Tetraspanin CD151 Regulates Glycosylation of α3β1 Integrin*

The tetraspanin CD151 forms a stoichiometric complex with integrin α3β1 and regulates its endocytosis. We observed that down-regulation of CD151 in various epithelial cell lines changed glycosylation of α3β1. In contrast, glycosylation of other transmembrane proteins, including those associated with CD151 (e.g. α6β1, CD82, CD63, and emmprin/CD147) was not affected. The detailed analysis has shown that depletion of CD151 resulted in the reduction of Fucα1–2Gal and bisecting GlcNAc-β(1→4) linkage on N-glycans of the α3 integrin subunit. The modulatory activity of CD151 toward α3β1 was specific, because stable knockdown of three other tetraspanins (i.e. CD9, CD63, and CD81) did not affect glycosylation of the integrin. Analysis of α3 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 α3β1. We also found that glycosylation of CD151 is also critical; Asn159 → Gln mutation in the large extracellular loop did not affect interactions of CD151 with other tetraspanins or α3β1 but negated its modulatory function. Changes in the glycosylation pattern of α3β1 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 α3β1 integrin and strongly suggest that changes in integrin glycosylation are critical for the promigratory activity of this tetraspanin.