title: L-NAME has opposite effects on the productions of S-adenosylhomocysteine and S-adenosylmethionine in V12-H-Ras and M-CR3B-Ras pheochromocytoma cells.
abstract: Homocysteine is a sulfur-containing, nonproteinogenic, neurotoxic amino acid biosynthesized during methyl cycles after demethylation of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH) and subsequent hydrolysis of SAH into homocysteine and adenosine. Formed homocysteine is either catabolized into cystathionine (transsulfuration pathway) by cystathionine beta-synthase, or remethylated into methionine (remethylation pathway) by methionine synthase. To demonstrate the specificity of Ras-elicited effects on the activity of methyl cycles, wild-type pheochromocytoma PC12, mutant oncogenic rasH gene (MVR) expressing PC12 pheochromocytoma and normal c-rasH stably transfected M-CR3B cells were incubated with the N(omega)-nitro-L-arginine methyl ester (L-NAME), and manumycin, (inhibitors of nitric oxide synthase and farnesyltransferase, respectively). We have found that L-NAME significantly changes the SAM/SAH ratio in both MCR and MVR cells. Moreover, these alterations have reciprocal character; in the MCR cells, the SAM/SAH ratio was raised, whereas in the MVR cells this ratio was decreased. We conclude that depletion of endogenous NO with L-NAME increased the production of SAH only in cells with mutated oncogenic RasH, possibly through enhancement of production of reactive oxygen species (ROS). Oxidative stress can increase cystathionine beta-synthase activity that switches methyl cycles from remethylation into transsulfuration pathway to maintain the intracellular glutathione pool (essential for the redox-regulating capacity of cells) via an adaptive process.
authors.affiliation: Laboratory of Neurochemistry, Institute of Physiology, 14 Gotua st., Tbilisi, 0160, Georgia.
authors.forename: Maia
authors.initials: M
authors.lastname: Sephashvili
authors.forename: Elene
authors.initials: E
authors.lastname: Zhuravliova
authors.forename: Tamar
authors.initials: T
authors.lastname: Barbakadze
authors.forename: Mukhran
authors.initials: M
authors.lastname: Khundadze
authors.forename: Nana
authors.initials: N
authors.lastname: Narmania
authors.forename: David G
authors.initials: DG
authors.lastname: Mikeladze
mesh_terms: D000818:Animals; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism* / Q000473:pathology; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000096:biosynthesis*
chemical_list: D017382:Reactive Oxygen Species; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D016283:Proto-Oncogene Proteins p21(ras); D019331:NG-Nitroarginine Methyl Ester