Edward W. Harhaj, Ph.D.

Assistant Professor of Microbiology and Immunology
Room 503, Papanicolaou Building
1550 NW 10th Avenue
Telephone: 305-243-7893
Fax: 305-243-6410
Email: eharhaj@med.miami.edu

Research Interests:

HTLV-I is a retrovirus that primarily infects CD4+ T lymphocytes and is etiologically linked to adult T cell leukemia (ATL) and an inflammatory autoimmune-like neurological disorder known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Tax is a trans-activating protein encoded by the HTLV-I genome that regulates viral and cellular gene expression. Tax influences host gene expression by interacting with and activating cellular signaling pathways that lead to uncontrolled growth and malignant transformation of cells. The underlying mechanisms of Tax-mediated oncogenesis are unclear and are the primary focus of research in the laboratory.

Mechanisms of HTLV-I Tax activation of NF-kB
NF-kB/Rel is an evolutionarily conserved transcription factor family that regulates a large number of genes involved in cell growth, apoptosis, development, and the immune response. NF-kB is negatively regulated by members of the IkB family that interact with and prevent NF-kB subunits from binding to DNA. NF-kB activation occurs when specific stimuli such as cytokines, bacterial LPS, or viral infection trigger the activation of the serine kinases IKKalpha and IKKbeta that phosphorylate IkB molecules leading to ubiquitination and rapid degradation by the proteasome thus allowing NF-kB to translocate to the nucleus to activate target genes. The IKK protein complex also contains IKKgamma, a regulatory subunit required for NF-kB activation through the canonical NF-kB activation pathway. The HTLV-I Tax protein stimulates the catalytic activity of IKKalpha and IKKbeta via a physical interaction with IKKgamma. However, it is unclear if upstream kinases or additional signaling adaptor molecules play a role in Tax-mediated activation of IKK. Future studies will focus on additional mechanisms of Tax-mediated activation of IKK and NF-kB.

Deregulation of CD40/CD40L by HTLV-I
CD40L and CD40 are members of the TNF/TNFR superfamily and together orchestrate cellular and humoral immune responses by controlling B cell activation and differentiation, Ig isotype class switching, and functional maturation of dendritic cells. Studies from the laboratory have revealed that the expression of both CD40 and CD40L are deregulated by HTLV-I infection, likely as a mechanism to avoid detection by the immune system and also to promote growth of infected cells. Specifically, HTLV-I downregulates CD40L expression and induces the aberrant expression of CD40 on infected T cells. CD40L expression is also downregulated on T cells from ATL patients resulting in defective dendritic cell maturation and anti-HTLV-I CD8+ T cell responses. Conversely, CD40L expression is overexpressed on T cells from HAM/TSP patients. Therefore, the lack of CD40L expression correlates with defective T cell responses and immune evasion in ATL patients, and prolonged CD40L expression correlates with neuro-inflammation and autoimmune-like responses in HAM/TSP patients. We are currently conducting experiments to determine the molecular mechanisms utilized by HTLV-I to deregulate CD40 and CD40L. It is clear that deregulation of CD40/CD40L interactions plays an important role in HTLV I-mediated immune evasion and disease pathogenesis.

Identification of novel Tax binding proteins
It is likely that Tax exerts many of its functional effects by interacting with and modulating the function of cellular signaling proteins. Therefore, another active area of research within the laboratory is to identify novel Tax binding proteins by diverse approaches including yeast two-hybrid, antibody interaction arrays, and proteomics. We hope to identify important cellular targets of Tax that may play a role in HTLV-I disease pathogenesis. Proteomic approaches will also be used to identify proteins that are differentially expressed in T cells from ATL, HAM/TSP patients, and asymptomatic HTLV-I-infected individuals.

Selected Publications:

Shembade, N, N.S. Harhaj, K. Parvatiyar, N.G. Copeland, N.A. Jenkins, L.M. Matesic and E.W. Harhaj. 2008.  The E3 ligase Itch negatively regulates inflammatory signaling pathways by controlling the function of the ubiquitin editing enzyme A20.  Nature Immunol. Epub Feb. 3.

Shembade, N, N.S. Harhaj, M. Yamamoto, S. Akira and E.W. Harhaj.  2007. The HTLV-I Tax oncoprotein requires the ubiquitin conjugating enzyme Ubc13 for NF-kB activation.  J. Virol. 81: 13735-42.

Shembade, N, N.S. Harhaj, D.J. Liebl and E.W. Harhaj. 2007. Essential role for TAX1BP1 in the termination of TNF-a, IL-1 and LPS-mediated NF-kB and JNK signaling. EMBO J. 26: 3910-22. [Highlighted in Nature Immunology 2007 8: 1039].

Harhaj, N.S., B. Janic, J.C. Ramos, W.J. Harrington and E.W. Harhaj.  2007.  Deregulated expression of CD40 Ligand in HTLV-I infection: distinct mechanisms of downregulation in HTLV-I transformed cell lines and ATL patients.  Virology. 362: 99-108.

Harhaj, N.S., S.C. Sun and E.W. Harhaj.  2007.  Activation of NF-kB by the human T cell leukemia virus type I (HTLV-I) Tax oncoprotein is associated with ubiquitin-dependent relocalization of IKK.  J. Biol. Chem. 282: 4185-92.

Ramos, J.C., P. Ruiz, Jr., L. Ratner, I.M. Reis, C. Brites, C. Pedreso, G.E. Byrne, Jr., N. K. Toomey, V. Andela, E.W. Harhaj, I. Lossos and W.J. Harrington. 2007.  IRF-4 and c-rel expression in antiviral therapy resistant adult T-cell leukemia/lymphoma. Blood.  109: 3060-8.

Kamanaka, M., S.T. Kim, Y.Y. Wan, F.S. Sutterwala, M. Lara-Tejero, J.E. Galan, E. Harhaj and R.A. Flavell. 2006.  Expression of Interleukin-10 in intestinal lymphocytes detected by an Interleukin-10 reporter knock-in tiger mouse.  Immunity.  25: 941-52.

Harhaj, E.W., N.S. Harhaj, C. Grant, K. Mostoller, T. Alefantis, S.C. Sun and B. Wigdahl. 2005.  Human T cell leukemia virus type I Tax activates CD40 gene expression via the NF-kappa B pathway.  Virology.  333: 145-158.

Liao, G., M. Zhang, E.W. Harhaj and S.-C. Sun. 2004. Regulation of the NF-kB inducing kinase by TRAF3-induced degradation.  J. Biol. Chem.  279: 26243-50.

Xiao, G., M. Cvijic, A. Fong, E.W. Harhaj, M.T. Uhlik, M. Waterfield and S.-C. Sun. (2001)  Retroviral oncoprotein Tax induces processing of NF-kB2/p100 in T cells: evidence for the involvement of IKKa.  EMBO J.  20: 6805-6815.

Xiao, G.*, E.W. Harhaj* and S.-C. Sun. (2001) NF-kB-Inducing kinase regulates the processing of NF-kB2 p100.  Mol. Cell 7: 401-409.   *equal contribution.