Cloning of a Novel Prolyl 4-Hydroxylase Subunit Expressed in the Fibrous Cap of Human Atherosclerotic Plaque

BACKGROUND: The production of collagen is fundamental to atherosclerosis and critically dependent on posttranslational modification by prolyl 4-hydroxylase. METHODS AND RESULTS: We report the cloning of a novel prolyl 4-hydroxylase catalytic (alpha) subunit from human vascular smooth muscle cells. The peptide displayed conservation of critical residues for interacting with Fe2+ and 2-oxoglutarate, essential cosubstrates for prolyl 4-hydroxylase activity. Furthermore, when the recombinant protein was expressed in cells, it associated with the beta-subunit of prolyl 4-hydroxylase and could catalyze prolyl 4-hydroxylation of a collagen-like peptide. The tissue distribution was dissimilar from that of the 2 previously cloned alpha-subunits, suggesting a role beyond redundancy. Importantly, the novel gene was expressed in the fibrous cap of human carotid atherosclerotic lesions. CONCLUSIONS: The discovery of a novel prolyl 4-hydroxylase alpha-subunit, here termed the alpha(III)-subunit, suggests a new participant in collagen synthesis that, in view of the expression findings, may be relevant to atherosclerotic disease.