Double-stranded RNA-dependent protein kinase activates transcription factor NF-kappa B by phosphorylating I kappa B.

Abstract

The induction of interferon (IN) genes by viruses or double-stranded RNA (dsRNA) requires the assembly of a complex set of trnscription factors on responsive DNA elements of ION gene promoters. One of the factors necessary for regulating IFN-P gene transcription is nuclear factor NF-KB, the activation of which is triggered by dsRNA. It has previously been suggested that the dsRNA-activated p68 protein kinase (PKR) may act as an Inducer-receptor, transducing the signal from dsRNA to NF-ucB through phosphorylation of the inhibitor IKB. We present direct evidence that PKR can phosphorylate IKB-a (MAD-3) and activate NF-KB DNA binding activity in vitro. We further show that dsRNA induces an unusual phosphorylated form of IKB-a. The expression of a transdominant mutant PKR is able to perturb the dsRNAmediated signaling pathway in vivo, suggesting a role for this kinase in IFN-P gene induction.

Double-stranded RNA-activated protein kinase is required for the LPS-induced activation of STAT1 inflammatory signaling in rat brain glial cells

“…Inhibition of NF-B activity did not affect the phosphorylation of PKR by LPS, whereas inhibition of PKR blocked NF-B activity. It has been reported that PKR can activate NF-B, either directly by phosphorylating its inhibitor I-B␣ (Kumar et al, 1994) or indirectly by activating the I-B kinase (IKK) complex (Gil et al, 2001). In addition, there are reports that activation of NF-B mediates transcription of IFN-␤ (Jacobs and Ignarro, 2001).…”

“…In addition to its role in translational regulation, PKR functions in signal transduction at the transcriptional level. PKR has been shown to mediate the activation of important transcription factors such as I B (Kumar et al, 1994;Zamanian-Daryoush et al, 2000), Tat protein encoded by the human immunodeficiency virus (HIV), the 90-kDa NFAT protein, M-phase-specific dsRNA-binding phosphoprotein MPP4, IFN regulatory factor-1 (IRF-1), and activating transcription factor-2 (ATF-2) (Kirchhoff et al, 1995;McMillan et al, 1995;Langland et al, 1999;Patel et al, 1999). These, in turn, regulate the expression of proinflammatory genes, including inducible nitric oxide synthase (iNOS), interleukin-1 (IL-1), and IL-6 (Uetani et al, 2000).…”

PKR; a sentinel kinase for cellular stress

“…Thus, there are no obvious clues in terms of sequence homology as to the identity of novel PKR substrates. PKR regulates NF-kB through phosphorylation of its inhibitor, IkB (Kumar et al, 1994). Although IkB can be phosphorylated by PKR in vitro, it is probably not a direct PKR substrate in vivo.…”

“…Although the PKR substrate in this pathway has not been identi®ed, the kinase activity of PKR is required and it does not perform only a sca olding role. Recombinant active PKR added to cell extracts can activate NF-kB DNA binding activity and transdominant mutants of PKR disrupt NF-kB dependent reporter activity in transient transfection assays (Kumar et al, 1994).…”

Evading innate immunity in nonviral mRNA delivery: don’t shoot the messenger

“…Besides this regulatory translational controlling function, PKR is also involved in various signaling pathways. Active PKR has been shown to provoke release of NF-κB from its inhibitory subunit, IκB, by stimulation of the IKK kinase complex, thereby activating the NF-κB transcription factor and promoting the expression of multiple genes [57]. Finally PKR also induces cellular apoptosis, which serves as a natural process of preventing further viral infection [56,58].…”