PP2A-B55 phosphatase counteracts Ki-67-dependent chromosome individualization during mitosis.

Cell cycle progression is regulated by the orderly balance between kinase and phosphatase activities. PP2A phosphatase holoenzymes containing the B55 family of regulatory B subunits function as major CDK1-counteracting phosphatases during mitotic exit in mammals. However, the identification of the specific mitotic roles of these PP2A-B55 complexes has been hindered by the existence of multiple B55 isoforms. Here, through the generation of loss-of-function genetic mouse models for the two ubiquitous B55 isoforms (B55α and B55δ), we report that PP2A-B55α and PP2A-B55δ complexes display overlapping roles in controlling the dynamics of proper chromosome individualization and clustering during mitosis. In the absence of PP2A-B55 activity, mitotic cells display increased chromosome individualization in the presence of enhanced phosphorylation and perichromosomal loading of Ki-67. These data provide experimental evidence for a regulatory mechanism by which the balance between kinase and PP2A-B55 phosphatase activity controls the Ki-67-mediated spatial organization of the mass of chromosomes during mitosis.

Comparative biological activity of palbociclib and ribociclib in hormone receptor-positive breast cancer.

This study examines the biological effects of palbociclib and ribociclib in hormone receptor-positive breast cancer, pivotal to the HARMONIA prospective phase III clinical trial. We explore the downstream impacts of these CDK4/6 inhibitors, focusing on cell lines and patient-derived tumor samples. We treated HR+ breast cancer cell lines (T47D, MCF7, and BT474) with palbociclib or ribociclib (100 nM or 500 nM), alone or combined with fulvestrant (1 nM), over periods of 24, 72, or 144 h. Our assessments included PAM50 gene expression, RB1 phosphorylation, Lamin-B1 protein levels, and senescence-associated ß-galactosidase activity. We further analyzed PAM50 gene signatures from the CORALLEEN and NeoPalAna phase II trials. Both CDK4/6 inhibitors similarly inhibited proliferation across the cell lines. At 100 nM, both drugs partially reduced p-RB1, with further decreases at 500 nM over 144 h. Treatment led to reduced Lamin-B1 expression and increased senescence-associated ß-galactosidase activity. Both drugs enhanced Luminal A and reduced Luminal B and proliferation signatures at both doses. However, the HER2-enriched signature significantly diminished only at the higher dose of 500 nM. Corresponding changes were observed in tumor samples from the CORALLEEN and NeoPalAna studies. At 2 weeks of treatment, both drugs significantly reduced the HER2-enriched signature, but at surgery, this reduction was consistent only with ribociclib. Our findings suggest that while both CDK4/6 inhibitors effectively modulate key biological pathways in HR+/HER2- breast cancer, nuances in their impact, particularly on the HER2-enriched signature, are dose-dependent, influenced by the addition of fulvestrant and warrant further investigation.

Kinase-inactivated CDK6 preserves the long-term functionality of adult hematopoietic stem cells.

ABSTRACT: Hematopoietic stem cells (HSCs) are characterized by the ability to self-renew and to replenish the hematopoietic system. The cell-cycle kinase cyclin-dependent kinase 6 (CDK6) regulates transcription, whereby it has both kinase-dependent and kinase-independent functions. Herein, we describe the complex role of CDK6, balancing quiescence, proliferation, self-renewal, and differentiation in activated HSCs. Mouse HSCs expressing kinase-inactivated CDK6 show enhanced long-term repopulation and homing, whereas HSCs lacking CDK6 have impaired functionality. The transcriptomes of basal and serially transplanted HSCs expressing kinase-inactivated CDK6 exhibit an expression pattern dominated by HSC quiescence and self-renewal, supporting a concept, in which myc-associated zinc finger protein (MAZ) and nuclear transcription factor Y subunit alpha (NFY-A) are critical CDK6 interactors. Pharmacologic kinase inhibition with a clinically used CDK4/6 inhibitor in murine and human HSCs validated our findings and resulted in increased repopulation capability and enhanced stemness. Our findings highlight a kinase-independent role of CDK6 in long-term HSC functionality. CDK6 kinase inhibition represents a possible strategy to improve HSC fitness.

