Degradation of Newly Synthesized Polypeptides by Ribosome-Associated RACK1/c-Jun N-Terminal Kinase/Eukaryotic Elongation Factor 1A2 Complex

Abstract

Folding of newly synthesized polypeptides (NSPs) into functional proteins is a highly regulated process. Rigorous quality control ensures that NSPs attain their native fold during or shortly after completion of translation. Nonetheless, signaling pathways that govern the degradation of NSPs in mammals remain elusive. We demonstrate that the stress-induced c-Jun N-terminal kinase (JNK) is recruited to ribosomes by the receptor for activated protein C kinase 1 (RACK1). RACK1 is an integral component of the 40S ribosome and an adaptor for protein kinases. Ribosome-associated JNK phosphorylates the eukaryotic translation elongation factor 1A isoform 2 (eEF1A2) on serines 205 and 358 to promote degradation of NSPs by the proteasome. These findings establish a role for a RACK1/JNK/eEF1A2 complex in the quality control of NSPs in response to stress.

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SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.01362-12.

ACKNOWLEDGMENTS

We thank Zhao-Qing Luo and Charlotte R. Knudsen for providing pGEX-6-P1/GST-eEF1A1 and pGEX-1/GST-eEF1A2, respectively. The pcDNA4/Myc-RACK1 and Myc-RACK1^R38D/K40E constructs were kindly provided by Mutsuhiro Takekawa. We are grateful to Martin Wiedmann, Martin Schmeing, Stefano Biffo, Jonathan M. Lee, and Yuri Svitkin for invaluable advice and Valerie Henderson for help with editing the manuscript. We thank Amy Archuleta and Mike Browning of Phosphosolution for providing the data for the protein phosphatase effect on p-eEF1A2.

V.G. was supported by an EMBO Long-Term fellowship. Support by NCI grant (CA051995) to Z.A.R. is gratefully acknowledged. I.T. is a CIHR Young Investigator and acknowledges support from CIHR and FRSQ. N.S. acknowledges support from CIHR and TFI.