Characterization of a new tissue-specific transcription factor binding to the simian virus 40 enhancer TC-II (NF-kappa B) element

Nuclear factor of activated T-cells (NFAT) plays a role in SV40 infection

Recent evidence highlighted a role for the transcription factor, nuclear factor of activated T-cells (NFAT), in the transcription of the human polyomavirus JCV. Here we show that NFAT is also important in the transcriptional control of the related polyomavirus, Simian Virus 40 (SV40). Inhibition of NFAT activity reduced SV40 infection of Vero, 293A, and HeLa cells, and this block occurred at the stage of viral transcription. Both NFAT3 and NFAT4 bound to the SV40 promoter through kappaB sites located within the 72 bp repeated enhancer region. In Vero cells, NFAT was involved in late transcription, but in HeLa and 293A cells both early and late viral transcription required NFAT activity. SV40 large T-Ag was found to increase NFAT activity and provided a positive feedback loop to transactivate the SV40 promoter.

Human tumor necrosis factor-alpha gene 3' untranslated region confers inducible toxin responsiveness to homologous promoter in monocytic THP-1 cells

To better define the role of 3' untranslated region (3'UTR) on transcriptional regulation of the human tumor necrosis factor (TNF)-alpha gene, monocytic human THP-1 cells were transfected with two TNF-alpha promoter constructs spanning base pairs -1897/-1 and -1214/-1, respectively, and linked to the rabbit beta-globin gene. Quantitative globin gene expression of chimerae was measured by reverse transcription-polymerase chain reaction. A construct linking the chicken beta-actin promoter and a deleted portion of the beta-globin gene was cotransfected and used as internal standard. Unexpectedly, when THP-1 cells were stimulated with lipopolysaccharide or toxic shock syndrome toxin-1, gene regulation was hardly detected. In contrast, endogenous TNF-alpha gene regulation measured by the same reverse transcription-polymerase chain reaction procedure was vigorous. Remarkably, ligation of 3'UTR to chimeric constructs led to a drastic drop in the basal level of chimeric gene expression, resulting in a 15- to 40-fold induction of the reporter gene. Consistently, when the TNF-alpha promoter was replaced by the cytomegalovirus early immediate promoter, gene expression was also uniformly reduced but was no longer up-regulated upon stimulation with lipopolysaccharide and toxic shock syndrome toxin-1. These data provide the first line of evidence that, in addition to its role in TNF-alpha transcript stability and translation, human TNF-alpha 3'UTR also participates in modulating gene expression at the transcriptional level.

Hex1: a new human Rad2 nuclease family member with homology to yeast exonuclease 1

Nucleolytic processing of chromosomal DNA is required in operations such as DNA repair, recombination and replication. We have identified a human gene, named HEX1 forhumanexonuclease 1, by searching the EST database for cDNAs that encode a homolog to the Saccharomyces cerevisiae EXO1 gene product. Based on its homology to this and other DNA repair proteins of the Rad2 family, most notably Schizosaccharomyces pombe exonuclease 1 (Exo1), Hex1 presumably functions as a nuclease in aspects of recombination or mismatch repair. Similar to the yeast proteins, recombinant Hex1 exhibits a 5'-->3' exonuclease activity. Northern blot analysis revealed that HEX1 expression is highest in fetal liver and adult bone marrow, suggesting that the encoded protein may operate prominently in processes specific to hemopoietic stem cell development. HEX1 gene equivalents were found in all vertebrates examined. The human gene includes 14 exons and 13 introns that span approximately 42 kb of genomic DNA and maps to the chromosomal position 1q42-43, a region lost in some cases of acute leukemia and in several solid tumors.

