PT  - JOURNAL ARTICLE
AU  - Beardsley, Dillon I.
AU  - Kim, Wan-Ju
AU  - Brown, Kevin D.
TI  - <em>N</em>-Methyl-<em>N</em>′-nitro-<em>N</em>-nitrosoguanidine Activates Cell-Cycle Arrest through Distinct Mechanisms Activated in a Dose-Dependent Manner
AID  - 10.1124/mol.105.013888
DP  - 2005 Oct 01
TA  - Molecular Pharmacology
PG  - 1049--1060
VI  - 68
IP  - 4
4099  - http://molpharm.aspetjournals.org/content/68/4/1049.short
4100  - http://molpharm.aspetjournals.org/content/68/4/1049.full
SO  - Mol Pharmacol2005 Oct 01; 68
AB  - SN1-alkylating agents, such as the mutagenic and cytotoxic drug N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), robustly activate the DNA damage-responsive G2 checkpoint. Establishment of this checkpoint is dependent on a functional mismatch repair (MMR) system; however, exposure to high doses of MNNG overrides the requirement for MMR to trigger G2 arrest. In addition, unlike moderate-dose exposure, in which the G2 checkpoint is attenuated in ataxia-telangiectasia, mutated (ATM)-deficient cells, high-dose MNNG treatment activates G2 arrest through an ATM-independent mechanism. We document that this arrest is sensitive to the pharmacological agents caffeine and 7-hydroxystaurosporine (UCN-01) that inhibit the checkpoint kinases ATM/ATM and Rad-3–related (ATR) and Chk1/Chk2, respectively. Furthermore, these agents block inactivation of the cell-cycle regulatory molecules Cdc25C and Cdc2, establishing the downstream mechanism through which high-dose MNNG establishes G2 arrest. Activation of both Chk2 and Chk1 was independent of ATM and MMR in response to high-dose MNNG, unlike the response to moderate doses of this drug. Chk2 was found to be dispensable for cell-cycle arrest in response to high-dose MNNG treatment; however, ATR deficiency and decreased Chk1 expression forced by RNA interference resulted in diminished checkpoint response. These results indicate that MNNG activates the G2 checkpoint through different mechanisms activated in a dose-dependent fashion.