Westwick J K, Fleckenstein J, Yin M, Yang S Q, Bradham C A, Brenner D A, Diehl A M
Department of Pharmacology, University of North Carolina, Chapel Hill 27599, USA.
Am J Physiol. 1996 Nov;271(5 Pt 1):G780-90. doi: 10.1152/ajpgi.1996.271.5.G780.
Adenosine 3',5'-cyclic monophosphate (cAMP) prevents epidermal growth factor (EGF)-induced DNA synthesis in many types of cultured cells, including hepatocytes, but its effects on cellular proliferation in vivo are unknown. This study compares the effects of supplemental cAMP on hepatocyte proliferation induced in vivo by 70% partial hepatectomy (PH) and in vitro by EGF and determines the effects of cAMP on AP-1, a family of growth-regulatory transcription factors, and the kinase cascades that normally activate AP-1. Although injection of dibutyryladenosine 3',5'-cyclic monophosphate (30 mg/kgip) at the time of PH increased liver cAMP concentrations at least 100-fold for several hours, it did not inhibit hepatic incorporation of [3H]thymidine or proliferating cell nuclear antigen expression 24 h after PH. cAMP treatment led to a complete inhibition of extracellular signal-related kinase (ERK) activity and transiently reduced NH2-terminal Jun nuclear kinase (JNK) activity after PH but did not decrease the expression of c-jun mRNA or protein. Consistent with the known cAMP stimulation of jun-B in cultured cells, cAMP treatment increased jun-B mRNA, protein, and DNA binding activity post-PH. Surprisingly, cAMP treatment enhanced Raf kinase activity after PH in rats. In primary hepatocyte cultures, supplemental cAMP inhibited JNK and ERK activity, total AP-1 and c-Jun transcriptional activities, and DNA synthesis. Thus elevated cAMP inhibited ERK and JNK activity in culture and in vivo and inhibited hepatocyte proliferation in culture but not in vivo. This suggests that in vivo mechanisms compensate for cAMP inhibition of certain growth-related signaling cascades and emphasizes potential risks of extrapolating from simple cell culture systems to explain physiology in intact animals.
3',5'-环磷酸腺苷（cAMP）可抑制多种培养细胞（包括肝细胞）中表皮生长因子（EGF）诱导的DNA合成，但其对体内细胞增殖的影响尚不清楚。本研究比较了补充cAMP对70%部分肝切除术（PH）诱导的体内肝细胞增殖以及EGF诱导的体外肝细胞增殖的影响，并确定了cAMP对AP-1（一种生长调节转录因子家族）以及通常激活AP-1的激酶级联反应的影响。尽管在PH时注射二丁酰环磷酸腺苷（30mg/kg腹腔注射）可使肝脏cAMP浓度在数小时内至少增加100倍，但在PH后24小时，它并未抑制[3H]胸腺嘧啶核苷的肝脏掺入或增殖细胞核抗原的表达。cAMP处理导致PH后细胞外信号调节激酶（ERK）活性完全抑制，并短暂降低氨基末端Jun核激酶（JNK）活性，但并未降低c-jun mRNA或蛋白质的表达。与已知的cAMP在培养细胞中对jun-B的刺激作用一致，cAMP处理增加了PH后jun-B mRNA、蛋白质和DNA结合活性。令人惊讶的是，cAMP处理增强了大鼠PH后的Raf激酶活性。在原代肝细胞培养中，补充cAMP抑制了JNK和ERK活性、总AP-1和c-Jun转录活性以及DNA合成。因此，升高的cAMP在培养中和体内均抑制ERK和JNK活性，并在培养中抑制肝细胞增殖，但在体内则不然。这表明体内机制可补偿cAMP对某些生长相关信号级联反应的抑制作用，并强调了从简单细胞培养系统推断完整动物生理学的潜在风险。
