Education and Post-Graduate Training
Jun-yuan Ji received his B.S. in Cell Biology from Lanzhou University in 1994, and a M.S. in Developmental Biology from the Institute of Genetics and Developmental Biology at the Chinese Academy of Sciences in 1997, where he worked in the laboratory of Professor Fang-zhen Sun. He obtained his Ph.D. in Zoology from the University of Washington at Seattle in 2003 working with Professor Gerold Schubiger. He then did postdoctoral research in Professor Nicholas Dyson’s laboratory at Massachusetts General Hospital Cancer Center and Harvard Medical School. Dr. Ji joined the faculty at the college in 2009.
Our laboratory is interested in cell cycle and transcriptional regulation during development and tumorigenesis. Using Drosophila and cultured human cancer cell lines as model systems, we combine genetic, cell biological, and biochemical approaches to elucidate the molecular and genetic regulatory circuits that control cell proliferation and gene expression. Specifically, our major focus is to study the functions and regulation of Cyclin-dependent kinase 8 (CDK8). By performing genetic screens using Drosophila, we identified CDK8 as a potent inhibitor of E2F1, which is a key transcription factor that regulates the G1 to S-phase transition. In both Drosophila and human cancer cells, we observed that CDK8 inhibits E2F1-dependent transcription by directly binding to and phosphorylating E2F1, which may turn off the re-initiation of E2F1-mediated transcription. Interestingly, CDK8 is recently identified as an oncoprotein in melanoma and colorectal cancer. The genes encoding CDK8 and its regulatory partner Cyclin C (CCNC) are frequently amplified or mutated in a variety of human cancers. Importantly, inhibiting CDK8 potently blocks the growth of colorectal cancer cells that harbor CDK8 amplification, suggesting that CDK8 kinase is a promising drug target. Therefore, it is important to understand the regulatory network, including both upstream regulators and downstream effectors, of CDK8-Cyclin C (CycC) in both normal development and tumorigenesis.
Recently, we have identified CDK8 and CycC as negative regulators of the lipogenic pathway in Drosophila, mammalian hepatocytes and mouse livers. The inhibitory effect of CDK8 and CycC on de novo lipogenesis is through CDK8 phosphorylation of the SREBP-1c transcription factor at a conserved threonine residue. Consistent with the physiologic regulation of lipid biosynthesis, the levels of CDK8 and CycC proteins are reduced by feeding and insulin. Taken together, these results suggest a novel and conserved role of CDK8 and CycC in regulating lipid homeostasis. Dysregulated transcription of key lipogenic enzymes has been observed in a variety of human cancers as well as diseases and conditions collectively known as metabolic syndrome. Further analyses of CDK8 functions and regulation may provide important insights to better understand how dysregulation of CDK8-CycC contributes tumorigenesis and other diseases.
Candidates interested in graduate study in the Ji laboratory at the Texas A&M University Health Science Center are encouraged to apply through the following programs:
- Xie, X.J., Hsu, F.N., Gao, X., Xu, W., Ni, J.Q., Xing, Y., Huang, L., Hsiao, H.C., Zheng, H., Wang, C., Zheng, Y., Xiaoli, A.M., Yang, F., Bondos, S.E., Ji, J.Y. (2015) CDK8-Cyclin C mediates nutritional regulation of developmental transitions through the Ecdysone Receptor in Drosophila. PLoS Biology 13(7), e1002207. doi:10.1371/journal.pbio.1002207.
- Zheng, Y., Hsu, F.N., Xu, W., Xie, X.J., Ren, X., Gao, X., Ni, J.Q., and Ji, J.Y. (2014) A developmental genetic analysis of the lysine demethylase KDM2 in Drosophila melanogaster. Mechanisms of Development 133, 36-53.
- Xu, W., Amire-Brahimi, B., Xie, X.J., Huang, L., Ji, J.Y. (2014) All-atomic molecular dynamic studies of human CDK8: Insight on A-loop, point mutations and binding with its partner CycC. Computational Biology and Chemistry 51, 1-14.
