GMNN and diffuse large B-cell lymphoma: In contrast, some DLBCL cells underwent S-phase arrest.8 Interestingly, a recent study suggested that lower concentrations of MLN4924 induce G2 arrest, whereas saturating doses of the drug cause a delay in S-phase progression.23 Genetic knockdowns of Cdt2, a conserved component of CRL4Cdt2 E3 ligase that targets Cdt1 for degradation, or of geminin, a negative regulator of Cdt1, lead to G2 arrest.34, 35 Thus, different means of inducing re-replication may result in activation of either intra-S or G2 checkpoints.