Abstract
Adhesion of human salivary gland (HSG) epithelial cells to fibronectin- or collagen I gel-coated substrates, mediated by beta1 integrins, has been shown to upregulate the expression of more than 30 genes within 3-6 h. Adhesion of HSG cells to fibronectin or collagen I for 6 h also enhanced total protein kinase C (PKC) activity by 1.8-2.3-fold. HSG cells expressed PKC-alpha, gamma, delta, epsilon, mu, and zeta. Adhesion of HSG cells to fibronectin or collagen I specifically activated PKC-gamma and PKC-delta. Cytoplasmic PKC-gamma and PKC-delta became membrane-associated, and immunoprecipitated PKC-gamma and PKC-delta kinase activities were enhanced 2.5-4.0-fold in HSG cells adherent to fibronectin or collagen I. In addition, adhesion of fibronectin-coated beads to HSG monolayers co-aggregated beta1 integrin and PKC-gamma and PKC-delta but not other PKC isoforms. Thus, integrin-dependent adhesion of HSG cells to fibronectin or collagen I activated PKC-gamma and PKC-delta. The role of this PKC upregulation on adhesion-responsive gene expression was then tested. HSG cells were treated with the specific PKC inhibitor bisindolylmaleimide I, cultured on non-precoated, fibronectin- or collagen I-coated substrates, and analyzed for changes in adhesion-responsive gene expression. Bisindolylmaleimide I strongly inhibited the expression of seven adhesion-responsive genes including calnexin, decorin, S-adenosylmethionine decarboxylase, steroid sulfatase, and 3 mitochondrial genes. However, the expression of two adhesion-responsive genes was not affected by bisindolylmaleimide I. Treatment with bisindolylmaleimide I did not affect cell spreading and did not significantly affect the actin cytoskeleton. These data suggest that adhesion of HSG cells to fibronectin or collagen I induces PKC activity and that this induction contributes to the upregulation of a variety of adhesion-responsive genes.
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