Two transcription factors, NF-kappa B and H2TF1, interact with a single regulatory sequence in the class I major histocompatibility complex promoter

A sequence centered 166 nucleotides upstream of the mouse H-2Kb class I major histocompatibility gene binds a nuclear factor, H2TF1, found in many cell types. Previous studies have shown that binding of H2TF1 to this sequence stimulates class I gene expression. Furthermore, this factor binds a similar sequence in the 72-base-pair repeat enhancer element of simian virus 40. We show here that NF-kappa B, an inducible B-cell-specific factor that binds the kappa immunoglobulin light chain gene enhancer, also binds the H2TF1 regulatory sequence. Methylation-interference experiments demonstrate that NF-kappa B closely interacts with six of the eight symmetrically positioned guanines that contact H2TF1. These experiments suggest that NF-kappa B may play a role in class I major histocompatibility gene expression and that H2TF1 and NF-kappa B may be related DNA-binding proteins.     

Cooperative inhibition of NF-kappa B and Tat-induced superactivation of human immunodeficiency virus type 1 long terminal repeat.

Human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR)-regulated gene expression is stimulated independently by the cellular trans-activator NF-kappa B and the viral protein Tat. Noncytotoxic concentrations of the drug pentoxifylline (PTX) inhibited interaction of NF-kappa B with its motif and the stimulation of HIV-1 LTR-driven gene expression in Jurkat cells. Tat protein (from a cotransfected Tat-expression vector) also induced activation of HIV-1 LTR-driven gene expression. This activation was unaffected by PTX when NF-kappa B sites in the HIV-1 LTR were mutated, suggesting that this drug does not directly influence Tat function, which, however, was inhibited by the Tat-inhibitor Ro 24-7429. Transient reporter gene expression regulated by HIV-1 LTR with wild-type NF-kappa B motifs in the presence of Tat protein was 10- to 60-fold higher than in the presence of either of the trans-activators alone, demonstrating superactivation of HIV-1 LTR by the concerted action of both the trans-activators. Treatment of cells with either PTX or Ro 24-7429 inhibited this superactivation of the HIV-1 LTR. The inhibitory effect of these two drugs in combination, at concentrations that alone did not significantly influence viral promoter activity, was far more than additive. A cooperative action of PTX (NF-kappa B inhibitor) and Ro 24-7429 (Tat inhibitor) on HIV-1 LTR-regulated gene expression is suggested. Concentrations of the drugs that induced maximum inhibition of HIV-1 LTR through their cooperative action are far below cytotoxic levels. Thus, the combination of these two inhibitors could be very effective for anti-HIV therapy.     

HIV-1 infection and expression in human colonic cells: infection and expression in CD4+ and CD4- cell lines

Three human colonic epithelial cell lines, SW620, HT29, and T84, were characterized with respect to HIV-1 infection and gene expression. SW620 and HT29, but not T84, could be infected with HIV-1. CD4 messenger RNA and its protein product were identified in SW620 cells but not in HT29 or T84 cells. Anti-CD4 antibody blocked infection of SW620 cells but had no effect on infection of HT29 cells. In SW620 and HT29 cells transfected with the HIV-1 long terminal repeat (LTR) linked to the chloramphenicol acetyl transferase (CAT) reporter gene, an intact HIV-1 enhancer element was required for stimulation of CAT activity by tumor necrosis factor alpha (TNF alpha) and phorbol ester. T84 was not able to mediate a TNF alpha or phorbol ester response. These studies provide further evidence that HIV-1 can infect cells by mechanisms other than those mediated by the CD4 receptor and describe complementary models for analyzing HIV-1 infection and expression in colonic epithelial cells.     

Activation of fibronectin gene expression by hepatitis B virus x antigen

The development of fibrosis and cirrhosis during chronic hepatitis B virus (HBV) infection correlates with the persistent expression of HBV x antigen (HBxAg), which acts in part, by stimulating selected signal transduction pathways, including nuclear factor kappa B (NF-kappa B). To identify NF-kappa B responsive genes that are differentially expressed in HBxAg-positive cells, HepG2 cells were stably transfected with HBxAg, and then with pZeoSV2 or pZeoSV2-I kappa B alpha. When RNAs from each culture were compared by PCR-select cDNA subtraction, fibronectin (FN) mRNA was shown to be strongly down-regulated by I kappa B alpha. Up-regulated expression of FN and co-expression between FN and HBxAg were observed in liver sections from HBV carriers that were stained for HBxAg and analysed for FN mRNA by in situ hybridization (ISH). In liver cell cultures, HBxAg increased the levels of FN mRNA and protein. This was because of the HBxAg-mediated trans-activation of the FN promoter, which was NF-kappa B-dependent. HBxAg also antagonized the repression of the FN promoter by the tumour suppressor, p53. Hence, the FN gene may be a natural target for HBxAg trans-activation, perhaps through activation of NF-kappa B and inactivation of p53, thereby contributing to the accumulation of FN in the liver over the course of chronic HBV infection.     

Expression of nuclear factor-kappa B in hepatocellular carcinoma and its relation with the X protein of hepatitis B virus

AIM: In this study we investigated the relationship of the X protein of HBV and nuclear factor-kappa B (NF-kappa B) and the expression of NF-kappa B in human hepatocellular carcinoma tissues. METHODS: Immunohistochemistry SP method was used to detect the expression of NF-kappa B and the X protein of HBV in human hepatocellular carcinoma tissues of 52 cases. Gene transfection mediated by lipofectamine was used to transfect the eukaryotic expression vector pCDNA3.1-HBX of HBV x gene into human hepatocellular carcinoma cell line HCC-9204 and NF-kappa B was detected. RESULTS: NF kappa B was widely expressed in human hepatocellular carcinoma tissues in a total of 52 cases and its expression was related to the X protein of HBV. NF-kappa B was localized both in the cytoplasm and the nuclei of hepatocellular carcinoma cells in 11 cases which were positive for the X protein of HBV while in 41 cases negative for the X protein of HBV, NF-kappa B was only localized in the cytoplasm of hepatocellular carcinoma cells but translocated to the nuclei of hepatocellular carcinoma cells after the eukaryotic expression vector pCDNA3.1-HBX was transfected into HCC-9204 cells. CONCLUSION: This study strongly suggests that the nuclear factor NF-kappa B is widely expressed in hepatocellular carcinoma tissues in different styles according to the expression of the X protein of HBV. NF-kappa B is abnormally activated in hepatocellular carcinoma, which is probably related to the X protein of HBV. The X protein of HBV can activate NF-kappa B to translocate into nuclei of hepatocellular carcinoma cells.