Transforming growth factor alpha (TGF/alpha) is a polypeptide mitogen of the epidermal growth factor (EGF) family that stimulates the replication of normal human keratinocytes. TGF/alpha is produced and autoinduced in cultured human keratinocytes and is expressed in normal epidermis. Epidermal growth control is complex. Human keratinocyte cell culture is a more simplified and representative model to examine autoregulation of proliferation and differentiation. The principal objective of these proposed studies is to examine the role of TGF/alpha expression in the proliferation an differentiation of human keratinocytes. We propose that TGF/alpha is a major autocrine/paracrine growth regulator of keratinocytes in culture, and expression of TGF/alpha protein stimulates normal epidermal keratinocyte renewal, re-epithelialization and benign and malignant epidermal hyperproliferation. The TGF/alpha autocrine/paracrine loop mediates growth regulation through the cognate receptor for TGF/alpha, the EGF receptor. Additional levels of growth control for keratinocytes include the negative growth regulator, transforming growth factor beta (TGF/beta) and other growth regulatory gene products such as c-myc. In this application, we propose to identify and characterize specific biological or chemical factors and culture conditions that modulate TGF/alpha expression and ligand-receptor activation. We hypothesize that a variety of biological substances exert their growth modulatory effects through the TGF/alpha autocrine/paracrine loop. Northern blot hybridization, radioreceptor and radioimmunoassays, biosynthetic labeling assays, and cellular transfection procedures will be employed to examine the role of these growth factors, receptors and activation pathways in growth control of human keratinocytes. Amplification of TGF/alpha expression and enhancement of keratinocyte replication may be linked events in epidermal hyperplasia induced by phorbol ester tumor promoters, wounding, and other disorders of epidermal hyperproliferation. Epidermis is an advantageous model system to examine epithelial growth control because of tissue accessibility, ability to transfer keratinocytes to culture and the spectrum of pathology that is exhibited by epidermal hyperplasia, dysplasia and malignancy. These studies are designed to elucidate the function and regulation of TGF/alpha in human keratinocytes and epidermis and will provide insight into the role of TGF/alpha in normal and pathologic states of epidermis, including wound healing, psoriasis and cutaneous carcinoma.
