The nucleoporin ALADIN regulates Aurora A localization to ensure robust mitotic spindle formation

The formation of the mitotic spindle is a complex process that requires massive cellular reorganization. Regulation by mitotic kinases controls this entire process. One of these mitotic controllers is Aurora A kinase, which is itself highly regulated. In this study, we show that the nuclear pore protein ALADIN is a novel spatial regulator of Aurora A. Without ALADIN, Aurora A spreads from centrosomes onto spindle microtubules, which affects the distribution of a subset of microtubule regulators and slows spindle assembly and chromosome alignment. ALADIN interacts with inactive Aurora A and is recruited to the spindle pole after Aurora A inhibition. Of interest, mutations in ALADIN cause triple A syndrome. We find that some of the mitotic phenotypes that we observe after ALADIN depletion also occur in cells from triple A syndrome patients, which raises the possibility that mitotic errors may underlie part of the etiology of this syndrome

Mitochondria-derived nuclear ATP surge protects against confinement-induced proliferation defects

The physical tissue microenvironment regulates cell state and behaviour. How mechanical confinement rewires the subcellular localisation of organelles and affects cellular metabolism is largely unknown. In this study, proteomics analysis revealed that cellular confinement induced a strong enrichment of mitochondrial proteins in the nuclear fraction. Quantitative live cell microscopy confirmed that mechanical cell confinement leads to a rapid re-localisation of mitochondria to the nuclear periphery in vitro, reflecting a physiologically relevant phenomenon in patient-derived tumours. This nucleus-mitochondria proximity is mediated by an endoplasmic reticulum-based net that entraps the mitochondria in an actin-dependent manner. Functionally, the nucleus-mitochondria proximity results in a nuclear ATP surge, which can be regulated by the genetic and pharmacological modulation of mitochondrial ATP production or via alterations of the actin cytoskeleton. The confinement-induced nuclear ATP surge has physiologically significant long-term effects on cell fitness, driven by changes in chromatin state, enhanced DNA damage repair, and cell cycle progression during mechanical cell deformation. Together, our data describe a confinement-induced metabolic adaptation that is required to enable prompt DNA damage repair and cell proliferation under mechanical confinement stress by facilitating chromatin state transitions

Nuclear localization of MTHFD2 is required for correct mitosis progression

Subcellular compartmentalization of metabolic enzymes establishes a unique metabolic environment that elicits specific cellular functions. Indeed, the nuclear translocation of certain metabolic enzymes is required for epigenetic regulation and gene expression control. Here, we show that the nuclear localization of the mitochondrial enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) ensures mitosis progression. Nuclear MTHFD2 interacts with proteins involved in mitosis regulation and centromere stability, including the methyltransferases KMT5A and DNMT3B. Loss of MTHFD2 induces severe methylation defects and impedes correct mitosis completion. MTHFD2 deficient cells display chromosome congression and segregation defects and accumulate chromosomal aberrations. Blocking the catalytic nuclear function of MTHFD2 recapitulates the phenotype observed in MTHFD2 deficient cells, whereas restricting MTHFD2 to the nucleus is sufficient to ensure correct mitotic progression. Our discovery uncovers a nuclear role for MTHFD2, supporting the notion that translocation of metabolic enzymes to the nucleus is required to meet precise chromatin needs.We acknowledge support of the Spanish Ministry of Science and Innovation through the Centro de Excelencia Severo Ochoa (CEX2020-001049-S, MCIN/AEI /10.13039/501100011033), and the Generalitat de Catalunya through the CERCA programme. We are grateful to the CRG Core Technologies Programme for their support and assistance in this work. We would like to thank the CRG and CNAG Sequencing Facilities (Barcelona, Spain) for all next-generation sequencing, the CRG Proteomics Facility (Barcelona, Spain) for the MTHFD2 interactome analysis, the CRG Flow Cytometry Facility (Barcelona, Spain) for the sorting, the IMIM Platform for molecular cytogenetics (Barcelona, Spain) for the karyotype analysis, and MARbiobank for provision of patient samples for organoid generation. The CRG/UPF Proteomics Unit is part of the Spanish Infrastructure for Omics Technologies (ICTS OmicsTech). We would like to thank Prof. Thomas Helleday for providing the MTHFD2 inhibitor TH9619 and for the fruitful discussions. N.P.L. was supported by a Boehringer Ingelheim Fonds Ph.D. fellowship. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 852343, ERC-StG-852343-EPICAMENTE) and from a Spanish Plan Estatal grant (Ministerio de Ciencia e Innovación, Project PID2019-110598GA-I00 funded by MICIU/AEI /10.13039/501100011033).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2020-001049-S).Peer reviewe

Identification of highly penetrant Rb-related synthetic lethal interactions in triple negative breast cancer.

