Yeast Sterol Regulatory Element-binding Protein (SREBP) Cleavage Requires Cdc48 and Dsc5, a Ubiquitin Regulatory X Domain-containing Subunit of the Golgi Dsc E3 Ligase

Emerson V Stewart,S Julie-Ann Lloyd,John S Burg,Christine C Nwosu,Robert E Lintner,Riza Daza,Carsten Russ,Karen Ponchner,Chad Nusbaum,Peter J Espenshade

doi:10.1074/jbc.m111.317370

Abstract

Schizosaccharomyces pombe Sre1 is a membrane-bound transcription factor that controls adaptation to hypoxia. Like its mammalian homolog, sterol regulatory element-binding protein (SREBP), Sre1 activation requires release from the membrane. However, in fission yeast, this release occurs through a strikingly different mechanism that requires the Golgi Dsc E3 ubiquitin ligase complex and the proteasome. The mechanistic details of Sre1 cleavage, including the link between the Dsc E3 ligase complex and proteasome, are not well understood. Here, we present results of a genetic selection designed to identify additional components required for Sre1 cleavage. From the selection, we identified two new components of the fission yeast SREBP pathway: Dsc5 and Cdc48. The AAA (ATPase associated with diverse cellular activities) ATPase Cdc48 and Dsc5, a ubiquitin regulatory X domain-containing protein, interact with known Dsc complex components and are required for SREBP cleavage. These findings provide a mechanistic link between the Dsc E3 ligase complex and the proteasome in SREBP cleavage and add to a growing list of similarities between the Dsc E3 ligase and membrane E3 ligases involved in endoplasmic reticulum-associated degradation.

Highlights

Yeast sterol regulatory element-binding protein (SREBP) proteolytic activation requires the Golgi Dsc E3 ligase and the proteasome
Through a genetic screen of the fission yeast non-essential haploid deletion collection, we identified four genes that, when deleted, confer a defect for SREBP cleavage, and we named these genes dsc1–dsc4 [8]. dsc1 was the only dsc gene with a characterized homolog, Saccharomyces cerevisiae TUL1 regulatory X; ER, endoplasmic reticulum; ERassociated degradation (ERAD), ER-associated degradation; MMS, methyl methanesulfonate; 5-FOA, 5-fluoroorotic acid; SRH, second region of homology; site-1 protease (S1P) and site-2 protease (S2P), site-1 and -2 protease, respectively
Mutagenesis and Selection of Genes Required for Sre1 Proteolytic Activation—To identify genes required for Sre1 cleavage, we developed reporter systems that rely on the N-terminal transcription factor domain of Sre1 (Sre1N) for activity

Summary

Background

Yeast sterol regulatory element-binding protein (SREBP) proteolytic activation requires the Golgi Dsc E3 ligase and the proteasome. The AAA (ATPase associated with diverse cellular activities) ATPase Cdc and Dsc, a ubiquitin regulatory X domain-containing protein, interact with known Dsc complex components and are required for SREBP cleavage These findings provide a mechanistic link between the Dsc E3 ligase complex and the proteasome in SREBP cleavage and add to a growing list of similarities between the Dsc E3 ligase and membrane E3 ligases involved in endoplasmic reticulumassociated degradation. We describe a genetic selection in S. pombe that identified new components of the Dsc E3 ligase complex required for fission yeast SREBP activation: Dsc, a UBX domain-containing protein, and Dsc6/Cdc. We describe a genetic selection in S. pombe that identified new components of the Dsc E3 ligase complex required for fission yeast SREBP activation: Dsc, a UBX domain-containing protein, and Dsc6/Cdc48 The discovery of these new members of the Dsc complex expands the similarities between the Dsc E3 ligase and the Hrd E3 ligase complex involved in ERAD. These findings provide a mechanism for delivery of proteins from the Dsc E3 ligase to the proteasome and establish the Dsc E3 ligase complex as an important system for understanding how cells identify and process specific membrane proteins

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION