Regulation, regulatory activities, and function of biglycan.

Biglycan is a member of the small leucine repeat proteoglycan family (SLRP). The biglycan gene is located on the X chromosome. Based on the amino acid sequence, the protein core of biglycan can be divided into six distinct domains: (1) a signal sequence, (2) a propeptide region, (3) a N-terminal glycosaminoglycan attachment region, (4) a cysteine loop, followed by (5) a leucine- rich repeat region domain (that makes up over 66% of the core protein), and (6) a final cysteine loop. Biglycan has been found in almost every organ within our body, but it is not uniformly distributed within an organ. Biglycan has been shown to be expressed on the cell surface, pericellularly, and sometimes within the extracellular matrices of a range of specialized cell types within the organ. Its expression pattern has been shown to be altered by growth factors and certain pathologic conditions. The regulation of biglycan expression occurs by both transcriptional and nontranscriptional mechanisms. The currently proposed biglycan functions appear to be dependent on the particular microenvironment and on the organ in question. In this review, we will focus on gene and protein structure, localization, expression, regulation, and function.