REGULATION OF HIV-1 GENE-EXPRESSION BY NF-IL6

Previous studies have shown that in human T-cells (Turkat) and hepatom a cells (HepG2), exogenous NF-IL6 can activate HIV-1 gene expression e ven in the absence of its consensus binding elements in the viral long terminal repeat (LTR). To identify the LTR elements that mediate this response, we have analysed constructs containing mutated and deleted LTR sequences. We have also examined heterologous plasmids to evaluate a potential requirement for the natural LTR sequences in producing HI V-1 gene activation by NF-IL6. As observed for Jurkat and HepG2 cells, we find that in the absence of NF-IL6 binding elements, NF-IL6 can el icit LTR-mediated gene expression in cotransient expression assays per formed in monocytic (U937) cells. However, we detect distinct modes of regulation depending on cell type. In U937 cells, the basal LTR seque nces retain a significant fraction (42%) of NF-IL6 responsiveness in t he absence of upstream regulatory elements in the LTR while these elem ents are required for maximal response. In HepG2 cells, NF-IL6 elicits a relatively low level of gene activation from the basal LTR elements ; response to, NF-IL6 is restored with either the Sp1 binding sequence s or the other upstream regulatory elements in the LTR. In addition, e ven though NF-IL6 induces a relatively low gene activity from the basa l LTR sequences analysed in HepG2 cells, study of a heterologous const ruct indicates that these sequences are required for the responsivenes s of Sp1 elements to NF-IL6 in this cellular background. (C) 1996 Acad emic Press Limited