title: Inhibition of the MAPK pathway abrogates BCL2-mediated survival of leukemia cells after exposure to low-dose ionizing radiation.
abstract: The ability of low-dose ionizing radiation (1 Gy) to modulate the activities of the mitogen-activated protein kinase (MAPK) and Jun NH2-terminal kinase (JNK1) cascades in human myeloid leukemia (HL60/pCEP4) cells and in cells overexpressing the anti-apoptosis protein BCL2 (HL60/Bcl-2) was investigated. Radiation exposure caused prolonged (3-4 h) activation of MAPK in HL60 cells. The ability of radiation to activate the MAPK pathway was attenuated by 30% in cells overexpressing BCL2. In contrast, low-dose irradiation of HL60/pCEP4 and HL60/Bcl-2 cells failed to modulate JNK1 activity. Inhibition of the MAPK pathway by use of the specific MEK1/2 inhibitor (10 microM PD98059) in both HL60/pCEP4 and HL60/Bcl-2 cells prior to irradiation permitted a similar prolonged radiation-induced activation of JNK1. Furthermore, combined treatment with PD98059 and radiation in both cell types caused a large decrease in growth of cells in suspension culture, a large increase in apoptosis, and a 90% decline in clonogenicity when compared to either treatment alone. Reduced proliferation after combined irradiation and PD98059 treatment in both cell types correlated with reduced Cdc2 activity and arrest in G2/M phase of the cell cycle. These data demonstrate that inhibition of MEK1/2 leading to blockade of the MAPK activation increases the radiation sensitivity of HL60 cells and decreases the ability of these cells to recover from the radiation-induced arrest at the G2/M-phase cell cycle checkpoint. In addition, our data demonstrate that elevated expression of BCL2 does not abrogate the ability of inhibition of MAPK to potentiate radiation-induced cell death in HL60 cells.
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002455:Cell Division / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects*; D005419:Flavonoids / Q000494:pharmacology; D016195:G2 Phase; D018922:HL-60 Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D008938:Mitosis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D011836:Radiation Tolerance; D020298:U937 Cells