Interactions of a transcriptional activator in the env gene of the mouse mammary tumor virus with activation-dependent, T cell-specific transacting factors

The mouse mammary tumor virus env gene contains a transcriptional activator (META) that can control transcription of the adjacent long terminal repeat region. Transcriptional control by META parallels that of several lymphokine genes, being specific to T cells, dependent on their activation, and inhibited by the immunosuppressive drug cyclosporine (CsA). DNase I footprinting indicated that nuclear factors from activated T lymphocytes bound a promoter-proximal site, META(P), and a promoter-distal site, META(D+), within the 400-base pair META region. Nuclear factors from unstimulated, but not from activated cells, bound a site, META(D-), adjacent to META(D+). META(D+) directed transcription of a linked luciferase gene, and gel shift analysis revealed binding of inducible, CsA-sensitive T cell factors, in parallel with transfection results. Authentic NFAT and NF-kappaB targets did not compete for the META(D+) binding factor(s). The SV40 core sequence competed for META(D+) binding factors, but META(D+) failed to compete for the complexes obtained with the SV40 probe. Our results, taken together, indicate that META(D+) is a novel transcriptional enhancer element that is similar in its cell-type specificity, activation dependence, and CsA sensitivity to the NFAT element. It may be relevant to the role of MMTV in expression of Mls antigens or the induction of T cell lymphomas.

The regulation of GM-CSF is dependent on a complex interplay of multiple nuclear proteins

GM-CSF is an important mediator of hematopoiesis and its dysregulation may play a role in neoplastic and inflammatory conditions. Previous studies have demonstrated that GM-CSF production depends upon the accumulation of specific mRNA, which occurs by transcriptional and post-transcriptional mechanisms. In order to dissect the cis-acting sequences responsible for its regulation, we performed an extensive mutagenesis study spanning 54 nucleotides 5' of the GM-CSF coding region. Our analysis suggests that the previously-described functional elements of the GM-CSF promoter, kappa B and a repetitive CATTT/A motif, the former co-exists with an overlapping 9 nucleotide site which silences promoter activity, and the CATTT/A complex binds multiple polypeptides which differentially contribute to basal and inducible promoter activity. These two sites interact to provide tissue-appropriate and stimulus-specific promoter function. Using DNA-protein cross-linking and co-transfection studies, we demonstrate that the c-rel-related proteins p65 and p50 bind to the GM-CSF promoter and that p65 binding is primarily responsible for the enhancing effects at this site. In addition, we show that the GM-CSF kappa B decanucleotide is inadequate to provide full binding affinity; mutation of nucleotides flanking this site affect promoter function by altering NF-kappa B binding affinity. Together these results suggest that the transcriptional response of GM-CSF is dependent on a complex interplay of multiple DNA binding proteins.

Mouse interleukin-2 receptor alpha gene expression. Interleukin-1 and interleukin-2 control transcription via distinct cis-acting elements

We have shown that interleukin-1 (IL-1) and IL-2 control IL-2 receptor alpha (IL-2R alpha) gene transcription in CD4-CD8- murine T lymphocyte precursors. Here we map the cis-acting elements that mediate interleukin responsiveness of the mouse IL-2R alpha gene using a thymic lymphoma-derived hybridoma (PC60). The transcriptional response of the IL-2R alpha gene to stimulation by IL-1 + IL-2 is biphasic. IL-1 induces a rapid, protein synthesis-independent appearance of IL-2R alpha mRNA that is blocked by inhibitors of NF-kappa B activation. It also primes cells to become IL-2 responsive and thereby prepares the second phase, in which IL-2 induces a 100-fold further increase in IL-2R alpha transcripts. Transient transfection experiments show that several elements in the promoter-proximal region of the IL-2R alpha gene contribute to IL-1 responsiveness, most importantly an NF-kappa B site conserved in the human and mouse gene. IL-2 responsiveness, on the other hand, depends on a 78-nucleotide segment 1.3 kilobases upstream of the major transcription start site. This segment functions as an IL-2-inducible enhancer and lies within a region that becomes DNase I hypersensitive in normal T cells in which IL-2R alpha expression has been induced. IL-2 responsiveness requires three distinct elements within the enhancer. Two of these are potential binding sites for STAT proteins.

