Abrogation of translation initiation factor eIF-2 phosphorylation causes malignant transformation of NIH 3T3 cells

Abstract

The interferon induced double-stranded RNA-activated kinase, PKR, has been suggested to act as a tumor suppressor since expression of a dominant negative mutant of PKR causes malignant transformation. However, the mechanism of transformation has not been elucidated. PKR phosphorylates translation initiation factor eIF-2α on Ser51, resulting in inhibition of protein synthesis and cell growth arrest. Consequently, it is possible that cell transformation by dominant negative PKR mutants is caused by inhibition of eIF-2α phosphorylation. Here, we demonstrate that in NIH 3T3 cells transformed by the dominant negative PKR mutant (PKRΔ6), eIF-2α phosphorylation is dramatically reduced. Furthermore, expression of a mutant form of eIF-2α, which cannot be phosphorylated on Ser51 also caused malignant transformation of NIH 3T3 cells. These results are consistent with a critical role of phosphorylation of eIF-2α in control of cell proliferation, and indicate that dominant negative PKR mutants transform cells by inhibition of eIF-2α phosphorylation.