Cross Talk Between Metabolism and the Cell Division Cycle.

Cell division requires a massive rewiring of cellular pathways, including molecular routes involved in providing energy for cell survival and functionality. The energetic requirements and the metabolic opportunities for generating energy change during the different phases of the cell cycle and how these processes are connected is still poorly understood. This chapter discusses basic concepts for a coordinated analysis of cell cycle progression and metabolism and provides specific protocols for studying these two connected processes in mammalian cells.

PLK1 inhibition dampens NLRP3 inflammasome-elicited response in inflammatory disease models.

Unabated activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome is linked with the pathogenesis of various inflammatory disorders. Polo-like kinase 1 (PLK1) has been widely studied for its role in mitosis. Here, using both pharmacological and genetic approaches, we demonstrate that PLK1 promoted NLRP3 inflammasome activation at cell interphase. Using an unbiased proximity-dependent biotin identification (Bio-ID) screen for the PLK1 interactome in macrophages, we show an enhanced proximal association of NLRP3 with PLK1 upon NLRP3 inflammasome activation. We further confirmed the interaction between PLK1 and NLRP3 and identified the interacting domains. Mechanistically, we show that PLK1 orchestrated the microtubule-organizing center (MTOC) structure and NLRP3 subcellular positioning upon inflammasome activation. Treatment with a selective PLK1 kinase inhibitor suppressed IL-1ß production in in vivo inflammatory models, including LPS-induced endotoxemia and monosodium urate-induced peritonitis in mice. Our results uncover a role of PLK1 in regulating NLRP3 inflammasome activation during interphase and identify pharmacological inhibition of PLK1 as a potential therapeutic strategy for inflammatory diseases with excessive NLRP3 inflammasome activation.

miR-203 drives breast cancer cell differentiation.

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.

Decoding protein methylation function with thermal stability analysis.

Protein methylation is an important modification beyond epigenetics. However, systems analyses of protein methylation lag behind compared to other modifications. Recently, thermal stability analyses have been developed which provide a proxy of a protein functional status. Here, we show that molecular and functional events closely linked to protein methylation can be revealed by the analysis of thermal stability. Using mouse embryonic stem cells as a model, we show that Prmt5 regulates mRNA binding proteins that are enriched in intrinsically disordered regions and involved in liquid-liquid phase separation mechanisms, including the formation of stress granules. Moreover, we reveal a non-canonical function of Ezh2 in mitotic chromosomes and the perichromosomal layer, and identify Mki67 as a putative Ezh2 substrate. Our approach provides an opportunity to systematically explore protein methylation function and represents a rich resource for understanding its role in pluripotency.

HOPE (SOLTI-1903) breast cancer study: real-world, patient-centric, clinical practice study to assess the impact of genomic data on next treatment decision-choice in patients with locally advanced or metastatic breast cancer.

Background: Metastatic breast cancer (mBC) causes nearly all BC-related deaths. Next-generation sequencing (NGS) technologies allow for the application of personalized medicine using targeted therapies that could improve patients' outcomes. However, NGS is not routinely used in the clinical practice and its cost induces access-inequity among patients. We hypothesized that promoting active patient participation in the management of their disease offering access to NGS testing and to the subsequent medical interpretation and recommendations provided by a multidisciplinary molecular advisory board (MAB) could contribute to progressively overcome this challenge. We designed HOPE (SOLTI-1903) breast cancer trial, a study where patients voluntarily lead their inclusion through a digital tool (DT). The main objectives of HOPE study are to empower mBC patients, gather real-world data on the use of molecular information in the management of mBC and to generate evidence to assess the clinical utility for healthcare systems. Trial design: After self-registration through the DT, the study team validates eligibility criteria and assists patients with mBC in the subsequent steps. Patients get access to the information sheet and sign the informed consent form through an advanced digital signature. Afterwards, they provide the most recent (preferably) metastatic archival tumor sample for DNA-sequencing and a blood sample obtained at the time of disease progression for ctDNA analysis. Paired results are reviewed by the MAB, considering patient's medical history. The MAB provides a further interpretation of molecular results and potential treatment recommendations, including ongoing clinical trials and further (germline) genetic testing. Participants self-document their treatment and disease evolution for the next 2 years. Patients are encouraged to involve their physicians in the study. HOPE also includes a patient empowerment program with educational workshops and videos about mBC and precision medicine in oncology. The primary endpoint of the study was to describe the feasibility of a patient-centric precision oncology program in mBC patients when a comprehensive genomic profile is available to decide on a subsequent line of treatment. Clinical trial registration: www.soltihope.com, identifier NCT04497285.

