Qian Xiaolan, Li Guorong, Asmussen Holly K, Asnaghi Laura, Vass William C, Braverman Richard, Yamada Kenneth M, Popescu Nicholas C, Papageorge Alex G, Lowy Douglas R
Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2007 May 22;104(21):9012-7. doi: 10.1073/pnas.0703033104. Epub 2007 May 15.
The three deleted in liver cancer genes (DLC1-3) encode Rho-GTPase-activating proteins (RhoGAPs) whose expression is frequently down-regulated or silenced in a variety of human malignancies. The RhoGAP activity is required for full DLC-dependent tumor suppressor activity. Here we report that DLC1 and DLC3 bind to human tensin1 and its chicken homolog. The binding has been mapped to the tensin Src homology 2 (SH2) and phosphotyrosine binding (PTB) domains at the C terminus of tensin proteins. Distinct DLC1 sequences are required for SH2 and PTB binding. DCL binding to both domains is constitutive under basal conditions. The SH2 binding depends on a tyrosine in DCL1 (Y442) but is phosphotyrosine-independent, a highly unusual feature for SH2 binding. DLC1 competed with the binding of other proteins to the tensin C terminus, including beta 3-integrin binding to the PTB domain. Point mutation of a critical tyrosine residue (Y442F) in DLC1 rendered the protein deficient for binding the tensin SH2 domain and binding full-length tensin. The Y442F protein was diffusely cytoplasmic, in contrast to the localization of wild-type DLC1 to focal adhesions, but it retained the ability to reduce the intracellular levels of Rho-GTP. The Y442F mutant displayed markedly reduced biological activity, as did a mutant that was RhoGAP-deficient. The results suggest that DLC1 is a multifunctional protein whose biological activity depends on cooperation between its tensin binding and RhoGAP activities, although neither activity depends on the other.
肝癌缺失基因1-3（DLC1-3）编码Rho-GTP酶激活蛋白（RhoGAP），其表达在多种人类恶性肿瘤中经常下调或沉默。RhoGAP活性是DLC依赖性肿瘤抑制活性所必需的。在此，我们报告DLC1和DLC3与人张力蛋白1及其鸡同源物结合。这种结合已定位到张力蛋白C末端的张力蛋白Src同源2（SH2）和磷酸酪氨酸结合（PTB）结构域。SH2和PTB结合需要不同的DLC1序列。在基础条件下，DCL与这两个结构域的结合是组成性的。SH2结合依赖于DCL1中的一个酪氨酸（Y442），但不依赖于磷酸酪氨酸，这是SH2结合的一个非常不寻常的特征。DLC1与其他蛋白竞争与张力蛋白C末端的结合，包括β3整合素与PTB结构域的结合。DLC1中一个关键酪氨酸残基（Y442F）的点突变使该蛋白缺乏与张力蛋白SH2结构域结合和与全长张力蛋白结合的能力。与野生型DLC1定位于粘着斑不同，Y442F蛋白呈弥漫性胞质分布，但它保留了降低细胞内Rho-GTP水平的能力。Y442F突变体的生物学活性明显降低，RhoGAP缺陷的突变体也是如此。结果表明，DLC1是一种多功能蛋白，其生物学活性取决于其与张力蛋白结合和RhoGAP活性之间的协同作用，尽管这两种活性并不相互依赖。
