Redox regulation of methylthioadenosine phosphorylase in liver cells: molecular mechanism and functional implications

Abstract

MTAP (5'-methylthioadenosine phosphorylase) catalyses the reversible phosphorolytic cleavage of methylthioadenosine leading to the production of methylthioribose-1-phosphate and adenine. Deficient MTAP activity has been correlated with human diseases including cirrhosis and hepatocellular carcinoma. In the present study we have investigated the regulation of MTAP by ROS (reactive oxygen species). The results of the present study support the inactivation of MTAP in the liver of bacterial LPS (lipopolysaccharide)-challenged mice as well as in HepG2 cells after exposure to t-butyl hydroperoxide. Reversible inactivation of purified MTAP by hydrogen peroxide results from a reduction of V(max) and involves the specific oxidation of Cys(136) and Cys(223) thiols to sulfenic acid that may be further stabilized to sulfenyl amide intermediates. Additionally, we found that Cys(145) and Cys(211) were disulfide bonded upon hydrogen peroxide exposure. However, this modification is not relevant to the mediation of the loss of MTAP activity as assessed by site-directed mutagenesis. Regulation of MTAP by ROS might participate in the redox regulation of the methionine catabolic pathway in the liver. Reduced MTA (5'-deoxy-5'-methylthioadenosine)-degrading activity may compensate for the deficient production of the precursor S-adenosylmethionine, allowing maintenance of intracellular MTA levels that may be critical to ensure cellular adaptation to physiopathological conditions such as inflammation.

Metabolomic profiling of permethrin-treated Drosophila melanogaster identifies a role for tryptophan catabolism in insecticide survival

“…Mannitol, a diet-derived antioxidant, not metabolised by Drosophila, is depleted in both larvae and adults on permethrin exposure (0.04-fold in larvae and 0.42-fold in female adults at 12 hours) suggesting increased oxidative stress. 5'-methyladenosine is increased in larvae (3.1-fold at 24 hours) and may also be indicative of oxidative stress because the metabolising enzyme has two catalytic cysteine residues of the active site that can be reversibly inactivated by oxidative stress resulting in a lesion of the pathway (Fernandez-Irigoyen et al, 2008).…”

Methylthioadenosine (MTA) Regulates Liver Cells Proteome and Methylproteome: Implications in Liver Biology and Disease

“…In addition, DMEM-F12 was also supplemented with 0.005 mg/ml insulin, 0.005 mg/ml transferrin, 5 ng/ml selenium, and 40 ng/ml dexamethasone. Sk-Hep1ϩ cells expressing MTAP were obtained in our laboratory in a previous project (30). Cells were always grown at 37°C in 5% CO 2 .…”

“…To elucidate if this alteration can be also related with liver cancer as well as the mechanisms involved, we have compared the proteome of SK-Hep1 cells lacking MTAP (40) and SK-Hep1ϩ, a variant of this cell line that was engineered in our lab to express MTAP (30). MTAP expression in SK-Hep1ϩ cells was similar to basal levels detected in HepG2 liver hepatoma cells and allowed a twofold decrease of intracellular MTA levels (Fig.…”

Obesity and Systemic Inflammation: Insights into Epigenetic Mechanisms

“…Although evidence is still weak, inflammation is a mechanism gaining interest in the cancer field mainly because obesity-related inflammatory markers are increasingly associated with worse cancer prognosis (Pierce et al, 2009). Chronic inflammation has been linked to initiation and progression of different cancer types, including gastric (Farinati et al, 2008), hepatocellular (Fernandez-Irigoyen et al, 2008;Lukasiak et al, 2008), and colorectal (Wang & DuBois, 2008) carcinoma. The tumor-associated stroma includes among other cell types adipocytes, inflammatory and immune cells and influences the development and progression of tumors through its interaction with transformed cells via soluble mediators, such as growth factors and cytokines (Mantovani et al, 2008;Ono et al, 2008).…”