Eukaryotic expression cloning with an antimetastatic monoclonal antibody identifies a tetraspanin (PETA-3/CD151) as an effector of human tumor cell migration and metastasis

A monoclonal antibody (mAb), 50-6, generated by subtractive immunization, w as found to specifically inhibit in vivo metastasis of a human epidermoid c arcinoma cell line, HEp-3. The cDNA of the cognate antigen of mAb 50-6 was isolated by a modified eukaryotic expression cloning protocol from a HEp-3 library. Sequence analysis identified the antigen as PETA-3/CD151, a recent ly described member of the tetraspanin family of proteins. The cloned antig en was also recognized by a preciously described antimetastatic antibody, m Ab 1A5, Inhibition of HEp-3 metastasis by the mAbs could not be attributed to any effect of the antibodies on tumor cell growth in vitro or in vivo. R ather, the antibodies appeared to inhibit an early step in the formation of metastatic foci, In a chemotaxis assay, HEp-3 migration was blocked by bot h antibodies. HeLa cells transfected with and overexpressing PETA-3/CD151 w ere more migratory than control transfectants expressing little CD151. The increase in HeLa migration was inhibitable by both mAb 50-6 and mAb 1A5, PE TA-3 appears not to be involved in cell attachment because adhesion did not correlate with levels of PETA-3 expression and was unaffected by mAb 50-6 or mAb 1A5. The ability of PETA-3 to mediate cell migration suggests a mech anism by which this protein may influence metastasis. These data identify P ETA-3/CD151 as the first member of the tetraspanin family to be linked as a positive effector of metastasis.