The Role of Sp Family Members, Basic Krupple-Like Factor, and E Box Factors in the Basal and IFN-γ Regulated Expression of the Human Complement C4 Promoter

Abstract

The fourth component of human complement (C4) is a serum protein that is expressed in the liver and other organs. The promoter region of the C4 gene has been analyzed in reporter gene assays in two cell lines that represent hepatic (HepG2) and monocytic (U937) lineages. Analysis indicated that regions important for basal transcription in HepG2 cells included Sp1 and E box sites within the first 100 bp upstream of the transcription initiation site but not the nuclear factor-1 site important in the control of the mouse C4 gene. Also, a region encompassing −468 to −310 was able to repress activity 2-fold. However, when a CACCC or GT box sequence at −140 was mutated the repressive activity of the upstream region resulted in almost no activity. The −140 region consists of a series of four closely positioned GT boxes that were shown to bind Sp1, Sp3, and basic Krupple-like factor in EMSA. This novel two-part regulatory element may be involved in the regulated expression of C4. However, IFN-γ a major activator of C4 expression did not signal through this two-part regulatory element. We were able to map the position of an IFN-γ responsive element in U937. IFN-γ was able to increase transcription by up to 20-fold with mutations in the E box sequence at −78 to −73, thus completely abolishing induction. We conclude that the E box binding factors, which appear to be distinct from upstream stimulatory factors 1 and 2, are totally responsible for IFN-γ induction of C4.

Transcriptional Repression of C4 Complement by Hepatitis C Virus Proteins

“…2C). Thus, the results agree with the previous report (33) suggesting that the region from nucleotides Ϫ310 to ϩ44 contains essential elements responsible for C4 promoter activation. IFN-␥ is the only known inducer of C4 expression in the liver.…”

“…Since we observed regulation of C4 at the mRNA level, we assumed that a HCV protein(s) regulates C4 complement component at the transcriptional level. In order to identify the viral proteins that are involved in C4 regulation, we constructed a C4 promoter (nucleotides Ϫ1148 to ϩ44) with a luciferase reporter gene (33) and studied the effect of HCV protein expression in a permissive cell culture system. Plasmid containing HCV core, NS2, NS3/NS4A, or NS5A DNA or the full-length (FL) genome was separately transfected along with the C4 promoter construct in Huh7 cells.…”

“…The C4 promoter region contains an interferon gene regulatory element (IRE) sequence, and transcription factors that respond to IFN-␥ are involved in promoter activation. Earlier studies on the C4 promoter identified a conserved E-box motif CA CGTG (E-C4) at positions Ϫ75 to Ϫ70, and point mutations within this motif reduced transcription by up to 90% compared to transcription in cells with the full-length promoter (33,34), indicating that it plays a major role in maintaining C4 basal activity. The E-C4 region is also recognized by USF-1 and may play a major role in C4 regulation.…”

Defining a transcriptional fingerprint of murine splenic B-cell development

“…Klf12 is a member of the basic Kruppel family of transcriptional regulators and is implicated in transcriptional suppression during hematopoietic cell differentiation. [72][73][74][75] Another set of genes encoding transcriptional regulators are progressively downregulated during the transitional maturation of B cells and thus may allow the expression of genes in mature B cells (by alleviating transcriptional repression) or result in the loss of proteins expressed in immature B cells (loss of positive regulation). For example, the genes Tcf12, Gfi1, Erg and E2f7 show the highest level of expression in the B220 þ marrow cells with declining expression in the most mature B cells.…”

Activation and Repression of Interleukin-12 p40 Transcription by Erythroid Kruppel-like Factor in Macrophages

“…KLFs have a broad biological function such as cellular proliferation/differentiation, apoptosis, angiogenesis, and tumorigenesis as reviewed recently (22). Recent evidence suggests that KLFs regulate the promoter activities of complement C4 (23) and iNOS (24), implicating a role of KLFs in immune system due to the gene-regulatory role via the CACCC cis-element. However, expression or function of KLFs has not been described in primary myeloid cells.…”