Abstract
Platelet-derived growth factor (PDGF) stimulates fibroblasts to move over collagen and contract three-dimensional collagen gels, processes important in wound repair and fibrocontractive diseases. These processes depend on alpha 2 beta 1 integrin ligation of collagen and PDGF induces the expression of this integrin. Several lines of evidence presented here suggest that PKC-zeta plays a role in alpha 2 integrin gene expression. The induction was blocked by chemical inhibitors for protein tyrosine kinases (PTK), genistein, and protein kinase C (PKC), chelerythrine, and bisindolylmaleimide GF 109203X. Cells depleted of phorbol 12-myristate 13-acetate (PMA)-inducible PKCs by chronic treatment with PMA still demonstrated an alpha 2 response to PDGF indicating that a non-PMA-sensitive PKC isoform was required. PDGF induced kinase activity in PKC-zeta immunoprecipitates. Antisense oligonucleotides complementary to 5' end of PKC-zeta mRNA sequences blocked the PDGF-induced increase of alpha 2 mRNA levels up to 70%, indicating PKC-zeta, a non-PMA-sensitive PKC isoform, is a component of the PDGF stimulatory pathway for alpha 2 mRNA synthesis. A 961-base pair (bp) upstream region of alpha 2 gene/CAT construct transfected into human dermal fibroblasts was positively regulated by PDGF as judged by CAT enzymatic levels. Both PTK and PKC inhibitors blocked PDGF-stimulation of the alpha 2 promoter fragment/CAT construct, indicating that the phosphorylation requirement occurred at alpha 2 promoter-directed transcription level. Therefore, we propose that PDGF-stimulatory pathway of alpha 2 integrin gene expression involves multiple cellular protein kinases, one of which is PKC-zeta.