RESUMO
AIM: To detect the mechanism by which colon tumor escapes the growth constraints imposed on normal cells by cell crowding and dense pericellular matrices. METHODS: An immunohistochemical study of integrin αvß6 and matrix metalloproteinase-9 (MMP-9) was performed on tissue microarrays of 200 spots, including 100 cases of colon tumors. RESULTS: High immunoreactivity for αvß6 (73.7%; 28/38) and MMP-9 (76.5%; 52/68) was observed in invasive tumor portions. Furthermore, the effects of integrin αvß6 on tumor invasive growth in nude mice were detected. Tumor invasive growth and high expression of both αvß6 and MMP-9 were only seen in tumors resulting from WiDr cells expressing αvß6 in the tumorigenicity assay. Flow cytometry was applied to analyze αvß6 expression in colon cancer WiDr and SW480 cells. The effects of cell density on αvß6 expression and MMP-9 secretion were also detected by Biotrak MMP-9 activity assay and gelatin zymography assay. High cell density evidently enhanced αvß6 expression and promoted MMP-9 secretion compared with low density. CONCLUSION: Integrin αvß6 sustains and promotes tumor invasive growth in tumor progression via a self-perpetuating mechanism. Integrin ανß6-mediated MMP-9 secretion facilitates pericellular matrix degradation at high cell density, which provides the basis of invasive growth.
