In vivo consequences of SAC abrogation

Interference with microtubule dynamics activates the spindle assembly checkpoint (SAC) to prevent chromosome segregation errors. The SAC induces mitotic arrest by inhibiting the anaphase-promoting complex (APC) via the mitotic checkpoint complex (MCC). The MCC component MAD2 neutralises the critical APC cofactor, CDC20, leading to mitotic arrest. In cancer cell lines, this can promote mitochondrial apoptosis involving pro-apoptotic BCL2 family members, including BH3-only proteins BIM and NOXA, as well as multi-domain proteins BAX and BAK. However, relevance and consequences of apoptosis after SAC perturbation in vivo are unclear. By conditional MAD2 overexpression across tissues, we observed that chronic SAC activation triggers bone marrow aplasia and fatal intestinal atrophy. While myelosuppression was compensated, gastrointestinal atrophy was detrimental. Remarkably, co-deletion of Bim/Bcl2l11, but not Bid, Puma/Bbc3 or Noxa/Pmaip, prevented developing gastrointestinal syndrome, identifying BIM as rate-limiting for apoptosis induction in the gastrointestinal epithelium. In contrast, BCL2 overexpression but none of the BH3-only protein deficiencies tested could mitigate myelosuppression, highlighting tissue and cell type-specific survival dependencies in response to SAC perturbation in vivo.

微管动力学受到干扰时，会激活纺锤体组装检验点（spindle assembly checkpoint, SAC），以阻止染色体分离错误。SAC通过有丝分裂检验点复合物（mitotic checkpoint complex, MCC）抑制后期促进复合物（anaphase-promoting complex, APC），从而诱导有丝分裂阻滞。MCC组分MAD2会中和关键APC辅因子CDC20，进而引发有丝分裂阻滞。在癌细胞系中，这一过程可通过促凋亡BCL2家族成员介导线粒体凋亡，这类成员包括仅含BH3结构域蛋白BIM与NOXA，以及多结构域蛋白BAX与BAK。然而，体内SAC扰动后细胞凋亡的相关性与具体后果仍不明确。本研究通过在各组织中实现条件性MAD2过表达，观察到慢性SAC激活会引发骨髓再生障碍与致死性肠道萎缩。尽管骨髓抑制可得到代偿，但胃肠道萎缩具有致死性。值得注意的是，共敲除Bim/Bcl2l11（而非Bid、Puma/Bbc3或Noxa/Pmaip）可阻止胃肠道综合征的发生，这表明BIM是胃肠道上皮细胞凋亡诱导过程中的限速因子。与之相反，过表达BCL2而非所测试的任一仅含BH3结构域蛋白缺陷，均可缓解骨髓抑制，这凸显了体内响应SAC扰动时，组织与细胞类型特异性的存活依赖机制。