The p38 Mitogen-Activated Protein Kinase Pathway Links the DNA Mismatch Repair System to the G₂ Checkpoint and to Resistance to Chemotherapeutic DNA-Methylating Agents

Abstract

Although human cells exposed to DNA-methylating agents undergo mismatch repair (MMR)-dependent G₂ arrest, the basis for the linkage between MMR and the G₂ checkpoint is unclear. We noted that mitogen-activated protein kinase p38α was activated in MMR-proficient human glioma cells exposed to the chemotherapeutic methylating agent temozolomide (TMZ) but not in paired cells made MMR deficient by expression of a short inhibitory RNA (siRNA) targeted to the MMR protein Mlh1. Furthermore, activation of p38α in MMR-proficient cells was associated with nuclear inactivation of the cell cycle regulator Cdc25C phosphatase and its downstream target Cdc2 and with activation of the G₂ checkpoint, actions which were suppressed by the p38α/β inhibitors SB203580 and SB202590 or by expression of a p38α siRNA. Finally, pharmacologic or genetic inhibition of p38α increased the sensitivity of MMR-proficient cells to the cytotoxic actions of TMZ by increasing the percentage of cells that underwent mitotic catastrophe as a consequence of G₂ checkpoint bypass. These results suggest that p38α links DNA MMR to the G₂ checkpoint and to resistance to chemotherapeutic DNA-methylating agents. The p38 pathway may therefore represent a new target for the development of agents to sensitize tumor cells to chemotherapeutic methylating agents.

ACKNOWLEDGMENTS

This work was supported by Public Health Service grant CA100011 from the National Cancer Institute and by a grant from Accelerate Brain Cancer Cure, Inc.

We thank Gregory Hannon, Cold Spring Harbor, for the pSHG-1 vector and Martin McMahon, UCSF Cancer Center, for the gWzl-Hygro retroviral construct.