Sp1 is a critical factor for the monocytic specific expression of human CD14

CD14 is a membrane glycoprotein expressed specifically on monocytes and macrophages, and its expression is markedly increased during the process of monocyte differentiation. In order to study CD14 gene regulation, the human CD14 gene was cloned from a partial EcoRI digested chromosome 5 library. A 5.5-kilobase genomic clone contained the full-length CD14 coding sequence and 4.2 kilobases of 5'-upstream sequence. One major and one minor transcription start site were identified 101 and 130 base pairs (bp) upstream, respectively, from the protein translation start ATG. A DNA fragment containing 128 bp of upstream sequence had strong, monocyte-specific promoter activity in the CD14 positive monocytic cell line Mono Mac 6 as compared to the nonmonocytic 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 activity, and these results, together with transactivation experiments, demonstrate that Sp1 plays a critical role in the tissue-specific expression of CD14 in monocytic cells. CD14 Sp1 site oligonucleotides bound preferentially to a 105-kDa Sp1 species, which is present in higher relative levels in monocytic than non-monocytic cells, suggesting that modification of Sp1, such as phosphorylation, may explain how the Sp1 site mediates monocytic specific promoter activity.