Hu J S, Olson E N
Department of Biochemistry and Molecular Biology, University of Texas, M. D. Anderson Cancer Center, Houston 77030.
J Biol Chem. 1988 Dec 25;263(36):19670-7.
Serum mitogens, fibroblast growth factor (FGF), and type beta transforming growth factor (TGF-beta) suppress differentiation of the mouse muscle cell line BC3H1; however, the signal transduction pathways whereby these growth factors exert their effects on this system are unknown. The goal of this study was to determine whether the program for differentiation of BC3H1 cells was susceptible to negative regulation by signaling pathways involving cAMP or protein kinase C and whether these intracellular effectors participate in the mechanism by which growth factors prevent establishment of the myogenic phenotype. Exposure of BC3H1 cells to dibutyryl cAMP, 8-bromo-cAMP, or compounds that stimulate adenylate cyclase, i.e. forskolin, prostaglandin E1, and cholera toxin, prevented up-regulation of muscle-specific gene products following growth arrest in mitogen-deficient medium. Conversely, addition of cAMP to differentiated BC3H1 myocytes caused down-regulation of muscle-specific mRNAs. In contrast to the ability of cAMP to block differentiation, chronic exposure to O-tetradecanoylphorbol-13-acetate, the potent activator of protein kinase C, exhibited no apparent effects on expression of muscle-specific gene products. The proto-oncogenes c-myc and c-fos were up-regulated rapidly by cAMP in a manner similar to that observed previously by serum, FGF, and TGF-beta. However, these growth factors failed to increase intracellular cAMP levels, and they did not induce ornithine decarboxylase, which was subject to positive regulation by cAMP and O-tetradecanoyl-13-acetate. Together, these data indicate that differentiation of BC3H1 cells is subject to negative regulation through a cAMP-dependent pathway and that serum mitogens, FGF, and TGF-beta inhibit differentiation through a mechanism independent of cAMP or protein kinase C.
血清促细胞分裂剂、成纤维细胞生长因子（FGF）和β型转化生长因子（TGF-β）可抑制小鼠肌肉细胞系BC3H1的分化；然而，这些生长因子对该系统发挥作用的信号转导途径尚不清楚。本研究的目的是确定BC3H1细胞的分化程序是否易受涉及cAMP或蛋白激酶C的信号通路的负调控，以及这些细胞内效应器是否参与生长因子阻止肌源性表型建立的机制。将BC3H1细胞暴露于二丁酰cAMP、8-溴-cAMP或刺激腺苷酸环化酶的化合物（即福斯可林、前列腺素E1和霍乱毒素），可防止在缺乏促细胞分裂剂的培养基中生长停滞后肌肉特异性基因产物的上调。相反，向分化的BC3H1肌细胞中添加cAMP会导致肌肉特异性mRNA的下调。与cAMP阻断分化的能力相反，长期暴露于蛋白激酶C的强效激活剂十四烷酰佛波醇-13-乙酸酯对肌肉特异性基因产物的表达没有明显影响。原癌基因c-myc和c-fos被cAMP迅速上调，其方式与先前观察到的血清、FGF和TGF-β相似。然而，这些生长因子未能提高细胞内cAMP水平，也未诱导鸟氨酸脱羧酶，而鸟氨酸脱羧酶受cAMP和十四烷酰-13-乙酸酯的正向调控。这些数据共同表明，BC3H1细胞的分化受cAMP依赖性途径的负调控，血清促细胞分裂剂、FGF和TGF-β通过独立于cAMP或蛋白激酶C的机制抑制分化。
