CHARACTERIZATION OF THE MECHANISM OF CELLULAR AND CELL-FREE PROTEIN-SYNTHESIS INHIBITION BY AN ANTITUMOR RIBONUCLEASE

Onconase, a protein with anti-tumor activity, causes potent inhibition of protein synthesis in the rabbit reticulocyte lysate (IC(50)10(-11)M) and when microinjected into Xenopus oocytes (IC(50)10(-10)M). Onconase is a member of the RNase A superfamily; however, unlike RNase A, the mechanism of protein synthesis inhibition does not involve apparent degradation of lysate or cellular ribosomal RNAs. Rather, reticulocyte and oocyte tRNA is hydrolyzed after Onconase treatment. Furthermore, re-addition of tRNA to Onconase pretreated lysates or oocytes restores the translational capacity of the system. Taken together these results suggest that Onconase causes potent protein synthesis inhibition by a mechanism involving inactivation Of cellular tRNA. (C) 1994 Academic Press, Inc.