Regulatory mechanisms of beta-adrenergic agonists induced-cell proliferation of rat submandibular glands and their alterations during aging

细胞增殖的调控机制在衰老或癌变的生化表现中具有重要意义。大鼠单次注射异丙肾上腺素（IPR）可显著刺激唾液腺的DNA合成。本研究的目的是探讨β -激动剂诱导细胞增殖的机制，以及诱导细胞增殖的信号转导的年龄依赖性改变。对腹腔注射IPR （100mg/kg）的大鼠颌下腺进行核分离。用[γ -^<32>P] ATP孵育后，组蛋白(H)和非组蛋白（nH）从细胞核中分离出来。第4周时nH磷酸化水平在注射IPR后10h开始升高，在22h达到最大值，然后恢复到对照水平。注射IPR后启动nH磷酸化刺激或恢复到对照水平所需的时间随着年龄的增长而显著增加。与染色质相关的蛋白激酶活性的年龄依赖性变化似乎与nH.3磷酸化的改变相对应。[^3H]胸腺嘧啶在4周龄大鼠注射IPR后14h开始在颌下腺DNA中掺入，在22h达到最大值，30h恢复到对照水平。随着年龄的增长，大鼠颌下腺DNA合成开始前的时间增加。在ipr注射前2h腹腔注射[^<32>P]正磷酸盐获得大鼠颌下腺。提取的核蛋白经抗c-fos抗体免疫沉淀，SDS-PAGE电泳。磷酸化的c-fos经放射自显影鉴定。IPR诱导了c-fos的表达，但对c-jun的表达没有影响。c-fosmRNA的年龄依赖性变化被认为与Gs的改变密切相关。综上所述，IPR通过信号转导级联刺激与染色质相关的蛋白激酶，其中腺苷酸环化酶受体刺激增加c-fos表达。这种激酶调节nH的磷酸化。nH磷酸化的延迟发生在衰老过程中对细胞增殖和细胞功能起调节作用。少

The regulatory mechanisms of cell proliferation are important in the biochemical manifestation of senescence or cancer. A single injection of isoproterenol (IPR) into rats results in a marked stimulation of DNA synthesis in the salivary glands. The aim of this study was to investigate the mechanism of cell proliferation induced by beta-agonists and the age-dependent alteration of the signal transduction lead to the induction of cell proliferation.1. Nuclei were isolated from the submandibular glands of rats which had been injected IPR (100mg/kg) intrapeitoneally. Histone(H) and non-histone(nH) proteins were separated from nuclei after the incubation with [gamma-^<32>P] ATP.The level of phosphorylation of nH at 4-week began to increase at 10h after injection of IPR,reaching a maximum at 22h and then returned to the control level. The time after the injection of IPR required to initiate the stimulation of the phosphorylation of nH or the return to the control level increased significantl … More y with age.2. Age-dependent changes in protein kinase activity associated in the choromatin were appeared to correspond to alteration in the phosphorylation of nH.3. The incorporation of [^3H] thymidine in submandibular gland DNA of 4-week old rats was initiated at 14h after the injection of IPR,reaching a maximum at 22h and returning to the control level at 30h. The time prior to the onset of the DNA synthesis in rat submandibular glands increased during aging.4. Submandibular glands were obtained from rats which had been injected with [^<32>P] orthophosphate intraperitoneally 2h before IPR-injection. The extracted nuclear proteins were subjected to immunoprecipitation with anti-c-fos antibody, followed by SDS-PAGE.Phosphorylated c-fos was identified by autoradiography. IPR induced the expression of c-fos, but not that of c-jun. The age-dependent changes in c-fosmRNA was regarded as being closely correlated with the alteration of Gs.In conclusions, IPR stimulates protein kinase associated with the chromatin through signal transduction cascade in which receptor stimulation of adenylate cyclase increases c-fos expression. This kinase regulates the phosphorylation of nH.The delayd onset of phosphorylation of nH play a regulatory role in cell proliferation and cell function during aging. Less