Host-virus interactions: HTLV antisense regulatory proteins play a role in the dysregulation of NF-κB pathway

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), an aggressive form of T-cell malignancy with no cure. The HTLV-1 oncoprotein Tax plays a key role in CD4+ T-cell transformation, mainly through constitutive activation of both the canonical and the alternative NF-κB pathways. The HTLV-1 basic zipper protein (HBZ), encoded by the antisense viral genome strand, plays an essential role in the oncogenic process in concert with Tax, mediating T-cell proliferation. Unlike HTLV-1, the genetically related retrovirus HTLV-2 is not associated with ATL diseases. Functional comparisons between HTLV-1 regulatory proteins, Tax-1 and HBZ, and the HTLV-2 homologs, Tax-2 and APH-2, may highlight different mechanisms of their oncogenic potential. The aim of this study is to investigate how the antisense proteins HBZ and APH-2 impaired the NF-κB pathway activation. We found that both HBZ and APH-2 antagonized the NF-κB promoter activity mediated by Tax, but not in the same extent. Analyzing the intracellular distribution of the antisense proteins, we found that APH-2 is retained in cytoplasm complexes, whereas HBZ is mainly distributed into the nucleus. We observed that in presence of APH-2 and Tax-2, the degradation of the IκB-α inhibitor was reduced. Moreover, we found that unlike HBZ, APH-2 formed complexes with an upstream inhibitor of the alternative NF-κB pathway, the TNF receptor-associated factor 3, TRAF3. We generated a TRAF3 knock-out cell line applying the CRISPR/Cas9-mediated genome editing. By luciferase assays, we showed that TRAF3 is not required for Tax mediated NFκB promoter activation. Analyses are in progress to test the inhibitory effect of the antisense HBZ and APH-2 proteins on NF-κB promoter activity in absence of TRAF3. The results of this study may contribute to clarify the effect of the alternative NF-κB viral deregulation pathway in the expression of proinflammatory genes