Tetraspanin CD151 Regulates Glycosylation of α3β1 Integrin

The tetraspanin CD151 forms a stoichiometric complex with integrin alpha 3 beta 1 and regulates its endocytosis. We observed that down-regulation of CD151 in various epithelial cell lines changed glycosylation of alpha 3 beta 1. In contrast, glycosylation of other transmembrane proteins, including those associated with CD151 (e. g. alpha 6 beta 1, CD82, CD63, and emmprin/CD147) was not affected. The detailed analysis has shown that depletion of CD151 resulted in the reduction of Fuc alpha 1-2Gal and bisecting GlcNAc-beta(1 -> 4) linkage on N-glycans of the alpha 3 integrin subunit. The modulatory activity of CD151 toward alpha 3 beta 1 was specific, because stable knockdown of three other tetraspanins(i. e. CD9, CD63, and CD81) did not affect glycosylation of the integrin. Analysis of alpha 3 glycosylation in CD151-depleted breast cancer cells with reconstituted expression of various CD151 mutants has shown that a direct contact with integrin is required but not sufficient for the modulatory activity of the tetraspanin toward alpha 3 beta 1. We also found that glycosylation of CD151 is also critical; Asn1593Gln mutation in the large extracellular loop did not affect interactions of CD151 with other tetraspanins or alpha 3 beta 1 but negated its modulatory function. Changes in the glycosylation pattern of alpha 3 beta 1 observed in CD151-depleted cells correlated with a dramatic decrease in cell migration toward laminin-332. Migration toward fibronectin or static adhesion of cells to extracellular matrix ligands was not affected. Importantly, reconstituted expression of the wild-type CD151 but not glycosylation-deficient mutant restored the migratory potential of the cells. These results demonstrate that CD151 plays an important role in post-translation modification of alpha 3 beta 1 integrin and strongly suggest that changes in integrin glycosylation are critical for the promigratory activity of this tetraspanin.