Liu, S.-T. | bioRxiv Science

bioRxiv2020

MTFR2 regulates mitochondrial fission and impacts spindle integrity during mitosis

Previously we reported that mitochondrial fission regulator 2 (MTFR2, also termed DUFD1 or FAM54A) is co-transcribed with core centromere/kinetochore components, indicating a possible role in mitosis regulation. Here we show that human MTFR2 is a mitochondrial outer membrane protein and participates in DRP1 dependent mitochondrial fission. Multiple MTFR2 variants identified in cancer samples are defective in triggering mitochondrial fission. Inducible MTFR2 depletion caused prolonged mitotic duration and increased chromosome mis-segregation, resulting in multi-nucleated daughter cells. MTFR2 knockout cells accumulated spindle defects, producing either multipolar spindles or short oscillating spindles due to loss of astral microtubules. MTFR2 is phosphorylated during mitosis. The phosphorylation mutant, as well as the cancer variants, failed to correct the prolonged mitotic duration. MTFR2 knockout also rendered cells more resistant to apoptosis caused by taxol treatment. As overexpressing MFN1 or DRP1-K38A also caused spindle defects, we conclude that mitochondrial fragmentation during mitosis ensures spindle integrity and chromosomal stability, and MTFR2 plays a critical role in bridging proper mitochondrial fission and chromosome segregation.

cell biology↗

bioRxiv2017

Coordination between discrete Mitotic Arrest Deficient 1 (MAD1) domains is required for efficient mitotic checkpoint signaling

As a sensitive signaling system, the mitotic checkpoint ensures faithful chromosome segregation by delaying anaphase onset when even a single kinetochore is unattached. The key signal amplification reaction for the checkpoint is the conformational conversion of open MAD2 (O-MAD2) into closed MAD2 (C-MAD2). The reaction was suggested to be catalyzed by an unusual catalyst, a MAD1:C-MAD2 tetramer, but how the catalysis is executed and regulated remains elusive. Here we report that in addition to the well-characterized middle region (MIM), both amino- and carboxyl-terminal domains (NTD and CTD) of MAD1 also contribute to the mitotic checkpoint. In contrast to MIM that stably associates with C-MAD2, MAD1-NTD and CTD surprisingly bind to both O-MAD2 and C-MAD2, suggesting their interactions with substrates and products of the O-C conversion. MAD1-NTD also interacts with CTD. MPS1 kinase interacts with and phosphorylates both NTD and CTD. The phosphorylation reduces the NTD:CTD interaction and CTD interaction with MPS1. Mutating CTD phosphorylation sites including Thr716 compromises MAD2 binding and the checkpoint responses. Ser610 and Tyr634 also contribute to the checkpoint. Our results have uncovered previously unknown interactions of MAD1-NTD and CTD with MAD2 conformers and their regulation by MPS1 kinase, providing novel insights into the mitotic checkpoint signaling.

cell biology↗