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Polyploidization in megakaryocytes is achieved by endomitosis, a specialized cell cycle in which DNA replication is followed by aberrant mitosis. Typical mitotic regulators such as Aurora kinases or Cdk1 are dispensable for megakaryocyte maturation, and inhibition of mitotic kinases may in fact promote megakaryocyte maturation. However, we show here that Polo-like kinase 1 (Plk1) is required for endomitosis, and ablation of the Plk1 gene in megakaryocytes results in defective polyploidization accompanied by mitotic arrest and cell death. Lack of Plk1 results in defective centrosome maturation and aberrant spindle pole formation, thus impairing the formation of multiple poles typically found in megakaryocytes. In these conditions, megakaryocytes arrest for a long time in mitosis and frequently die. Mitotic arrest in wild-type megakaryocytes treated with Plk1 inhibitors or Plk1-null cells is triggered by the spindle assembly checkpoint (SAC), and can be rescued in the presence of SAC inhibitors. These data suggest that, despite the dispensability of proper chromosome segregation in megakaryocytes, an endomitotic SAC is activated in these cells upon Plk1 inhibition. SAC activation results in defective maturation of megakaryocytes and cell death, thus raising a note of caution in the use of Plk1 inhibitors in therapeutic strategies based on polyploidization regulators., Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub

The cyclin-dependent kinase 6 (CDK6) and CDK4 have redundant functions in reg- ulating cell-cycle progression. We describe a novel role for CDK6 in hematopoietic and leukemic stem cells (hematopoietic stem cells [HSCs] and leukemic stem cells [LSCs]) that exceeds its function as a cell-cycle regulator. Although hematopoiesis appears normal under steady-state conditions, Cdk62/2 HSCs do not efficiently repopulate upon competitive transplantation, and Cdk6-deficient mice are significantly more sus- ceptible to 5-fluorouracil treatment. We find that activation of HSCs requires CDK6, which interferes with the transcription of key regulators, including Egr1. Transcrip- tional profiling of HSCs is consistent with the central role of Egr1. The impaired repopulation capacity extends to BCR-ABLp2101 LSCs. Transplantation with BCR- ABLp2101–infected bone marrow from Cdk62/2 mice fails to induce disease, although recipient mice do harbor LSCs. Egr1 knock-down in Cdk62/2 BCR-ABLp2101 LSKs significantly enhances the potential to form colonies, underlining the importance of the CDK6-Egr1 axis. Our findings define CDK6 as an important regulator of stem cell activation and an essential component of a transcriptional complex that suppresses Egr1 in HSCs and LSCs., Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub

This work has been in part financed by benefactors, through the crowdfunding project “Match point against breast cancer” (PRECIPITA PR242, 2019; FECYT; Spanish Ministry of Science and Innovation, MICINN, led by MS‑R), and donations to Asociación Española contra el Cáncer (AECC). We are extremely thankful to all our donors. The work has been also funded by the Spanish Ministry of Science and Innovation and the Ministry of Economy and Competitiveness (supported with European Regional Development funds): PID2021‑128726 to MM, CNS2022‑135364 to MS‑R, PI20/00590 to CS, as well as by Comunidad de Madrid (Y2020/BIO‑6519 and S2022/BMD‑7437) to MM. MS‑R was supported by AECC (AIOA120833SALA and INVES18005SALA), a Juan de la Cierva incorporación and a Ramón y Cajal contract (RYC2020028929‑I, from the MICINN, FSE/ Agencia Estatal de Investigación). NGM‑I was supported by AECC (PRDMA19003GARC)., A hallmark of many malignant tumors is dedifferentiated (immature) cells bearing slight or no resemblance to the normal cells from which the cancer originated. Tumor dedifferentiated cells exhibit a higher capacity to survive to chemo and radiotherapies and have the ability to incite tumor relapse. Inducing cancer cell differentiation would abolish their self-renewal and invasive capacity and could be combined with the current standard of care, especially in poorly differentiated and aggressive tumors (with worst prognosis). However, differentiation therapy is still in its early stages and the intrinsic complexity of solid tumor heterogeneity demands innovative approaches in order to be efficiently translated into the clinic. We demonstrate here that microRNA 203, a potent driver of differentiation in pluripotent stem cells (ESCs and iPSCs), promotes the differentiation of mammary gland tumor cells. Combining mouse in vivo approaches and both mouse and human-derived tridimensional organoid cultures, we report that miR-203 influences the self-renewal capacity, plasticity and differentiation potential of breast cancer cells and prevents tumor cell growth in vivo. Our work sheds light on differentiation-based antitumor therapies and offers miR-203 as a promising tool for directly confronting the tumor-maintaining and regeneration capability of cancer cells., Ministerio de Ciencia e Innvoación, Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub

Work in the authors’ laboratories is funded by grants from MINECO (SAF2012-36079 to PB and SAF201238215, SAF2014-57791-REDC, and BFU2014-52125-REDT to MM), and Comunidad de Madrid (S2010/BMD2470)., An attractive strategy for cancer therapy is to stop cell proliferation by means of agents that directly arrest the cell cycle. Microtubule poisons such as taxanes block mitosis, eventually leading to cell death in a process frequently known as mitotic catastrophe. However, some cells are able to bypass this mitotic arrest and survive, thus contributing to chemoresistance to those therapies. We have recently observed that mitotic arrest induces an early autophagic flux response that results in autophagy-dependent mitochondrial degradation and a dramatic energetic deficit. The subsequent increase in the AMP/ATP ratio results in the activation of the metabolic sensor AMPK followed by phosphorylation and activation of PFKFB3, an enzyme required for glycolysis. Thus, mitophagy can be considered as a critical effector of the therapeutic effect of mitotic therapies, while both AMPK and PFKFB3 are critical for survival. The manipulation of these molecular routes may therefore have therapeutic benefits in the presence of microtubule poisons., Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub

Salazar-Roa, Maria as first author. M.S.R. thanks the Asociación Española contra el Cáncer (AECC) for support. Research in the laboratory of the authors is supported by grants from the Comunidad de Madrid (S2010/BMD-2470), Spanish Ministry of Economy and Competitiveness (BFU2014-52125-REDT, SAF2014-57791-REDC, PCIN-2015-007 and SAF2015-69920-R cofunded by ERDF-EU), Worldwide Cancer Research (WCR no. 15-0278), and the European Commission Seventh Framework Programme (MitoSys project HEALTH-F5-2010-241548 and NEURON8-Full-815-094)., Cell division is a complex process with high energy demands. However, how cells regulate the generation of energy required for DNA synthesis and chromosome segregation is not well understood. Recent data suggest that changes in mitochondrial dynamics and metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis crosstalk with, and are tightly regulated by, the cell division machinery. Alterations in energy availability trigger cell-cycle checkpoints, suggesting a bidirectional connection between cell division and general metabolism. Some of these connections are altered in human disease, and their manipulation may help in designing therapeutic strategies for specific diseases including cancer. We review here recent studies describing the control of metabolism by the cell-cycle machinery., Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub

E.D., C.M. and M.S.-R. were supported by the Spanish Fondo de Investigaciones Sanitarias (Madrid), MINECO (Juan de la Cierva programme) and Asociación Española contra el Cáncer (AECC), respectively. L.E.-M. is a recipient of a JAE predoctoral fellowship from the CSIC. A.K.S. was supported by USPHS grants RO1DK19514, RO1DK67509. G.V. was supported by grants from the Spanish Ministry of Economy and Competitiveness (MINECO) and Fondo Europeo de Desarrollo Regional (FEDER) (PI12/02248), Fundació La Marató de TV3 (m12 20134031), and Fundación Mutua Madrileña (AP101042012). M.L. was supported by the European Community’s Seventh Framework Programme under grant agreement no. 281854—the ObERStress (European Research Council project). E.R. was financially supported by a MINECO grant (SAF 2010-20256). Work in the R.M. laboratory was supported by the Fundación Botín, Banco Santander and MINECO (BFU2011-30121, BFU2014-52125-REDT and Consolider RNAREG CSD2009-00080). Work in the P.B. laboratory is supported by a grant from the Spanish Ministry for Economy and Competitiveness (MINECO; SAF2012-36079). Work in the M.M. laboratory was supported by grants from the MINECO (SAF2012-38215), Consolider-Ingenio 2010 Programme (SAF2014-57791-REDC), Excellence Network CellSYS (BFU2014-52125-REDT), the OncoCycle Programme (S2010/BMD-2470) from the Comunidad de Madrid, Worldwide Cancer Research (WCR no. 15-0278), and the European Union Seventh Framework Programme (MitoSys project; HEALTH-F5-2010-241548)., Blocking mitotic progression has been proposed as an attractive therapeutic strategy to impair proliferation of tumour cells. However, how cells survive during prolonged mitotic arrest is not well understood. We show here that survival during mitotic arrest is affected by the special energetic requirements of mitotic cells. Prolonged mitotic arrest results in mitophagy-dependent loss of mitochondria, accompanied by reduced ATP levels and the activation of AMPK. Oxidative respiration is replaced by glycolysis owing to AMPK-dependent phosphorylation of PFKFB3 and increased production of this protein as a consequence of mitotic-specific translational activation of its mRNA. Induction of autophagy or inhibition of AMPK or PFKFB3 results in enhanced cell death in mitosis and improves the anti-tumoral efficiency of microtubule poisons in breast cancer cells. Thus, survival of mitotic-arrested cells is limited by their metabolic requirements, a feature with potential implications in cancer therapies aimed to impair mitosis or metabolism in tumour cells., Depto. de Bioquímica y Biología Molecular, Fac. de Ciencias Biológicas, TRUE, pub