The Molecular Mechanism Of Membrane Protein TDE2/Serinc1in The Regulation Of Tumor Cell Proliferation

Human TDE2(human Tumor Differentially Expressed2, hSerincl) is a new gene cloned by our laboratory while screening for differentially expressed genes in hepatoma, and has an accession number as AF087902in Genebank. hTDE2belongs to Serinc protein family, which is a unique protein family only first appearing in eukaryotes, and shows no homologue to any other protein families. The family consists of five members (Serinc1, Serinc2, Serinc3, Serinc4, and Serinc5) in mammals. And the members of Serinc family are highly conserved, showing about30%to80%homologue of their amino acid sequences. All Serinc proteins contain multiple hydrophobic domains, and almost exclusively encode an N-terminal signal peptide. Previous reports have shown that both human and mice Serinc proteins are always up-regulated in carcinomatous tissues, though their precise physiological roles are still unclear. This thesis is about the primary investigation of the physiological roles of hTDE2/hSerincl.We first checked the hTDE1mRNA level in both liver cancer and lung cancer tissues with RT-PCR and Real-Time Quantitative PCR. And the results show that TDE1is up-regulated in both cancerous tissues. We also labeled TDE2with EGFP and observed its cellular localization. Combining with software analysis of protein domains, our results are consistent with the membrane destination of this protein family. To further study TDE2function, we knocked down the expression of TDE1with siRNA fragments in both human hepatoma cell lines and human lung cancer cell lines. Our data indicated that knock-down of TDE1caused cell cycle arrest and apoptosis. Furthermore, our colony formation assay and cell growth curve results are consistent with the previous cell cycle and apoptosis data. However, exogenous expression of TDE1does not show any obvious effects.P21/WAF1functions as an important cell cycle regulator, and its transcription is regulated by multiple transcriptional factors including P53, SREBPs (sterol regulatory element-binding proteins), and etc. The cis-acting element SRE is required for membrane biogenesis, which obviously is critical in cell growth and proliferation. Previous report has indicated that rat Serinc5might be closely correlated with myelin biosynthesis. Moreover, Inuzuka et al. also showed evidences that rat Serinc proteins (Serincl, Serinc2, and Serinc5) might play significant roles in membrane lipids synthesis. Therefore, we checked endogenous P21expression with TDE2being knocked down. Our data showed that both the mRNA and protein levels of P21are up-regulated, so as those of SREBPs (SREBP-la and SREBP-2). Moreover, we also constructed a luciferase reporter system under the control of endogenous P21promoter (harboring the SRE element). We found that expression of the reporter increased when TDE2was knocked down. In conclusion, our preliminary results indicated that TDE2might have an effect on tumor cell growth via influencing the expression of SREBPs and P21. The tumor suppressor gene TP53participates in many cellular pathways. Once being activated,TP53may result in the expression of multiple genes which affect cell cycle progression, DNA repair, and/or apoptosis if the repair fails. The TP53codon72polymorphism (Arg/Pro) has been studied extensively. However, there has been no consistence in the role of this polymorphism as a risk factor for the development of throat cancer.To access the association of TP53Arg72Pro polymorphism and the susceptibility to throat cancer, we performed a Meta analysis.27articles have been selected, and totally contain3966cases of throat cancer patients and4387control cases. With all the genetic models, our primary analysis indicates there is no significant association between this72Arg/Pro polymorphism and risk of throat cancer. Then we performed a stratified Meta analysis according to ethnicity and quality score of the studies. We analyzed the relation of TP53Arg72Pro polymorphism to the risks of different throat cancers including oral cancer, oropharyngeal cancer, laryngeal cancer, nasopharyngeal cancer, and mixed tumors. And the only significant association found is between the polymorphism and nasopharyngeal cancer with homozygote comparison model (OR=0.47,95%CI:0.32-0.68), heterozygote comparison model (OR=0.53,95%CI:0.037-0.75), and dominant model (OR=0.51,95%CI:0.37-0.71). We get the same results if only high quality studies are used:homozygote comparison model (OR=0.44,95%CI:0.30-0.64), heterozygote comparison model (OR=0.48,95%CI:0.34-0.69), and dominant model (OR=0.47,95%CI:0.34-0.66). According to ethnicity, our stratified analysis shows a significant association between TP53Arg72Pro and nasopharyngeal cancer in Caucasian with homozygote comparison model (OR=0.43,95%CI:0.24-0.78), heterozygote comparison model (OR=0.47,95%CI:0.27-0.83), and dominant model (OR=0.46,95%CI:0.28-0.78). And in Asian, there is only significant association with homozygote comparison model (OR=0.55,95%CI:0.32-0.95).Though there are limitations of this Meta analysis, our result indicates there is no correlation between TP53Arg72Pro and throat cancer. A more precise estimation of the role of TP53Arg72Pro in throat cancer required more future studies.