In SA and SE cells, MT dynamics are altered and, as expected, the checkpoint appears to be active, as revealed by the deleterious effect of MAD2 deletion.
As expected, CHEK2 (checkpoint kinase 2), PALB2 (partner and localizer of BRCA2), BRIP1 (BRCA1-interacting protein 1), and RAD50 (human homolog of Saccharomyces cerevisiae RAD50) have been shown to have rare, moderate-risk BrCa-associated variants, which have also been studied in the Finnish population [ 11- 14].
Bearing in mind these reports and their implication that the C-terminal domain of Chk1 may have a negative impact on its catalytic activity, we might have expected that the checkpoint proficient Chk1D469G mutant would display an elevated level of kinase activity both in the absence and presence of damage.
Ionising radiation (8 Gy) induced the expected G2-M checkpoint arrest G2-M: 28.9% vs 3.5% in non-irradiated cells.
As expected, when the checkpoint is compromised in cdc13-1 chk1Δ, cdc13-1 rad9Δ or cdc13-1 rad53Δ cells, no accumulation at medial nuclear division is observed over 9 h (Fig. 5A).
Consequently, and considering that these cells were proliferating, we expected these DDR checkpoints to appear down-regulated.
Cdk2 activity was reduced in the presence of an active intra-S-phase checkpoint, as expected.
Cells that are arrested at the mitotic checkpoint are expected to die if they unable to restore proper mitosis.
PD 65, but not PD 43 cells, also stained strongly positive for phospho-H2AX and phospho-T68-Chk2, markers of an activated DNA damage checkpoint, as expected for replicatively senescent cells containing defective telomeres [ 30].
The spindle checkpoint would be expected to prevent anaphase after failure or bypass of the decatenation checkpoint.
