mRNA translation is compartmentalized to the endoplasmic reticulum following physiological inhibition of cap-dependent translation

  1. Rachel S. Lerner and
  2. Christopher V. Nicchitta
  1. Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA

Abstract

Eukaryotic cells utilize a cycle of ribosome trafficking on the endoplasmic reticulum (ER) to partition mRNAs between the cytosol and ER compartments. In this process, ribosomes engaged in the synthesis of signal sequence-bearing proteins are trafficked to the endoplasmic reticulum via the signal-recognition particle pathway and are released from the ER upon translation termination. Though the processes governing ribosome trafficking to the ER are well understood, little is known regarding the complementary ribosome release process. In this study, Coxsackie B virus (CBV) infection was used to inactivate the initiation stage of protein synthesis, thereby limiting translation to the elongation and termination stages. Ribosome partitioning between the cytosol and ER compartments was examined to determine the role of termination in ribosome release from the ER. CBV infection resulted in efficient cleavage of eIF4G and PABP, coincident with polyribosome breakdown in the cytosol and ER compartments. Termination resulted in the continued association of ribosomes with the ER compartment, rather than the expected process of ribosome release. Analyses of ribosome/mRNA loading patterns in the cytosol and ER revealed that CBV infection was accompanied by a suppression of mRNA translation in the cytosol and the sustained, although reduced, translation in the ER compartment. Direct biosynthetic labeling experiments demonstrated that protein synthesis on the ER was enhanced relative to the cytosol following CBV infection. In total, these data demonstrate that ribosome and mRNA release from the ER is regulated independent of translation termination and identify the ER as a privileged site for protein synthesis.

Keywords

Footnotes

  • Reprint requests to: Christopher V. Nicchitta, Department of Cell Biology, Box 3709, Duke University Medical Center, Durham, NC 27710, USA; e-mail: c.nicchitta{at}cellbio.duke.edu; fax: (919) 684-5481.

  • Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.2318906.

  • Abbreviations:CBV, Coxsackie B3 virus; eIF, eukaryotic initiation factor; ER, endoplasmic reticulum; IRES, internal ribosome-entry site; PABP, poly(A)-binding protein; SRP, signal recognition particle; UPR, unfolded protein response; z-vad-fmk, benzyloxycarbonyl-VAD-fluoromethyl ketone.

    • Received December 9, 2005.
    • Accepted January 20, 2006.
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