Uniformed Services University of the Health Sciences
Department of Microbiology and Immunology
4301 Jones Bridge Road
Bethesda, Maryland 20814-4799
Phone: (301) 295-9624
FAX: (301) 295-1545
Professor & Vice Chair
Ph.D., University of Connecticut, 1983
The research in my lab revolves around the molecular biology and pathogenesis of human viruses. We have a long standing interest in human T-lymphotropic virus type 1 (HTLV-1), human immunodeficiency virus (HIV), and more recently Kaposi sarcoma-associated herpesvirus/human herpesvirus type 8 (KSHV/HHV-8). We are particularly interested in the mechanisms of action of viral regulatory proteins and how they impact mRNA transcription, cell cycle control, and signal transduction pathways to effect viral replication and pathogenesis, especially, oncogenesis. Through the study of the trans-activator/oncoprotein, Tax, of the human T-lymphotropic virus type 1 (HTLV-1), we have found recently that persistent and potentially oncogenic activation of NF-κB triggers a defense mechanism that commits cells into senescence, an irreversible state of cell cycle arrest (Zhi et al., 2011). This checkpoint is turned on by hyper-activated p65/RelA and is mediated by two cyclin-dependent kinase inhibitors, p21 and p27, in a p53- and pRb-independent manner (Kuo and Giam, 2006; Liu et al., 2008). This checkpoint is often impaired in cancer cells whose NF-κB pathway becomes chronically activated (Ping et al., 2006). Our results anticipate that the anti-sense protein of HTLV-1, HBZ, which down-regulates NF-κB and HTLV-1 trans-activation by Tax, would mitigate or prevent Tax-induced senescence. This prediction has been borne out experimentally. Thus, Tax promotes robust HTLV-1 replication, potent NF-κB activation and senescence, while HBZ attenuates Tax-driven viral replication and NF-κB activation to allow proliferation of infected cells and persistent infection. Finally, our data support the notion that inactivation of the senescence checkpoint facilitates chronic NF-κB hyper-activation, a critical step in leukemia development. Current efforts concentrate on understanding how NF-κB hyper-activation induces cellular senescence and how the senescence checkpoint becomes impaired in cancer cells whose NF-κB signaling is chronically activated. Results from the studies of HTLV-1 and KSHV are providing important insights into these key events of carcinogenesis.
A model for HTLV-1 Leukemogenesis. HTLV-1 is transmitted by cell-to-cell contact. The expression levels of Tax and HBZ modulate the outcomes of infection. Robust viral replication stimulated by Tax is accompanied by cellular senescence. HBZ moderates trans-activation by Tax, thereby down-regulates viral replication and Tax expression to allow oligoclonal expansion of infected T cells. Cytotoxic T lymphocyte (CTL) killing can control virus replication in asymptomatic carriers and select for cells that carry latent proviral DNA. HTLV-1-infected cells develop chromosomal instability. Loss of p16INK4a, p15INK4b, and other tumor suppressors and constitutive Jak/Stat activation may contribute to the inactivation of the senescence checkpoint to allow persistent Tax expression and NF-?B activation. Loss of Tax expression is favored because Tax is a primary CTL target and has a propensity to induce genomic instability and cellular senescence. Inactivation of the senescence checkpoint can facilitate potent NF-?B activation by Tax at the early stage of leukemogenesis and aid the development of Tax-independent NF-?B activation later. The mitogenic activity of HBZ mRNA may help sustain the ATL tumor phenotype.
Immunoblots of HeLa cells transduced with LV-Tax or LV-GFP. Cell lysates were prepared and immunoblotted using cyclin B1, human securin (Securin), p21CIP1/WAF1, p27KIP1, p16INK4a, Tax, and actin antibodies as described. (RIght) Expression of the senescence-associated ?-galactosidase (SA-?-Gal) in HeLa cells transduced with LV-Tax. Asynchronously growing HeLa cells (2.5 x 104 cells/well in 6-well plates) were transduced with LV-Tax or LV-GFP at an m.o.i. of 5, grown for 3 days, and stained with X-Gal overnight at 37ºC.
HTLV-1 Tax-expressing HeLa-FUCCI (fluorescent ubiquitin cell cycle indicator) cells bypass mitosis and become senescent. Ad-Tax-transduced cells were released from G1/S arrest and photographed every hour for 140 hours. The image of cells at the 140th hour is shown. Image processing software was used to move the Tax-expressing senescent cell (top) in close proximity to the normal growing colony (bottom). Cells with red, yellow, and green nuclei are in G1, G1/S, and S/G2 phases of the cell cycle respectively. Time-lapses movies showing the progression of Tax-expressing cells through cell cycle can be found here.
Zhi H, Yang L, Kuo YL, Ho YK, Shih HM, Giam CZ. NF-κB Hyper-Activation by HTLV-1 Tax Induces Cellular Senescence, but Can Be Alleviated by the Viral Anti-Sense Protein HBZ. PLoS Pathog. Apr;7(4):e1002025. Epub 2011.
