Poster abstracts
Poster number 109 submitted by Rocio Zaldivar
Loss of the intragenic viral enhancer and viral CTCF binding site impairs HTLV-1 pathogenesis
Rocio Zaldivar (MCDB), Cameron Phelps (Veterinary Biosciences, OSU), Amelie Mockbee (Veterinary Biosciences, OSU), Patrick Green, Stefan Niewiesk (Veterinary Biosciences, OSU), Amanda Panfil (Veterinary Biosciences, OSU)
Abstract:
Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that infects CD4 T cells and causes a persistent, life-long infection leading to the development of an aggressive malignancy known as adult T-cell leukemia/lymphoma (ATLL). Patients with ATLL have a poor prognosis and limited therapeutic options. HTLV-1 integrates its genetic material within the host genome, forming a provirus. Encoded on the anti-sense genomic strand, the viral gene Hbz is consistently expressed throughout infection and disease. Previous studies have demonstrated Hbz promotes survival, cellular proliferation and immune escape of infected T cells. Recently, two regulatory DNA elements within the HTLV-1 provirus have been identified: a viral CTCF-binding site (vCTCF-BS) that limits the spread of repressive DNA methylation, and a downstream viral enhancer (vEnhancer) bound by ELK-1 and SRF transcription factors. Our previous studies demonstrated that loss of either element individually reduced Hbz expression in vitro, but had minimal impact in vivo, suggesting potential functional redundancy or cooperation. Herein, we investigated the combined contribution of the vCTCF-BS and vEnhancer to regulate Hbz, viral persistence and disease progression. We have constructed mutant proviral clones lacking the vCTCF-BS, vEnhancer, or both elements, and established stable virus-producing cell lines. All mutant viruses could infect and immortalize T cells in vitro. However, qRT-PCR analyses revealed that primary T cells immortalized with HTLV-1.∆vCTCF-BS/vEnhancer virus had significantly less Hbz expression and proviral load compared to wt or single mutant virus alone. Using a rabbit model of HTLV-1 infection and persistence, our in vivo studies similarly showed reduced proviral load and lower Hbz expression in the HTLV-1.∆vCTCF-BS/vEnhancer virus infected animals. Using a humanized mouse model of disease, we found combined loss of vCTCF-BS and vEnhancer significantly increased survival. Collectively, our findings support a cooperative role for the vCTCF-BS and vEnhancer in maintaining Hbz expression, viral persistence and disease progression.
Keywords: HTLV-1, retroviruses, ATLL