The function of RhoBTB proteins

描述（由申请人提供）：肿瘤抑制基因（TSG）的研究已导致对癌症的基础生物学和正常细胞途径（包括细胞周期、细胞凋亡和DNA修复）的许多重要见解。RhoBTB 2最近被鉴定为位于染色体8 p21的候选TSG，该位点在乳腺癌、肺癌、前列腺癌和卵巢癌中经常发生杂合性丢失。RhoBTB 2含有与Rho家族GTP酶相关的N-末端GTP酶结构域和串联BTB结构域。我们开始研究以了解RhoBT 2的功能并确定它是否是TSG。我们使用酵母双杂交筛选鉴定了RhoBTB 2相互作用蛋白。我们的初步筛选显示RhoBTB 2与泛素连接酶Cul 3结合。RhoBTB 2以Cul 3依赖性方式被泛素化，并且RhoBTB 2的细胞水平由Cul 3依赖性降解调节。在肺癌细胞系中发现的RhoBTB 2突变体不能与Cul 3结合，并且其表达不受Cul 3调节，这表明与Cul 3的相互作用可能是RhoBTB 2作为肿瘤抑制剂的功能的重要组成部分。这些数据还表明，RhoBTB 2可能是一个衔接子，其主要作用是招募另一种蛋白质到Cul 3上进行降解。其他cullin蛋白的衔接子也是肿瘤抑制因子。我们进行了额外的两个杂交筛选，并确定了其他相互作用的蛋白质，表明RhoBTB 2的功能。我们的目标是确定RhoBTB 2是否是TSG，详细了解RhoBTB 2功能的途径，并描述Cul 3和泛素化在调节RhoBTB 2功能中所起的作用。我们计划通过三个具体目标实现这些目标。我们将：1）定义RhoBTB 2作为肿瘤抑制因子的作用; 2）确定RhoBTB 2的功能;和3）描述Cul 3在RhoBTB 2功能中的作用。这些研究的结果可能揭示了一种参与癌症发展的新途径，并促进了我们对转化基础生物学的理解。

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.