Regulatory elements of microfibril-associated glycoprotein-1 gene expression in muscle cells

The Mfap2 gene encodes the microfibril-associated glycoprotein-1 (MAGP1), an extracellular matrix protein of microfibrillar structures. The gene is transcribed from a major transcription start site embedded in a CpG island. Mapping of transcriptionally active regions in the 5' flanking sequence identified a region, located between nucleotides -339 and -109 as the Mfap2 basal promoter. Site-directed and random mutagenesis demonstrated that a KLF sequence motif at -256/-270, an E-box at -222/-229, and a GC-box at -117/-125, are critical for the promoter function. Using electrophoresis mobility shift assays, we find that the KLF motif mediates the binding of GKLF/KLF4, whereas the E-box is a target for both Upstream Stimulatory Factors 1 and 2, and the GC box at -117/-125 forms complexes with Sp1 and Sp3, but not with Sp4 or AP2alpha. A sequence element spanning position -150 may represent the binding motif of an uncharacterized transcription factor. The basal transcriptional regulation of Mfap2 in muscle cells is discussed.