COBRE PROJ 7: CONTROL OF TUMOR GROWTH BY RAS-RELATED PROTEINS

这个子项目是众多研究子项目之一

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Specific Aim 1: Investigation of the RASSF family of Ras effectors in transformation The Ras oncogene has been implicated as a key player in the development of more than a third of human cancers. Ras appears to function by activating multiple, heterologous effector proteins that regulate synergistic signaling pathways controlling growth and development. Experimentally, excess Ras activation leads to vigorous transformation and the best characterized Ras effector proteins are themselves oncoproteins. However, excessive activation of Ras can also cause cells to undergo growth arrest and apoptosis. This suggests that Ras proteins may activate a sub-set of effectors that, rather than promoting transformation, mediate growth inhibition. It would seem reasonable to suppose that such effector systems would have to be subverted during the transformation process to allow progression to tumorigenicity. Specific Aim 2: Development of novel small molecule inhibitors of Ras action Ras has been identified as a prime candidate for targeted anti-cancer therapy for more than two decades, but attempts to develop specific inhibitors of Ras have so far proved ineffective. The best known attempt involved a series of Farnesyl transferase inhibitors that actually do work well on H-Ras but are ineffective against the most important member of the family, K-Ras. Recent work has shown that the most important Ras effector for transformation in human systems is the RalGDS group of effectors. This contrasts with results in murine systems which have implicated Rafs as the key effectors. No inhibitors of RalGDS function have been described. Studies and Results 1. Allen et al, Oncogene, 2007 in press (epub April 2007). In this paper we have identified and characterized a novel member of the RASSF family, designated RASSF6. We show that RASSF6 exhibits the characteristics of a Ras effector/tumor suppressor but that it has several unique features compared to other family members. These include the ability to negatively modulate the NFkB pathway. This may provide a mechanistic explanation for the genetic link that has recently been demonstrated between RASSF6 and sensitivity to severe Respiratory Syncytial Virus infection. 2. We have shown that the RASSF2 family member is frequently down-regulated in prostate cancer and that knockdown of RASSF2 enhances the tumorigenic phenotype of prostate tumor cell lines. Moreover, we have shown that RASSF2 forms an endogenous complex with the tumor suppressor PAR-4 (Prostate apoptosis response gene 4). Thus, we appear to have identified a role and a novel mechanism for the involvement of RASSF2 in prostate cancer. 3. We have identified the novel protein Salvador as a binding partner for RASSF1A and have shown that Salvador exhibits tumor suppressor properties. We have developed evidence that RASSF1A uses Salvador to promote the activation of the LATs tumor suppressors. 4. We have used micro array analysis to demonstrate that RASSF5 (Nore1a) activates the p21 cdk inhibitor. We have confirmed this by Western analysis and shown that p21 -/- MEFs are resistant to Nore1a mediated growth inhibition. 5. We have initiated a virtual screen for inhibitors of the Ras/RalGDS interaction with the Molecular Modeling Core. Significance: We were the first to identify and characterize RASSF6 as a novel tumor suppressor. Moreover, we have demonstrated a potential mechanism by which it modulates both tumor suppression and contributes to the pathogenicity of Respiratory Syncytial Virus infection. We have identified three distinct novel signaling pathways utilized by different RASSF family members. These are the Salvador tumor suppressor for RASSF1A, the PAR-4 tumor suppressor for RASSF2 and the p21 WAF/CIP cdk inhibitor for Nore1a. In each case, the pathway is deeply implicated in the development of the transformed phenotype. These findings begin to explain the mechanisms that RASSF family members use to impede transformation.