Tyrosine phosphorylation of the beta(4) integrin cytoplasmic domain mediates Shc signaling to extracellular signal-regulated kinase and antagonizes formation of hemidesmosomes

Ligation of the alpha (6)beta (4) integrin induces tyrosine phosphorylation of the beta (4) cytoplasmic domain, followed by recruitment of the adaptor protein She and activation of mitogen-activated protein kinase cascades. W e have used Far Western analysis and phosphopeptide competition assays to m ap the sites in the cytoplasmic domain of a, that are required for interact ion with She. Our results indicate that, upon phosphorylation, Tyr(1440), o r secondarily Tyr(1422), interacts with the SH2 domain of She, whereas Tyr( 1526), Or secondarily Tyr(1642), interacts with its phosphotyrosine binding (PTB) domain. An inactivating mutation in the PTB domain of She, but not o ne in its SM2 domain, suppresses the activation of She by alpha (6)beta (4) In addition, mutation of beta (4) Tyr(1526) which binds to the PTB domain of She, but not of Tyr(1422) and Tyr(1440) which interact with its SH2 doma in, abolishes the activation of ERK by alpha (6)beta (4). Phenylalanine sub stitution of the beta (4) tyrosines able to interact with the SH2 or PTB do main of She does not affect incorporation of alpha (6)beta (4) in the hemid esmosomes of 804G cells. Exposure to the tyrosine phosphatase inhibitor ort hovanadate increases tyrosine phosphorylation of beta (4) and disrupts the hemidesmosomes of 804G cells expressing recombinant wild type beta (4). Thi s treatment, however, exerts a decreasing degree of inhibition on the hemid esmosomes of cells expressing versions of beta (4) containing phenylalanine substitutions at Tyr(1422) and Tyr(1440), at Tyr(1526) and Tyr(1642), or a t all four tyrosine phosphorylation sites. These results suggest that beta (4) Tyr(1526) interacts in a phosphorylation-dependent manner with the PTB domain of She. This event is required for subsequent tyrosine phosphorylati on of She and signaling to ERK but not formation of hemidesmosomes.