UHRF1 depletion causes a G ₂/M arrest, activation of DNA damage response and apoptosis

UHRF1 [ubiquitin-like protein, containing PHD (plant homeodomain) and RING finger domains 1] is required for cell cycle progression and epigenetic regulation. In the present study, we show that depleting cancer cells of UHRF1 causes activation of the DNA damage response pathway, cell cycle arrest in G ₂/M-phase and apoptosis dependent on caspase 8. The DNA damage response in cells depleted of UHRF1 is illustrated by: phosphorylation of histone H2AX on Ser ¹³⁹, phosphorylation of CHK (checkpoint kinase) 2 on Thr ⁶⁸, phosphorylation of CDC25 (cell division control 25) on Ser ²¹⁶ and phosphorylation of CDK1 (cyclin-dependent kinase 1) on Tyr ¹⁵. Moreover, we find that UHRF1 accumulates at sites of DNA damage suggesting that the cell cycle block in UHRF1-depleted cells is due to an important role in damage repair. The consequence of UHRF1 depletion is apoptosis; cells undergo activation of caspases 8 and 3, and depletion of caspase 8 prevents cell death induced by UHRF1 knockdown. Interestingly, the cell cycle block and apoptosis occurs in p53-containing and -deficient cells. From the present study we conclude that UHRF1 links epigenetic regulation with DNA replication.