Franklin C C, Kraft A S
Department of Medicine, University of Alabama, Birmingham 35294.
Biochim Biophys Acta. 1992 Mar 16;1134(2):137-42. doi: 10.1016/0167-4889(92)90036-b.
Phorbol esters, epidermal growth factor (EGF) and serum induce the transient expression of the c-jun and c-fos proto-oncogenes in quiescent fibroblasts. While phorbol esters such as phorbol 12-myristate 13-acetate (PMA) are thought to induce the transcription of these genes by activating protein kinase C (PKC), the signal transduction pathway(s) mediating the effects of EGF and serum are still unclear. We have investigated whether PKC and/or calcium play a role in mediating EGF-stimulated c-jun and c-fos RNA and protein expression in quiescent NIH 3T3 fibroblasts. PMA, EGF or serum stimulated a rapid, transient increase in c-jun and c-fos expression and cJun protein synthesis in quiescent NIH 3T3 cells. Depletion of whole cell PKC activity by pretreatment with PMA abolished any subsequent response to PMA, but had no effect on the ability of EGF or serum to induce c-jun and c-fos RNA and cJun protein expression. Nuclear run-on analysis indicated that EGF-induced gene expression was due to an increase in the rate of transcription of c-jun and c-fos in both naive and PKC-depleted cells. The role of calcium in the EGF-induced expression of c-jun and c-fos was also investigated using an NIH 3T3 cell line (HER-14) overexpressing the wild type human EGF receptor. Removal of extracellular calcium by chelation with excess EGTA or use of the non-specific calcium channel blocker lanthanide, both of which abolish the EGF-induced calcium transient in HER-14 cells, had no effect on the PMA or EGF induced c-jun or c-fos response. These findings suggest that EGF induces c-jun and c-fos transcription and cJun protein synthesis in a manner independent of an increase in intracellular calcium or activation of PKC in quiescent NIH 3T3 cells.
佛波酯、表皮生长因子（EGF）和血清可诱导静止成纤维细胞中c-jun和c-fos原癌基因的瞬时表达。虽然诸如佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）等佛波酯被认为通过激活蛋白激酶C（PKC）来诱导这些基因的转录，但介导EGF和血清作用的信号转导途径仍不清楚。我们研究了PKC和/或钙在介导静止的NIH 3T3成纤维细胞中EGF刺激的c-jun和c-fos RNA及蛋白表达中是否起作用。PMA、EGF或血清刺激静止的NIH 3T3细胞中c-jun和c-fos表达以及cJun蛋白合成迅速、短暂增加。用PMA预处理使全细胞PKC活性耗竭消除了随后对PMA的任何反应，但对EGF或血清诱导c-jun和c-fos RNA及cJun蛋白表达的能力没有影响。细胞核连续分析表明，EGF诱导的基因表达是由于在未处理和PKC耗竭的细胞中c-jun和c-fos转录速率增加所致。还使用过表达野生型人EGF受体的NIH 3T3细胞系（HER-14）研究了钙在EGF诱导的c-jun和c-fos表达中的作用。用过量EGTA螯合去除细胞外钙或使用非特异性钙通道阻滞剂镧系元素，这两种方法均可消除HER-14细胞中EGF诱导的钙瞬变，但对PMA或EGF诱导的c-jun或c-fos反应没有影响。这些发现表明，在静止的NIH 3T3细胞中，EGF以独立于细胞内钙增加或PKC激活的方式诱导c-jun和c-fos转录以及cJun蛋白合成。
