Human integrin β₃ gene expression: Evidence for a megakaryocytic cell- specific cis-acting element

The human integrin β₃ participates in a wide range of adhesive biologic functions and is expressed in a selected subset of tissues, but little is known about the cis-acting DNA elements or trans-acting factors responsible for this regulation. Using cell lines characterized for β₃ expression, a number of upstream regulatory regions in the β₃ gene were identified. (1) The three regions from -1159 to -584, -290 to -146, and -126 to -115 demonstrated positive, negative, and negative activity, respectively. (2) The region from -115 to +29 of the β₃ gene was sufficient for cell- specific activity. Deletion of the sequence from -115 to -89 produced a 6- to 40-fold reduction in reporter gene activity in β₃-expressing megakaryocytic cell lines (K562, Dami, and HEL), but only a 1.7- and 2.7-fold reduction, respectively, in β₃-expressing endothelial and melanoma cell lines, and 1.3- and 2.8-fold reduction, respectively, in non-β₃-expressing Chinese hamster ovary and 293 cell lines. This sequence also bound nuclear proteins in a cell-specific manner in electrophoretic mobility shift assays. Mutational analysis indicated that the sequence GAGGGG (positions -113 to - 108) is a megakaryocytic cell line-specific cis-acting element. (3) The region from -89 to +29 promoted lower activity in all cell lines. We also provide evidence that a CCCACCC sequence at position -70 has transcriptional activity, most likely through the Sp1 transcription factor. These data supply the first detailed map of the transcriptional regulatory elements of the 5' region of the β₃ gene, define positive regulatory sequences with potent megakaryocyte preferential activity, and indicate that the ubiquitous transcription factor, Sp1, may augment β₃ gene expression.