C/EBPβ regulates human immunodeficiency virus 1 gene expression through its association with cdk9

Abstract

Transcriptional regulation of the human immunodeficiency virus type 1 (HIV-1) is a complex event that requires the cooperative action of both viral (e.g. Tat) and cellular (e.g. C/EBPβ, NF-κB) factors. The HIV-1 Tat protein recruits the human positive transcription elongation factor P-TEFb, consisting of cdk9 and cyclin T1, to the HIV-1 transactivation response (TAR) region. In the absence of TAR, Tat activates the HIV-1 long terminal repeat (LTR) through its association with several cellular factors including C/EBPβ. C/EBPβ is a member of the CCAAT/enhancer-binding protein family of transcription factors and has been shown to be a critical transcriptional regulator of HIV-1 LTR. We examined whether Tat–C/EBPβ association requires the presence of the P-TEFb complex. Using immunoprecipitation followed by Western blot, we demonstrated that C/EBPβ–cyclin T1 association requires the presence of cdk9. Further, due to its instability, cdk9 was unable to physically interact with C/EBPβ in the absence of cyclin T1 or Tat. Using kinase assays, we demonstrated that cdk9, but not a cdk9 dominant-negative mutant (cdk9-dn), phosphorylates C/EBPβ. Our functional data show that co-transfection of C/EBPβ and cdk9 leads to an increase in HIV-1 gene expression when compared to C/EBPβ alone. Addition of C/EBP homologous protein (CHOP) inhibits C/EBPβ transcriptional activity in the presence and absence of cdk9 and causes a delay in HIV-1 replication in T-cells. Together, our data suggest that Tat–C/EBPβ association is mediated through cdk9, and that phosphorylated C/EBPβ may influence AIDS progression by increasing expression of HIV-1 genes.

Analysis of the effects of HIV‐1 Tat on the survival and differentiation of vessel wall‐derived mesenchymal stem cells

“…In addition, Tat increased the expression of C/EBPb and C/EBPd, two transcription factors that play a pivotal role in the early steps of adipogenesis. The linkage between Tat and the C/EBP family factors has already been described in other cellular targets than MSCs [Liu et al, 2002;Mameli et al, 2007]. Tat induced C/EBPb expression and cooperated in LTR promoter modulation with C/EBP family members to increase the HIV transcription [Liu et al, 2002].…”

Modulation of JC virus transcription by C/EBPβ

“…The JCV E -CAT promoter mutants m1 and m2 were made by site-directed mutagenesis using the QuickChange II XL Site-Directed Mutagenesis Kit (Stratagene, La Jolla, CA) with double stranded oligonucleotides with the sequences 5’-aaaaacaactcaatttccctggcctcc-3’ and 5’-aaaaacaagggactctccctggcctcc-3’ respectively. The expression plasmids pCMV-p65, pCMV-CHOP and pCMV-C/EBPβ were described previously (Gorrill and Khalili, 2005; Mameli et al, 2007). pCMV-LIP and pCMV-LAP were kindly provided by Dr. Ueli Schibler, University of Geneva.…”

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

“…It is tempting to speculate that the DS1 site may be involved in mediating Tat transactivation and productive virus replication perhaps by tethering and stabilizing Tat binding to the TAR element. Tat has been shown to increase expression of the C/EBP␤ protein and binding of C/EBP␤ to DNA in vitro (55), in addition to physically and functionally interacting (in vitro and in vivo) with C/EBP␤ to induce interleukin 6 and MCP-1 (monocyte chemoattractant protein 1 or CCL2 (55)(56)(57)(58)). Moreover, Mameli et al (58) demonstrated that the Tat-C/EBP␤ functional and physical association is mediated through cyclin T1/cdk9 in U-87MG astrocytic cells and possibly influences cates in perivascular macrophages, and spreads to resident macrophages (1,2,8,69).…”