The expression of PDGF-α but not PDGF-β receptors is suppressed in Swiss/3T3 fibroblasts over-expressing protein kinase C-α

The generation and characterization of Swiss/3T3 cells which stably over-express protein kinase C (PKC)-α were previously described by us. In these cells over-expression of PKC-α reduced the expression of epidermal growth factor (EGF) receptor molecules [(1990) J. Biol. Chem. 265, 13290-13296]. Here we show that the expression of PDGF-α receptors, but not PDGF-β receptors, was specifically decreased in these cells. Not only were the levels of PDGF-α receptor mRNA transcript and protein significantly diminished in the PKC-α over-producing cells, but their ability to respond to short- and long-term growth factor signals was appropriately compromised. This was reflected in a reduced tyrosine autophosphorylation signal in response to PDGF-AA, as well as in decreased growth rates of PKC-α over-expressing cells when supplied with external PDGF-AA. A similar decrease in PDGF-α receptors was also demonstrated in parental Swiss/3T3 cells treated with phorbol esters. Our studies imply that PKC-α is involved in a cellular mechanism suppressing the expression of PDGF-α receptors in Swiss/3T3 cells. Hence, activation of PKC-α or alterations in its cellular levels may affect, in turn, the expression of a specific set of cell surface receptors and their responses to external growth factors.