cDNA cloning and expression of the mRNA for cytochrome P‐450_kd which shows a fatty acid ω‐hydroxylating activity

We have recently purified three distinct forms of fatty acid ω‐hydroxylase cytochrome P‐450 (P‐450), designated P‐450_ka‐1, P‐450_ka‐2 and P‐450_kd, from rabbit kidney cortex microsomes, and isolated and sequenced cDNA clones corresponding to P‐450_ka‐1 and P‐450_ka‐2 [Yokotani, N., Bernhardt, R., Sogawa, K., Kusunose, E., Gotoh, M., Kusunose, M. & Fujii‐Kuriyama, Y. (1989) J. Biol. Chem. 264, 21665–21669]. The present paper describes cloning, sequencing and expression of a cDNA for the third fatty acid, ω‐hydroxylase, P‐450_kd, from a rabbit kidney cDNA library. The cDNA for P‐450_kd encodes a polypeptide of 511 amino acids with sequence similarity of 87% to P‐450_ka‐1. Its deduced NH₂‐terminal sequence of amino acids 5–24 is in complete agreement with the NH₂‐terminal sequence of P‐450_kd. The identity of the cDNA was further confirmed by its expression in COS‐7 cells. When ¹⁴C‐labeled lauric acid was added to the culture medium of COS‐7 cells transfected with the cDNA, significant amounts of radioactive dodecanedioic acid, together with ω‐ and (ω‐1)‐hydroxylauric acids, were produced. Microsomes prepared from the transfected cells also efficiently catalyzed the ω‐ and (ω‐1)‐hydroxylation of lauric acid without formation of dodecanedioic acid. RNA blot analysis demonstrated that the mRNA for P‐450_kd gave a single band at the approximately 2.6‐kb position. The mRNA for P‐450_kd was expressed in the liver and kidney, but not in many other tissues examined. Treatment of rabbits with clofibrate resulted in a elevated level of mRNA for P‐450_kd in both liver and kidney. Furthermore, the mRNA was remarkably increased in the kidney by the administration of cyclosporin A.