Lack of collagen type specificity for lysyl hydroxylase isoforms

Lysyl hydroxylase is the enzyme catalyzing the formation of hydroxylysyl re sidues in collagens. Large differences in the extent of hydroxylysyl residu es are found among collagen types. Three lysyl hydroxylase isoenzymes (LH1, LH2, LH3) have recently been characterized from human and mouse tissues. N othing is known about the distribution of these isoforms within cells or wh ether they exhibit collagen type specificity, We measured mRNA levels of th e three isoforms, as well as the mRNAs of the main collagen types I, III, I V, and V and the alpha subunit of prolyl 4-hydroxylase, another enzyme invo lved in collagen biosynthesis, in different human cell lines. Large variati ons mere found in mRNA expression of LH1 and LH2 but not LH3. Immunoblottin g mas utilized to confirm the results of Northern hybridization. The levels of mRNA of LH1, LH2, and the alpha subunit of prolyl 4-hydroxylase showed significant correlations with each other. The LH3 mRNA levels did not corre late with those of LH1, LH2, or the alpha subunit of prolyl 4-hydroxylase, clearly indicating a difference in the regulation of LH3. No correlation wa s observed between LH isoforms and individual collagen types, indicating a lack of collagen type specificity for lysyl hydroxylase isoforms. Our obser vations suggest that LH1, LH2, and the alpha subunit of prolyl 4-hydroxylas e are coregulated together with total collagen synthesis but not with the s pecific collagen types and indicate that LH3 behaves differently from LH1 a nd LH2, implying a difference in their substrates, These observations set t he basis for further studies to define the functions of lysy1 hydroxylase i soforms.