon cancerous and paraneoplastic tissues of 138 cases via tissue microarray (TMA)- immunohistochemistry. And their clinical significance as well as the two proteins’ correlation was also investigated. The expression of eIF4E was significantly associated with clinical TNM stage (P = 0.009), while T stage (P = 0.011) and TNM stage (P = 0.012) were significantly associated with integrin αvβ6 expression. Moderately weak correlation exists between the two proteins (r =0.299, P <0.001). The survival analysis by Kaplan-Meier and Cox regression model showed that protein expression of high eIF4E and positive integrin αvβ6, as independent prognostic factors (RR = 2.417, P = 0.001 and RR = 2.393, P = 0.001), tended to have a significantly poorer 5-year survival rate (P = 0.013 and 0.025, respectively, the log-rank test).

Conclusion

eIF4E and Integrin αvβ6 were indicators of tumor’s progression and poor prognosis of patients with colon cancer. And the potential signaling loop involving them may provide a helpful therapeutic target in prevention and treatment of colon cancer.

The role of c-Src in integrin (α6β4) dependent translational control

Background

Integrin α6β4 contributes to cancer progression by stimulating transcription as well as translation of cancer related genes. Our previous study demonstrated that α6β4 stimulates translation initiation of survival factors such as VEGF by activating mTOR pathway. However, the immediate early signaling events that link α6β4 to mTOR activation needs to be defined.

Results

In the current studies, we demonstrated that c-Src is an immediate early signaling molecule that acts upstream of α6β4 dependent mTOR activation and subsequent translation of VEGF in MDA-MB-435/β4 and MDA-MB-231 cancer cells. m⁷GTP-Sepharose–binding assay revealed that Src activity is required to form eIF4F complex which is necessary for Cap-dependent translation in α6β4 expressing human cancer cells.

Conclusions

Overall, our studies suggest that integrin β4 and c-Src activation is important early signaling events to lead mTOR activation and cap-dependent translation of VEGF.

Mena binds α5 integrin directly and modulates α5β1 function

Mena binds to the cytoplasmic tail of α5 integrin and modulates key α5β1 integrin functions in adhesion, motility, and fibrillogenesis.

Mena is an Ena/VASP family actin regulator with roles in cell migration, chemotaxis, cell–cell adhesion, tumor cell invasion, and metastasis. Although enriched in focal adhesions, Mena has no established function within these structures. We find that Mena forms an adhesion-regulated complex with α5β1 integrin, a fibronectin receptor involved in cell adhesion, motility, fibronectin fibrillogenesis, signaling, and growth factor receptor trafficking. Mena bound directly to the carboxy-terminal portion of the α5 cytoplasmic tail via a 91-residue region containing 13 five-residue “LERER” repeats. In fibroblasts, the Mena–α5 complex was required for “outside-in” α5β1 functions, including normal phosphorylation of FAK and paxillin and formation of fibrillar adhesions. It also supported fibrillogenesis and cell spreading and controlled cell migration speed. Thus, fibroblasts require Mena for multiple α5β1-dependent processes involving bidirectional interactions between the extracellular matrix and cytoplasmic focal adhesion proteins.

Focal adhesion-chromatin linkage controls tumor cell resistance to radio- and chemotherapy

Cancer resistance to therapy presents an ongoing and unsolved obstacle, which has clear impact on patient's survival. In order to address this problem, novel in vitro models have been established and are currently developed that enable data generation in a more physiological context. For example, extracellular-matrix- (ECM-) based scaffolds lead to the identification of integrins and integrin-associated signaling molecules as key promoters of cancer cell resistance to radio- and chemotherapy as well as modern molecular agents. In this paper, we discuss the dynamic nature of the interplay between ECM, integrins, cytoskeleton, nuclear matrix, and chromatin organization and how this affects the response of tumor cells to various kinds of cytotoxic anticancer agents.

Integrin subunits alpha5 and alpha6 regulate cell cycle by modulating the chk1 and Rb/E2F pathways to affect breast cancer metastasis

Background

Although integrins have been implicated in the progression of breast cancer, the exact mechanism whereby they exert this regulation is clearly not understood. To understand the role of integrins in breast cancer, we examined the expression levels of several integrins in mouse breast cancer cell lines by flow cytometry and the data were validated by Western and RT-PCR analysis. The importance of integrins in cell migration and cell invasion was examined by in vitro assays. Further the effect of integrins on metastasis was investigated by in vivo experimental metastasis assays using mouse models.

