Inhibitory Effect Of Melatonin On Murine Gastric Cancer And The Relationship With Membrane Receptors

Gastric carcinoma is one of the most common malignant tumors in Chinacharacterized by a rapid progression, poor prognosis and low5-year survival rate,which seriously affect the health and living standards of the people. Melatonin (MLT)is a neuroendocrine hormone mainly secreted by the pineal gland, which has avariety of physiological functions including regulation of sleep/wake cycle, immuneregulation, apoptosis regulation and antioxidation. In recent years a large number ofstudies have demonstrated that melatonin has strong anti-tumor effects. Itsanti-tumor effect is dependent on the characteristics of the antioxidant, immunestimulation and induction of apoptosis. Melatonin membrane receptors MT1andMT2involved in mediating the anti-tumor cell proliferation mechanism. To ourknowledge, there is not publicly reported about study on direct relationship amongthe melatonin, gastric cancer and melatonin membrane receptor. This study aims atlooking for new ideas for auxiliary treatment of gastric cancer by MLT in the futurethrough profoundly investigation of inhibitory effect of melatonin on gastric cancerin mice and relationship between melatonin with membrane receptors and theMAPKs, PI3K-Akt signaling pathways.1The function of anti-mouse gastric cancer of melatonin and the effect on theexpression of melatonin membrane receptors MT1and MT2in vivoIn order to study the role of anti mouse gastric carcinoma of melatonin and therelationship between melatonin with MT1,MT2, the tumor-bearing mouse model ofgastric cancer was established from pre-carcinoma cell MFC in this part of theresearch. The expression changes of related factors were detected by real-timefluorescence quantitative PCR and western blot after the intervention of differentconcentrations of melatonin. The results demonstrate that:1. Melatonin reduced thetumor volume and the tumor weight of the gastric cancer-bearing mice to reach the anti-tumor effect;2. Melatonin inhibited tumor cell proliferation and promotedapoptosis of tumor cells by down-regulation of Bcl-2expression and up-regulationBax and p21expresson of tumor cells;3. The fact that melatonin promoted theexpression of membrane receptors MT1and MT2in tumor tissues indicated that thefunction of anti-mouse gastric cancer growth of melatonin may be by membranereceptors of MT1and MT2.2The proliferative inhibition effect on mouse gastric cancer cells of melatoninand the effect on the expression of melatonin membrane receptors MT1andMT2in vitroIn order to investigate inhibitory effect of melatonin on mouse gastric cancercell proliferation and relationship between melatonin with melatonin membranereceptors MT1, MT2in vitro, we performed a cell model by MFC cells treatmentwith different concentrations and time points of melatonin in this section. Flowcytometry, CCK-8, real-time fluorescent quantitative RT-PCR, Western blotmethods were performed to detect the activity of gastric cancer cell proliferation, cellcycle changes, the gene and protein expression of Bcl-2, Bax, p21, MT1and MT2.The antisense nucleic acid technology to silence MT2expression was implementedto observe the change on cell proliferation activity. The results demonstrated that:1.the results of CCK-8showed that inhibition of melatonin to gastric cancer cellproliferation was dose and time dependent;2. The result of flow cytometry showedthat melatonin inhibited mouse gastric cancer cell proliferation and was relation toG1/S phase block in cell cycle;3. As melatonin inhibits proliferation of gastriccancer cell, melatonin reduced Bcl-2expression and increased expression of p21andBax in gastric cancer cell.4. The melatonin promoted mouse gastric cancer cellmembrane receptor MT1and MT2expression;5. SiRNA-mediated the MT2silentsignificantly antagonized the inhibitory effect of melatonin on gastric cancer cellproliferation. This result suggested that the effect of melatonin on promoting tumorcell apoptosis and inhibiting tumor cell proliferation may be associated withmelatonin membrane MT2expression. 3The roles of MAPKs and PI3K-Akt signal pathway in melatonin-mediatedinhibition of murine gastric cancer cell proliferation in vitroIn order to study the roles of MAPKs and PI3K-Akt in melatonin-mediatedinhibition of cancer cell proliferation, we performed a cell model by MFC cellstreatment with different time points of melatonin in this section. The expressions ofp-ERK/ERK and p-Akt/Akt were detected by Western blot. The method of siRNAwere performed to silence MT2expression to explore inhibitive roles of the MAPKsand the PI3K/Akt signaling pathway on gastric cancer cell proliferation. The resultsshowed that:1. The significantly down-regulation of ERK1/2and AKTphosphorylation of MFC cell after24h with melatonin suggested that melatonininhibited gastric cancer cell proliferation by inhibiting ERK1/2and AKTphosphorylation.2. Being partially blocked of inhibition of melatonin to ERK1/2and AKT phosphorylation of by silence MT2suggested that melatonin inhibited thephosphorylation of ERK1/2and AKT by MT2.In summary, the in vivo and in vitro experiments confirmed that melatonin caninhibit gastric cancer cell proliferation. The hypothesis of mechanisms may includeinhibition of anti-apoptotic gene Bcl-2expression, promote the pro-apoptotic Baxexpression, promote the expression of p21and increase of MT1of MT2. Melatoninalso can inhibit phosphorylation of ERK1/2and Akt by MT2receptors, therebypromoting tumor cell apoptosis and inhibit tumor cell proliferation.