Involvement of the MKK6-p38γ Cascade in γ-Radiation-Induced Cell Cycle Arrest

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Abstract
The p38 group of kinases belongs to the mitogen-activated protein (MAP) kinase superfamily with structural and functional characteristics distinguishable from those of the ERK, JNK (SAPK), and BMK (ERK5) kinases. Although there is a high degree of similarity among members of the p38 group in terms of structure and activation, each member appears to have a unique function. Here we show that activation of p38γ (also known as ERK6 or SAPK3), but not the other p38 isoforms, is required for γ-irradiation-induced G2arrest. Activation of the MKK6-p38γ cascade is sufficient to induce G2 arrest in cells, and expression of dominant negative alleles of MKK6 or p38γ allows cells to escape the DNA damage-induce G2 delay. Activation of p38γ is dependent on ATM and leads to activation of Cds1 (also known as Chk2). These data suggest a model in which activation of ATM by γ irradiation leads to the activation of MKK6, p38γ, and Cds1 and that activation of both MKK6 and p38γ is essential for the proper regulation of the G2checkpoint in mammalian cells.