Results

Integrin α5 subunit is highly expressed in the nonmetastatic cell line 67NR and is significantly low in the highly invasive cell line 4T1. In contrast, expression levels of integrin α6 subunit are high in 4T1 cells and low in 67NR cells. In vitro data indicated that overexpression of α5 subunit and knockdown of α6 integrin subunit inhibited cell proliferation, migration, and invasion. Our in vivo findings indicated that overexpression of integrin α5 subunit and knockdown of α6 subunit decreased the pulmonary metastasis property of 4T1 cells. Our data also indicated that overexpression of alpha 5 integrin subunit and suppression of alpha6 integrin subunit inhibited cells entering into S phase by up-regulating p27, which results in downregulation of cyclinE/CDK2 complexes, This suggests that these integrins regulate cell growth through their effects on cell-cycle-regulated proteins. We also found that modulation of these integrins upregulates E2F, which may induce the expression of chk1 to regulate cdc25A/cyclin E/CDK2/Rb in a feedback loop mechanism.

Conclusion

This study indicates that Integrin α5 subunit functions as a potential metastasis suppressor, while α6 subunit functions as a metastasis promoter. The modulation of integrins reduces cdc25 A, another possible mechanism for downregulation of CDK2. Taken together we demonstrate a link between integrins and the chk1-cdc25-cyclin E/CDK2-Rb pathway.

Mnk mediates integrin α6β4-dependent eIF4E phosphorylation and translation of VEGF mRNA

It was previously shown that integrin α6β4 contributes to translation of cancer-related mRNAs such as VEGF via initiation factor eIF4E. In this study, we found that integrin α6β4 regulates the activity of eIF4E through the Ser/Thr kinase Mnk. Although a role for Mnk in various aspects of cancer progression has been established, a link between integrin and Mnk activity has not. Here we show that Mnk1 is a downstream effector of integrin α6β4 and mediates the α6β4 signaling, important for translational control. Integrin α6β4 signals through MEK and p38 MAPK to increase phosphorylation of Mnk1 and eIF4E. Inhibition of Mnk1 activity by CGP57380 or downregulation by shRNA blocks α6β4-dependent translation of VEGF mRNA. Our studies suggest that Mnk1 could be a therapeutic target in cancers where the integrin α6β4 level is high.

Thrombospondin-1 (TSP-1) Stimulates Expression of Integrin alpha6 in Human Breast Carcinoma Cells: A Downstream Modulator of TSP-1-Induced Cellular Adhesion

Thrombospondin-1 (TSP-1) is involved in a variety of different cellular processes including cell adhesion, tumor progression, and angiogenesis. This paper reports the novel finding that TSP-1 upregulates integrin α6 subunit in human keratinocytes and human breast cancer cells resulting in increased cell adhesion and tumor cell invasion. The effect of TSP-1 on α6 subunit expression was examined in human keratinocytes and breast adenocarcinoma cell lines (MDA-MB-231) treated with TSP-1 and in TSP-1 stably transfected breast cancer cells. TSP-1 upregulated α6 message and protein in these cells as revealed by differential display, Northern and Western blot analysis and immunohistochemical localization studies. The increased expression of α6 was shown to mediate adhesion and invasion of these cells to laminin, a major component of the basement membrane and extracellular matrix (ECM). These data suggest that TSP-1 plays an integral role in the attachment of cells to the ECM facilitating cell motility and angiogenesis.

Translation initiation: a critical signalling node in cancer

Mammalian target of rapamycin (mTOR) is a master regulator of translation initiation that controls the recruitment of ribosomes to mRNA templates in response to intracellular and extracellular cues. Evidence suggests that mTOR and its direct downstream targets, S6K and eIF4E/4E-BP, play significant roles in oncogenesis, and that inhibiting this pathway holds promise as an anti-proliferative approach. Recent genome-wide analyses of mutations in human cancers indicate that transformed cells activate a handful of processes and signalling pathways that are major contributors to their phenotype. Here we review the current literature implicating mTOR and translation initiation downstream of many of these various signalling pathways and processes usurped in human cancers. This review highlights the widespread activation of mTOR/eIF4E following acquisition of oncogenic lesions and its implication in promoting the transformation phenotype and indicates that targeting the control of translation initiation makes logical sense as a broad-acting therapeutic approach.

Multiple shRNA-mediated knockdown of TACE reduces the malignancy of HeLa cells

Tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE) is a key enzyme involved in the proteolytic shedding of the ectodomain of several membrane-bound growth factors, cytokines and receptors. Here, we constructed a multiple short hairpin RNA (shRNA) expression vector containing four shRNAs against TACE. We found that in HeLa cells our multiple shRNAs vector produced a higher level of TACE knockdown than any single shRNA vector containing only one TACE shRNA. Silencing TACE expression in HeLa cells decreased their malignancy by decreasing the proliferation, adhesion and migration, as well as inducing apoptosis in these cells. Furthermore, our data suggest that the effects of TACE on the malignancy of HeLa cells may be mediated via activation of the EGFR (epidermal growth factor receptor) signaling pathway. Our findings suggest that using a combination of shRNAs within one vector to silence the expression of TACE might be a potential therapeutic strategy for tumors.