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 protein kinase implicated in integrin signaling. To investigate the functions of ILK in vivo, we have analyzed the expression and regulation of ILK in the skin, in which proper control of cell-extracellular matrix interactions and cell proliferation is essential for its normal development and homeostasis. We report here that ILK is abundantly expressed throughout the extracellular matrix-rich dermis. ILK mRNA was also detected in the hair follicles and the basal cells of the interfollicular epidermis. However, ILK expression is lost in the suprabasal layers of keratinocytes that are undergoing terminal differentiation. PINCH, an ILK-binding protein, exhibited a similar expression pattern in the skin. Recent studies have indicated that erbB-2, a member of the epidermal growth factor receptor family, plays a pivotal role in epidermal 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 coordinating the integrin signaling pathways and the growth factor signaling pathways in the development of the skin and the pathogenesis of skin diseases.