TRANSCRIPTIONAL REGULATION OF C-FES IN MYELOID-LEUKEMIA CELLS

The c-Fes proto-oncogene encodes a myeloid-specific protein-tyrosine k inase that is expressed preferentially in differentiated myeloid cells , but not in early myeloblast progenitor cells. To examine the basis f or the phenotypic expression of c-Fes, the transcription initiation si tes of the human c-Fes gene were mapped in myeloid leukemia cells and regulatory elements in the genomic c-Fes sequence were characterized, Two major transcription initiation sites were found in the myeloid leu kemia cell line THP-1 which delineated exon 1 to be 72-83 bp. When the activity of the CAT reporter gene under the control of the c-Fes prom oter region, untranslated exon 1 and intron was measured in TF-1, K562 and MCF-7 cells, only TF-1 cells exhibited chloramphenicol acetyltran sferase activity. In contrast, all cell lines supported reporter gene activity when intron 1 was deleted. Deletion analyses revealed a negat ive regulatory region in intron 1, which was localized by Southwestern analysis and DNA footprinting to a 14 bp region. This negative regula tory region suppressed reporter CAT activity in K562 and TF-1 cells wh en inserted downstream to the SV40 early promoter. These results sugge st that the tissue-specific expression of c-Fes may result, in part, f rom the negative regulation of transcription in myeloid and nonmyeloid cells.