MECHANISM OF CAMP ACTION IN GROWTH CONTROL, DIFFERENTIATION, AND GENE REGULATION

8-Cl-cAMP的显著的生长抑制作用与其作用机制有关。 选择性结合和激活蛋白激酶同工酶：它结合 对位点B具有高亲和力但对位点A具有低亲和力的RII， 使II型蛋白激酶保持全酶形式，同时与 位点A和位点B对RI具有中等高亲和力， RI亚基的解离和I型蛋白的下调 激酶。8-Cl-cAMP诱导的细胞生长抑制引起不同程度的细胞凋亡， 在测试的细胞系中的作用，包括抑制 癌基因和转化生长因子α（TGF α），以及形态学 变化、分化和逆向转化。尽管 出现成熟表型的标志物和明确的生长停滞， 经8-Cl-cAMP处理的白血病细胞的细胞周期无变化 相位因此，8-Cl-cAMP产生生长抑制，同时允许 细胞通过其正常的细胞周期进展，虽然在一个缓慢的 这可能会导致最终恢复细胞之间的平衡， 癌细胞的增殖和分化。与细胞毒性不同， 药物，8-Cl-cAMP不起作用，以防止有丝分裂，但作用是改变 生长比率，细胞出生与细胞死亡的比率，通过恢复 癌细胞中RI/RII的平衡。生长背后的细胞事件 8-Cl-cAMP对肿瘤细胞的抑制和诱导分化作用 包括RII β快速核易位，这种易位 RII β进入细胞核与转录增加相关 与cAMP反应元件特异性结合的癌细胞因子 （CRE）。因此，8-Cl-cAMP在抑制细胞凋亡中的作用机制可能是一种新的机制。 恶性肿瘤可能涉及正常基因转录的恢复， RII β cAMP受体在其中起重要作用的癌细胞。通过 利用定点突变技术， RI和RII的分析目前正在进行中。RI和Rll是 其特点是自磷酸化和核转位 特性. RII在蛋白水解位点具有自磷酸化位点， 敏感铰链区周围的R和C相互作用的网站，而RI有一个 假磷酸化位点。Rll而不是RI含有一个核 定位信号，K K R K。自磷酸化与核定位 序列或者在RII β中点突变，或者被引入RII α， 来具体评估这些序列在生长中的作用， 调节功能。这些研究有助于了解 cAMP调控细胞生长和分化机制 治疗癌症的方法。

The striking growth inhibitory effect of 8-Cl-cAMP has been related to its selective binding and activation of protein kinase isozymes: It binds to RII with a high affinity for Site B but with a low affinity for Site A, keeping type Il protein kinase in the holoenzyme form, while binding with moderately high affinity for both Site A and Site B to RI, facilitating dissociation of the RI subunit and down-regulation of type I protein kinase. The growth inhibition induced by 8-Cl-cAMP brought about various effects among the cell lines tested, including the suppression of oncogenes and transforming growth factor a (TGFalpha), and morphological changes, differentiation, and reverse transformation. Despite the appearance of markers of mature phenotype and definitive growth arrest, the 8-Cl-cAMP-treated leukemic cells exhibited no change in the cell cycle phase. 8-Cl-cAMP therefore produces growth inhibition while allowing the cells to progress through their normal cell cycle, albeit at a slower rate, and this may lead to eventual restoration of a balance between cell proliferation and differentiation in cancer cells. Thus, unlike cytotoxic drugs, 8-Cl-cAMP does not act to prevent mitosis but acts to alter the growth ratio, the ratio of cell births to cell deaths, via restoration of the RI/RII balance in cancer cells. The cellular events underlying growth inhibition and differentiation of cancer cells induced by 8-Cl-cAMP include a rapid nuclear translocation of RIIbeta, and such translocation of RIIbeta into the nucleus correlates with an increase n transcription factors in cancer cells that bind specifically to cAMP response element (CRE). Thus, the mechanism of action of 8-Cl-cAMP in the suppression of malignancy may involve the restoration of normal gene transcription in cancer cells where the RIIbeta cAMP receptor plays an important role. By the use of site-directed mutagenesis technique, the structure-function analysis of RI and Rll is currently underway. The RI and Rll are distinguished by their autophorylation and nuclear translocation properties. RII has an autophosphorylation site at a proteolytically sensitive hinge region around the R and C interaction site while RI has a pseudo-phosphorylation site. The Rll but not the RI contains a nuclear location signal, K K R K. The autophosphorylation and nuclear location sequences are either point-mutated in RIIbeta of introduced into RIalpha to specifically assess the role of these sequences in the growth regulatory function. These studies contribute to understanding the mechanism of cAMP control cell growth and differentiation and provide new approaches to the treatment of cancer.