p27Kip1 V109G as a biomarker for CDK4/6 inhibitors indication in hormone receptor-positive breast cancer.

CDK4/6 inhibitors benefit a minority of patients who receive them in the breast cancer adjuvant setting. p27Kip1 is a protein that inhibits CDK/Cyclin complexes. We hypothesized that single-nucleotide polymorphisms that impaired p27Kip1 function could render patients refractory to endocrine therapy but responsive to CDK4/6 inhibitors, narrowing the patient subpopulation that requires CDK4/6 inhibitors. We found that the p27Kip1 V109G single-nucleotide polymorphism is homozygous in approximately 15% of hormone-positive breast cancer patients. Polymorphic patients experience rapid failure in response to endocrine monotherapy compared with wild-type or heterozygous patients in the first-line metastatic setting (progression-free survival: 92 vs 485 days, P < .001); when CDK4/6 inhibitors are added, the differences disappear (progression-free survival: 658 vs 761 days, P = .92). As opposed to wild-type p27Kip1, p27Kip1 V109G is unable to suppress the kinase activity of CDK4 in the presence of endocrine inhibitors; however, palbociclib blocks CDK4 kinase activity regardless of the p27Kip1 status. p27Kip1 genotyping could constitute a tool for treatment selection.

Harnessing transcriptionally driven chromosomal instability adaptation to target therapy-refractory lethal prostate cancer.

Metastatic prostate cancer (PCa) inevitably acquires resistance to standard therapy preceding lethality. Here, we unveil a chromosomal instability (CIN) tolerance mechanism as a therapeutic vulnerability of therapy-refractory lethal PCa. Through genomic and transcriptomic analysis of patient datasets, we find that castration and chemotherapy-resistant tumors display the highest CIN and mitotic kinase levels. Functional genomics screening coupled with quantitative phosphoproteomics identify MASTL kinase as a survival vulnerability specific of chemotherapy-resistant PCa cells. Mechanistically, MASTL upregulation is driven by transcriptional rewiring mechanisms involving the non-canonical transcription factors androgen receptor splice variant 7 and E2F7 in a circuitry that restrains deleterious CIN and prevents cell death selectively in metastatic therapy-resistant PCa cells. Notably, MASTL pharmacological inhibition re-sensitizes tumors to standard therapy and improves survival of pre-clinical models. These results uncover a targetable mechanism promoting high CIN adaptation and survival of lethal PCa.

Mammalian CDC14 phosphatases control exit from stemness in pluripotent cells.

Maintenance of stemness is tightly linked to cell cycle regulation through protein phosphorylation by cyclin-dependent kinases (CDKs). However, how this process is reversed during differentiation is unknown. We report here that exit from stemness and differentiation of pluripotent cells along the neural lineage are controlled by CDC14, a CDK-counteracting phosphatase whose function in mammals remains obscure. Lack of the two CDC14 family members, CDC14A and CDC14B, results in deficient development of the neural system in the mouse and impairs neural differentiation from embryonic stem cells (ESCs). Mechanistically, CDC14 directly dephosphorylates specific proline-directed Ser/Thr residues of undifferentiated embryonic transcription Factor 1 (UTF1) during the exit from stemness, triggering its proteasome-dependent degradation. Multiomic single-cell analysis of transcription and chromatin accessibility in differentiating ESCs suggests that increased UTF1 levels in the absence of CDC14 prevent the proper firing of bivalent promoters required for differentiation. CDC14 phosphatases are dispensable for mitotic exit, suggesting that CDC14 phosphatases have evolved to control stemness rather than cell cycle exit and establish the CDK-CDC14 axis as a critical molecular switch for linking cell cycle regulation and self-renewal.

