EGF-induced MAPK Signaling Inhibits Hemidesmosome Formation through Phosphorylation of the Integrin β4

Migration of keratinocytes requires a regulated and dynamic turnover of hemidesmosomes (HDs). We and others have previously identified three serine residues on the integrin beta 4 cytoplasmic domain that play a critical role in the regulation of HD disassembly. In this study we show that only two of these residues (Ser-1356 and Ser-1364) are phosphorylated in keratinocytes after stimulation with either PMA or EGF. Furthermore, in direct contrast to previous studies performed in vitro, we found that the PMA- and EGF-stimulated phosphorylation of beta 4 is not mediated by PKC, but by ERK1/2 and its downstream effector kinase p90RSK1/2. EGF-stimulated phosphorylation of beta 4 increased keratinocyte migration, and reduced the number of stable HDs. Furthermore, mutation of the two serines in beta 4 to phospho-mimicking aspartic acid decreased its interaction with the cytoskeletal linker protein plectin, as well as the strength of alpha 6 beta 4-mediated adhesion to laminin-332. During mitotic cell rounding, when the overall cell-substrate area is decreased and the number of HDs is reduced, beta 4 was only phosphorylated on Ser-1356 by a distinct, yet unidentified, kinase. Collectively, these data demonstrate an important role of beta 4 phosphorylation on residues Ser-1356 and Ser-1364 in the formation and/or stability of HDs.