Vascular smooth muscle biglycan represents a highly conserved proteoglycan within the arterial wall

Two overlapping cDNA clones containing sequences homologous to human bone biglycan were isolated from a rat vascular smooth muscle (VSM) cell cDNA library. Nucleotide sequence analysis demonstrated that these clones encoded the rat VSM biglycan complete core protein sequence. A high degree of genetic conservation was observed for biglycan since nucleotide sequence homology comparisons revealed an 88% homology occurring between rat and human biglycan cDNA coding regions. The deduced core protein for the secreted form of VSM biglycan was found to be composed of ten leucine-rich repeating units whose consensus sequence was similar to that present in human bone and bovine cartilage biglycans. Protein homology comparisons revealed that the mature rat VSM biglycan core protein was 97% homologous to both human bone and bovine cartilage biglycan core proteins. Most of the amino acid substitutions in the secreted form of rat VSM biglycan are of the conservative type thereby maintaining the hydrophobic property of this proteoglycan within the arterial wall. The highest frequency of amino acid substitutions occurring between rat, bovine and human biglycan core proteins was found to reside within a small hypervariable region located near the N-terminus of these proteoglycans. Rat VSM biglycan was found to contain dinucleotide repeat elements located in the 3' untranslated region of its mRNA which may influence the expression of this transcript. Biglycan mRNA levels were not found to vary significantly as a function of VSM cell density. However, biglycan transcript levels did vary significantly as a function of VSM cell growth state. Similar studies revealed that collagen, fibronectin, and laminin were able to influence biglycan mRNA levels in quiescent VSM cells.(ABSTRACT TRUNCATED AT 250 WORDS)