The role of Sp family members, basic Krupple-like factor, and E box factors in the basal and IFN-gamma regulated expression of the human complement C4 promoter

The fourth component of human complement (C4) is a serum protein that is ex pressed in the liver and other organs, The promoter region of the C4 gene h as been analyzed in reporter gene assays in two cell lines that represent h epatic (HepG2) and monocytic (U937) lineages, Analysis indicated that regio ns important for basal transcription in HepG2 cells included Spl 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 activit y 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 th at were shown to bind Spl, Sp3, and basic Krupple-like factor in EMSA, This novel two-part regulatory element may be involved in the regulated express ion of C4, However, IFN-gamma a major activator of C4 expression did not si gnal through this two-part regulatory element. We were able to map the posi tion of an IFN-gamma responsive element in U937, IFN-gamma was able to incr ease 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 b ox binding factors, which appear to be distinct from upstream stimulatory f actors 1 and 2, are totally responsible for IFN-gamma induction of C4.