Selective Interferon-α/β Effects on Platelet-Derived Growth Factor-Stimulated Processes in Quiescent BALB/c-3T3 Fibroblasts

Interferon-α/β (IFN-α/β) suppresses cell cycle activation by platelet-derived growth factor (PDGF) as well as the induction of the 31-kD (pI) and the 35-kD (pH) proteins in density-arrested BALB/c-3T3 cells.^(1,2) We report that elevation of [Ca²⁺]_i by ionomycin induces the synthesis of the 31-kD protein, but not that of the 35-kD protein. Since IFN blocks the PDGF-induced elevation of [Ca²⁺]_i,⁽³⁾ these results suggest that IFN treatment may suppress pI induction by impairing this PDGF-activated signal transduction pathway. In contrast, because ionomycin did not induce the 35-kD protein, the suppression by IFN of PDGF-induced pII appears to be mediated via a pathway distinct from that operating in the suppression of pI. In BALB/c-3T3 cells, IFN-α/β did not itself affect the turnover or de novo synthesis of inositol phospholipids and the cellular content of diacylglycerol, nor did IFN block the enhancement of these parameters by PDGF.