The MASTL/PP2A cell cycle kinase-phosphatase module restrains PI3K-Akt activity in an mTORC1-dependent manner.

The AKT-mTOR pathway is a central regulator of cell growth and metabolism. Upon sustained mTOR activity, AKT activity is attenuated by a feedback loop that restrains upstream signaling. However, how cells control the signals that limit AKT activity is not fully understood. Here, we show that MASTL/Greatwall, a cell cycle kinase that supports mitosis by phosphorylating the PP2A/B55 inhibitors ENSA/ARPP19, inhibits PI3K-AKT activity by sustaining mTORC1- and S6K1-dependent phosphorylation of IRS1 and GRB10. Genetic depletion of MASTL results in an inefficient feedback loop and AKT hyperactivity. These defects are rescued by the expression of phosphomimetic ENSA/ARPP19 or inhibition of PP2A/B55 phosphatases. MASTL is directly phosphorylated by mTORC1, thereby limiting the PP2A/B55-dependent dephosphorylation of IRS1 and GRB10 downstream of mTORC1. Downregulation of MASTL results in increased glucose uptake in vitro and increased glucose tolerance in adult mice, suggesting the relevance of the MASTL-PP2A/B55 kinase-phosphatase module in controlling AKT and maintaining metabolic homeostasis.

CoQ10 reduces glioblastoma growth and infiltration through proteome remodeling and inhibition of angiogenesis and inflammation.

PURPOSE: Most monotherapies available against glioblastoma multiforme (GBM) target individual hallmarks of this aggressive brain tumor with minimal success. In this article, we propose a therapeutic strategy using coenzyme Q10 (CoQ10) as a pleiotropic factor that crosses the blood-brain barrier and accumulates in cell membranes acting as an antioxidant, and in mitochondrial membranes as a regulator of cell bioenergetics and gene expression. METHODS: Xenografts of U251 cells in nu/nu mice were used to assay tumor growth, hypoxia, angiogenesis, and inflammation. An orthotopic model was used to explore microglial infiltration, tumor growth, and invasion into the brain parenchyma. Cell proliferation, migration, invasion, proteome remodeling, and secretome were assayed in vitro. Conditioned media were used to assay angiogenesis, monocyte chemoattraction, and differentiation into macrophages in vitro. RESULTS: CoQ10 treatment decreased tumor volume in xenografts and orthotopic models, although its effect on tumor cell proliferation was not direct. Tumors from mice treated with CoQ10 were less hypoxic and vascularized, having less infiltration from inflammatory cells. Treatment-induced downregulation of HIF-1α and NF-kB led to a complete remodeling of the tumor cells proteome and secretome, impacting angiogenesis, monocyte infiltration, and their differentiation into macrophages. Besides, tumor cell migration and invasion were drastically restricted by mechanisms involving modulation of the actin cytoskeleton and downregulation of matrix metalloproteases (MMPs). CONCLUSIONS: CoQ10 has a pleiotropic effect on GBM growth, targeting several hallmarks simultaneously. Thus, its integration into current treatments of this fatal disease should be considered.

Biallelic germline mutations in MAD1L1 induce a syndrome of aneuploidy with high tumor susceptibility.

