Nair B G, Yu Y, Rashed H M, Sun H, Patel T B
Department of Pharmacology, University of Tennessee, Memphis 38163, USA.
J Cell Physiol. 1995 Aug;164(2):232-9. doi: 10.1002/jcp.1041640203.
Studies presented in this report were designed to investigate the effects of transforming growth factor-beta 1 (TGF-beta 1) on epidermal growth factor (EGF)-mediated stimulation of cAMP accumulation in cardiac myocytes and elucidate the mechanism(s) involved in this modulation. TGF-beta 1 (20 pM) treatment of cardiac myocytes, in a time-dependent manner, decreased the ability of EGF (100 nM) to increase cAMP accumulation. Significant attenuation of EGF-elicited cAMP accumulation was observed 2 h after exposure to TGF-beta 1 and 18 h after addition of TGF-beta 1, the ability of EGF to increase cAMP accumulation was completely obliterated. TGF-beta 1 neither decreased immunoprecipitable EGF receptors in membranes from cardiomyocytes nor altered the specific binding of [125I]EGF to cardiomyocyte membranes. However, TGF-beta 1 decreased the ability of EGF to phosphorylate membrane proteins on tyrosine residues. TGF-beta 1 treatment of cardiomyocytes also decreased the ability of forskolin to augment cAMP accumulation in intact cells and stimulate adenylyl cyclase activity. Similarly, in membranes of TGF-beta 1-treated cells, neither isoproterenol nor EGF stimulated adenylyl cyclase activity. Interestingly, as assessed by the ability of A1F4- to stimulate adenylyl cyclase, TGF-beta 1 did not alter the coupling between Gs and catalytic subunits. Likewise, TGF-beta 1 did not alter the functional activity of the inhibitory regulatory element of the system, Gi. Western analysis of cellular proteins revealed that TGF-beta 1 did not alter the amounts of Ga alpha, Gi alpha 2, and Gi alpha 3. We conclude that TGF-beta 1 attenuates EGF-elicited cAMP accumulation in cardiomyocytes, in part, by decreasing the EGF receptor kinase function and that TGF-beta 1-mediated alterations in the activity of adenylyl cyclase catalytic subunit also contribute toward the regulation of adenylyl cyclase by various agonists.
本报告中呈现的研究旨在探究转化生长因子-β1（TGF-β1）对表皮生长因子（EGF）介导的心肌细胞中环磷酸腺苷（cAMP）积累刺激作用的影响，并阐明这种调节作用所涉及的机制。用TGF-β1（20 pM）处理心肌细胞，呈时间依赖性地降低了EGF（100 nM）增加cAMP积累的能力。在暴露于TGF-β1 2小时后以及添加TGF-β1 18小时后，观察到EGF引发的cAMP积累显著减弱，EGF增加cAMP积累的能力完全丧失。TGF-β1既未降低心肌细胞膜中可免疫沉淀的EGF受体数量，也未改变[125I]EGF与心肌细胞膜的特异性结合。然而，TGF-β1降低了EGF使膜蛋白酪氨酸残基磷酸化的能力。用TGF-β1处理心肌细胞也降低了福斯高林增强完整细胞中cAMP积累以及刺激腺苷酸环化酶活性的能力。同样，在经TGF-β1处理的细胞的膜中，异丙肾上腺素和EGF均未刺激腺苷酸环化酶活性。有趣的是，通过AlF4-刺激腺苷酸环化酶的能力评估发现，TGF-β1并未改变Gs与催化亚基之间的偶联。同样，TGF-β1也未改变该系统抑制性调节元件Gi的功能活性。对细胞蛋白的蛋白质免疫印迹分析表明，TGF-β1并未改变Gαα、Giα2和Giα3的量。我们得出结论，TGF-β1部分通过降低EGF受体激酶功能来减弱EGF引发的心肌细胞中cAMP积累，并且TGF-β1介导的腺苷酸环化酶催化亚基活性改变也有助于各种激动剂对腺苷酸环化酶的调节。
