Thioredoxin reductase (TrxR) is one class of the most important antioxidant selenoproteins and is involved in regulating tumor genesis and progression. It has been reported that naphthoquinones can target and inhibit TrxR1 activity therefore produce reactive oxygen species (ROS) mediated by TrxR1, resulting into cellular redox imbalance and making the naphthoquinone compounds to become potential antitumor chemotherapy drugs. The purpose of this work is to explore the interaction between TrxR1 and menadione using biochemical and mass-spectrometric (MS) analyses, to further reveal the detailed mechanisms of TrxR1-mediated naphthoquinone reduction and inhibition of TrxR1 by naphthoquinone compounds. Using the site-directed mutagenesis and recombinantly expressed TrxR1 variants, we measured the steady-state kinetic parameters of menadione reduction mediated by TrxR1 and its variants, performed the inhibition analysis of menadione on TrxR1 activity, and eventually identified the interaction between menadione and TrxR1 through MS analysis. We found that Sec-to-Cys mutation at residue of 498 significantly enhanced the efficiency of TrxR1-mediated menadione reduction, though the Sec⁴⁹⁸ is capable to catalyze the menadione reduction, indicating that TrxR1-mediated menadione reduction is dominantly in a Se-independent manner. Mutation experiments showed that Cys⁴⁹⁸ is mainly responsible for menadione catalysis in comparison to Cys⁴⁹⁷, while the N-terminal Cys⁶⁴ is slightly stronger than Cys⁵⁹ regarding the menadione reduction. LC-MS results detected that TrxR1 was arylated with one molecule of menadione, suggesting that menadione irreversibly modified the hyper-reactive Sec residue at the C-terminus of selenoprotein TrxR1. This study revealed that TrxR1 catalyzes the reduction of menadione in a Se-independent manner meanwhile its activity is irreversibly inhibited by menadione. Hereby it will be useful for the research and development of naphthoquinone anticancer drugs targeting TrxR1.
Catalysis ; Drug Development ; Oxidation-Reduction ; Thioredoxin Reductase 1/metabolism* ; Vitamin K 3/metabolism*

The study was aimed to investigate the possible mechanism of vitamin K(2) (VK(2)) on myelodysplastic syndrome (MDS) cell line MUTZ-1 in vitro. The flow cytometry was used to analyze apoptosis rate and the change of cell cycle. The expression of apoptosis-related genes bcl-2, survivin and bax were detected by reverse transcription-polymerase chain reaction (RT-PCR). The activity of caspase-3 was detected by chemiluminescence assay. The results indicated that the apoptosis peak on FCM and positive Annexin-V FITC on cell membrane showed that VK(2) induced apoptosis of MUTZ-1 cells in a dose-and-time-dependent manner, S and G(2) cell decrement, G(0)/G(1) cell arrest, VK(2) significantly down-regulated the expression of bcl-2 and survivin, but had no effect on the expression of bax, the activity of caspase-3 was significantly increased. It is concluded that VK(2) induces apoptosis of MUTZ-1 cells through activating caspase-3 pathways and the apoptosis-related genes bcl-2 and survivin may play important roles in the process of apoptosis induction.
Antineoplastic Agents ; pharmacology ; Apoptosis ; drug effects ; Caspase 3 ; metabolism ; Cell Line, Tumor ; Humans ; Inhibitor of Apoptosis Proteins ; Microtubule-Associated Proteins ; biosynthesis ; genetics ; Myelodysplastic Syndromes ; drug therapy ; pathology ; Neoplasm Proteins ; biosynthesis ; genetics ; Proto-Oncogene Proteins c-bcl-2 ; biosynthesis ; genetics ; RNA, Messenger ; biosynthesis ; genetics ; Vitamin K 2 ; pharmacology ; bcl-2-Associated X Protein ; biosynthesis ; genetics

To study the effects and possible mechanism of Vitamin K(2) (VK(2)) in the treatment of MDS-JSN04 cells, the changes of morphologic features of MDS-JSN04 cells were investigated by cytomorphology, the apoptosis of MDS-JSN04 cells was observed by transmission electron microscope; cellular proliferation was determined by the MTT assay; cell apoptosis, cell cycle shift and expression of myeloid-specific differentiation antigen (CD11b, CD13) were analyzed by flow cytometry (FCM). The expression of apoptosis-related genes bcl-2, survivin and bax were detected by retrotranscriptase polymerase chain reaction (RT-PCR); the activity of caspase-3 was determined by chemiluminescence assay. The results showed that the typical apoptotic morphological features appeared in cells treated with VK(2) for 72 hours; VK(2) induced apoptosis of MDS-JSN04 cells and in a dose-and-time-dependent manner, G(0)/G(1) cell arrest and significantly down-regulated the expression of bcl-2 and survivin, but had no effect on the expression of bax; the activity of caspase-3 significantly increased. It is concluded that VK(2) induces apoptosis of MDS-JSN04 cells through activating caspase-3 pathways and the apoptosis-related genes bcl-2, survivin may play an important role in this process.
Apoptosis ; drug effects ; CD11b Antigen ; analysis ; CD13 Antigens ; analysis ; Caspase 3 ; metabolism ; Cell Line, Tumor ; Cell Proliferation ; drug effects ; Flow Cytometry ; Gene Expression Regulation, Neoplastic ; Humans ; Inhibitor of Apoptosis Proteins ; Luminescent Measurements ; methods ; Microscopy, Electron, Transmission ; Microtubule-Associated Proteins ; genetics ; Myelodysplastic Syndromes ; genetics ; metabolism ; pathology ; Neoplasm Proteins ; genetics ; Proto-Oncogene Proteins c-bcl-2 ; genetics ; Reverse Transcriptase Polymerase Chain Reaction ; methods ; Vitamin K 2 ; pharmacology ; bcl-2-Associated X Protein ; genetics