EXPRESSION OF THE INTEGRIN-LINKED KINASE (ILK) IN MOUSE SKIN - LOSS OF EXPRESSION IN SUPRABASAL LAYERS OF THE EPIDERMIS AND UP-REGULATION BY ERBB-2

Integrin-linked kinase (ILK) is a newly identified serine/threonine pr otein kinase implicated in integrin. signaling. To investigate the fun ctions of ILK In vivo, we have analyzed the expression and regulation of ILK in the skin, in which proper control of cell-extracellular matr ix: interactions and cell proliferation is essential for its normal de velopment and homeostasis. We report here that ILK is abundantly expre ssed throughout the extracellular matrix-rich dermis, ILK mRNA was als o detected in the hair follicles and the basal cells of the interfolli cular epidermis. However, ILK expression is lost in the suprabasal lay ers of keratinocytes that are undergoing terminal differentiation, PIN CH, an ILK-binding protein, exhibited a similar expression pattern in the skin. Recent studies have indicated that erbB-2, a member of the e pidermal growth factor receptor family, plays a pivotal role in epider mal growth, differentiation, and hair follicle morphogenesis. Using a transgenic mouse system in which an activated erbB-2 is overexpressed in the epidermis, we show that ILK; expression is regulated by erbB-2. The in vivo expression and regulation patterns of ILK, together with its biochemical activities, suggest an important role of ILK in coordi nating the integrin signaling pathways and the growth factor signaling pathways in the development of the skin and the pathogenesis of skin diseases.