Melittin protein inhibits the proliferation of MG63 cells by activating inositol-requiring protein-1α and X-box binding protein 1-mediated apoptosis

The aim of the present study was to explore the pro-apoptotic effect and specific mechanism of action of melittin (MEL) in humans. The effects of MEL on apoptosis in osteosarcoma and fetal osteoblast cells were investigated, and the mechanism that induced MG63 cell growth was also explored. The effects of MEL on cell proliferation were detected by a 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide analysis. Apoptosis was detected by flow cytometric analysis. MEL protein, inositol-requiring protein-1 (IRE-alpha), phosphorylated-protein kinase R-like endoplasmic reticulum (ER) kinase, spliced X-box-1 (XBP1), eukaryotic translation initiation factor-2 alpha, cleaved activating transcription factor-6, caspase-12 and C/EBP homology protein (CHOP) were detected in three groups and two cell lines by western blot analysis. The results indicated that the expression or incubation of MEL in the MG63 cells triggered apoptosis and the inhibition of proliferation. One protein from the ER stress unfolded protein response pathway, IRE-alpha, was involved in the MEL-induced apoptosis in MG63 cells. Furthermore, spliced XBP1 protein was significantly increased in the MEL peptide incubated and MEL expressing groups of MG63 cells. Furthermore, CHOP protein expression was activated in MG63 cells following being incubated with or expressing MEL. In conclusion, MEL serves as an effective factor that inhibits the proliferation of MG63 cells via activating the ER stress-mediated apoptosis pathway. This activation is triggered by the IRE-alpha pathway mediated by inducing CHOP protein expression.