Extracellular gamma-synuclein promotes tumor cell motility by activating β1 integrin-focal adhesion kinase signaling pathway and increasing matrix metalloproteinase-24,-2 protein secretion

Background: Increasing evidence reveals a significant correlation between gamma-synuclein (SNCG) level and tumor invasion and metastasis in various human cancers. Our previous investigation showed that SNCG could secrete into extracellular environment and promoted tumor cell motility, but the mechanism is unknown. Methods: The membrane binding ability of SNCG was characterized by immunohistochemical staining, immunofluorescence staining and fractionation of colorectal cancer (CRC) cell membrane. Association between SNCG and beta 1 integrin was validated by coimmunoprecipitation and far Western blot. After inhibition of beta 1 integrin and focal adhesion kinase (FAK), effect of SNCG on cell motility was measured by transwell chamber assays and changes of protein levels were detected by Western blot. Association between SNCG and activated beta 1 integrin levels in human CRC tissues was determined by Spearman's rank correlation analysis. Secreted proteins in conditioned medium (CM) were screened by antibody array. Results: Extracellular SNCG bound beta 1 integrin on CRC cell membrane and increased levels of activated beta 1 integrin and FAK. Correspondingly, SNCG-enhanced cell motility was counteracted by knockdown or inhibition of beta 1 integrin or FAK. Further study revealed that high SNCG level indicated poor outcome and SNCG levels positively correlated with those of activated beta 1 integrin and phospho-FAK (Tyr(397)) in human CRC tissues. Additionally, extracellular SNCG promoted secretion of fibronectin (FN), vitronectin (VN), matrix metalloproteinase (MMP)-2, and MMP-24 from HCT116 cells. Protease activity of MMP-2 in the CM of HCT116 cells was increased by treatment with SNCG, which was abolished by inhibiting beta 1 integrin. Conclusion: Our results highlight the potential role of SNCG in remodeling extracellular microenvironment and inducing beta 1 integrin-FAK signal pathway of CRC cells.