Contrasting role of phospholipase C-γ1 in the expression of immediate early genes induced by epidermal or platelet-derived growth factors

While significant progress has been achieved in identifying the signal transduction elements that operate downstream of activated receptor tyrosine kinases, it remains unclear how different receptors utilize these signaling elements to achieve a common response. This study compares the capacity of epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) to elicit the induction of immediate early gene (IEG) mRNAs in the presence or absence of phospholipase C-γ1 (PLC-γ1). The results show that while PDGF induction of nearly all IEG mRNAs is abrogated in plcg1 null cells, EGF induction of the same genes is variable in the null cells and exhibits three distinct responses. Five IEG mRNAs ( Nup475, Cyr61, TF, Gly, TS7) are completely inducible by EGF in the presence or absence of PLC-γ1, while three others ( JE, KC, FIC) exhibit a stringent requirement for the presence of PLC-γ1. The third type of response is exhibited by c-fos and COX-2. While these mRNAs are completely induced by EGF in the absence of PLC-γ1, the time course of their accumulation is significantly delayed. No IEG was identified as completely inducible by EGF and PDGF in the absence of PLC-γ1. Electrophoretic mobility shift assays (EMSA) demonstrate that PLC-γ1 is necessary for nuclear extracts from PDGF-treated cells, but not EGF-treated cells, to interact with probes for AP-1 or NF-κB.