MAD2, a novel MAD2 isoform, reduces mitotic arrest and is associated with resistance in testicular germ cell tumors

Background: Prolonged mitotic arrest in response to anti-cancer chemotherapeutics, such as DNA-damaging agents, induces apoptosis, mitotic catastrophe, and senescence. Disruptions in mitotic checkpoints contribute resistance to DNA-damaging agents in cancer. MAD2 has been associated with checkpoint failure and chemotherapy response. In this study, a novel splice variant of MAD2, designated MAD2, was identified, and its association with the DNA damage response was investigated.Methods: Endogenous expression of MAD2 and full-length MAD2 (MAD2) was measured using RT-PCR in cancer cell lines, normal foreskin fibroblasts, and tumor samples collected from patients with testicular germ cell tumors (TGCTs). A plasmid expressing MAD2 was transfected into HCT116 cells, and its intracellular localization and checkpoint function were evaluated according to immunofluorescence and mitotic index.Results: MAD2 was expressed in several cancer cell lines and non-cancerous fibroblasts. Ectopically expressed MAD2 localized to the nucleus and reduced the mitotic index, suggesting checkpoint impairment. In patients with TGCTs, the overexpression of endogenous MAD2, but not MAD2, was associated with resistance to cisplatin-based chemotherapy. Likewise, cisplatin induced the overexpression of endogenous MAD2, but not MAD2, in HCT116 cells.Conclusions: Overexpression of MAD2 may play a role in checkpoint disruption and is associated with resistance to cisplatin-based chemotherapy in TGCTs.