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  • Recent studies have indicated that V


    Recent studies have indicated that V-ATPase activity negatively regulates vacuolar fusion in vivo[17]. Since we have demonstrated that the pah1Δ Protease Inhibitor Cocktail (EDTA-Free, 100X in DMSO) have a more acidic vacuolar pH than the WT cells, and the genes involved in the pump activity are upregulated compared to WT, the pah1Δ cells' acidity could be a contributing factor to the fragmented vacuolar phenotype. As such, we provide evidence to show the role of Pah1p in the expression of V-ATPase genes, vacuole acidification and vacuolar fragmentation.
    Introduction Plant-derived polyphenols have attracted attention due to their biological properties, including health-promoting benefits. Promising antioxidant, antimicrobial, and anticarcinogenic activities have been repeatedly reported for flavonoids, which comprise a large family of polyphenolic macronutrients (Dragsted, 2003, Upadhyay and Dixit, 2015). The flavonoid myricetin (Fig. 1A, 3,3’,4’,5,5’,7-hexahydroxyflavone) is abundant in a glycoside form rather than as a free aglycone in several plant-based foods, including berries, vegetables, teas and wines, and this draws attention to its beneficial health effects (Ong and Khoo, 1997, Semwal et al., 2016). Previous studies have shown that myricetin has strong antioxidant activity, scavenges oxygen radicals to prevent lipid peroxidation, and exhibits anticarcinogenic, antiviral, anti-inflammatory, and antihyperglycemic effects (Devi et al., 2015). These broad effects indicate that myricetin interacts with several target proteins in divergent cell types. Indeed, it has been reported that myricetin (typically 20–100μM) inhibits mitogen-activated protein kinase (Gutierrez-Venegas et al., 2014), Janus kinase (Kang et al., 2011), DNA topoisomerase (Shiomi et al., 2013) and α-amylase (Williams et al., 2012). To establish the pharmacological profile of myricetin, it is important to examine its effects in various biological assay systems. H+, K+-ATPase is a member of the P2-type ATPase family and functions as a proton pump in gastric parietal cells. Proton pump inhibitors such as omeprazole and lansoprazole are widely used in the treatment of gastric acid-related diseases, including peptic ulcer disease, erosive esophagitis and gastroesophageal reflux disease (Robinson and Horn, 2003, van Driel and Callaghan, 1995). However, recent meta-analyses suggest that long-term use of proton pump inhibitors increases the risks for chronic kidney disease, infection and dementia (Freedberg et al., 2017, Yu et al., 2017). Therefore, nutraceutical products may be desirable for the prevention of gastric acid-related diseases, and it is important to identify food components that inhibit gastric H+, K+-ATPase. In this paper, we report that myricetin inhibits H+, K+-ATPase and attenuates gastric acid secretion.
    Materials and methods
    Discussion The natural plant-derived flavonoid myricetin has various biological properties, such as pronounced antioxidant activity and anticarcinogenic, antiviral, anti-inflammatory, and antihyperglycemic effects, as has been described in previous studies (Devi et al., 2015). In this study, we found that myricetin dose-dependently inhibits P2-type ATPases; IC50 values for H+, K+-ATPase, Na+, K+-ATPase and Ca2+-ATPase were 0.58, 5.73 and 3.90μM, respectively. The inhibition potency against H+, K+-ATPase was about an order of magnitude higher than against Na+, K+-ATPase and Ca2+-ATPase. Therefore, myricetin seems to preferentially inhibit H+, Protease Inhibitor Cocktail (EDTA-Free, 100X in DMSO) K+-ATPase among P2-type ATPases. Although there are few papers that investigate the effects of flavonoids on H+, K+-ATPase, Murakami et al. (Murakami et al., 1999) previously reported that hydroxy groups at the 3-, 5- and 7-positions of the flavonoid backbone are essential for inhibition of H+, K+-ATPase. Consistent with this report, our study indicated that additional hydroxy groups at the 6-, 2’-, 3’-, and 5’-positions significantly enhanced the inhibitory activity against H+, K+-ATPase. Moreover, these hydroxy groups were also important for inhibiting Na+, K+-ATPase and Ca2+-ATPase. Therefore, these hydroxy groups of myricetin are probably important for the inhibitory action on P2-type ATPase family members. Comparing catalytic α-subunits, H+, K+ -ATPase has 62% and 29% amino acid sequence identities with Na+, K+-ATPase and Ca2+-ATPase, respectively (Fujii et al., 2015, Munson et al., 2005, Shull and Lingrel, 1987). P2-type ATPase family members share several functionally essential regions, such as ATP-binding and hydrolysis sites with conserved structures. Perhaps myricetin binds to a conserved region present in the P2-type ATPases.