Mitochondrial ceramidase overexpression up-regulates Bcl-2 protein level in K562 cells probably through its metabolic product sphingosine-1-phosphate / 中国病理生理杂志

ABSTRACT

AIM: To investigate the role of mitochondrial ceramidase in mitochondrial functions, especially in the regulation of apoptosis. METHODS: pCDNA3.1/His-MtCDase plasmid, containing mitochondrial ceramidase cDNA sequence, was transfected into K562 cells by liposome, and G418 was used to screen the positive clones. A stable transfected K562 cell line was established and defined as ‘K562TC’. The differences between K562 and K562TC cells in serum withdrawal resistance and Bcl-2 protein expression were evaluated by annexin V/PI test, flow cytometry and Western blotting, respectively. RESULTS: K562TC cells with elevated Bcl-2 protein expression level identified by FCM or Western blotting showed stronger resistance to apoptosis induced by serum withdrawal than their parental cells. Inhibition of mitochondrial ceramidase expression in K562TC cells by its specific antisense oligodeoxynucleotide was correlated with a decrease in Bcl-2 protein level. N, N'-dimethylsphingosine (DMS), a sphingosine kinase inhibitor, depleted intracellular sphingosine-1-phosphate (SPP) production, also abrogated Bcl-2 protein expression in K562TC cells, while exogenous sphingosine-1-phosphate up-regulated Bcl-2 protein level in K562 cells. CONCLUSION: Mitochondrial ceramidase overexpression in K562 cells leads to markedly elevated level of Bcl-2 protein and results in more resistance to serum withdrawal. This effect is initiated not by sphingosine, the direct metabolite of mitochondrial ceramidase, but via sphingosine-1-phosphate, its phosphorylated form, indicating that mitochondrial ceramidase, through its sphingoid metabolite sphingosine-1-phosphate, up-regulates Bcl-2 protein expression in K562 cells.