Members of the nuclear factor kappa B family transactivate the murine c-myb gene

Expression of the c-myb proto-oncogene is primarily detected in normal tissue and tumor cell lines of immature hematopoietic origin, and the down-regulation of c-myb expression is associated with hematopoietic maturation. Cell lines that represent mature, differentiated hematopoietic cell types contain 10-100-fold less c-myb mRNA than immature hematopoietic cell types. Differences in steady-state c-myb mRNA levels appear to be primarily maintained by a conditional block to transcription elongation that occurs in the first intron of the gene. The block to transcription elongation has been mapped, using nuclear run-on analysis, to a region of DNA sequence that is highly conserved between mouse and man. Two sets of DNA-protein interactions, flanking the site of the block to transcription elongation, were detected that exhibited DNA-binding activities that strongly correlated with low steady-state c-myb mRNA levels. Several criteria demonstrated that members of the nuclear factor kappa B (NF-kappa B) family of transcription factors were involved in the DNA-protein interactions identified in these two sets. Surprisingly, cotransfection experiments demonstrated that coexpression of members of the NF-kappa B family, specifically p50 with p65 and p65 with c-Rel, transactivated a c-myb/chloramphenicol acetyltransferase reporter construct that contained 5'-flanking sequences, exon I, intron I, and exon II of the c-myb gene. Transactivation by these heterodimer combinations was dependent on regions of the c-myb first intron containing the NF-kappa B-binding sites. These findings suggest that NF-kappa B family members may be involved in either modifying the efficiency of transcription attenuation or acting as an enhancer-like activity to increase transcription initiation. Thus, the regulation of c-myb transcription may be quite complex, and members of the NF-kappa B family likely play an important role in this regulation.

Chronic human immunodeficiency virus type 1 infection stimulates distinct NF-kappa B/rel DNA binding activities in myelomonoblastic cells

The relationship between human immunodeficiency virus type 1 (HIV-1) infection and the induction of NF-kappa B binding activity was examined in a myeloid cell model of HIV-1 infection derived from the PLB-985 cell line. Chronic infection of PLB-985 cells led to increased monocyte-specific surface marker expression, increased c-fms gene transcription, and morphological alterations consistent with differentiation along the monocytic pathway. PLB-IIIB cells displayed a constitutive NF-kappa B-like binding activity that was distinct from that induced by tumor necrosis factor alpha or phorbol 12-myristate 13-acetate treatment of the parental PLB-985 cell line. This unique DNA binding activity consisted of proteins of 70, 90, and 100 kDa with a high degree of binding specificity for the NF-kappa B site within the PRDII domain of beta interferon. In this report, we characterize the nature of these proteins and demonstrate that binding of these proteins is also induced following Sendai paramyxovirus infection. The 70-kDa protein corresponds to the NF-kappa B RelA (p65) subunit, which is activated in response to an acute paramyxovirus infection or a chronic HIV-1 infection. Virus infection does not appear to alter the amount of RelA (p65) or NFKB1 (p50) but rather affects the capacity of I kappa B alpha to sequester RelA (p65), therefore leading to constitutive levels of RelA DNA binding activity and to increased levels of NF-kappa B-dependent gene activity. The virally induced 90- to 100-kDa proteins have a distinct binding specificity for the PRDII domain and an AT-rich sequence but do not cross-react with NF-kappa B subunit-specific antisera directed against NFKB1 (p105 or p50), NFKB2 (p100 or p52), RelA (p65), or c-rel. DNA binding of the 90- to 100-kDa proteins was not inhibited by recombinant I kappa B alpha/MAD-3 and was resistant to tryptic digestion, suggesting that these proteins may not be NF-kappa B related. Transient cotransfection experiments demonstrated that RelA and NFKB1 expression maximally stimulated HIV-1 LTR- and NF-kappa B-dependent reporter genes; differences in NF-kappa B-like binding activity were also reflected in higher constitutive levels of NF-kappa B-regulated gene expression in HIV-1-infected myeloid cells.