Identification of Rbd2 as a candidate protease for sterol regulatory element binding protein (SREBP) cleavage in fission yeast

• Published in: Biochemical and biophysical research communications Vol. 468; no. 4; pp. 606 - 610
• Main Authors: Kim, Jinsil, Ha, Hye-Jeong, Kim, Sujin, Choi, Ah-Reum, Lee, Sook-Jeong, Hoe, Kwang-Lae, Kim, Dong-Uk
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25-12-2015
• Subjects: 60 APPLIED LIFE SCIENCES; ANOXIA; Binding Sites; CALORIMETRY; Cell Proliferation - physiology; CLEAVAGE; Enzyme Activation; GENE REGULATION; HOMEOSTASIS; Hypoxia; LIGASES; Lipid homeostasis; MUTANTS; Oxidative Stress - physiology; Oxygen - metabolism; Peptide Hydrolases - chemistry; Peptide Hydrolases - metabolism; Peptide Hydrolases - physiology; PHENOTYPE; Protein Binding; PROTEOLYSIS; Rbd2; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - physiology; Schizosaccharomyces - metabolism; Schizosaccharomyces pombe; Sre1; SREBP; Sterol Regulatory Element Binding Proteins - chemistry; Sterol Regulatory Element Binding Proteins - metabolism; STEROLS; Substrate Specificity; TRANSCRIPTION FACTORS; YEASTS; Rbd2; Schizosaccharomyces pombe; Hypoxia; SREBP; Lipid homeostasis; Sre1
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2015.10.165

Lipid homeostasis in mammalian cells is regulated by sterol regulatory element-binding protein (SREBP) transcription factors that are activated through sequential cleavage by Golgi Site-1 and Site-2 proteases. Fission yeast SREBP, Sre1, engages a different mechanism involving the Golgi Dsc E3 ligase complex, but it is not clearly understood exactly how Sre1 is proteolytically cleaved and activated. In this study, we screened the Schizosaccharomyces pombe non-essential haploid deletion collection to identify missing components of the Sre1 cleavage machinery. Our screen identified an additional component of the SREBP pathway required for Sre1 proteolysis named rhomboid protein 2 (Rbd2). We show that an rbd2 deletion mutant fails to grow under hypoxic and hypoxia-mimetic conditions due to lack of Sre1 activity and that this growth phenotype is rescued by Sre1N, a cleaved active form of Sre1. We found that the growth inhibition phenotype under low oxygen conditions is specific to the strain with deletion of rbd2, not any other fission yeast rhomboid-encoding genes. Our study also identified conserved residues of Rbd2 that are required for Sre1 proteolytic cleavage. All together, our results suggest that Rbd2 is a functional SREBP protease with conserved residues required for Sre1 cleavage and provide an important piece of the puzzle to understand the mechanisms for Sre1 activation and the regulation of various biological and pathological processes involving SREBPs.
•An rbd2-deleted yeast strain shows defects in growth in response to low oxygen levels.•rbd2-deficient cells fail to generate cleaved Sre1 (Sre1N) under hypoxic conditions.•Expression of Sre1N rescues the rbd2 deletion mutant growth phenotype.•Rbd2 contains conserved residues potentially critical for catalytic activity.•Mutation of the conserved Rbd2 catalytic residues leads to defects in Sre1 cleavage.