Methionine Sulfoxide Reductase B1 Regulates Hepatocellular Carcinoma Cell Proliferation and Invasion via the Mitogen-Activated Protein Kinase Pathway and Epithelial-Mesenchymal Transition.

Methionine sulfoxide reductase B1 (MsrB1) is a member of the selenoprotein family, which contributes to the reduction of methionine sulfoxides produced from reactive oxygen species (ROS) by redox processes in energy pathways. However, few studies have examined the role of MsrB1 in human hepatocellular carcinoma (HCC). We observed that MsrB1 is highly expressed in HCC tissues and that its expression correlated with the prognoses of patients with HCC after hepatectomy. In vitro, knockdown of MsrB1 inhibits HCC cell growth by MTT and EdU proliferation assay, and MsrB1 interference enhances H2O2/trx-induced apoptosis. We observed that phosphorylation of the key proteins of the MAPK pathway, namely, ERK, MEK, and p53, was inhibited, but PARP and caspase 3 were increased, thus infecting mitochondrial integrity. In vivo, MsrB1 knockdown effectively inhibited tumor growth. Furthermore, MsrB1 knockdown reduced HCC cell migration and invasion in a transwell assay through inhibition of cytoskeletal rearrangement and spread. This change was linked to epithelial-mesenchymal transition (EMT) inhibition resulting from increases in E-cadherin expression and decreases in expression in TGF-ß1, Slug, MMP-2/9, and so on. MsrB1 regulates HCC cell proliferation and migration by modulating the MAPK pathway and EMT. Thus, MsrB1 may be a novel therapeutic target with respect to the treatment of HCC.

Identification of activators of methionine sulfoxide reductases A and B.

The methionine sulfoxide reductase (Msr) family of enzymes has been shown to protect cells against oxidative damage. The two major Msr enzymes, MsrA and MsrB, can repair oxidative damage to proteins due to reactive oxygen species, by reducing the methionine sulfoxide in proteins back to methionine. A role of MsrA in animal aging was first demonstrated in Drosophila melanogaster where transgenic flies over-expressing recombinant bovine MsrA had a markedly extended life span. Subsequently, MsrA was also shown to be involved in the life span extension in Caenorhabditis elegans. These results supported other studies that indicated up-regulation, or activation, of the normal cellular protective mechanisms that cells use to defend against oxidative damage could be an approach to treat age related diseases and slow the aging process. In this study we have identified, for the first time, compounds structurally related to the natural products fusaricidins that markedly activate recombinant bovine and human MsrA and human MsrB.

Methionine sulfoxide reductase A attenuates heme oxygenase-1 induction through inhibition of Nrf2 activation.

Methionine sulfoxide reductase A (MsrA) functions as a protein repair enzyme by catalyzing the stereospecific reduction of methionine-S-sulfoxide to methionine. We previously identified that MsrA deficiency inhibits normal cell growth via activation of the p53-p21 pathway. In this study, we report a critical role of MsrA in expression of heme oxygenase-1 (HO-1), a highly inducible enzyme that has an anti-proliferative effect mediated by up-regulation of p21. Down-regulation of MsrA induced HO-1 expression in mammalian cells with increased p21 levels, but MsrA overexpression did not affect HO-1 expression. MsrA depletion activated Nrf2 by increasing its expression and nuclear translocation. Nrf2 activation was associated with increased reactive oxygen species production. MsrA overexpression in MsrA-depleted cells led to the reduction of increased HO-1 expression, and suppressed nuclear accumulation of Nrf2. Taken together, the data suggest that MsrA attenuates HO-1 induction by inhibiting Nrf2 activation.

A study of enzymatic activity in cell cultures via the analysis of volatile biomarkers.

Aldehyde dehydrogenase (ALDH) enzymes are responsible for the metabolism of aldehydes, including acetaldehyde (AA), and are linked to disease. We describe a method to study ALDH activity in cell cultures involving the measurement of AA concentrations in the gas/vapour phase. This has been achieved using selected ion flow tube mass spectrometry (SIFT-MS), developed for the rapid quantification of trace gases in humid media. Human cells of the hepG2 hepatocellular carcinoma cell line and primary bone marrow-derived mesenchymal stem cells (hMSCs) depleted AA from the culture media, but the application of ALDH inhibitors diethylaminobenzaldehyde (DEAB) and disulfiram (DSF), suppressed this depletion or in some cases resulted in elevated AA concentrations. Further, the cells were shown to reduce the dimethyl sulphoxide (DMSO) to dimethyl sulphide, which is mediated by methionine sulfoxide reductase A (MsrA) enzymes. Interestingly, this process was also inhibited by DEAB and DSF. The results of this study indicate that SIFT-MS gas phase analysis could be applied to the study of volatile metabolites of intracellular enzyme reactions, this having potential utility in disease research and drug discovery.

