Cell proliferation and differentiation: genetics and epigenetics
The Anaphase-promoting complex in differentiation
The Anaphase-Promoting Complex or Cyclosome (APC/C) is an E3 ubiquitin ligase whose activation requires the binding of a cofactor, either Cdc20 or Cdh1, which are critical for selecting the substrates that will be ubiquitinated for proteasome-dependent degradation. By selecting multiple cell cycle regulatory proteins, the APC/C plays major roles in cell cycle progression and exit. While APC/C-Cdc20 is a major player during the metaphase-to-anaphase transition and mitotic exit, APC/C-Cdh1 plays a central role in maintaining quiescence and controlling the onset of DNA replication. In addition, APC/C-Cdh1 is essential for endoreduplication, a process in which several rounds of DNA synthesis occur without mitosis. Recent data suggest that the APC/C is also involved in differentiation and metabolism, and plays important roles in postmitotic cells such as neurons.
In the last years, we also studied the relevance of the APC/C during tumor progression and its possible use as a target in cancer therapy. By participating in cell cycle exit and differentiation, Cdh1 may be considered as a tumor suppressor and its deletion contributes to unscheduled cell proliferation in several scenarios. On the other hand, Cdc20 may have specific uses as a cancer target owed to its essential role during mitotic progression.
Summary of multiple functions of the APC/C in a variety of cell types (Eguren et al. Semin. Cell Dev. Biol. 2011)
One of the mechanisms that explain resistance to mitotic drugs is mitotic slippage. In the presence of antimitotic drugs such as microtubule poisons or Plk1 inhibitors, the activity of the SAC prevents the degradation of cyclin B1, inactivation of Cdk1 and mitotic exit. However, this arrest is transient as a consequence of the slow but maintained degradation of cyclin B1 even in the presence of an active checkpoint. This arrest is likely insufficient for an efficient therapeutic response and cells that exit mitosis can remain viable.
It has been therefore proposed that blocking mitotic exit may have stronger effects than targeting the spindle or mitotic entry. In fact, we demonstrated that elimination of Cdc20, the APC/C cofactor required for cyclin B1 degradation and mitotic exit, is highly efficient in killing cells in mitosis and preventing tumor growth in vivo. Small-molecule inhibitors of the APC/C are now available for preclinical studies. We also reported that prolonged mitotic arrest, such as the one induced by APC/C-Cdc20 inhibitors result in mitochondria exhaustion and strong dependence of glycolysis for survival. These data suggest that preventing mitotic slippage or modulating the metabolic pathways that support survival during mitotic arrest could enhance the efficacy of other antimitotic compounds.
Cell Cycle regulators and the epigenetic code
During the chromosome cycle, the chromatin undergoes multiple changes required for the control of transcription, but also higher-level reorganizations required for the proper segregation of sister chromatids during cell division. The epigenetics code, based on a variety of post-translational modifications in histones, is critical for both of these processes. Mitotic kinases, such as Aurora B or Haspin are known to phosphorylate histones to promote some of the changes required for cell cycle progression.
We are currently investigating the regulatory crosslinks that may control chromatin structure during cell cycle progression, or differentiation/undifferentiation, including the changes required for reprogramming to pluripotent cells or the differentiation of these cells towards multiple tissue types.
Bueno, M.J., Pérez de Castro, I., Gómez de Cedrón, M., Santos, J., Calin, G.A., Cigudosa, J.C., Croce, C.M., Fernández-Piqueras, J. and Malumbres, M. (2008) Genetic and Epigenetic Silencing of microRNA-203 Enhances ABL1 and BCR-ABL1 Oncogene Expression. Cancer Cell 13, 496-506.
Eguren, M., Manchado, E. and Malumbres, M. (2011) Non-mitotic functions of the Anaphase-promoting complex. Semin. Cell Dev. Biol. 22, 572-578.
Eguren, M, Porlan, E., Manchado, E., García-Higuera, I., Cañamero, M., Fariñas, I. and Malumbres, M. (2013) The APC/C cofactor Cdh1 prevents replicative stress and p53-dependent cell death in neural progenitors. Nat. Commun. 4, 2880.
Fernández-Miranda, G., Trakala, M., Martín, J., Escobar, B., González, A., Ghyselinck, N.B., Ortega, S., Cañamero, M., Pérez de Castro, I. and Malumbres, M. (2011) Genetic disruption of Aurora B uncovers an essential role for Aurora C during early mammalian development. Development 138, 2661-2672.
García-Higuera, I., Manchado, E., Dubus, P., Cañamero, M., Mendez, J., Moreno, S. and Malumbres, M. (2008) Genomic Stability and Tumor Suppression by the APC/C Cofactor Cdh1. Nat. Cell Biol. 10, 802-811.
Guillamot, M., Manchado, E., Chiesa, M., Gómez-López, G., Pisano, D.G., Sacristán, M. and Malumbres, M. (2011) Cdc14b regulates mammalian RNA polymerase II and represses cell cycle transcription. Sci. Reports 1, 189.
Hurtado, B., Trakala, M., Ximénez-Embún, P., El Bakkali, A., Partida, D., Sanz-Castillo, B., Álvarez-Fernández, M., Maroto, M., Sánchez-Martínez, R., Martínez, L., Muñoz, J., García de Frutos, P., Malumbres, M. (2018) Thrombocytopenia-associated mutations in Ser/Thr kinase MASTL deregulate actin cytoskeletal dynamics in platelets. J. Clin. Invest. 128, 5351-5367.
Hydbring, P., Malumbres, M. and Sicinski, P. (2016) Non-canonical functions of cell cycle cyclins and cyclin-dependent kinases. Nat. Rev. Mol. Cell. Biol. 17, 280-292.
Malumbres, M. (2013) miRNAs and cancer: An epigenetics view. Mol. Aspects Med. 34, 863–874.
Manchado, E., Guillamot, M., de Cárcer, G., Eguren, M., Trickey, M., García-Higuera, I., Moreno, S., Yamano, H., Cañamero, M. and Malumbres, M. (2010) Targeting mitotic exit leads to tumor regression in vivo: modulation by Cdk1, Mastl, and the PP2A/B55alpha, delta phosphatase. Cancer Cell 18, 641-654.
Trakala, M., Rodríguez-Acebes, S., Maroto, M., Symonds, C.E., Santamaría, D., Ortega, S., Barbacid, M., Méndez, J. and Malumbres, M. (2015) Functional reprogramming of polyploidization in megakaryocytes. Dev. Cell 32, 155-167.