Inhibitory effects of arotinoids on tRNA biogenesis

The effects of five arotinoids (Ro 13-7410, Ro 15-0778, Ro 15-1570, Ro 13-6298, Ro 40-8757) on ribonuclease P (RNase P) activity were studied in a cell-free system derived from Dictyostelium discoideum. RNase P is a ribonucleoprotein that endonucleolytically cleaves all tRNA precursors to produce the mature 5' end. Kinetic analysis showed that these compounds behave as classical competitive inhibitors with Ki values 4.35, 3.6, 2.8 and 0.045 mM for Ro 13-6298, Ro 15-1570, Ro 15-0778 and Ro 13-7410, respectively. Ro 13-7410 was 62, 80 and 97 times more potent in inhibiting the enzyme activity as compared to Ro 15-0778, Ro 15-1570 and Ro 13-6298, respectively, whereas Ro 40-8757 showed no effect on RNase P activity. These results project the significance of the acidic polar terminus in the arotinoid molecule binding to the enzyme. The kinetics of inhibition reflects allosteric interactions of arotinoids with D. discoideum RNase P. Moreover, our findings indicate that the inhibitory effects of arotinoids on tRNA biogenesis can be mediated through mechanisms not involving the retinoid nuclear receptors.