K2P potassium channels stabilize the resting membrane potential in nearly all cells and have been implicated in several neuronal, cardiovascular, and immune diseases. DCPIB, a known specific and potent inhibitor of volume-regulated anion channels (VRAC), has been reported to activate TREK1 and TREK2 in astrocytes and in vitro recently. In the present study, we demonstrated DCPIB also voltage dependently activated TRAAK besides TREK1/TREK2, showing DCPIB activated all TREK subfamily members. In contrast, the compound potently inhibited several other K2P channels with no voltage dependence, including TRESK, TASK1, and TASK3. DCPIB displayed superior selectivity toward TRESK with an IC50 of 0.14 μM, demonstrating at least 100-fold higher affinity over TREK1/TRAAK channels. Furthermore, the impaired ion selectivity filter region greatly impaired the activating effect of DCPIB on TREK1 but not the inhibitory effect of DCPIB on TRESK. This indicates distinct molecular determinants underlying the effect of DCPIB on TREK1 or TRESK channels. Our results showed that DCPIB played diverse effects on K2P channels and could be a useful tool for further investigating structure–function studies of K2P channels.

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Most of the existing chemotherapeutic drugs have plenty of side effects. Chinese herbal medicine has been used for pharmaceutical and dietary therapy for thousands of years with more effective and fewer side effects. Cestrum nocturnum (CN) has long been used to treat digestive diseases for centuries in China. Our previous study first proved that the n-butanol part isolated from the flowers of CN produced an inhibitory effect on the proliferation of malignant cells. However, the fractions responsible for the antiproliferation effect of n-butanol part from CN flowers and related mechanisms remain unknown. Thus, in this study, we extracted fractions C4 and C5 from n-butanol part of CN flowers and investigated their immune toxicity and antitumor activities. It was found that fractions C4 and C5 exhibited great cytotoxicity to cancer cell lines but had low immune toxicity towards T and B lymphocytes in vitro. The tested fractions also attenuated proliferation and induced apoptosis at G0/G1 and G2/M phases in Bel-7404 cells through inducing DNA damage and inhibiting topoisomerase II relaxation activity. These results suggest that fractions C4 and C5 may represent important sources of potential antitumor agents due to their pronounced antitumor effects and low immune toxicity.

The aim of the present study was to investigate the cytotoxic effects and underlying molecular mechanisms of nitidine chloride (NC) in hepatocellular carcinoma cells via quantitative proteomics. MTT assays were used to detect the inhibitory effects of NC in Bel-7402 liver cancer cells, and the number of apoptotic cells was measured by flow cytometry. Quantitative proteomics technology based on iTRAQ was used to discover differential expressed proteins after NC treatment, and bioinformatic techniques were further used to screen potential targets of NC. Molecular docking was applied to evaluate the docking activity of NC with possible upstream proteins, and their expression was detected at the mRNA and protein levels by quantitative reverse transcription PCR and western blotting. NC inhibited the proliferation of Bel-7402 cells after 24 h of treatment and stimulated apoptosis in vitro. The proteomics experiment showed that NC triggers mitochondrial damage in HCC cells and transcription factor AP-1 (c-Jun) may be a potential target of NC (fold change = 4.36 ± 0.23). Molecular docking results revealed the highest docking score of NC with c-Jun N-terminal kinase (JNK), one of the upstream proteins of c-Jun. Moreover, the mRNA and protein expression of c-Jun and JNK were significantly increased after NC treatment (p < 0.05). These findings indicate that NC significantly induced mitochondrial damage in HCC cells, and induced apoptosis by activating JNK/c-Jun signaling.