Yang, L., Kotomura, N., Ho, Y., Zhi, H., Bixler, S., and Giam, CZ. Complex Cell Cycle Abnormalities Caused by HTLV-1 Tax. J. Virol. 85: 3001-3009, 2011. (JVI March 2011 cover).
Zhai B, Zhou H, Yang L, Zhang J, Jung K, Giam CZ, Xiang X, Lin X. Polymyxin B, in combination with fluconazole, exerts a potent fungicidal effect. J Antimicrob Chemother. 2010 May;65(5):931-8. Epub 2010 Feb 18.
Zhang L, Zhi H, Liu M, Kuo YL, Giam CZ. Induction of p21(CIP1/WAF1) expression by human T-lymphotropic virus type 1 Tax requires transcriptional activation and mRNA stabilization. Retrovirology. 2009 Apr 8;6:35.
Liu M, Yang L, Zhang L, Liu B, Merling R, Xia Z, Giam CZ. Human T-cell leukemia virus type 1 infection leads to arrest in the G1 phase of the cell cycle. J. Virol. 82(17):8442-55. 2008.
Merling R, Chen C, Hong S, Zhang L, Liu M, Kuo YL, Giam CZ. HTLV-1 Tax mutants that do not induce G1 arrest are disabled in activating the anaphase promoting complex. Retrovirology. May 29;4:35. 2008.
Hong S., Wang L., Gao, X., Kuo, Y.-L., Liu, B., Merling, R., Kung, H-J., Shih, H-M, and Giam C-Z. Heptad Repeats Regulate IKKg/NEMO Access by Protein Phosphatase 2A and are Targeted by HTLV-1 Tax. J. Biol. Chem. 282(16):12119-26. 2007.
Zhang, L., M. Liu, R. Merling, and C. Z. Giam. Versatile reporter systems show that transactivation by human T-cell leukemia virus type 1 Tax occurs independently of chromatin remodeling factor BRG1. J. Virol. 80:7459-7468. 2006.
Yu-Liang Kuo and Chou-Zen Giam. Activation of the anaphase promoting complex by HTLV-1 tax leads to senescence. EMBO Journal. 25(8):1741-52. 2006
Liu B, Hong S, Tang Z, Yu H, Giam CZ. HTLV-I Tax Directly Binds the Cdc20-associated Anaphase-promoting Complex and Activates It Ahead of Schedule. Proceedings of the National Academy of Sciences of the United States of America. 102(1), 63-8 2005.
Jeang KT, Giam CZ, Majone F, Aboud M, Life, Death, and Tax: Role of HTLV-I Oncoprotein in Genetic Instability and Cellular Transformation. The Journal of Biological Chemistry. 279(31), 31991-4. Jul 2004
Liao W, Tang Y, Kuo YL, Liu BY, Xu CJ, Giam CZ, Kaposi's Sarcoma-associated Herpesvirus/human Herpesvirus 8 Transcriptional Activator Rta Is An Oligomeric DNA-binding Protein That Interacts With Tandem Arrays of Phased A/T-trinucleotide Motifs. Journal of Virology. 77(17), 9399-411. Sep 2003
Liu B, Liang MH, Kuo YL, Liao W, Boros I, Kleinberger T, Blancato J, Giam CZ, Human T-lymphotropic Virus Type 1 Oncoprotein Tax Promotes Unscheduled Degradation of Pds1p/securin and Clb2p/cyclin B1 and Causes Chromosomal Instability. Molecular and Cellular Biology. 23(15), 5269-81. Aug 2003
Liao W, Tang Y, Lin SF, Kung HJ, Giam CZ. K-bZIP of Kaposi's Sarcoma-Associated Herpesvirus/Human Herpesvirus 8 (KSHV/HHV-8) Binds KSHV/HHV-8 Rta and Represses Rta-Mediated Transactivation. Journal of Virology. 77(6), 3809-15. Mar 2003
Fu DX, Kuo YL, Liu BY, Jeang KT, Giam CZ, Human T-lymphotropic Virus Type I Tax Activates I-kappa B Kinase By Inhibiting I-kappa B Kinase-associated Serine/threonine Protein Phosphatase 2A The Journal of Biological Chemistry.278(3), 1487-93. Jan 2003
Liang MH, Geisbert T, Yao Y, Hinrichs SH, Giam CZ. Human T-Lymphotropic Virus Type 1 Oncoprotein Tax Promotes S-Phase Entry but Blocks Mitosis. Journal of Virology.76(8), 4022-33. Apr 2002
Mori N, Morishita M, Tsukazaki T, Giam CZ, Kumatori A, Tanaka Y, Yamamoto N, Human T-cell Leukemia Virus Type I Oncoprotein Tax Represses Smad-dependent Transforming Growth Factor Beta Signaling Through Interaction With CREB-binding Protein/p300. Blood. 97(7), 2137-44. Apr 2001