Proteasome-dependent endoplasmic reticulum-associated protein degradation: An unconventional route to a familiar fate

Proteasome-dependent endoplasmic reticulum-associated protein degradation: An unconventional route to a familiar fate

^*Biology Department, University of Nevada, Reno, NV 89557; and ^‡Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260

Abstract

Until recently, the degradation of aberrant and unassembled proteins retained in the endoplasmic reticulum (ER) was thought to involve unidentified ER-localized proteases. We now show that the ER-associated degradation (ERAD) of two mutant proteins that accumulate in the ER lumen is inhibited in a proteasome-defective yeast strain and when cytosol from this mutant is used in an in vitro assay. In addition, ERAD is limited in vitro in the presence of the proteasome inhibitors, 3,4-dichloroisocoumarin and lactacystin. Furthermore, we find that an ERAD substrate is exported from ER-derived microsomes, and the accumulation of exported substrate is 2-fold greater when proteasome mutant cytosol is used in place of wild-type cytosol. We conclude that lumenal ERAD substrates are exported from the yeast ER to the cytoplasm for degradation by the proteasome complex.

Footnotes

↵ † e-mail: werner{at}med.unr.edu.
↵ § e-mail: jbrodsky+@pitt.edu.
↵ ¶ To whom reprint requests should be addressed at: Department of Biology—314, University of Nevada, Reno, NV 89557. e-mail: mccracke{at}cmb.unr.edu.
William T. Wickner, Dartmouth Medical School, Hanover, NH
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Abbreviations: ER, endoplasmic reticulum; ERAD, ER-associated protein degradation; DCI, 3,4-dichloroisocoumarin.