THE HUMAN BETA-2 INTEGRIN CD18 PROMOTER CONSISTS OF 2 INVERTED ETS CIS-ELEMENTS

To define the minimal promoter responsible for expression of CD18 in m yeloid and lymphoid cells, we generated 5' and 3' deletion constructs of a-segment extending 785 bp upstream and 19 bp downstream of a major transcription start site and determined their effects on driving expr ession of the luciferase reporter gene in transfected hematopoietic ce ll lines. A region extending from nucleotides (nt) -302 to +19 was suf ficient for cell-restricted and phorbol ester-inducible expression. DN ase I footprinting of this region revealed two adjacent protected segm ents extending from nt -81 to -68 (box A) and -55 to - 41 (box B). Whe n a construct of 47 nt in length containing box A and box B and lackin g other 3' or 5' elements was cloned into a promoterless vector, it co nferred tissue-specific and phorbol ester-inducible expression. Gel re tardation revealed that the protein components of two major protein-DN A complexes that form on both box A and box B and are required for tra nscriptional activation are members of the Ets oncoprotein family; one is related to the GA-binding protein (GABP), and the other is related to PU.1/Spi-1. The minimal CD18 promoter, lacking TATA, CAAT, and ini tiator elements and consisting primarily of Ets repeats, may exemplify an emerging class of promoters with which the concerted binding of Et s factors is necessary and sufficient to mediate transcriptional activ ation through direct recruitment of the basal transcription machinery.