Phospholipase A2-independent Ca2+ entry and subsequent apoptosis induced by melittin in human MG63 osteosarcoma cells

Sau Tung Chu, He Hsiung Cheng, Chun Jen Huang, Hong Chiang Chang, Chao Chuan Chi, Hsing Hao Su, Shu Shong Hsu, Jue Long Wang, I. Shu Chen, Shiuh Inn Liu, Yih Chau Lu, Jong Khing Huang, Chin Man Ho, Chung Ren Jan*

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

66 Scopus citations

Abstract

Melittin, a peptide from bee venom, is thought to be a phospholipase A2 activator and Ca2+ influx inducer that can evoke cell death in different cell types. However, the effect of melittin on cytosolic free Ca2+ concentration ([Ca2+]i) and viability has not been explored in human osteoblast-like cells. This study examined whether melittin altered [Ca2+]i and killed cells in MG63 human osteosarcoma cells. [Ca2+]i changes and cell viability were measured by using the fluorescent dyes fura-2 and WST-1, respectively. Melittin at concentrations above 0.075 μM increased [Ca2+]i in a concentration-dependent manner. The Ca2+ signal was abolished by removing extracellular Ca2+. Melittin-induced Ca2+ entry was confirmed by Mn2+ quenching of fura-2 fluorescence at 360 nm excitation wavelength which was Ca2+-insensitive. The melittin-induced Ca2+ influx was unchanged by modulation of protein kinase-C activity with phorbol 12-myristate 13-acetate (PMA) and GF 109203X, or inhibition of phospholipase A2 with AACOCF3 and aristolochic acid; but was substantially inhibited by blocking L-type Ca2+ channels. At concentrations of 0.5 μM and 1 μM, melittin killed 33% and 45% of cells, respectively, via inducing apoptosis. Lower concentrations of melittin failed to kill cells. The cytotoxic effect of 1 μM melittin was completely reversed by pre-chelating cytosolic Ca2+ with BAPTA. Taken together, these data showed that in MG63 cells, melittin induced a [Ca2+]i increase by causing Ca2+ entry through L-type Ca2+ channels in a manner independent of protein kinase-C and phospholipase A2 activity; and this [Ca2+]i increase subsequently caused apoptosis.

Original languageEnglish
Pages (from-to)364-369
Number of pages6
JournalLife Sciences
Volume80
Issue number4
DOIs
StatePublished - 02 01 2007
Externally publishedYes

Keywords

  • Apoptosis
  • BAPTA
  • Ca
  • Fura-2
  • MG63 cells
  • Melittin
  • Osteosarcoma cells

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