CHEK1 and acute myeloid leukemia: Interestingly, we found increased peptide activation of cell cycle regulators Rb, Rb-like-1, CDC25B, CDC6, RAP1GAP1, RAC1, CCND1 and p21cip1 that showed a strong difference in absolute peptide activation intensities between AML as compared with CD34+ NBM in coexistence with a decrease in 14-3-3 eta, BRCA1, Chk1 and E2F1 peptide activity.