Vasoactive intestinal peptide and epidermal growth factor: Co-mitogens or inhibitors of keratinocyte proliferation in vitro?

Vasoactive intestinal peptide (VIP) is a neuropeptide with a broad range of biological activities in various tissues. Interactions of VIP and epiderma l growth factor (EGF) are of particular interest for dermatology, They may be either co-mitogenic or inhibitory. HaCaT keratinocytes cultivated under serum-free conditions in vitro have been used to investigate the interactio ns of VIP and EGF. EGF was found to induce cell growth, whereas preincubati on with VIP inhibited EGF-induced proliferation in a dose-dependent manner. Maximum growth inhibition was 46% (p<0.01) at a VIP concentration of 10(-7 ) M. EGF-induced growth is mediated by tyrosine kinase (TK). Therefore we s tudied the effect of VIP on TK activity. Cells were incubated with VIP (10( -13)-10(-7) M) for 48 h and stimulated with EGF at a final concentration of 500 ng/ml. SDS-PAGE and Western blot with the antibody RC20H against TK we re performed. We found a dose dependent decrease of EGF receptor TK activit y. At VIP concentration of 10(-7) M a residual TK activity of 65% was detec ted. To investigate the possibly involved signal transduction pathways, we performed inhibition experiments with wortmannin, pertussis toxin, 2'5'diac ylglycerol and adenosine-3':5'-mono-phosphorothioate. However, none of the inhibitors was effective in abolishing growth inhibition by VIP. VIP was sh own to be growth inhibitory for human keratinocytes. The data suggest that EGF receptor TK is involved in signal transduction of VIP. Thus TK activity is a possible common target of both EGF- and VIP-induced cellular response s.