KAI-1 / CD82 affects cancer cell migration and enzyme expression

Objectives: A metastasis suppressor, CD82 / KAI-1, that is a member of the tetraspanin superfamily, regulates biological activity by associating with cell surface receptors or proteins. To identify the function of tetraspanins in tumor cell migration, we focused on the effect of CD82 / KAI-1 on the migration of tumor cells and enzyme expression.

Materials and Methods: The H1299 (nonsmall cell lung carcinoma) cell line was employed in this study. The pZeoSV and CD82 cDNA plasmids were provided by Dr. Fedor Berditchevski (University of Birmingham, UK). The h1299 / zeo and h1299 / CD82 cell lines were generated by transfection of h1299 cells with pZeoSV and pZeoSV / CD82 respectively. Indirect immunofluorescence staining and immunoprecipitation were performed to analyze protein expression and protein interactions. The activation of Rac1 / Cdc42, RhoA and Ras was measured using pull-down assay kits. The cell lysates, immunoprecipitates and pull-down samples were subjected to immunoblot analysis. The phosphatidylinositol 3-kinase (PI3K) kinase assay and quantification of enzyme protein were carried out with an ELISA kit. Enzyme activity was measured with a fluorometric method.

Results: The CD82-transfected h1299 cells significantly suppressed lamellipodial protrusion and cell migration. Transfected CD82 attenuated c-Met signaling via the Ras-Cdc42 / Rac and the PI3K / Cdc42 / Rac pathways and altered the expression of cell migration-related enzyme proteins. In contrast, a second c-Met signaling pathway that involves PI3K / Akt and PI3K / mitogen activated protein kinase was not affected by CD82. Thus CD82 selectively attenuates c-Met signaling pathways that modulate cell migration.

Conclusion: These results indicate that the CD82-c-Met complex inhibits cancer cell migration by the inactivation of small GTP-binding proteins of the Rho family resulting in selective inhibition of cell migration signaling.