The amino-terminal transforming region of Simian Virus 40 large T and small t antigens functions as a J domain
The amino-terminal transforming region of Simian Virus 40 large T and small t antigens functions as a J domain
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DOI：
10.1128/mcb.17.8.4761
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发表时间：
1997-08-01
影响因子：
5.3
通讯作者：
Pipas, JM
中科院分区：
文献类型：
--
作者：
Srinivasan, A;McClellan, AJ;Pipas, JM
猿猴病毒40 （SV40）编码两种蛋白，大T抗原和小T抗原，这两种蛋白有助于病毒诱导的肿瘤发生。已知708个氨基酸的大T抗原的靶标包括视网膜母细胞瘤蛋白家族的三个成员（pRb， p107和p130），转录适配器蛋白CBP家族的成员（cap-binding protein [CBP]， p300和p400），以及肿瘤抑制因子p53，小T抗原改变磷酸酶pp2A的活性并激活细胞周期蛋白A启动子。大T抗原和小T抗原的前82个氨基酸是相同的，遗传实验表明，另一个重要的转化靶标与这些序列相互作用，该区域包含一个类似于J结构域的基序，J结构域是分子伴侣家族中发现的一个保守序列。我们在这里表明，J结构域的突变取消了大T抗原转化哺乳动物细胞的能力。为了检验从T抗原氨基端纯化的136个氨基酸片段是否作为dnaj样伴侣，我们研究了该片段是否刺激了两个hsc70的ATP酶活性，发现ATP水解被刺激了4到9倍。此外，全长T抗原的ATP缺陷突变体以及野生型小T抗原刺激了hsc70的ATP酶活性。由于T抗原的J结构域在病毒DNA复制、转录控制、病毒粒子组装和肿瘤发生中起着至关重要的作用，我们得出结论，该区域可能伴随多蛋白复合物的重排。
Simian virus 40 (SV40) encodes two proteins, large T antigen and small t antigen that contribute to virus-induced tumorigenesis. Both proteins act by targeting key cellular regulatory proteins and altering their function, Known targets of the 708-amino-acid large T antigen include the three members of the retinoblastoma protein family (pRb, p107, and p130), members of the CBP family of transcriptional adapter proteins (cap-binding protein [CBP], p300, and p400), and the tumor suppressor p53, Small t antigen alters the activity of phosphatase pp2A and transactivates the cyclin A promoter, The first 82 amino acids of large T antigen and small t antigen are identical, and genetic experiments suggest that an additional target(s) important for transformation interacts with these sequences, This region contains a motif similar to the J domain, a conserved sequence found in the DnaJ family of molecular chaperones, We show here that mutations within the J domain abrogate the ability of large T antigen to transform mammalian cells, To examine whether a purified 136-amino-acid fragment from the T antigen amino terminus acts as a DnaJ-like chaperone, we investigated whether this fragment stimulates the ATPase activity of two hsc70s and discovered that ATP hydrolysis is stimulated four- to ninefold, In addition, ATPase-defective mutants of full-length T antigen, as well as wild-type small t antigen, stimulated the ATPase activity of hsc70. T antigen derivatives were also able to release an unfolded polypeptide substrate from an hsc70, an activity common to DnaJ chaperones, Because the J domain of T antigen plays essential roles in viral DNA replication, transcriptional control, virion assembly, and tumorigenesis, we conclude that this region may chaperone the rearrangement of multiprotein complexes.