Inhibitory role of alpha 6 beta 4-associated erbB-2 and phosphoinositide 3-kinase in keratinocyte haptotactic migration dependent on alpha 3 beta 1 integrin

Keratinocytes and other epithelial cells express two receptors for the base ment membrane (BM) extracellular matrix component laminin-5 (Ln-5). integri ns alpha3 beta1 and alpha6 beta4. While alpha3 beta1 mediates adhesion, spr eading, and migration (Kreidberg, J.A. 2000. Curr: Opin. Cell Biol. 12:548- 553), alpha6 beta4 is involved in BM anchorage via hemidesmosomes (Borrador i, L., and A. Sonnenberg. 1999. J. Invest. Dermatol. 112:411-418). We inves tigated a possible regulatory interplay between alpha3 beta1 and alpha6 bet a4 in cell motility using HaCaT keratinocytes as a model. We found that alp ha6 beta4 antibodies inhibit alpha3 beta1-mediated migration on Ln-5, but o nly when migration is haptotactic (i.e., spontaneous or stimulated by alpha 3 beta1 activation), and not when chemotactic (i.e., triggered by epidermal growth factor receptor). Inhibition of migration by alpha6 beta4 depends u pon phosphoinositide 3-kinase (PI3-K) since it is abolished by PI3-K blocke rs and by dominant-negative PI3-K, and constitutively active PI3-K prevents haptotaxis. In HaCaT cells incubated with anti-alpha6 beta4 antibodies. ac tivation of PI3-K is mediated by alpha6 beta4-associated erbB-2, as indicat ed by erbB-2 autophosphorylation and erbB-2/p85 PI3-K coprecipitation. Furt hermore, dominant-negative erbB-2 abolishes inhibition of haptotaxis by ant i-alpha6 beta4 antibodies. These results support a model whereby (a) haptot actic cell migration on Ln-5 is regulated by concerted action of alpha3 bet a1 and alpha6 beta4 integrins, (b) alpha6 beta4-associated erbB-2 and PI3-K negatively affect haptotaxis, and (c) chemotaxis on Ln-5 is not affected b y alpha6 beta4 antibodies and may require PI3-K activity. This model could be of general relevance to motility of epithelial cells in contact with BM.