Heaton J H, Nebes V L, O'Dell L G, Morris S M, Gelehrter T D
Department of Human Genetics, University of Michigan Medical School, Ann Arbor 48109-0618.
Mol Endocrinol. 1989 Jan;3(1):185-92. doi: 10.1210/mend-3-1-185.
Primary cultures of rat hepatocytes produce tissue-type plasminogen activator (tPA) and plasminogen activator-inhibitor type 1 (PAI-1). Incubation of hepatocytes with 50 microM 8-(4-chlorophenylthio)cAMP (CPT-cAMP) results in a 4-fold increase in tPA activity, whereas the synthetic glucocorticoid dexamethasone (1 microM) causes a more than 90% decrease. In combination, dexamethasone completely overcomes the CPT-cAMP effect and markedly decreases PA activity. PAI-1 is induced by both CPT-cAMP and dexamethasone, and the effects of these agents are additive. Accumulation of tPA mRNA is increased more than 4-fold by CPT-cAMP and is greatly decreased by incubation with dexamethasone. Dexamethasone in combination with CPT-cAMP totally blocks this cAMP effect. The protein synthesis inhibitor cycloheximide does not prevent either the dexamethasone-induced decrease or the CPT-cAMP-induced increase in tPA message and, in fact, augments the cAMP-induced increase in tPA mRNA. Hepatocyte PAI-1 mRNA levels are increased 2-fold by incubation with either CPT-cAMP or dexamethasone; in combination, these effectors cause a 4-fold increase in PAI-1 mRNA. Cycloheximide alone causes a marked increase in PAI-1 mRNA, but does not block the induction by either CPT-cAMP or dexamethasone. We conclude that incubation of hepatocytes with CPT-cAMP induces tPA activity by increasing tPA mRNA accumulation and that dexamethasone causes a decrease in tPA activity by both decreasing tPA mRNA and increasing PAI-1 mRNA and activity. Concomitant protein synthesis is not required for the regulation of tPA or PAI-1 mRNA by either CPT-cAMP or dexamethasone, indicating a primary effect of these agents on gene transcription or mRNA stability.
大鼠肝细胞原代培养物可产生组织型纤溶酶原激活物（tPA）和1型纤溶酶原激活物抑制剂（PAI-1）。用50微摩尔8-（4-氯苯硫基）环磷酸腺苷（CPT-cAMP）孵育肝细胞会使tPA活性增加4倍，而合成糖皮质激素地塞米松（1微摩尔）则导致其活性降低90%以上。联合使用时，地塞米松完全抵消了CPT-cAMP的作用，并显著降低PA活性。CPT-cAMP和地塞米松均可诱导PAI-1产生，且二者的作用具有叠加性。CPT-cAMP可使tPA mRNA积累增加4倍以上，而用地塞米松孵育则使其大幅减少。地塞米松与CPT-cAMP联合使用可完全阻断这种cAMP效应。蛋白质合成抑制剂环己酰亚胺既不能阻止地塞米松诱导的tPA减少，也不能阻止CPT-cAMP诱导的tPA增加，实际上，它还增强了cAMP诱导的tPA mRNA增加。用CPT-cAMP或地塞米松孵育均可使肝细胞PAI-1 mRNA水平增加2倍；联合使用时，这些效应物可使PAI-1 mRNA增加4倍。单独使用环己酰亚胺可使PAI-1 mRNA显著增加，但不能阻断CPT-cAMP或地塞米松的诱导作用。我们得出结论，用CPT-cAMP孵育肝细胞可通过增加tPA mRNA积累来诱导tPA活性，而地塞米松则通过降低tPA mRNA以及增加PAI-1 mRNA和活性来降低tPA活性。CPT-cAMP或地塞米松对tPA或PAI-1 mRNA的调节不需要伴随蛋白质合成，这表明这些物质对基因转录或mRNA稳定性具有主要作用。
