Inhibition of cap-dependent translation via phosphorylation of eIF4G by protein kinase Pak2.
Translation is downregulated in response to a variety of moderate stresses, including serum deprivation, hyperosmolarity and ionizing radiation. The cytostatic p21-activated protein kinase 2 (Pak2)/gamma-PAK is activated under the same stress conditions. Expression of wild-type Pak2 in cells and addition of Pak2 to reticulocyte lysate inhibit translation, while kinase-inactive mutants have no effect. Pak2 binds to and phosphorylates initiation factor (eIF)4G, which inhibits association of eIF4E with m(7)GTP, reducing initiation. The Pak2-binding site maps to the region on eIF4G that contains the eIF4E-binding site; Pak2 and eIF4E compete for binding to this site. Using an eIF4G-depleted reticulocyte lysate, reconstitution with mock-phosphorylated eIF4G fully restores translation, while phosphorylated eIF4G reduces translation to 37%. RNA interference releases Pak2-induced inhibition of translation in contact-inhibited cells by 2.7-fold. eIF4G mutants of the Pak2 site show that S896D inhibits translation, while S896A has no effect. Activation of Pak2 in response to hyperosmotic stress inhibits cap-dependent, but not IRES-driven, initiation. Thus, a novel pathway for mammalian cell stress signaling is identified, wherein activation of Pak2 leads to inhibition of cap-dependent translation through phosphorylation of eIF4G.
Ling
Jun
J
Department of Biochemistry, University of California, Riverside, CA 92521, USA.
Morley
Simon J
SJ
Traugh
Jolinda A
JA
D001665:Binding Sites; D002460:Cell Line; D015536:Down-Regulation / Q000502:physiology*; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism*; D006801:Humans; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D012315:RNA Caps / Q000037:antagonists & inhibitors* / Q000502:physiology*; D034622:RNA Interference; D012156:Reticulocytes / Q000201:enzymology; D012270:Ribosomes / Q000502:physiology; D054462:p21-Activated Kinases
C113920:EIF4G1 protein, human; D039603:Eukaryotic Initiation Factor-4G; D012315:RNA Caps; C515907:PAK2 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases