Degradation of unassembled soluble Ig subunits by cytosolic proteasomes: Evidence that retrotranslocation and degradation are coupled events

Roberta Mancini, Claudio Fagioli, Anna M. Fra, Claudia Maggioni, Roberto Sitia

Research output: Contribution to journalArticle

Abstract

Many aberrant or unassembled proteins synthesized in the endoplasmic reticulum (ER) are degraded by cytosolic proteasomes. To investigate how soluble glycoproteins destined for degradation are retrotranslocated across the ER membrane, we analyzed the fate of two IgM subunits, μ and J, retained in the ER by myeloma cells that do not synthesize light chains. Degradation of μ and J is prevented by proteasome inhibitors, suggesting that both chains are retrotranslocated to be disposed of by proteasomes. Indeed, when proteasomes are inhibited, some deglycosylated J chains that no longer contain intrachain disulfide bonds accumulate in the cytosol. However, abundant glycosylated J chains are still present in the ER at time points in which degradation would have been almost complete in the absence of proteasome inhibitors, suggesting that retrotranslocation and degradation are coupled events. This was confirmed by protease protection and cell fractionation assays, which revealed that virtually all μ chains are retained in the ER lumen in a glycosylated state when proteasomes are inhibited. Association with calnexin correlated with the failure of μ chains to dislocate to the cytosol. Taken together, these results suggest that active proteasomes are required for the extraction of Ig subunits from the ER, though the requirements for retrotranslocation may differ among individual substrates.

Original languageEnglish
Pages (from-to)769-778
Number of pages10
JournalFASEB Journal
Volume14
Issue number5
Publication statusPublished - 2000

Keywords

  • IgM
  • Quality control
  • Redox regulation
  • Secretion

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry
  • Cell Biology

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