iASPP–PP1 complex is required for cytokinetic abscission by controlling CEP55 dephosphorylation

Cell Death & Disease, May 2018

Cytokinesis is the last step of cell division and is concluded by the abscission of the intercellular bridge that connects two daughter cells. The tight regulation of cytokinesis completion is essential because cytokinesis failure is associated with various human diseases. Here, we report that iASPP, a member of the apoptosis-stimulating proteins of p53 (ASPP) family, is required for proper cell division. iASPP depletion results in abnormal midbody structure and failed cytokinesis. We used protein affinity purification methods to identify the functional partners of iASPP. We found that iASPP associates with centrosomal protein of 55 kDa (CEP55), an important cytokinetic abscission regulator. Mechanically, iASPP acts as a PP1-targeting subunit to facilitate the interaction between PP1 and CEP55 and to remove PLK1-mediated Ser436 phosphorylation in CEP55 during late mitosis. The latter step is critical for the timely recruitment of CEP55 to the midbody. The present observations revealed a previously unrecognized function of iASPP in cytokinesis. This function, in turn, likely contributes to the roles of iASPP in tumor development and genetic diseases.

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iASPP–PP1 complex is required for cytokinetic abscission by controlling CEP55 dephosphorylation

Abstract Cytokinesis is the last step of cell division and is concluded by the abscission of the intercellular bridge that connects two daughter cells. The tight regulation of cytokinesis completion is essential because cytokinesis failure is associated with various human diseases. Here, we report that iASPP, a member of the apoptosis-stimulating proteins of p53 (ASPP) family, is required for proper cell division. iASPP depletion results in abnormal midbody structure and failed cytokinesis. We used protein affinity purification methods to identify the functional partners of iASPP. We found that iASPP associates with centrosomal protein of 55 kDa (CEP55), an important cytokinetic abscission regulator. Mechanically, iASPP acts as a PP1-targeting subunit to facilitate the interaction between PP1 and CEP55 and to remove PLK1-mediated Ser436 phosphorylation in CEP55 during late mitosis. The latter step is critical for the timely recruitment of CEP55 to the midbody. The present observations revealed a previously unrecognized function of iASPP in cytokinesis. This function, in turn, likely contributes to the roles of iASPP in tumor development and genetic diseases. Introduction Cytokinesis is the final stage of cell division, and its completion results in the irreversible partitioning of a single eukaryotic cell into two daughter cells. Cytokinesis failure causes tetra- and polyploidization, which, in turn, can lead to genetic instability1. Similar to the other stages of cell division, cytokinesis is necessary for the proper growth and development of many organisms2. The deregulation of cytokinesis has been linked to various diseases, such as genetic disorders and cancers2. Cytokinesis comprises several steps. The final stage of cytokinesis, termed abscission, requires the breakage of the midbody, a thin membranous stalk that connects nascent daughter cells. Cytokinetic abscission is a complex process that requires tight spatiotemporal regulation to ensure the equal distribution of genomic and cytoplasmic material between two nascent daughter cells3. Abscission, which involves membrane fission induced from the inside of the cell, is topologically similar to membrane fission during viral budding and multivesicular body formation4. The ESCRT-III membrane-remodeling complex is a key factor required by diverse membrane fission events4. Centrosomal protein of 55 kDa (CEP55) localizes in the midbody and plays crucial roles in cytokinesis5,6. CEP55 acts as an adaptor that interacts with the central MKLP-1 component of the midbody and ESCRT-I subunits TSG101 and ALIX, which recruit the ESCRT-III complex to cut the membrane link between newly formed daughter cells7. iASPP, encoded by Protein Phosphatase 1 Regulatory subunit 13 Like (PPP1R13L), is evolutionarily conserved from worms to humans8. iASPP is a member of the Apoptosis Stimulating Proteins of p53 (ASPP) family proteins, which includes ASPP1 and ASPP2. iASPP inhibits, whereas ASPP1/2 stimulates, the proapoptotic activities of p53 (as well as family members p63 and p73)9. In addition to binding with p53, iASPP interacts with the NF-κB subunit p65RelA and inhibits its transcriptional activity10. iASPP strongly interacts with the catalytic subunits of protein phosphatase 1 (PP1) via a noncanonical motif (RNYF)11. iASPP likely acts as a regulatory subunit and targets the catalytic subunits of PP1 in specific subcellular compartments to selectively bind and dephosphorylate substrates; however, the exact substrates regulated by the iASPP–PP1 complex have not been reported11. Physiopathologically, iASPP is an important oncogene, and its expression is upregulated in various types of human cancers12. Moreover, PPP1R13L mutations in human, mice, or cattle all lead to a cardio–cutaneous syndrome associated with fatal dilated cardiomyopathy13,14,15. However, the molecular mechanism underlying these pathologies remains poorly understood. We previously used tandem affinity purification (TAP) methods to reveal that ASPP1/2 is associated with a subset of kinetochore proteins16. Further studies demonstrated that ASPP1/2 are required for chromosome segregation and kinetochore–microtubule attachments16. In the present study, we showed that iASPP plays a critical role in cytokinetic abscission, the last step of cell division. Through TAP methods, we found that CEP55, a cytokinetic abscission regulator, is an interaction partner of iASPP. Moreover, we demonstrated that iASPP acts as a PP1-targeting subunit to facilitate the interaction between PP1 and CEP55. We also demonstrated that the iASPP–PP1 complex removes PLK1-mediated Ser436 in CEP55 during late mitosis. This step is critical for the timely recruitment of CEP55 to the midbody. Our study revealed that iASPP is a novel midbody-associated PP1 targeting subunit that plays critical roles in cytokinesis. This function might contribute to the tumor-promoting activity of iASPP. Results Identification of iASPP interactomes (...truncated)


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Kun Gao, Yuanyuan Zhang, Qing Shi, Jianong Zhang, Liang Zhang, Huiru Sun, Dongyue Jiao, Xiayin Zhao, Hongru Tao, Youheng Wei, Yuqi Wang, Hexige Saiyin, Shi-Min Zhao, Yao Li, Pingzhao Zhang, Chenji Wang. iASPP–PP1 complex is required for cytokinetic abscission by controlling CEP55 dephosphorylation, Cell Death & Disease, 2018, Issue: 9, DOI: 10.1038/s41419-018-0561-6