Vultur Adina, Arulanandam Rozanne, Turkson James, Niu Guilian, Jove Richard, Raptis Leda
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Mol Biol Cell. 2005 Aug;16(8):3832-46. doi: 10.1091/mbc.e04-12-1104. Epub 2005 May 25.
To investigate the role of Stat3 (signal transducer and activator of transcription-3) in neoplastic transformation by the Large Tumor antigen of Simian Virus 40 (TAg), murine fibroblasts were rendered deficient in Stat3 activity through expression of a Stat3-specific siRNA or a Cre-loxP recombination system. The results demonstrate that growth rate, formation of foci overgrowing a monolayer of normal cells and colony formation in soft agar were dramatically reduced in Stat3-deficient cells. In addition, TAg expression led to increased Stat3 tyrosine phosphorylation, DNA binding, and transcriptional activity, suggesting that Stat3 is required for TAg-mediated neoplasia. Stat3 activation was prevented by blocking the binding of TAg to pRb (retinoblastoma-susceptibility gene product), whereas genetic ablation of pRb increased Stat3 activity, suggesting that pRb inactivation by TAg might be responsible for the observed Stat3 activation. Stat3 activation by TAg was suppressed after inhibition of c-Src, JAKs or the insulin-like growth factor receptor. On the other hand, targeted disruption of the Fer kinase or pharmacological inhibition of Abl had no effect. Inhibition of Src activity led to Stat3 down-regulation as well as apoptosis of sparsely growing, TAg-transformed cells. However, Src inhibition was relatively ineffective in confluent cells, consistent with previous results indicating that cell to cell adhesion activates Stat3 by a Src-independent mechanism. Direct Stat3 inhibition on the other hand induced apoptosis very effectively in confluent cells, which could have significant therapeutic implications. Taken together, our results suggest that Stat3 is an important component of a pathway emanating from TAg and leading to neoplastic conversion.
为了研究信号转导与转录激活因子3（Stat3）在猿猴病毒40大T抗原（TAg）介导的肿瘤转化中的作用，通过表达Stat3特异性小干扰RNA（siRNA）或Cre-loxP重组系统使小鼠成纤维细胞的Stat3活性缺失。结果表明，Stat3缺陷细胞的生长速率、覆盖正常细胞单层的集落形成以及软琼脂中的集落形成均显著降低。此外，TAg表达导致Stat3酪氨酸磷酸化、DNA结合及转录活性增加，提示Stat3是TAg介导的肿瘤形成所必需的。通过阻断TAg与视网膜母细胞瘤易感基因产物（pRb）的结合可防止Stat3激活，而pRb基因敲除则增加Stat3活性，提示TAg导致的pRb失活可能是观察到的Stat3激活的原因。抑制c-Src、JAKs或胰岛素样生长因子受体后，TAg介导的Stat3激活受到抑制。另一方面，靶向破坏Fer激酶或对Abl进行药理学抑制则无作用。抑制Src活性导致Stat3下调以及稀疏生长的TAg转化细胞凋亡。然而，Src抑制在汇合细胞中相对无效，这与先前的结果一致，即细胞间黏附通过非Src依赖机制激活Stat3。另一方面，直接抑制Stat3在汇合细胞中非常有效地诱导凋亡，这可能具有重要的治疗意义。综上所述，我们的结果表明Stat3是TAg引发并导致肿瘤转化的信号通路的重要组成部分。
