Mullane K P, Ratnofsky M, Culleré X, Schaffhausen B
Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts, USA.
Mol Cell Biol. 1998 Dec;18(12):7556-64. doi: 10.1128/MCB.18.12.7556.
Polyomavirus causes a broad spectrum of tumors as the result of the action of its early proteins. This work compares signaling from middle T antigen (MT), the major transforming protein, to that from small T antigen (ST). The abilities of MT mutants to promote cell cycle progression in serum-starved NIH 3T3 cells were compared. Transformation-defective mutants lacking association with SHC or with phosphatidylinositol 3-kinase (PI3-K) retained the ability to induce DNA synthesis as measured by bromodeoxyuridine incorporation. Only when both interactions were lost in the Y250F/Y315F double mutant was MT inactive. ST promoted cell cycle progression in a manner dependent on its binding of protein phosphatase 2A (PP2A). Since the Y250F/Y315F MT mutant was wild type for PP2A binding yet unable to promote cell cycle progression, while ST was capable of promoting cell cycle progression, these experiments revealed a functional difference in MT and ST signaling via PP2A. Assays testing the abilities of MT and ST to induce the c-fos promoter and to activate c-jun kinase led to the same conclusion. ST, but not Y250F/Y315F MT, was able to activate the c-fos promoter through its interaction with PP2A. In contrast, MT, but not ST, was able to activate c-jun kinase by virtue of its interaction with PP2A.
多瘤病毒因其早期蛋白的作用可引发多种肿瘤。这项研究比较了主要转化蛋白中T抗原（MT）与小T抗原（ST）的信号传导。比较了MT突变体在血清饥饿的NIH 3T3细胞中促进细胞周期进程的能力。缺乏与SHC或磷脂酰肌醇3激酶（PI3-K）结合的转化缺陷型突变体仍保留诱导DNA合成的能力，这可通过溴脱氧尿苷掺入来测定。只有当Y250F/Y315F双突变体中两种相互作用都丧失时，MT才无活性。ST以依赖于其与蛋白磷酸酶2A（PP2A）结合的方式促进细胞周期进程。由于Y250F/Y315F MT突变体在与PP2A结合方面是野生型，但无法促进细胞周期进程，而ST能够促进细胞周期进程，这些实验揭示了MT和ST通过PP2A进行信号传导时的功能差异。检测MT和ST诱导c-fos启动子以及激活c-jun激酶能力的实验得出了相同的结论。ST能够通过与PP2A的相互作用激活c-fos启动子，但Y250F/Y315F MT不能。相反，MT能够凭借其与PP2A的相互作用激活c-jun激酶，但ST不能。
