title: Valproic acid downregulates heme oxygenase-1 independently of Nrf2 by increasing ubiquitination and proteasomal degradation.
abstract: Heme oxygenase-1 (HO-1; HMOX1 in human, Hmox1 in mice) is an antioxidative enzyme affecting wide range of sub-cellular processes. It was shown to modulate tumor growth or vascular-related diseases, thus being putative molecular target for tailored therapies. Therefore it is of importance to elucidate novel compounds regulating HO-1 activity/expression and to delineate mechanisms of their action. In the present study we aimed to understand mode of action of valproic acid (VA), an antiepileptic drug, on HO-1 expression.
  
  
  
  We demonstrated that HO-1 expression is decreased by VA at protein but not mRNA level in human alveolar rhabdomyosarcoma cell line CW9019. Nrf2 transcription factor, the activator of HO-1 expression through ARE sequence, was excluded as a mediator of HO-1 decrease, as VA downregulated Bach1, a Nrf2 repressor, concomitantly upregulating ARE activation. Also miRNA-dependent inhibition was excluded as a mechanism of HMOX1 regulation. However, co-immunoprecipitation assay showed a higher level of ubiquitinated HO-1 after VA treatment. Accordingly, MG132, an inhibitor of proteasomal degradation, reversed the effect of VA on HO-1 suggesting that decrease in HO-1 expression by VA is through protein stability. The inhibitory effect of VA on HO-1 was also observed in murine cells including embryonic fibroblasts isolated from Nrf2-deficient mice, what confirms Nrf2-independent effect of the compound. Importantly, VA decreased also HO-1 expression and activity in murine skeletal muscles in vivo.
  
  
  
  Our data indicate that VA downregulates HO-1 by acting through ubiquitin-proteasomal pathway leading to decrease in protein level.
authors.affiliation: Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Mateusz
authors.initials: M
authors.lastname: Jez
authors.affiliation: Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Ciesla
authors.affiliation: Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Stepniewski
authors.affiliation: Kardio-Med Silesia, M. Curie-Skłodowskiej 10c, Zabrze, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Langrzyk
authors.affiliation: Fourth Department of Internal Medicine and Institute of Medical Biochemistry and Laboratory Medicine, First Faculty of Medicine, Charles University in Prague, Prague, Czech Republic.
authors.forename: Lucie
authors.initials: L
authors.lastname: Muchova
authors.affiliation: Fourth Department of Internal Medicine and Institute of Medical Biochemistry and Laboratory Medicine, First Faculty of Medicine, Charles University in Prague, Prague, Czech Republic.
authors.forename: Libor
authors.initials: L
authors.lastname: Vitek
authors.affiliation: Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Alicja
authors.initials: A
authors.lastname: Jozkowicz
authors.affiliation: Department of Medical Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland; Kardio-Med Silesia, M. Curie-Skłodowskiej 10c, Zabrze, Poland. Electronic address: jozef.dulak@uj.edu.pl.
authors.forename: Jozef
authors.initials: J
authors.lastname: Dulak
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects*; D054875:Ubiquitination / Q000187:drug effects*; D014635:Valproic Acid / Q000494:pharmacology*
chemical_list: D000927:Anticonvulsants; D004791:Enzyme Inhibitors; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D014635:Valproic Acid; D051547:Heme Oxygenase-1; D046988:Proteasome Endopeptidase Complex
keywords: Heme Oxygenase-1; Nrf2; Rhabdomyosarcoma; Ubiquitination; Valproic acid