Methionine sulfoxide reductase A down-regulation in human breast cancer cells results in a more aggressive phenotype.

Breast cancer is one of the most frequent of human malignancies, and it is therefore fundamental to identify the underlying molecular mechanisms leading to cancer transformation. Among other causative agents in the development of breast cancers, an important role for reactive oxygen species (ROS) has emerged. However, most studies on the role of ROS in cancer have not reached specific conclusions, and many issues remain controversial. In the present study, we show that methionine sulfoxide reductase A (MsrA), which is known to protect proteins from oxidation and which acts as a ROS scavenger, is down-regulated in a number of breast cancers. Moreover, levels of MsrA correlate with advanced tumor grade. We therefore investigated the functional role of MsrA in breast cancer cells. Our data show that reduction of MsrA levels results in increased cell proliferation and extracellular matrix degradation, and consequently in a more aggressive cellular phenotype, both in vivo and in vitro. We also show that the underlying molecular mechanisms involve increased ROS levels, resulting in reduction of phosphatase and tensin homolog deleted on chromosome ten protein (PTEN), and activation of the phosphoinositide 3-kinase pathway. In addition, MsrA down-regulation results in up-regulation of VEGF, providing additional support for tumor growth in vivo.

Insights into function, catalytic mechanism, and fold evolution of selenoprotein methionine sulfoxide reductase B1 through structural analysis.

Methionine sulfoxide reductases protect cells by repairing oxidatively damaged methionine residues in proteins. Here, we report the first three-dimensional structure of the mammalian selenoprotein methionine sulfoxide reductase B1 (MsrB1), determined by high resolution NMR spectroscopy. Heteronuclear multidimensional spectra yielded NMR spectral assignments for the reduced form of MsrB1 in which catalytic selenocysteine (Sec) was replaced with cysteine (Cys). MsrB1 consists of a central structured core of two ß-sheets and a highly flexible, disordered N-terminal region. Analysis of pH dependence of NMR signals of catalytically relevant residues, comparison with the data for bacterial MsrBs, and NMR-based structural analysis of methionine sulfoxide (substrate) and methionine sulfone (inhibitor) binding to MsrB1 at the atomic level reveal a mechanism involving catalytic Sec(95) and resolving Cys(4) residues in catalysis. The MsrB1 structure differs from the structures of Cys-containing MsrBs in the use of distal selenenylsulfide, residues needed for catalysis, and the mode in which the active form of the enzyme is regenerated. In addition, this is the first structure of a eukaryotic zinc-containing MsrB, which highlights the structural role of this metal ion bound to four conserved Cys. We integrated this information into a structural model of evolution of MsrB superfamily.

A high-throughput screening compatible assay for activators and inhibitors of methionine sulfoxide reductase A.

The methionine sulfoxide reductase (Msr) system has been shown to play an important role in protecting cells against oxidative damage. This family of enzymes can repair damage to proteins resulting from the oxidation of methionine residues to methionine sulfoxide, caused by reactive oxygen species. Previous genetic studies in animals have shown that increased levels of methionine sulfoxide reductase enzyme A (MsrA), an important member of the Msr family, can protect cells against oxidative damage and increase life span. A high-throughput screening (HTS) compatible assay has been developed to search for both activators and inhibitors of MsrA. The assay involves a coupled reaction in which the oxidation of NADPH is measured by either spectrophotometric or fluorometric analysis. Previous studies had shown that MsrA has a broad substrate specificity and can reduce a variety of methyl sulfoxide compounds, including dimethylsulfoxide (DMSO). Since the chemicals in the screening library are dissolved in DMSO, which would compete with any of the standard substrates used for the determination of MsrA activity, an assay has been developed that uses the DMSO that is the solvent for the compounds in the library as the substrate for the MsrA enzyme. A specific activator of MsrA could have important therapeutic value for diseases that involve oxidative damage, especially age-related diseases, whereas a specific inhibitor of MsrA would have value for a variety of research studies.