Retinoic acid and calcitriol inhibition of growth and NADH oxidase of normal and immortalized human keratinocytes.

Plasma membranes were isolated by aqueous two-phase partition from normal human keratinocytes (HKc) and from human keratinocytes immortalized with human papillomavirus type 16 DNA (HKc/HPV16). The NADH oxidase of plasma membrane vesicles of normal HKc was stimulated by epidermal growth factor whereas that of HKc/HPV16 was not. The NADH oxidase of the plasma membranes from both normal HKc and HKc/HPV16 was inhibited by calcitriol (1 alpha-1,25-dihydroxy vitamin D-3) and retinoic acid. However, with plasma membranes from HKc/HPV16 the NADH oxidase was more susceptible to inhibition by retinoic acid than were membranes from normal HKc. Similarly, clonal growth of HKc/HPV16 was inhibited by retinoic acid at lower concentrations than normal HKc whereas inhibition of clonal growth of normal HKc and HKc/HPV16 by calcitriol showed similar dose-dependencies. Comparing normal HKc and HKc/HPV16, the results demonstrate parallel inhibition of clonal growth and NADH oxidase by both retinoic acid and calcitriol of HKc/HPV16 but not of normal HKc. These results suggest that an increased sensitivity of the plasma membrane NADH oxidase of HKc/HPV16 to retinoic acid may be related to the increased sensitivity of these cells to growth control by retinoic acid. In addition, since plasma membrane NADH oxidase of HKc/HPV16 shows altered responsiveness to growth modulators such as EGF, retinoic acid and calcitriol, it appears that HKc/HPV16 express an NADH oxidase with different characteristics than those of normal HKc.