TRANSCRIPTIONAL REGULATION OF THE HUMAN BIGLYCAN GENE

The small leucine-rich proteoglycan biglycan is involved in several ph ysiological and pathophysiological processes through the ability of it s core protein to interact with other extracellular matrix molecules a nd transforming growth factor-beta (TGF-beta). To learn more about the regulation of biglycan core protein expression, we have cloned and se quenced 1218 base pairs from the 5'-flanking region of the human bigly can gene, demonstrated functional promoter activity, and investigated the molecular mechanisms through which various agents modulate its tra nscriptional activity. Sequencing revealed the presence of several cis -acting elements including multiple AP-2 sites and interleukin-6 respo nse elements, a NF-kappa B site, a TGF-beta negative element, and an E -box. The TATA and CAAT box-lacking promoter possesses many features o f a growth-related gene, e.g. a GC-rich immediate 5' region, many Sp1 sites, and the use of multiple transcriptional start sites. Transient transfections of the tumor cell lines MG-63, SK-UT-1, and T47D with va rious biglycan 5'-flanking region-luciferase reporter gene constructs showed that the proximal 78 base pairs are sufficient for full promote r activity. Several agents among them interleukin-6, and tumor necrosi s factor-alpha. were capable of altering biglycan promoter activity. H owever, in MG-63 cells, TGF-beta 1 failed to increase either activity of the biglycan promoter constructs or specific transcription from the endogenous biglycan gene. Since TGF-beta 1 also did not alter the sta bility of cytoplasmic biglycan mRNA as determined from Northern analys is after inhibition of transcription with 5,6-dichloro-1 beta-D-ribofu ranosylbenzimidazole, an as yet unidentified nuclear post-transcriptio nal mechanism was considered responsible for the TGF-beta effect in th is cell type. These results might help to elucidate the molecular path ways leading to pathological alterations of biglycan expression observ ed in atherosclerosis, glomerulonephritis, and fibrosis.