THE INTRACELLULAR FUNCTIONS OF ALPHA(6)BETA(4) INTEGRIN ARE REGULATEDBY EGF

Upon ligand binding, the alpha(6) beta(4) integrin becomes phosphoryla ted on tyrosine residues and combines sequentially with the adaptor mo lecules She and Grb2, linking to the ras pathway, and with cytoskeleta l elements of hemidesmosomes. Since alpha(6) beta(4) is expressed in a variety of tissues regulated by the EGF receptor (EGFR), we have exam ined the effects of EGF on the cytoskeletal and signaling functions of alpha(6) beta(4). Experiments of immunoblotting with anti-phosphotyro sine antibodies and immunoprecipitation followed by phosphoamino acid analysis and phosphopeptide mapping showed that activation of the EGFR causes phosphorylation of the beta(4) subunit at multiple tyrosine re sidues, and this event: requires ligation of the integrin by laminins or specific antibodies. Immunoprecipitation experiments indicated that stimulation with EGF does not result in association of alpha(6) beta( 4) with Shc. In contrast, EGF can partially suppress the recruitment o f She to ligated alpha(6) beta(4) Immunofluorescent analysis revealed that EGF treatment does not induce increased assembly of hemidesmosome s, but instead causes a deterioration of these adhesive structures. Fi nally, Boyden chamber assays indicated that exposure to EGF results in upregulation of alpha(6) beta(4)-mediated cell migration toward lamin ins. We conclude that EGF-dependent signals suppress the association o f activated alpha(6) beta(4) with both signaling and cytoskeletal mole cules, but upregulate alpha(6) beta(4)-dependent cell migration. The c hanges in alpha(6) beta(4) function induced by EGF may play a role dur ing wound healing and tumorigenesis.