Effect of interferon on protein translation during growth stages of 3T3 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 beta-interferon during specific periods of growth of mouse 3T3-F442A and 3T3-C2 cells. Treatment of preconfluent mouse 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-2 alpha 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-2 alpha, and diminished eIF-2B activity. These results suggest that interferon regulates the initiation of protein synthesis by a mechanism involving PKR, eIF-2 alpha 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.