The Interplay between HTLV-1 Viral Factors, Tax and HBZ, During T-cell Transformation

Abstract

Human T-cell leukemia virus type 1 (HTLV-1) is a tumorigenic retrovirus that infects an estimated 15-20 million people worldwide. HTLV-1 is responsible for an aggressive T-cell malignancy termed adult T-cell leukemia/lymphoma (ATLL). The incidence of disease associated with HTLV-1 infection is 2-6% over the lifetime of an infected individual, with symptoms taking up to 3-4 decades to present. Despite the long clinical latency period, HLTV-1-associated malignancies are chemotherapy resistant and the median survival time is <1 year. The detailed mechanism of how HTLV-1 transforms cells is still unknown, but several studies have indicated that two viral factors, Tax and HBZ, are individually linked to oncogenic transformation. However, the interplay between Tax and HBZ in the transformation process is unknown. Herein, we investigated the relationship between Tax and HBZ using a dual-inducible lentiviral expression system. Tax and HBZ cDNAs were cloned into the cumate-inducible and doxycycline-inducible expression vectors, respectively. These vectors were transduced into CTLL-2 cells and stable cellular clones were selected using drug resistance and single cell dilution. Clones that responded best to drug induction (as measured by mRNA levels and protein functionality) were selected for further experiments. Using the established CTLL-2 T-cell transformation assay, we sought to determine whether the presence of HBZ and Tax drives these cells from an IL-2-dependent to independent growth, a characteristic indicative of cellular transformation. Our results indicate that both Tax and HBZ enhance transformation. Ultimately, our work will provide better insight into the transformation landscape of T-cells in humans and the molecular pathogenesis of ATLL development.