Role of MMP-2 in the Regulation of IL-6/Stat3 Survival Signaling via Interaction With α5β1 Integrin in glioma

MMP-2 plays pivotal role in the degradation of extracellular matrix, and thereby enhances the invasive, proliferative and metastatic potential in cancer. Knockdown of MMP-2 using MMP-2 siRNA (pM) in human glioma xenograft cell lines 4910 and 5310 decreased cell proliferation compared to mock- and pSV-(scrambled vector)treatments, as determined by BrDU incorporation, Ki-67 staining and clonogenic survival assay. Cytokine array and Western blotting using tumor conditioned media displayed modulated secretory levels of various cytokines including GM-CSF, IL-6, IL-8, IL-10, TNF-α, angiogenin, VEGF and PDGF-BB in MMP-2 knockdown cells. Further, cDNA PCR array indicated potential negative regulation of JAK/Stat3 pathway in pM-treated cells. Mechanistically, MMP-2 is involved in complex formation with α5 and β1 integrins and MMP-2 downregulation inhibited α5β1 integrin mediated Stat3 phosphorylation and nuclear translocation. EMSA and ChIP assays showed inhibited Stat3 DNA-binding activity and recruitment at CyclinD1 and c-Myc promoters in pM-treated cells. In individual experiments, IL-6 or siRNA-insensitive MMP-2 overexpression by pM-FL-A141G counteracted and restored the pM-inhibited Stat3 DNA-binding activity suggesting IL-6/Stat3 signaling suppression in pM-treated 4910 and 5310 cells. MMP-2/α5β1 binding is enhanced in rhMMP-2 treatments resulting in elevated Stat3 DNA-binding activity and recruitment on CyclinD1 and c-Myc promoters. Activation of α5β1 signaling by Fibronectin adhesion elevated pM-inhibited Stat3 phosphorylation whereas blocking α5β1 abrogated constitutive Stat3 activation. In vivo experiments with orthotropic tumor model revealed the decreased tumor size in pM-treatment compared to mock- or pSV-treatments. Immunoflorescence studies in tumor sections corroborated our in vitro findings evidencing high expression and co-localization of MMP-2/α5β1, which is decreased upon pM-treatment along with significantly reduced IL-6, phospho-Stat3, CyclinD1, c-Myc, Ki-67 and PCNA expression levels. Our data indicates the possible role of MMP-2/α5β1 interaction in the regulation of α5β1-mediated IL-6/Stat3 signaling activation and signifies the therapeutic potential of blocking MMP-2/α5β1 interaction in glioma treatment.