ABROGATION OF TRANSLATION INITIATION-FACTOR EIF-2 PHOSPHORYLATION CAUSES MALIGNANT TRANSFORMATION OF NIH 3T3 CELLS

The interferon induced double-stranded RNA-activated kinase, PKR, has been suggested to act as a tumor suppressor since expression of a domi nant negative mutant of PKR causes malignant transformation. However, the mechanism of transformation has not been elucidated. PKR phosphory lates translation initiation factor eIF-2 alpha on Ser51, resulting in inhibition of protein synthesis and cell grow th arrest. Consequently , it is possible that cell transformation by dominant negative PKR mut ants is caused by inhibition of eIF-2 alpha phosphorylation. Here, we demonstrate that in NIH 3T3 cells transformed by the dominant negative PKR mutant (PKR Delta 6), eIF-2 alpha phosphorylation is dramatically reduced. Furthermore, expression of a mutant form of eIF-2 alpha whic h cannot be phosphorylated on Ser51 also caused malignant transformati on of NIH 3T3 cells. These results are consistent with a critical role of phosphorylation of eIF-2 alpha in control of cell proliferation, a nd indicate that dominant negative PKR mutants transform cells by inhi bition of eIF-2 alpha phosphorylation.