Although defects in the RB1 tumour suppressor are one of the more common driver alterations found in triple-negative breast cancer (TNBC), therapeutic approaches that exploit this have not been identified. By integrating molecular profiling data with data from multiple genetic perturbation screens, we identified candidate synthetic lethal (SL) interactions associated with RB1 defects in TNBC. We refined this analysis by identifying the highly penetrant effects, reasoning that these would be more robust in the face of molecular heterogeneity and would represent more promising therapeutic targets. A significant proportion of the highly penetrant RB1 SL effects involved proteins closely associated with RB1 function, suggesting that this might be a defining characteristic. These included nuclear pore complex components associated with the MAD2 spindle checkpoint protein, the kinase and bromodomain containing transcription factor TAF1, and multiple components of the SCFSKP Cullin F box containing complex. Small-molecule inhibition of SCFSKP elicited an increase in p27Kip levels, providing a mechanistic rationale for RB1 SL. Transcript expression of SKP2, a SCFSKP component, was elevated in RB1-defective TNBCs, suggesting that in these tumours, SKP2 activity might buffer the effects of RB1 dysfunction

Role of the Kinases NEK6, NEK7 and NEK9 in the Regulation of the Centrosome Cycle

[eng] This thesis project is focused on the study of the signaling module formed by the NIMA-related protein Nek6, Nek7, and Nek9 and their function during early mitosis, with particular interest in centrosome separation and maturation. Nek9/Nercc1 was identified by Dr. Joan Roig. Nek9 is expressed in all cell lines and tissues studied is inactive during interphase while during mitosis is activated through phosphorylation by Plk1 which is in fact able to bind Nek9 and subsequently phosphorylates Nek9 on its activation loop. During mitosis Nek6 and Nek7 bind the C-terminal of Nek9. Once active, Nek9 can phosphorylate Nek6 and Nek7, thus activating them. Active Nek9 localizes at centrosome, suggesting that Nek9/Nek6-7 has important functions in the organization of microtubules during cell division. Confirming this idea, it has been shown that the microinjection of anti-Nek9 module induces arrest in prometaphase with disorganized spindle structures and misaligned chromosomes, or leads to abnormal mitosis resulting in aneuploidy. In the same direction, interference with the function of Nek7 or Nek6 leads to abnormal mitotic progression and spindle formation. We described how the Nek9/Nek6-7 module could provide a link connecting Plk1 and Eg5 in the context of centrosome separation. we analyzed the effects of Plk1, Eg5, Nek9, Nek6 or Nek7 down-regulation by RNAi on the extent of separation of duplicated centrosomes in prophase cells and we observed how this downregulation was affecting centrosome separation. We determine whether the activation of Nek9 or Nek6 could induce centrosome separation trasfecting cells with the active form of these two kinases; a considerable amount of cells that were in interphase shown separate centrosome demonstrating that Nek9/Nek6 are sufficient to induce centrosome separation. To test whether active Nek9 and Nek6 exerted their effect through the regulation of Eg5 we simultaneously transfected the cells with Eg5 siRNAs and we completely lost the centrosome separation described above. We demonstrated by immunofluorescence that the key event during centrosome separation was the recruitment of Eg5 at centrosomes and that the down-regulation of Plk1, Nek6, Nek7 or Nek9 resulted in prophase cells with unseparated centrosomes because Eg5 was not properly recruited. To prove whether the phosphorylation on Ser-1033 controls the accumulation of Eg5 to centrosomes and centrosome separation during early mitosis we transfected cells with wild type Eg5 or Eg5 S1033A; the wild type form of the kinesin was able to localize at centrosome and rescue the normal phenotype while Eg5 S1033A was not able to localize and resulted in cells delayed in mitosis. Plk1, the Nek9 activator, is involved in the regulation of centrosome maturation during early mitosis. Centrosome maturation refers to the process through which centrosomes increase size and microtubule nucleation activity and requires the accumulation of γ-TuRC complexes at centrosome. This recruitment depends on Nedd1 that acts as γ-Tubulin targeting factor. Plk1 depletion prevents accumulation of Nedd1 at centrosome. Our experiments show the importance of Nek9 in the regulation of centrosome maturation downstream of Plk1. Depletion of Nek9 by siRNA determined a decrease of γ-Tubulin and Nedd1 at centrosome. Further we investigated the upstream role of Plk1 depleting Plk1 and trasfecting active Nek9 and it was able to rescue the normal phenotype. Nek9 can interact with Nedd1 during mitosis and phosphorylates it provoking its accumulation at centrosome. The no-phosphorylable form of Nedd1 was not able to accumulate at centrosome and support the accumulation of γ-Tubulin there, determining a delay of the cells in prometaphase. Our results show that Nek9 is the link between Plk1 activity and the recruitment of Nedd1 to the centrosome and that the pathway formed by Plk1/Nek9/Nedd1 can be a key element in the control of mitotic centrosome maturation

MTHFD2 in healthy and cancer cells: Canonical and non-canonical functions

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) is a mitochondrial enzyme of the folate-mediated one-carbon metabolism pathway. MTHFD2 has become a highly attractive therapeutic target due to its consistent upregulation in cancer tissues and its major contribution to tumor progression, although it also performs vital functions in proliferating healthy cells. Here, we review the diversity of canonical and non-canonical functions of this key metabolic enzyme under physiological conditions and in carcinogenesis. We provide an overview of its therapeutic potential and describe its regulatory mechanisms. In addition, we discuss the recently described non-canonical functions of MTHFD2 and the mechanistic basis of its oncogenic function. Finally, we speculate on novel therapeutic approaches that take into account subcellular compartmentalization and outline new research directions that would contribute to a better understanding of the fundamental roles of this metabolic enzyme in health and disease