title: Metabolically regulated endoplasmic reticulum-associated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase: evidence for requirement of a geranylgeranylated protein.
abstract: In mammalian cells, the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), which catalyzes the rate-limiting step in the mevalonate pathway, is ubiquitylated and degraded by the 26 S proteasome when mevalonate-derived metabolites accumulate, representing a case of metabolically regulated endoplasmic reticulum-associated degradation (ERAD). Here, we studied which mevalonate-derived metabolites signal for HMGR degradation and the ERAD step(s) in which these metabolites are required. In HMGR-deficient UT-2 cells that stably express HMGal, a chimeric protein between β-galactosidase and the membrane region of HMGR, which is necessary and sufficient for the regulated ERAD, we tested inhibitors specific to different steps in the mevalonate pathway. We found that metabolites downstream of farnesyl pyrophosphate but upstream to lanosterol were highly effective in initiating ubiquitylation, dislocation, and degradation of HMGal. Similar results were observed for endogenous HMGR in cells that express this protein. Ubiquitylation, dislocation, and proteasomal degradation of HMGal were severely hampered when production of geranylgeranyl pyrophosphate was inhibited. Importantly, inhibition of protein geranylgeranylation markedly attenuated ubiquitylation and dislocation, implicating for the first time a geranylgeranylated protein(s) in the metabolically regulated ERAD of HMGR.
authors.affiliation: Department of Human Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Gil S
authors.initials: GS
authors.lastname: Leichner
authors.forename: Rachel
authors.initials: R
authors.lastname: Avner
authors.forename: Dror
authors.initials: D
authors.lastname: Harats
authors.forename: Joseph
authors.initials: J
authors.lastname: Roitelman
mesh_terms: D002460:Cell Line; D004224:Diterpenes / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics / Q000378:metabolism*; D054878:Lipoylation / Q000502:physiology*; D008798:Mevalonic Acid / Q000378:metabolism; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D012717:Sesquiterpenes / Q000378:metabolism; D054875:Ubiquitination / Q000502:physiology*
chemical_list: D004224:Diterpenes; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; C004808:farnesyl pyrophosphate; C040155:geranylgeranic acid; C553220:HMGCR protein, human; D006903:Hydroxymethylglutaryl CoA Reductases; D008798:Mevalonic Acid