The MEK/ERK pathway acts upstream of NF kappa B1 (p50) homodimer activity and Bcl-2 expression in a murine B-cell lymphoma cell line. MEK inhibition restores radiation-induced apoptosis.
In a previously published report (Kurland, J. F., Kodym, R., Story, M. D., Spurgers, K. B., McDonnell, T. J., and Meyn, R. E. (2001) J. Biol. Chem. 276, 45380-45386), we described the NF kappa B status for two murine B-cell lymphoma cell lines, LY-as (apoptosis-sensitive) and LY-ar (apoptosis-refractory) and provided evidence that NF kappa B1 (p50) homodimers contribute to the expression of Bcl-2 in the LY-ar line. In the present study, we investigated the upstream signals leading to p50 homodimer activation and Bcl-2 expression. We found that in LY-ar cells, ERK1 and ERK2 were constitutively phosphorylated, whereas LY-as cells had no detectable ERK1 or ERK2 phosphorylation. Treatment of LY-ar cells with the MEK inhibitors PD 98059, U0126, and PD 184352 led to a loss of phosphorylated ERK1 and ERK2, a reversal of nuclear p50 homodimer DNA binding, and a decrease in Bcl-2 protein expression. Similarly, activation of the MEK/ERK pathway in LY-as cells by phorbol ester led to Bcl-2 expression that could be blocked by PD 98059. Furthermore, treatment of LY-ar cells with tumor necrosis factor-alpha, an I kappa B kinase activator, did not alter the suppressive effect of PD 98059 on p50 homodimer activity, suggesting an I kappa B kinase-independent pathway for p50 homodimer activation. Lastly, all three MEK inhibitors sensitized LY-ar cells to radiation-induced apoptosis. We conclude that the MEK/ERK pathway acts upstream of p50 homodimer activity and Bcl-2 expression in this B-cell lymphoma cell system and suggest that the use of MEK inhibitors could be useful clinically in combination with ionizing radiation to treat lymphoid malignancies.
Kurland
John F
JF
Department of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Voehringer
David W
DW
Meyn
Raymond E
RE
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016393:Lymphoma, B-Cell / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D019253:Proto-Oncogene Proteins c-bcl-2; D020928:Mitogen-Activated Protein Kinases