CCAAT/Enhancer Binding Proteins Are Not Required for HIV-1 Entry but Regulate Proviral Transcription by Recruiting Coactivators to the Long-Terminal Repeat in Monocytic Cells

Abstract

CCAAT/enhancer binding proteins (C/EBP) have been shown to be required for HIV-1 transcription and replication in macrophages. However, whether these transcription factors influence the ability of virus to establish infection by altering cytokine or receptor expression or primarily regulate HIV-1 transcription has not been determined. By inhibiting endogenous C/EBP activity with a dominant-negative protein, we demonstrate that functional C/EBPs are not required for HIV-1 infection and that these factors influence replication by a transcriptional mechanism. C/EBPbeta recruits coactivators to the HIV-1 long-terminal repeat (LTR) and physically interacts with histone acetyltransferase (HAT) complexes, suggesting that C/EBPs participate in remodeling the chromatin organization of the HIV-1 provirus. Furthermore, overexpression of a C/EBP dominant-negative inhibits displacement of nucleosomes located at the HIV-1 transcriptional start site. These results provide insight into the general mechanisms by which C/EBPs regulate macrophage-restricted HIV-1 transcription.

Novel Function of Prothymosin Alpha as a Potent Inhibitor of Human Immunodeficiency Virus Type 1 Gene Expression in Primary Macrophages

“…Differential requirements for transcriptional regulators of HIV in cells of monocytic compared to lymphocytic origin have been described elsewhere (20). Several reports demonstrate that CCAAT binding proteins (C/EBP) are necessary for HIV replication in primary macrophages but not in lymphocytes (20,21,26). We examined whether CCAAT box binding transcriptional factors are involved in ProT␣ suppression.…”

Regulation of SIVmac239 Basal Long Terminal Repeat Activity and Viral Replication in Macrophages

“…At this early time point there is an abundance of the C/EBP␤ isoform in macrophages (5,69) that bind the JC1 and DS1 sites of the SIV-LTR. C/EBP␤ recruits histone acetyltransferases such as CBP/p300 and PCAF (15,16,70), leading to chromatin remodeling events. Such events, as demonstrated previously in vitro and in vivo in our SIV/macaque model (4), mediate transcriptional activation of the LTR, most likely through the JC1 site.…”

“…Between 10 and 21 days p.i., LIP expression predominates in the brain (5), which effectively competes with the C/EBP␤ for occupancy of JC1 and DS1 sites due to the higher affinity of LIP compared with C/EBP␤ for both sites. LIP lacks the transactivating domain (71) and does not interact with histone acetyltransferases leading to repression of LTR activity (4,15). As a result, chromatin remodeling events subside, evidenced by the decrease in acetylated histone H4 both in vitro and in vivo (4), and expression of SIV RNA decreases (3).…”

“…To be consistent with previous studies by several groups, including those studies of C/EBP␤-mediated regulation of the HIV LTR (15,20), we used the rat homologs of C/EBP␤ (LAP) and LIP (42)(43)(44)(45)(46). We carried out EMSAs with these proteins after confirming (supplemental Fig.…”

Role of Downstream Elements in Transcriptional Regulation of the HIV-1 Promoter

“…NFAT family members illustrate an example of this mechanism; NFATs cooperate with AP-1 and C/EBP, which act by recruiting HATs and SWI/SNF complex [46][47][48][49][50][51]. Similarly, C/EBP family members are known to interact with chromatin remodeling machinery resulting in synergistic LTR activation, for example, C/EBP β associates with CBP/p300, PCAF, SWI/SNF remodeling factors, and other co activators [52][53][54]. Another important aspect of HIV-1 pathogenesis with respect to the downstream region is the convergence of signaling pathways at this region in response to activation signals (Figure 2).…”