Characterization of rat CD14 promoter and its regulation by transcription factors AP1 and Sp family proteins in hepatocytes

CD14, a 55 kDa glycoprotein, serves as a lipopolysaccharide (LPS) recogniti on molecule. CD14 is a monocyte differentiation antigen expressed by myeloi d-derived cells, or other cells such as hepatocytes, as either a membrane-b ound protein or a soluble serum protein. Increasing evidence indicates that soluble CD14 in plasma is an acute-phase protein derived, among other sour ces, from liver cells. Although information is available on the cellular ex pression of CD14. little is known about the cis- and transacting factors th at regulate basal CD14 transcription in liver cells. We show here that live r cells have a relatively high basal CD14 transcription rate as determined by nuclear run-on assay. We cloned and sequenced an 853 bp 5'-flanking regi on of the rat CD14 gene and demonstrated functional promoter activity in li ver cells. Sequence analysis revealed that, like in the human and mouse CD1 4 genes, multiple Sp1 and AP1 binding elements exist in rat CD14. Site-dire cted mutagenesis and transient transfection assays demonstrated that an Sp1 element located at - 836 and an AP1 element located at -270 are required f or basal promoter activity in liver cells. Electrophoretic mobility shift a ssays indicate that both Sp1 and Sp3 nuclear factors interact with the -836 Sp1 element, while the AP1-related proteins Fra-2 and JunD bind to the AP1 motif These data provide novel insights into the regulation of basal CD14 expression in liver cells. (C) 2000 Elsevier Science B.V. All rights reserv ed.