MECHANISMS OF TUMOR PROMOTION AND CARCINOGENESIS

确定允许肿瘤细胞经历 不受控制的增殖对于理解致癌作用至关重要。 最近的一些研究表明，蛋白磷酸酶，如蛋白质 激酶，在细胞周期调控中发挥重要而特异的作用; 因此，这些蛋白质的表达或调节的改变可 影响细胞周期进程，甚至可以让细胞进行 不受控制的扩散。 蛋白磷酸酶在肿瘤中的作用 促进过程也出现在冈田酸的研究中， 微囊藻毒素-LR和calyculin A，三种高度特异性和有效的 某些丝氨酸/苏氨酸蛋白磷酸酶（PP酶）的抑制剂 具有促肿瘤活性。 我们克隆并鉴定了 三种人PPase，和一种命名为PP 5的PPase特别有吸引力， 进行进一步的研究。PP 5被冈田酸有效抑制， calyculin A，小鼠皮肤中两种有效的肿瘤促进剂。 但不同于 其它已知的以恒定水平表达的PPase，PP 5 在对数生长期表达高，而在生长期低或检测不到。 静止或分化的细胞培养物。 PP 5的表达是 在某些细胞中加入血清和/或17 β-雌二醇诱导 PP 5表达的抑制增强了两者的能力， p53肿瘤抑制蛋白和地塞米松，一种合成的 糖皮质激素激动剂，诱导p21细胞周期蛋白的表达， 依赖性激酶抑制剂蛋白。 综合这些 研究表明，PP 5在G1/S-调节中起重要作用。 相变 本提案旨在检验以下假设： 蛋白磷酸酶在细胞周期进程中起重要作用; 因此，干扰它们的活动可能有助于异常的 肿瘤细胞的增殖行为。 这些研究将重点 具体目标如下：目标1。 进一步描述角色 PP 5在细胞周期进程的正常和异常控制。 目的2.探讨PP 5在糖皮质激素介导的人肝癌细胞凋亡中的作用。 抑制细胞生长和信号网络之间的“串扰” 由激素和生长因子引起的。 目标3.描述 PP 5的表达调控机制。 通过这些研究，我们 希望进一步描述蛋白磷酸酶在 调节细胞周期，并深入了解蛋白质如何 磷酸酶可能参与肿瘤细胞的异常增殖， 细胞

Determining the mechanisms that allow neoplastic cells to undergo uncontrolled proliferation is crucial to understanding carcinogenesis. Several recent studies indicate that protein phosphatases, like protein kinases, play important and specific roles in cell-cycle regulation; thus alterations in the expression or regulation of these proteins may affect cell-cycle progression and could even allow cells to undergo unregulated proliferation. A role for protein phosphatases in the tumor promotion process has also emerged from studies with okadaic acid, microcystin-LR, and calyculin A, three highly specific and potent inhibitors of certain serine/threonine protein phosphatases (PPases) that have tumor promoting activity. We have cloned and characterized three human PPases, and one, designated PP5, is particularly attractive for further studies. PP5 is potently inhibited by okadaic acid and calyculin A, two potent tumor promoters in mouse skin. However, unlike the other known PPases, which are expressed at constant levels, PP5 expression is high during log phase growth and low or undetectable in quiescent or differentiated cell cultures. The expression of PP5 is induced by the addition of serum and/or 17beta-estradiol in some cell types, and the inhibition of PP5 expression enhances the ability of both the p53 tumor suppressor protein and dexamethasone, a synthetic glucocorticoid agonist, to induce the expression of the p21 cyclin- dependent kinase inhibitor protein in A549 cells. Together these studies suggest that PP5 plays an important role in the regulation G1/S- phase transition. This proposal is designed to test the hypothesis that protein phosphatases play an important role in cell cycle progression; thus, the interference of their activity may contribute to the aberrant proliferative behavior of neoplastic cells. These studies will focus on the following specific aims: Aim 1. Further characterize the roles of PP5 in the normal and aberrant control of cell cycle progression. Aim 2.Characterize the relationship of PP5 in glucocorticoid mediated inhibition of cell growth and "cross talk" between signaling networks induced by hormones and growth factors. Aim 3.Characterize the mechanisms regulating the expression of PP5. Through these studies we hope to further characterize the role of protein phosphatases in the regulation of cell cycle and gain insight into the how protein phosphatases may be involved in the aberrant proliferation of neoplastic cells.