The roles of glutathione S-transferase pi 1 (GSTP1), glutathione S-transferase mu 2 (GSTM2) and glutathione S-transferase alpha 1 (GSTA1) in cisplatin (DDP)-resistance of solid cancer cells (A549/DDP, SKOV3/DDP and SGC7901/DDP) were compared following expression downregulation with small interfering RNAs (siRNAs). DDP cytotoxicity was reflected by its half maximal inhibition concentration (IC 50 ) calculated from data using a Cell Counting Kit-8 assay; cell apoptosis was examined using flow cytometry and Hoechst 33342 staining. Higher activities of GST were detected in the cytosol of DDP-resistant cells, compared with those in the parental DDP-susceptible cells. The silencing efficacy of each positive siRNA was supported by western blot analysis. GSTP1 silencing resulted in a 4-fold sensitization of SGC7901/DDP cells to DDP cytotoxicity, but negligible sensitization of SKOV3/DDP and A549/DDP cells. GSTM2 silencing sensitized SKOV3/DDP and A549/DDP cells to DDP cytotoxicity by ~2-fold, but did not sensitize SGC7901/DDP cells. Notably, GSTA1 silencing enhanced DDP cytotoxicity in SGC7901/DDP cells by 6-fold, in A549/DDP cells by 5-fold and in SKOV3/DDP cells by 2-fold. The combined actions of positive siRNAs and DDP increased the percentages of apoptotic cells in the DDP-resistant solid cancer cells compared with the combined actions of DDP and the negative siRNAs. The present findings indicated that GSTA1 is a predominant GST isozyme associated with DDP resistance of SGC7901/DDP, A549/DDP and SKOV3/DDP cells; GSTA1-specific inhibitors may be general sensitizers of SGC7901/DDP, A549/DDP and SKOV3/DDP cells to DDP cytotoxicity through the promotion of cell apoptosis.
While detection of microRNA with or without signal amplification is highly informative, nanosensors with high specificity for cell-specific RNA detection are rare.Methods: In this study, a tetrahedral DNA nanostructure (TDN) with a specific function was combined with gold nanoparticles (Au-NP) possessing fluorescence quenching effects and a large surface area to fabricate a fluorescence resonance energy transfer based nanosensor (Au-TDNN). The presence of miR-21 (target) can separate the fluorescent dye-labeled detection probe on Au-TDNNs from Au-NPs, which separates the donor and acceptor, thus inducing an intensive fluorescence signal. High specificity for discerning point mutation targets was achieved by rationally designing the nucleic acid strand displacement reaction to occur spontaneously with ΔG0 ≈ 0 based on thermodynamic parameters; under this condition, slight thermodynamic changes caused by base mismatch exert significant effects on hybridization yield.Results: Chemically synthesized DNA of three single-base-changed analogues of target, let-7d, and miR-200b were tested. A discrimination factor (DF) of 15.4 was produced by the expected detection probe on Au-NPs for proximal single-base mismatch. As the control group, the DF produced by an ordinary detection probe on Au-NPs only reached 2.4. The feasibility of the proposed strategy was also confirmed using hepatocyte cancer cells (HepG2).Conclusion: This improved nanosensor opens a new avenue for the specific and easy detection of microRNA in live cells.
Homogenous bioaffinity analysis with tryptophan/tyrosine residues in native proteins as FÖrster-resonance-energy-transfer (FRET) donors is feasible when suitable fluorophors can act as FRET acceptors in ligands (FRET probes) and FRET efficiency in complexes of proteins and FRET probes is high enough. In complexes of proteins and FRET probes, suitable acceptors should have excitation peaks around 335 nm and high rotation freedom, are preferred to have sufficient quantum yields and excitation valleys around 280 nm. In protein binding sites mimicked with mixtures of neutral phosphate buffer and organic solvents, quantum yields of candidate acceptors are altered inconsistently but their excitation peaks show tiny changes. Fluorophores as acceptors in such FRET probes are buried inside glutathione-S-transferase and have low rotation freedom, but are localized on streptavidin surface and display high rotation freedom; FRET efficiency in complexes of streptavidin and its FRET probes is much stronger than that in complexes of glutathione-S-transferase and its FRET probes. Specially, the quantum yield is about 0.70 for free 1-naphthylamine probe in neutral phosphate buffer, about 0.50 for 1-naphthylamine probe bound by streptavidin, and about 0.15 for that bound by glutathione-S-transferase. The quantum yield is about 0.06 for free dansylamide probe, about 0.11 for dansylamide probe bound by streptavidin and about 0.27 for that bound by glutathione-S-transferase. Therefore, 1-naphthylamine and dansylamide are effective acceptors when they localize on surfaces of complexes of proteins and FRET probes.
To determine inhibition constant (K(i)) of tight-binding inhibitor, the putative method estimated an apparent K(i) from the response of initial rates to total concentrations of the inhibitor considering its depletion during binding for conversion into the true K(i), but was impractical with glutathione S-transferase of sophisticated kinetics. A fluorometric titration assay of dissociation constant (K(d)) was thus proposed. Schistosoma japonicum glutathione S-transferase (SjGST) action on a nonfluorescent divalent pro-inhibitor and glutathione yielded a divalent product in active site to act as a tight-binding inhibitor, whose binding quenched fluorescence of SjGST at 340 nm under the excitation at 280 nm. K(d) was estimated from the response of fluorescence of SjGST at 340 nm to total concentrations of the divalent product considering its depletion during binding. By fluorometric titration assay, K(d) of two tested nonfluorescent divalent products varied from subnanomolar to nanomolar, but both were resistant to change of SjGST levels and consistent with their apparent K(i) estimated via the putative method. Hence, fluorometric titration assay of K(d) of nonfluorescent tight-binding inhibitors/ligands was effective to GST and may be universally applicable to common enzymes/proteins; affinities of tight-binding inhibitors of GST can be approximated by their apparent K(i) estimated via the putative method.
Progranulin (PGrn) is a secreted growth factor involved in pleiotropic functions, particularly angiogenesis. a distinctly different placental expression of PGrn has been reported between normal pregnancies and pregnancies with complications, such as pre-eclampsia or fetal growth restriction. However, the role of PGrn in placental vascular development remains to be elucidated. in the present study, PGRN-knockout mice (PGRN-/-) were used to investigate the role of PGrn in the development of placental blood vessels and placental formation. Placental weights and pup body weights were significantly lower in the PGRN-/mice compared with the wild-type mice. reduced labyrinthine layer areas and aberrant vascularization were also observed via hematoxylin and eosin staining of PGRN-/mice at embryonic day 14.5 (e14.5) and e17.5. in addition, the morphological data obtained via immunohistochemistry, immunofluorescence staining and western blotting demonstrated decreased expression levels of the blood vessel markers α-smooth muscle actin and cd31 in PGRN-/placentas. Furthermore, vasodilator endothelial nitric oxide synthase was reduced in the PGRN-/placenta. These results indicated that PGrn serves an essential role in the normal angiogenesis of the placental labyrinth in mice.
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