- Zhang, T., Liao, Y., Hsu, F.N., Zhang, R., Searle, J.S., Pei, X., Li, X., Ryoo, H.D., Ji, J.Y., Du, W. (2014) Elevated TORC1 activity mediates synthetic lethal interaction between deregulated Wnt signaling and Rb inactivation. PLoS Genetics 10, e1004357.
- Wang, C., Ji, J.Y., Tian, L., and Pestell, R.G. (2014) Transcriptional regulation of lipogenesis as a therapeutic target for cancer treatment. R. Kumar (ed.) Nuclear Signaling Pathways and Targeting Transcription in Cancer, Cancer Drug Discovery and Development, pp 259-275. DOI 10.1007/978-1-4614-8039-6_10; Springer New York
- Gu, W., Wang, C., Li, W., Zhou, J., Yuan, C., Xie, X.J., Addya, S., Kong, B. and Ji, J.Y. (2013) Tumor suppressive effects of CDK8 in endometrial cancer cells. Cell Cycle 12, 987-999.
- Ji, J.Y., Miles, W.O. Korenjak, M., Zheng, Y., and Dyson, N.J. (2012) In vivo regulation of E2F1 by Polycomb group genes in Drosophila. G3: Genes, Genomes, Genetics 2, 1651-1660.
- Zhao, X.*, Feng, D.*, Wang, Q.*, Abdulla, A., Xie, X.J., Zhou, J., Sun, Y., Yang, E.S., Liu, L.P., Vaitheesvaran, B., Bridges, L., Kurland, I., Strich, R., Ni, J.Q., Wang, C., Ericsson, J., Pessin, J.E., Ji, J.Y.#, and Yang, F.# (2012) Regulation of lipogenesis by cyclin-dependent kinase 8–mediated control of SREBP-1. Journal of Clinical Investigation 122, 2417-2427. (* Equal contribution authors; # Corresponding authors)
- Xu, W., and Ji, J.Y. (2011) Dysregulation of CDK8 and Cyclin C in tumorigenesis. Journal of Genetics and Genomics 38, 439-452.
- Ji, J.Y., and Dyson, N.J. (2010) Interplay between E2F-dependent transcription and cyclin-dependent kinases. G. Enders (ed.) Cell Cycle Deregulation in Cancer, Springer Science, pp 23-41.
- Zhang, J.M., Ji, J.Y., Yu, M., Overholtzer, M., Smolen, G.A., Wang, R., Brugge, J.S., Dyson, N.J., and Haber, D.A. (2009) YAP-dependent secretion of amphiregulin contributes to its role in cellular transformation and progenitor expansion. Nature Cell Biology 11, 1444-1450.
- Morris, E.J. *, Ji, J.Y.*, Yang, F., Di Stefano, L., Herr, A., Moon, N.S., Kwon, E.J., Haigis, K.M., Näär, A.M., and Dyson, N.J. (2008) E2F1 represses β-catenin transcription and is antagonized by both pRB and CDK8. Nature 455, 552-556. * Equal contribution authors)
- Di Stefano, L., Ji, J.Y., Moon, N.S., Herr, A., and Dyson, N. (2007) Mutation of Drosophila Lsd1 disrupts H3-K4 methylation, resulting in tissue-specific defects during development. Current Biology 17, 808-812.
- Ji, J.Y., Crest, J., and Schubiger, G. (2005). Genetic interactions between Cdk1-CyclinB and the Separase complex in Drosophila. Development 132, 1875-1884.
- Ji, J.Y., Squrriell, J.M., and Schubiger, G. (2004). Both Cyclin B levels and DNA-replication checkpoint regulate the early embryonic mitoses in Drosophila.Development 131, 401-411. (Cover image)
- Ji, J.Y., Haghnia, M., Trusty, C., Goldstein, L.S.B., and Schubiger, G. (2002). A genetic screen for suppressors and enhancers of the Drosophila Cdk1-Cyclin B identifies maternal factors that regulate microtubule and microfilament stability. Genetics 162, 1179-1195.