Showing papers by "Bassel E. Sawaya published in 2007"
TL;DR: A role for p65 in regulating the ERVWE1 promoter and in TNFalpha-mediated induction of syncytin-1 in multiple sclerosis is illustrated.
49 citations
TL;DR: It is demonstrated that ectopic expression of p65 along with Tat increases p65 binding to HIV‐1 LTR, and that this increase correlates with enhanced HIV‐2 promoter activity, and a delicate balance of interaction between p65, C/EBPβ, and Tat can dictate the level of HIV‐ 1 LTR transcription.
Abstract: In human immunodeficiency virus type 1 (HIV-1) latently infected cells, NF-kappaB (NF-kappaB) plays a critical role in the transcriptional induction of the HIV-1 promoter. The trans-activating ability of NF-kappaB can be modified by another nuclear factor C/EBPbeta that can physically bind to NF-kappaB and regulate its activity. Because the HIV-1 promoter also contains a C/EBPbeta site adjacent to the NF-kappaB site, the present study examined cooperative functional in vivo interaction of the p65 subunit of NF-kappaB and C/EBPbeta, and the impact of Tat in this event. We demonstrated that ectopic expression of p65 along with Tat increases p65 binding to HIV-1 LTR, and that this increase correlates with enhanced HIV-1 promoter activity. Further, co-expression of C/EBPbeta and Tat leads to a decrease in p65 binding, which allows C/EBPbeta to bind more efficiently to the LTR. Inhibition of p65 expression by siRNA significantly decreases C/EBPbeta-binding and LTR expression. Using ChIP assay, we confirmed the existence of an interchange between p65 and C/EBPbeta and their abilities to bind to the LTR in vivo. These observations demonstrate that a delicate balance of interaction between p65, C/EBPbeta, and Tat can dictate the level of HIV-1 LTR transcription.
33 citations
TL;DR: The functional data show that co-transfection of C/EBPbeta and cdk9 leads to an increase in HIV-1 gene expression when compared to C/ eBPbeta alone, and that phosphorylated C/ EBPbeta may influence AIDS progression by increasing expression of HIV- 1 genes.
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.
18 citations
TL;DR: It is shown that β1‐integrin and pS‐IRS‐1 colocalize in PC12 cells and in primary cortical neurons and that IGF‐I counteracts TNFα‐mediated accumulation of pS •IRS •1–β1‐Integrin complexes supporting the stability of neuronal processes.
Abstract: Tumor necrosis factor-alpha (TNFalpha) released in the brain by HIV-activated macrophages/microglia is suspected to compromise neuronal survival. Previously, we have demonstrated that activated receptor for insulin-like growth factor I (IGF-IR) protects neurons from TNFalpha-induced neuronal damage (Wang et al. [ 2006] J. Neurosci. Res. 83:7-18). Because TNFalpha triggers phosphorylation of insulin receptor substrate 1 (IRS-1) on serine residues (pS-IRS-1; Rui et al. [ 2001] J. Clin. Invest. 107:181-189), and pS-IRS-1 binds integrins (Reiss et al. [ 2001] Oncogene 20:490-500), we asked how these events affect neuronal processes. We show that beta1-integrin and pS-IRS-1 colocalize in PC12 cells and in primary cortical neurons. TNFalpha treatment elevated membrane-associated pS-IRS-1, enhanced pS-IRS-1 interaction with beta1-integrin, and attenuated cell attachment to collagen IV. In contrast, IGF-I inhibited pS-IRS-1-beta1-integrin complexes and improved cell attachment. The domain of IRS-1 involved in beta1-integrin binding mapped between amino acids 426 and 740, and the expression of 426-740/IRS-1 mutant attenuated neuronal outgrowth. Our results indicate that TNFalpha facilitates the interaction of pS-IRS-1 and beta1-integrin and destabilizes neuronal processes. IGF-I counteracts TNFalpha-mediated accumulation of pS-IRS-1-beta1-integrin complexes supporting the stability of neuronal processes.
14 citations