title: Modulation of heme/substrate binding cleft of neuronal nitric-oxide synthase (nNOS) regulates binding of Hsp90 and Hsp70 proteins and nNOS ubiquitination.
abstract: Like other nitric-oxide synthase (NOS) enzymes, neuronal NOS (nNOS) turnover and activity are regulated by the Hsp90/Hsp70-based chaperone machinery, which regulates signaling proteins by modulating ligand binding clefts (Pratt, W. B., Morishima, Y., and Osawa, Y. (2008) J. Biol. Chem. 283, 22885-22889). We have previously shown that nNOS turnover is due to Hsp70/CHIP-dependent ubiquitination and proteasomal degradation. In this work, we use an intracellular cross-linking approach to study both chaperone binding and nNOS ubiquitination in intact HEK293 cells. Treatment of cells with N(G)-nitro-L-arginine, a slowly reversible competitive inhibitor that stabilizes nNOS, decreases both nNOS ubiquitination and binding of Hsp90, Hsp70, and CHIP. Treatment with the calcium ionophore A23187, which increases Ca(2+)-calmodulin binding to nNOS, increases nNOS ubiquitination and binding of Hsp90, Hsp70, and CHIP in a manner that is specific for changes in the heme/substrate binding cleft. Both Hsp90 and Hsp70 are bound to the expressed nNOS oxygenase domain, which contains the heme/substrate binding cleft, but not to the reductase domain, and binding is increased to an expressed fragment containing both the oxygenase domain and the calmodulin binding site. Overexpression of Hsp70 promotes nNOS ubiquitination and decreases nNOS protein, and overexpression of Hsp90 inhibits nNOS ubiquitination and increases nNOS protein, showing the opposing effects of the two chaperones as they participate in nNOS quality control in the cell. These observations support the notion that changes in the state of the heme/substrate binding cleft affect chaperone binding and thus nNOS ubiquitination.
authors: Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
authors: Hwei-Ming
authors: HM
authors: Peng
authors: Yoshihiro
authors: Y
authors: Morishima
authors: William B
authors: WB
authors: Pratt
authors: Yoichi
authors: Y
authors: Osawa
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D061207:Calcium Ionophores / Q000494:pharmacology; D020134:Catalytic Domain / Q000502:physiology; D057809:HEK293 Cells; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000235:genetics / Q000378:metabolism; D006801:Humans; D052248:Nitric Oxide Synthase Type I / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D059748:Proteolysis; D051381:Rats; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects / Q000502:physiology*
chemical_list: D061207:Calcium Ionophores; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D000001:Calcimycin; D006418:Heme; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; C540442:Stub1 protein, rat; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex