Vassbotn F S, Skar R, Holmsen H, Lillehaug J R
Department of Biochemistry, University of Bergen, Norway.
Exp Cell Res. 1992 Sep;202(1):98-104. doi: 10.1016/0014-4827(92)90408-z.
The effect of platelet-derived growth factor (PDGF) on c-fos mRNA transcription was studied in the immortalized mouse embryo fibroblast C3H/10T1/2 Cl 8 (10T1/2) cells and the chemically transformed, tumorigenic subclone C3H/10T1/2 Cl 16 (Cl 16). In the 10T1/2 cells as well as the Cl 16 subclone, the dose-dependent PDGF stimulation of c-fos mRNA synthesis was similar in both logarithmically growing and confluent cultures. c-fos mRNA was induced severalfold by 12-O-tetradecanoylphorbol-13-acetate (TPA) in both 10T1/2 and Cl 16. Down-regulation of protein kinase C (PKC) activity by TPA pretreatment inhibited PDGF-stimulated c-fos mRNA expression in Cl 16 cells but did not affect this induction in the 10T1/2 cells. This inhibition was not a general phenomenon of 3-methylcholanthrene-mediated transformation of 10T1/2 cells since experiments with another transformed 10T1/2 cell clone, C3H/10T1/2 TPA 482, gave qualitatively the same results as the 10T1/2 cells. Receptor binding experiments showed that the nontransformed and transformed cells had a comparable number of PDGF receptors, 1.3 x 10(5) and 0.7 x 10(5) receptors per cell, respectively. Furthermore, cAMP-induced c-fos expression induced by forskolin is formerly shown to be independent of PKC down-regulation. In our experiments, forskolin induced c-fos expression in both clones. However, PKC down-regulation inhibited the forskolin-induced c-fos expression in Cl 16 cells. This apparently demonstrates cross talk between PKC and PKA in the c-fos induction pathway. The present results provide evidence for an impaired mechanism for activating c-fos expression through PKC-independent, PDGF-induced signal transduction in the chemically transformed Cl 16 fibroblasts compared to that in nontransformed 10T1/2 cells.
在永生化小鼠胚胎成纤维细胞C3H/10T1/2 Cl 8（10T1/2）细胞和化学转化的致瘤亚克隆C3H/10T1/2 Cl 16（Cl 16）中研究了血小板衍生生长因子（PDGF）对c-fos mRNA转录的影响。在10T1/2细胞以及Cl 16亚克隆中，对数生长期和汇合培养的细胞中，PDGF对c-fos mRNA合成的剂量依赖性刺激相似。在10T1/2和Cl 16细胞中，12-O-十四烷酰佛波醇-13-乙酸酯（TPA）均可使c-fos mRNA诱导数倍增加。TPA预处理下调蛋白激酶C（PKC）活性可抑制Cl 16细胞中PDGF刺激的c-fos mRNA表达，但不影响10T1/2细胞中的这种诱导作用。这种抑制作用并非3-甲基胆蒽介导的10T1/2细胞转化的普遍现象，因为对另一个转化的10T1/2细胞克隆C3H/10T1/2 TPA 482进行的实验与10T1/2细胞得到了定性相同的结果。受体结合实验表明，未转化和转化细胞的PDGF受体数量相当，分别为每个细胞1.3×10⁵和0.7×10⁵个受体。此外，以前的研究表明，福斯高林诱导的cAMP诱导的c-fos表达与PKC下调无关。在我们的实验中，福斯高林在两个克隆中均诱导了c-fos表达。然而，PKC下调抑制了Cl 16细胞中福斯高林诱导的c-fos表达。这显然证明了在c-fos诱导途径中PKC和PKA之间存在相互作用。目前的结果提供了证据，表明与未转化的10T1/2细胞相比，化学转化的Cl 16成纤维细胞中通过PKC非依赖性、PDGF诱导的信号转导激活c-fos表达的机制受损。
