title: Involvement of ALAD-20S Proteasome Complexes in Ubiquitination and Acetylation of Proteasomal α2 Subunits.
abstract: The ubiquitin-proteasome pathway has gained attention as a potential chemotherapeutic target, owing to its importance in the maintenance of protein homeostasis and the observation that cancer cells are more dependent on this pathway than normal cells. Additionally, inhibition of histone deacetylases (HDACs) by their inhibitors like Vorinostat (SAHA) has also proven a useful strategy in cancer therapy and the concomitant use of proteasome and HDAC inhibitors has been shown to be superior to either treatment alone. It has also been reported that delta-aminolevulinic acid dehydratase (ALAD) is a proteasome-associated protein, and may function as an endogenous proteasome inhibitor. While the role of ALAD in the heme biosynthetic pathway is well characterized, little is known about its interaction with, and the mechanism by which it inhibits, the proteasome. In the present study, this ALAD-proteasome complex was further characterized in cultured prostate cancer cells and the effects of SAHA treatment on the regulation of ALAD were investigated. ALAD interacts with the 20S proteasomal core, but not the 19S regulatory cap. Some ubiquitinated species were detected in ALAD immunoprecipitates that have similar molecular weights to ubiquitinated proteasomal α2 subunits, suggesting preferred binding of ALAD to ubiquitinated α2. Additionally, SAHA treatment increases levels of ALAD protein and an acetylated protein with a molecular weight similar to the ubiquitinated α2 subunit. Thus, the results of this study suggest that ALAD may play a regulatory role in a previously unreported post-translational modification of proteasomal α subunits.
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State School of Medicine, Detroit, Michigan.
authors.forename: Sara M
authors.initials: SM
authors.lastname: Schmitt
authors.affiliation: Department of Public Health Sciences, Henry Ford Health System, Detroit, Michigan.
authors.forename: Christine
authors.initials: C
authors.lastname: Neslund-Dudas
authors.affiliation: Department of Pharmacology, Wayne State School of Medicine, Detroit, Michigan.
authors.forename: Min
authors.initials: M
authors.lastname: Shen
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State School of Medicine, Detroit, Michigan.
authors.forename: Cindy
authors.initials: C
authors.lastname: Cui
authors.affiliation: Department of Biochemistry, Wayne State School of Medicine, Detroit, Michigan.
authors.forename: Bharati
authors.initials: B
authors.lastname: Mitra
authors.affiliation: Department of Oncology and Karmanos Cancer Institute, Wayne State School of Medicine, Detroit, Michigan.|Department of Pharmacology, Wayne State School of Medicine, Detroit, Michigan.
authors.forename: Q Ping
authors.initials: QP
authors.lastname: Dou
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000818:Animals; D002417:Cattle; D045744:Cell Line, Tumor; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008297:Male; D000623:Porphobilinogen Synthase / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D000077337:Vorinostat
chemical_list: D006877:Hydroxamic Acids; D000077337:Vorinostat; D046988:Proteasome Endopeptidase Complex; D000623:Porphobilinogen Synthase
keywords: ACETYLATION; ALAD; PROSTATE CANCER; PROTEASOME; UBIQUITINATION