Alterations of ceramide/sphingosine 1-phosphate Rheostat Involved in the Regulation of Resistance to Imatinib-Induced Apoptosis in K562 Human Chronic Myeloid Leukemia Cells

J Biol Chem. 2007 Apr 13;282(15):10922-34. doi: 10.1074/jbc.M610157200. Epub 2007 Feb 15.

Abstract

In this study, mechanisms of resistance to imatinib-induced apoptosis in human K562 cells were examined. Continuous exposure to stepwise increasing concentrations of imatinib resulted in the selection of K562/IMA-0.2 and -1 cells, which expressed approximately 2.3- and 19-fold resistance, respectively. Measurement of endogenous ceramides by high performance liquid chromatography/mass spectroscopy showed that treatment with imatinib increased the generation of ceramide, mainly C18-ceramide, which is generated by the human longevity assurance gene 1 (hLASS1), in sensitive, but not in resistant cells. Inhibition of hLASS1 by small interfering RNA partially prevented imatinib-induced cell death in sensitive cells. In reciprocal experiments, overexpression of hLASS1, and not hLASS6, in drug-resistant cells caused a marked increase in imatinib-induced C18-ceramide generation, and enhanced apoptosis. Interestingly, there were no defects in the levels of mRNA and enzyme activity levels of hLASS1 for ceramide generation in K562/IMA-1 cells. However, expression levels of sphingosine kinase-1 (SK1) and generation of sphingosine 1-phosphate (S1P) were increased significantly in K562/IMA-1 cells, channeling sphingoid bases to the sphingosine kinase pathway. The partial inhibition of SK1 expression by small interference RNA modulated S1P levels and increased sensitivity to imatinib-induced apoptosis in resistant cells. On the other hand, forced expression of SK1 in K562 cells increased the ratio between total S1P/C18-ceramide levels approximately 6-fold and prevented apoptosis significantly in response to imatinib. Additional data indicated a role for SK1/S1P signaling in the up-regulation of the Bcr-Abl expression at the post-transcriptional level, which suggested a possible mechanism for resistance to imatinib-mediated apoptosis. In conclusion, these data suggest a role for endogenous C18-ceramide synthesis mainly via hLASS1 in imatinib-induced apoptosis in sensitive cells, whereas in resistant cells, alterations of the balance between the levels of ceramide and S1P by overexpression of SK1 result in resistance to imatinib-induced apoptosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Apoptosis / drug effects*
  • Benzamides
  • Ceramides / metabolism*
  • Drug Resistance, Neoplasm / drug effects*
  • Fusion Proteins, bcr-abl / metabolism
  • Humans
  • Imatinib Mesylate
  • K562 Cells
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / genetics
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology*
  • Lysophospholipids / metabolism*
  • Membrane Potential, Mitochondrial / drug effects
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Piperazines / pharmacology*
  • Pyrimidines / pharmacology*
  • RNA, Small Interfering / genetics
  • Sphingosine / analogs & derivatives*
  • Sphingosine / metabolism
  • Sphingosine N-Acyltransferase
  • Time Factors
  • Up-Regulation

Substances

  • Benzamides
  • Ceramides
  • Lysophospholipids
  • Membrane Proteins
  • Piperazines
  • Pyrimidines
  • RNA, Small Interfering
  • sphingosine 1-phosphate
  • Imatinib Mesylate
  • CERS1 protein, human
  • Sphingosine N-Acyltransferase
  • Fusion Proteins, bcr-abl
  • Sphingosine