Polyubiquitination is essential modification for most of protein degradation by proteasome. The polyubiquitination occurs at lysine (K) residue of ubiquitin, and the K48-linkage are the best-characterized type of ubiquitin chain and closely associated with protein degradation. Recent studies have demonstrated that protein polyubiquitiation also play an important role in the activation of cell proliferative and survival signal transduction. For example, K63-linked ubiquitination of Akt is important for Akt phosphorylation and activation induced by growth factor. During the NFkB activation by TNFa, K63-linked ubiquitination of TRAF2, cIAP1/2 and RIP1 are needed for recruiting IKK complexes and then phosphorylating IkB by IKK. The Ras/Skp2/LKB1 signal pathway is associated with cell proliferation and against energy stress in tumor. Interestingly, K63-linked ubiquitination of LKB1 was found to be involved in the activation of LKB1. MCPIP1 and MCPIP4 belongs to CCCH-type zinc finger protein superfamily and are identified as a transcription factor. MCPIP1 is induced by MCP-1 and plays a negative role in inflammation. MCPIP4 is originally reported as a putative tumor suppressor due to it is deregulated or mutated in several types of tumor. We have found that MCPIP1 and MCPIP4 were downregulated in human stage T3 colorectal cancer tissues, and overexpression of MCPIP1 or MCPIP4 resulted in cell cycle arrest and even cell death. Using the TCGA database, our preliminary results found that alteration of MCPIP1 and MCPIP4 expression are associated with low survival rate in colorectal cancer patients and breast cancer patients, respectively. In addition, the expression of MCPIP1 and MCPIP4 are correlated with the TNF/NFkB- and Akt/FoxO-regulated, respectively, target gene expression. Our preliminary data also found that MCPIP1 and MCPIP4 can only remove the K63-linked ubiquitin, and MCPIP4 can decrease the phosphorylation and ubiquitination of Akt. Based on our recent findings, we hypothesize that MCPIP1 might inactivate NFkB signal transduction through deubiquitination of TRAF2, cIAP1/2, or RIP1. However, the detail mechanisms is still unclear. In addition, it is still not clear what he correlation between clinical features or genetic profiles and the expression patterns of MCPIPs family members. Therefore, we hope to achieve the following Specific Goals in this 3-years plan. Year 1. To investigate whether MCPIP1 can remove the K63-linked ubiquitin of TRAF2, cIAP1/2, and RIP1, and then inhibit the NFkB survival signal. We will use the TNFa-activated NFkB cell model to examine the deubiquitination ability of MCPIP1 in TRAF2, cIAP1/2, and RIP1, and then inhibit NFkB and result in cell death. Year 2. To investigate whether MCPIP4 can inhibit tumor cell proliferation through K63-linked deubiquitination of Akt. We will use cell model to examine the K63-linked deubiquitination ability of MCPIP4 in various cell proliferation conditions, and use animal xenograft tumor model to examine the anti-tumor activity of MCPIP1 and MCPIP4. Year 3. To investigate whether MCPIP1 and MCPIP4 can decrease tumor cell survival through decreasing K63-linked ubiquitin of LKB1, and analyze the relationships between MCPIPs family members and clinical features or genetic profiles by TCGA database.
|Effective start/end date||8/1/16 → 7/31/17|