Inhibition of Ribonuclease P Activity by Retinoids

Abstract The effect of two naturally occurring (retinol and all-trans retinoic acid) and two synthetic (isotretinoin and acitretin) analogs of vitamin A (retinoids) on tRNA biogenesis was investigated employing the RNase P ofDictyostelium discoideum as an in vitroexperimental system. RNase P is an ubiquitous and essential enzyme that endonucleolytically cleaves all tRNA precursors to produce the mature 5′ end. All retinoids tested revealed a dose-dependent inhibition of RNase P activity, indicating that these compounds may have a direct effect on tRNA biogenesis. Detailed kinetic analysis showed that all retinoids behave as classical competitive inhibitors. The K i values determined were 1475 μmfor retinol, 15 μm for all-trans retinoic acid, 20 μm for isotretinoin, and 8.0 μmfor acitretin. On the basis of these values acitretin is a 184, 2.5, and 1.9 times more potent inhibitor, as compared with retinol, isotretinoin, and all-trans retinoic acid, respectively. Taking into account that retinoids share no structural similarities to precursor tRNA, it is suggested that their kinetic behavior reflects allosteric interactions of these compounds with hydrophobic site(s) ofD. discoideum RNase P.