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The mechanism through which cisplatin ( cis -diamminedichloroplatinum) inhibits protein synthesis in rabbit reticulocyte lysate was characterized. Cisplatin and transplatin caused a progressive slowing in the rate of protein synthesis culminating in the complete arrest of translation. Inhibition was dependent upon the aquation of the compounds. Addition of eukaryotic initiation factor eIF-2, eIF-2B, cAMP, MgGTP, or dithiothreitol neither prevented nor reversed the inhibition induced by cisplatin, indicating that the mechanism of cisplatin-induced translational inhibition is distinct from the inhibition induced by other toxic heavy metal ions (Hurst, R., Schatz, J. R., and Matts, R. L. (1987) J. Biol. Chem. 262, 15939–15945; Matts, R. L., Schatz, J. R., Hurst, R., and Kagen, R. (1991) J. Biol. Chem. 266, 12695–12702). Analysis of the polyribosome profile of cisplatin-inhibited reticulocyte lysate indicated that cisplatin arrests the elongation stage of protein synthesis. Agarose gel electrophoresis and Northern blot analysis indicated that mRNA and rRNA become crosslinked to form very high-molecular-weight adducts upon extraction of the RNA from polyribosomes of cisplatin-treated lysates. Diethyldithiocarbamate, which reduces the cytotoxicity of cisplatin in vivo, protects protein synthesis in reticulocyte lysate from inhibition by cisplatin. The data suggest that extensive derivatization of reticulocyte lysate RNA by cis- and transplatin results in the arrest of translating ribosomes. Since arrest of translational elongation is a well-defined mechanism of action of several families of toxins, we suggest that it may contribute to the cytotoxic action of cisplatin observed in certain populations of cells.

Interferons (IFNs) elicit a spectrum of biological responses from target cells, including inhibition of proliferation in several types of cells in vivo and in culture. The mechanism of action of IFN is complex and not fully understood. Previous evidence has indicated that part of the antiproliferative effect of IFN is due to modulation of protein translation. Here we report that there is a transient autocrine production of β-interferon during specific periods of growth of mouse 3T3-F442A and 3T3-C2 cells. Treatment of preconfluent mouse 3T3-F442A and 3T3-C2 cells with interferon reduced protein synthesis in these cells. This reduction began after 3 h of interferon treatment and was correlated with the appearance of phosphorylated double-stranded RNA dependent eIF-2α kinase (PKR) measured in vitro. This inhibition of protein synthesis was associated with diminished exchange of GTP for GDP in the elF-2·GDP complex. This diminished guanine nucleotide exchange activity was due to the inhibition of eukaryotic initiation factor eIF-2B, the factor required for the dissociation of GDP from eIF-2, and the formation of the functional eIF-2·GTP complex. The autocrine effect of IFN resulted in elevated PKR activity, increased phosphorylation of eIF-2α, and diminished eIF-2B activity. These results suggest that interferon regulates the initiation of protein synthesis by a mechanism involving PKR, eIF-2α phosphorylation, and eIF-2B activity. Since 3T3-F442A cells produce and secrete interferon in a transient fashion during growth, this regulatory mechanism may be significant in the normal growth and differentiation of these cells.