SP1 IS A CRITICAL FACTOR FOR THE MONOCYTIC SPECIFIC EXPRESSION OF HUMAN CD14

CD14 is a membrane glycoprotein expressed specifically on monocytes an d macrophages, and its expression is markedly increased during the pro cess of monocyte differentiation. In order to study CD14 gene regulati on, the human CD14 gene was cloned from a partial EcoRI digested chrom osome 5 library. A 5.5-kilobase genomic clone contained the full-lengt h CD14 coding sequence and 4.2 kilobases of 5'-upstream sequence. One major and one minor transcription start site were identified 101 and 1 30 base pairs (bp) upstream, respectively, from the protein translatio n start ATG. A DNA fragment containing 128 bp of upstream sequence had strong, monocyte-specific promoter activity in the CD14 positive mono cytic cell line Mono Mac 6 as compared to the non-monocytic cell lines HeLa and REX. Four regions in this DNA fragment interact with nuclear proteins isolated from monocytic cells. The Sp1 transcription factor bound to three different regions in the CD14 promoter. Mutation of the major Sp1 binding site (-110 bp) decreased tissue-specific promoter a ctivity, and these results, together with transactivation experiments, demonstrate that Sp1 plays a critical role in the tissue-specific exp ression of CD14 in monocytic cells. CD14 Sp1 site oligonucleotides bou nd preferentially to a 105-kDa Spl species, which is present in higher relative levels in monocytic than non-monocytic cells, suggesting tha t modification of Sp1, such as phosphorylation, may explain how the Sp 1 site mediates monocytic specific promoter activity.