Loss of Geminin induces rereplication in the presence of functional p53

Abstract

Strict regulation of DNA replication is essential to ensure proper duplication and segregation of chromosomes during the cell cycle, as its deregulation can lead to genomic instability and cancer. Thus, eukaryotic organisms have evolved multiple mechanisms to restrict DNA replication to once per cell cycle. Here, we show that inactivation of Geminin, an inhibitor of origin licensing, leads to rereplication in human normal and tumor cells within the same cell cycle. We found a CHK1-dependent checkpoint to be activated in rereplicating cells accompanied by formation of γH2AX and RAD51 nuclear foci. Abrogation of the checkpoint leads to abortive mitosis and death of rereplicated cells. In addition, we demonstrate that the induction of rereplication is dependent on the replication initiation factors CDT1 and CDC6, and independent of the functional status of p53. These data show that Geminin is required for maintaining genomic stability in human cells.

Role of geminin: from normal control of DNA replication to cancer formation and progression?

“…35 Interestingly, geminin depletion causes partial DNA over-replication in HCT116, U2OS cancer cells and diploid fibroblasts TIG3 human cells, accompanied by an activation of a different ATR/ATM checkpoint pathway. 36 Significantly, this over-replication did not occur when Cdt1 was also repressed. 36 Interestingly, it has been described that geminin inactivation causes centrosome overduplication without passage through mitosis in human cancer cells.…”

“…36 Significantly, this over-replication did not occur when Cdt1 was also repressed. 36 Interestingly, it has been described that geminin inactivation causes centrosome overduplication without passage through mitosis in human cancer cells. The geminin-depleted cells show abnormal and multipolar spindles, when driven into mitosis by checkpoint abrogation, suggesting a new general role for geminin in coordinating the centrosome duplication besides licensing inhibitor of DNA replication.…”

“…9,30,53,54 The ability of geminin to suppress initiation of DNA replication in Xenopus egg extracts led to the hypothesis that this protein acts as an inhibitor of cell proliferation and might be a tumor suppressor gene. 42,36 However, geminin expression in normal and cancer cells does not correlate with a decrease in cellular proliferation. Immunohistochemistry and immunoblotting for geminin revealed that, except in testis, where its expression is high, this protein is absent in organs with minimal proliferation activity (heart, nerves, prostate, kidney, lung and scheletric muscle) and it is specifically expressed in proliferating lymphocytes, male germ cells and epithelial cells.…”

“…It has been shown by Melixian et al, that depletion of geminin does not lead to DNA over-replication in HeLa cells as seen in HCT116, US2OS and normal fibroblast. 31,36,38 Further information is necessary to better delineate the role(s) played by geminin in the regulation of cell cycle machinery in both normal and cancer cells. In our opinion, in transformed cells whose proliferation has escaped the control of important cell cycle regulators such as geminin protein, cell cycle progression may occur independently of what geminin may do to maintain a correct pattern of DNA replication and to control specific mechanisms regulating cell cycle, thus, acting to promote tumor progression rather than as a classic tumor suppressor.…”

The Coordination between DNA Replication Initiation and Other Cell Cycle Events

“…Consequently, DNA replication licensing is prohibited in S phase and G2 phase largely by the geminin inhibiting mechanism in metazoans (Wohlschlegel et al 2000). Depletion of geminin leads to substantial re-replication in primary cells and mouse embryos (Melixetian et al 2004, Gonzalez et al 2006. Recent studies show that DNA replication licensing inhibitor geminin might also function in the centrosome duplication licensing system as an inhibitor.…”