Mutations in MEC1 have been shown to lead to multiple defects, including sensitivity to DNA damage, impaired checkpoint functions, chromosome breakage, and loss of telomeric silencing [32], [33].
Importantly, we show that NSCLC TICs exhibited inadequate activation of DDR signaling, impaired checkpoint arrest and a significantly attenuated apoptotic response.
Depletion of Gwl from Xenopus egg extracts impaired checkpoint recovery, as judged by persistent activation of checkpoint proteins and delayed reactivation of Cdk1 after removal of DNA damage.
Impairing checkpoint pathways, for example rad9Δ, partially suppresses the temperature sensitivity of cdc13-1 strains (Weinert et al, 1994; Zubko et al, 2004).
We, therefore, began our study by hypothesizing that the mrc1 deletion phenotype reflects lack of scaling due to an impaired checkpoint.
Some N-APC mutants have been shown to impair spindle checkpoint and contribute to mis-segregation of chromosomes [ 41, 45- 47].
Therefore, in agreement with the cell culture result, loss of GRASP65 expression in the GRASP65[LacZ] mice we generated should not impair this checkpoint either.
Further characterization of ATR-Seckel cells showed impaired phosphorylation of ATR-dependent substrates, impaired G2/M checkpoint arrest and supernumery centrosomes in mitotic cells, clearly demonstrating a role for ATR in the maintenance of centrosome stability [ 82].
Thus wortmannin-treated normal fibroblasts exhibit increased sensitivity to radiation-induced cell killing, lack of temporary block in transition from G1 to S phase following irradiation (i.e. impaired G1/S checkpoint), and radioresistant DNA synthesis (i.e. impaired S phase checkpoint).
