The human T-cell leukaemia virus type 1 and type 2 (HTLV-1/HTLV-2) antisense proteins HBZ and APH-2 play key roles in the HTLV lifecycles and persistence in the host. Nuclear Factors Associated with double-stranded RNA (NFAR) proteins NF90/110 function in the lifecycles of several viruses and participate in host innate immunity against infection and oncogenesis. Using GST pulldown and co-immunoprecipitation assays we demonstrate specific novel interactions between HBZ/APH-2 and NF90/110 and characterised the protein domains involved. Moreover we show that NF90/110 significantly enhance Tax mediated LTR activation, an effect that was abolished by HBZ but enhanced by APH-2. Additionally we found that HBZ and APH-2 modulate the promoter activity of survivin and are capable of antagonising NF110-mediated survivin activation. Thus interactions between HTLV antisense proteins and the NFAR protein family have an overall positive impact on HTLV infection. Hence NFARs may represent potential therapeutic targets in HTLV infected cells.

It has recently been demonstrated that HTLV-1 and HTLV-2 utilise antisense transcription to express the viral proteins, HBZ and APH-2, respectively. Studies have shown that HBZ is a key player in the pathogenesis of HTLV-1 as its temporal expression appears to be critical for the development of ATL and HAM/TSP. To date very little is known about the role of APH-2 in HTLV-2 infection. Thus, to investigate its role in the pathogenesis of HTLV-2, we recently performed yeast two hybrid screens of several cDNA libraries using APH-2 as bait. We identified a member of the Nuclear Factors Associated with double-stranded RNA (NFAR) proteins as a potential interacting protein of APH-2. The NFARs have been shown to be involved in the regulation of gene expression and most notably; host antiviral defence. Our research affords the opportunity to investigate the interaction of APH-2 and NFARs and determine how this interaction impacts on HTLV-2 lifecycle events. Our findings indicate that APH-2 and NFARs interact in vivo and in vitro. Immunofluorescence demonstrates that APH-2 and NFARs localise to the nucleus. We have also performed knockdown studies to determine the effect of NFAR proteins on HTLV-2 LTR promoter activity. Our results reveal that NFARs exert no effect on basal LTR activation, but inhibit Tax2B-mediated viral transcription. Additionally we report that in the presence of APH-2, NFARs enhance Tax2B-mediated LTR activation. Overall, this study will provide novel insights into the functional role of APH-2 and NFAR proteins in the pathogenesis of HTLV-2.