The laboratory of Patrick Green is internationally recognized for their contributions to the understanding of the molecular basis of T-lymphocyte transformation and induction of leukemia/lymphoma and neurological disease by the human T-cell leukemia viruses (HTLVs). The Green lab has three areas of research focus investigating viral and cellular regulators of HTLV gene expression/replication, cellular transformation, and virus survival or persistence in the infected host.
One aim of our laboratory is to understand the mechanism of action and biological role of a unique HTLV-1 accessory/regulatory gene, termed Hbz. It is the only gene transcribed from the antisense strand of the viral proviral genome and is expressed in all adult T-cell leukemia (ATL) cells, whereas tax oncogene expression is typically undetectable. We have discovered that HBZ is dispensable in cell culture, but is required to enhance virus replication and survival in the infected host. More recently utilizing a Hbz shRNA knockdown approach and NOD/SCIDγc-/-(NOG) mice we discovered that Hbz expression enhances the proliferative capacity of HTLV-1 infected cells in culture and plays a critical role in infected cell survival and ultimately HTLV-1 tumorigenesis. HBZ, originally thought to be unique to HTLV-1 has been hypothesized to play a role in pathogenesis. Our overall hypothesis is that uncovering the mechanism of actions of Hbz and defining the interplay between Hbz and the viral transactivator, Tax, will provide important insight into HTLV-1 cellular transformation and disease and ultimately will provide means for therapeutic targeting to erradicate HTLV-1 persistence in the host.
We will dissect the mechanisms of action of Hbz focusing on Hbz mRNA activities, the functional role of HBZ post-translational modification, and effects on cellular protein interactions and pathways with emphasis on Jun, and NFκB and interferon (IRF-1, IRF-7) regulation. We will combine in vitro (transformation assays) and in vivo (transgenic and humanized mice) approaches to determine the interplay between Hbz and Tax in the cellular transformation and tumor induction process. Recently, an antisense protein of HTLV-2 (APH-2) was identified. Despite its lack of a typical b-ZIP domain, APH-2, like HBZ, interacts with CREB and down-regulates Tax-mediated viral transcription. We will investigate in detail the mechanism of action of APH-2. Importantly, since HTLV-1 and HTLV-2 are closely related retroviruses, but have distinct etiological roles in human disease, we hypothesize that comparative studies on anti-sense proteins of HTLV-1 and HTLV-2 will provide fundamental insights into their distinct pathogenic properties.
Recently, our research team has focused to address the relevance of the arginine methyltransferase enzyme, PRMT5, to malignant disease and investigate the therapeutic potential of a new class of drugs to inhibit this enzyme. PRMT5 is an epigenetic modifier that silences the transcription of many key regulatory cellular genes through symmetric di-methylation (S2Me) of arginine (R) residues on histone proteins (H4R3 & H3R8). We are testing the hypothesis that PRMT5 contributes to HTLV-1-driven cellular transformation and leukemia, and ultimately determine the efficacy of PRMT5 inhibitors (PRMT5i) in a preclinical ATL mouse model. We found that PRMT5 expression was upregulated during HTLV-1-mediated T-cell transformation, as well as in established lymphocytic leukemia/lymphoma cell lines and ATLL patient PBMCs. shRNA-mediated reduction in PRMT5 protein levels or its inhibition by a small molecule inhibitor (PRMT5i) in HTLV-1-infected lymphocytes resulted in increased viral gene expression and decreased cellular proliferation. PRMT5i also had selective toxicity in HTLV-1-transformed T-cells. Finally, we demonstrated that PRMT5 and the HTLV-1 p30 protein had an additive inhibitory effect on HTLV-1 gene expression. Our study provides evidence for PRMT5 as a host cell factor important in HTLV-1-mediated T-cell transformation, and a potential target for ATLL treatment. Our next steps are to determine the therapeutic effects of PRMT5i in an in vivo ATL mouse model by examining viral replication kinetics, tumor size, and survival. These studies are the necessary first step to identify PRMT5 as an important epigenetic factor during HTLV-1-mediated cellular transformation and pathogenesis, and will ultimately provide important insight towards its potential as an ATL therapy target.
- "Retrovirus Models of Cancer"
Principle Investigator: Patrick L. Green, Ph.D.
Agency: National Institutes of Health/National Cancer Institute
Type: Projects 1-3 Cores A-C of PO1CA100730
Period: 08/01/14 - 07/31/19
- " Role of PRMT5 in HTLV-1 transformation and disease"
Principle Investigator: Patrick L. Green, Ph.D.
Agency: National Institutes of Health/NIAID
Period: 11/01/14 - 10/31/16