HUMAN PKR TRANSFECTED INTO MURINE CELLS STIMULATES EXPRESSION OF GENES UNDER CONTROL OF THE HIV-1 OR HTLV-1 LTR

We have analyzed the effect of transfection into murine NIH/3T3 cells of the human dsRNA-activated kinase PKR on the expression of the beta- galactosidase reporter gene, placed under control of the HIV1 or the H TLV-I LTR. beta-Galactosidase expression is stimulated when the report er plasmids are cotransfected with wild-type PKR but inhibited when co transfected with a catalytically inactive mutant PKR. In the case of H IV1, beta-galactosidase expression was not stimulated when cotransfect ion was carried out with PKR harboring mutations in the dsRNA binding domains, indicating that stimulation depends on the classical mode of PKR activation through dsRNA binding. In contrast, the dsRNA binding m utants of PKR could still partially stimulate beta-galactosidase expre ssion from the HTLV-I LTR, suggesting that PKR activation in this case may involve different/additional mechanisms. These results show that, in addition to the known down-regulation of protein synthesis through elF2 phosphorylation, PKR can also positively stimulate gene expressi on in vivo, most probably through phosphorylation of a substrate disti nct from elF2. (C) 1995 Academic Press, Inc.