The function of RhoBTB proteins

描述（由申请人提供）：肿瘤抑制基因（TSGs）的研究为癌症和正常细胞通路（包括细胞周期、细胞凋亡和DNA修复）的基本生物学提供了许多重要的见解。RhoBTB2最近被确定为位于染色体8p21上的候选TSG，该位点是乳腺癌、肺癌、前列腺癌和卵巢癌中常见的杂合性缺失位点。RhoBTB2包含一个n端GTPase结构域，与Rho家族GTPase结构域和串联BTB结构域相关。我们开始研究RhoBT2的功能，并确定它是否是一种TSG。我们利用酵母双杂交筛选鉴定了RhoBTB2相互作用蛋白。我们的初步筛选显示RhoBTB2与泛素连接酶Cul3结合。RhoBTB2以cul3依赖性方式泛素化，RhoBTB2的细胞水平受cul3依赖性降解调节。在肺癌细胞系中发现的RhoBTB2突变体不能与Cul3结合，其表达不受Cul3的调节，这表明与Cul3的相互作用可能是RhoBTB2作为肿瘤抑制因子功能的重要组成部分。这些数据还表明RhoBTB2可能是一个适配器，其主要作用是招募另一种蛋白质来降解Cul3。其他cullin蛋白的接头也是肿瘤抑制因子。我们进行了另外两个杂交筛选，并确定了其他表明RhoBTB2功能的相互作用蛋白。我们的目标是确定RhoBTB2是否是一个TSG，详细了解RhoBTB2的功能途径，并描述Cul3和泛素化在调节RhoBTB2功能中的作用。我们计划通过三个具体目标来实现这些目标。我们将：1)明确RhoBTB2作为肿瘤抑制因子的作用；2)确定RhoBTB2的功能；3)阐明Cul3在RhoBTB2功能中的作用。这些研究结果可能揭示了癌症发展的新途径，并促进了我们对基本生物学转化的理解。

DESCRIPTION (provided by applicant): The study of tumor suppressor genes (TSGs) has resulted in many important insights into the basic biology of cancer and normal cellular pathways including the cell cycle, apoptosis and DNA repair. RhoBTB2 was recently identified as a candidate TSG located at chromosome 8p21, a site of frequent loss of heterozygosity in breast, lung, prostate and ovarian cancer. RhoBTB2 contains an N-terminal GTPase domain, related to those of Rho family GTPases, and tandem BTB domains. We began investigations to understand the function of RhoBT2 and to determine whether it is a TSG. We identified RhoBTB2 interacting proteins using yeast two hybrid screens. Our initial screen revealed that RhoBTB2 binds to the ubiquitin ligase Cul3. RhoBTB2 is ubiquitinated in a Cul3-dependent manner and the cellular levels of RhoBTB2 are regulated by Cul3-dependent degradation. A RhoBTB2 mutant found in a lung cancer cell line fails to bind to Cul3 and its expression is not regulated by Cul3, indicating that interaction with Cul3 is probably an essential component of the function of RhoBTB2 as a tumor suppressor. These data also suggest that RhoBTB2 may be an adaptor whose primary role is to recruit another protein(s) to Cul3 for degradation. Adaptors for other cullin proteins are also tumor suppressors. We conducted additional two hybrid screens and have identified other interacting proteins that indicate the function of RhoBTB2. Our goals in this proposal are to determine whether RhoBTB2 is a TSG, understand in detail the pathways in which RhoBTB2 functions, and delineate the roles played by Cul3 and ubiquitination in regulating RhoBTB2 function. We plan to achieve these goals through three specific aims. We will: 1) Define the role of RhoBTB2 as a tumor suppressor; 2) Determine the function of RhoBTB2; and 3) Delineate the role of Cul3 in RhoBTB2 function. The results of these studies may reveal a new pathway involved in the development of cancer and advance our understanding of the basic biology of transformation.