Regulation of HIV-1 expression by NF-IL6
Abstract
The long terminal repeat (LTR) of the human immunodeficiency virus type-1 (HIV-1) contains elements which mediate the transcriptional regulatory effects of viral and cellular factors. Within nucleotides -173 to -165 of the LTR is a consensus binding site for NF-IL6, a human C/EBP family member and a critical mediator of the immune and inflammatory response. Exogenous synthesis of NF-IL6 upregulates LTR activity in Jurkat, U937 and HepG2 cells, yet a mutation of the -173/-165 site does not affect LTR activation by NF-IL6 in Jurkat and HepG2 cells, and may make only a minor contribution to the overall transactivation effect in U937 cells. Bandshift assays demonstrated that complex formation between nuclear extracts and this region of the LTR is dominated by the binding of USF to an E box that overlaps the NF-IL6 recognition sequence. However, an insertional mutation in this E box still did not enable NF-IL6 to activate LTR expression through its -173/-165 binding site in HepG2 cells. In sequence contexts other than the LTR, this site can mediate NF-IL6 transactivation: NF-IL6 activates multimers of the LTR sequence spanning this site from a heterologous construct. Surprisingly, in U937 cells the HIV-1 core promoter region mediates high levels of activity induced by NF-IL6. In HepG2 cells, NF-IL6 elicits only low levels of activity from the sequence spanning HIV-1 core promoter, yet full transactivation is observed in the presence of the LTR sequence spanning the Sp1 binding sites. The role of the Sp1-binding sequence is general, however, since other upstream sequences can also facilitate high levels of transactivation by NF-IL6. In a cell-type dependent manner, another C/EBP family member, human C/EBP$\alpha$, regulates LTR activity through the HIV-1 core promoter region: C/EBP$\alpha$ suppresses LTR activity in HepG2 cells. Together, these results imply that the HIV-1 core promoter region can directly mediate viral regulation by C/EBP family members. Through this direct a mechanism, HIV-1 may exploit the NF-IL6 immune response pathway to activate viral expression.
Degree
Ph.D.
Advisors
Bina, Purdue University.
Subject Area
Biochemistry|Molecular biology
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