The heme-regulated eukaryotic initiation factor 2 alpha kinase - A potential regulatory target for control of protein synthesis by diffusible cases

Nitric oxide (NO) has been reported to inhibit protein synthesis in eukaryo tic cells by increasing the phosphorylation of the ru-subunit of eukaryotic initiation factor (eIF) 2, However, the mechanism through which this incre ase occurs has not been characterized. In this report, we examined the effe ct of the diffusible gases nitric oxide (NO) and carbon monoxide (CO) on th e activation of the heme-regulated eIF2 alpha kinase (HRI) in rabbit reticu locyte Lysate. Spectral analysis indicated that both NO and CO bind to the N-terminal heme-binding domain of HRI. Although NO was a very potent activa tor of HRI, CO markedly suppressed NO-induced HRI activation. The NO-induce d activation of HRI was transduced through the interaction of NO with the N -terminal heme-binding domain of HRI and not through S-nitrosylation of HRI , We postulate that the regulation of HRI activity by diffusible gases may be of wider physiological significance, as we further demonstrate that NO g enerators increase eIF2 alpha phosphorylation levels in NT2 neuroepithelial and C2C12 myoblast cells and activate HRI immunoadsorbed from extracts of these non-erythroid cell lines.