The tetraspanin CD9 associates with the integrin alpha 6 beta 4 in cultured human epidermal keratinocytes and is involved in cell motility

Integrins are involved in several ways in keratinocyte physiology, includin g cell motility. CD9 is a member of the tetraspanin protein family which is found in association with other transmembrane proteins like the integrins, CD9 is expressed in the epidermal tissue, but this expression is not regul ated by differentiation. The present work focuses on association of CD9 wit h the integrin alpha 6 beta 4 in keratinocytes. In vivo, CD9 does not co-lo calize with alpha 6 beta 4, and is not internalized with the integrin upon basal detachment with dispase, In vitro, CD9 is found partly in co-localiza tion with alpha 6 beta 4 and is internalized with the integrin after kerati nocyte detachment with dispase, Using blocking antibodies in a phagokinetic tracks assay, we show that CD9, and to a lesser extent alpha 6 beta 4, but not the tetraspanin CD82, promote motility of subconfluent keratinocytes o n collagen I. Our observations also suggest that CD9 is involved in the for mation of lamellipodia. We also report that the phorbol ester TPA has no ef fect on CD9 expression and association with alpha 6 beta 4, but increases k eratinocyte motility, possibly through modulation of integrin subunits expr ession, or through upregulation of collagenase-1 expression. Together, thes e results confirm that CD9 associates with alpha 6 beta 4 in cultured kerat inocytes, possibly in order to regulate the function of the integrin, and t hat CD9 is involved in keratinocyte motility on collagen. The data suggest that regulation of adhesion characteristics by CD9 in keratinocytes may pla y a role in epidermal repair.