Germline mutations leading to aneuploidy are rare, and their tumor-promoting properties are mostly unknown at the molecular level. We report here novel germline biallelic mutations in MAD1L1, encoding the spindle assembly checkpoint (SAC) protein MAD1, in a 36-year-old female with a dozen of neoplasias. Functional studies demonstrated lack of full-length protein and deficient SAC response, resulting in ~30 to 40% of aneuploid blood cells. Single-cell RNA analysis identified mitochondrial stress accompanied by systemic inflammation with enhanced interferon and NFκB signaling both in aneuploid and euploid cells, suggesting a non-cell autonomous response. MAD1L1 mutations resulted in specific clonal expansions of γδ T cells with chromosome 18 gains and enhanced cytotoxic profile as well as intermediate B cells with chromosome 12 gains and transcriptomic signatures characteristic of leukemia cells. These data point to MAD1L1 mutations as the cause of a new variant of mosaic variegated aneuploidy with systemic inflammation and unprecedented tumor susceptibility.

Mitotic Checkpoint Imbalances in Familial Cancer.

Numerical chromosomal aberrations are highly frequent in cancer cells. However, tumor-associated mutations in regulators of the mitotic machinery that controls chromosome segregation are rather rare. By sequencing families with hereditary cancer, Chen and colleagues report two novel heterozygous mutations in CDC20, a coactivator of the anaphase-promoting complex (APC/C) and a target of the spindle assembly checkpoint (SAC) that prevents chromosome missegregation during mitosis. CDC20 mutations result in partial SAC functionality and segregate with tumor susceptibility in families with aneuploid ovarian cancers and other malignancies. The expression of these mutations in a knock-in mouse model accelerates the development of Myc-induced lymphomas and mortality, strongly supporting the notion that partial dysfunction of mitotic regulators may have profound implications in spontaneous and hereditary cancer. See related article by Chen et al., p. 3499.

Haspin participates in AURKB recruitment to centromeres and contributes to chromosome congression in male mouse meiosis.

Chromosome segregation requires that centromeres properly attach to spindle microtubules. This essential step regulates the accuracy of cell division and must therefore be precisely regulated. One of the main centromeric regulatory signaling pathways is the haspin-H3T3ph-chromosomal passenger complex (CPC) cascade, which is responsible for the recruitment of the CPC to the centromeres. During mitosis, the haspin kinase phosphorylates histone H3 at threonine 3 (H3T3ph), an essential epigenetic mark that recruits the CPC, in which the catalytic component is Aurora B kinase (AURKB). However, the centromeric haspin-H3T3ph-CPC pathway remains largely uncharacterized in mammalian male meiosis. We have analyzed haspin functions by either its chemical inhibition with LDN-192960 in cultured spermatocytes, or the ablation of the Haspin gene in Haspin-/- mice. Our studies suggest that haspin kinase activity is required for proper chromosome congression both during meiotic divisions and for the recruitment of Aurora B and kinesin MCAK (also known as KIF2C) to meiotic centromeres. However, the absence of H3T3ph histone mark does not alter borealin (or CDCA8) and SGO2 centromeric localization. These results add new and relevant information regarding the regulation of the haspin-H3T3ph-CPC pathway and centromere function during meiosis.

Genetic interaction between PLK1 and downstream MCPH proteins in the control of centrosome asymmetry and cell fate during neural progenitor division.

Alteration of centrosome function and dynamics results in major defects during chromosome segregation and is associated with primary autosomal microcephaly (MCPH). Despite the knowledge accumulated in the last few years, why some centrosomal defects specifically affect neural progenitors is not clear. We describe here that the centrosomal kinase PLK1 controls centrosome asymmetry and cell fate in neural progenitors during development. Gain- or loss-of-function mutations in Plk1, as well as deficiencies in the MCPH genes Cdk5rap2 (MCPH3) and Cep135 (MCPH8), lead to abnormal asymmetry in the centrosomes carrying the mother and daughter centriole in neural progenitors. However, whereas loss of MCPH proteins leads to increased centrosome asymmetry and microcephaly, deficient PLK1 activity results in reduced asymmetry and increased expansion of neural progenitors and cortical growth during mid-gestation. The combination of PLK1 and MCPH mutations results in increased microcephaly accompanied by more aggressive centrosomal and mitotic abnormalities. In addition to highlighting the delicate balance in the level and activity of centrosomal regulators, these data suggest that human PLK1, which maps to 16p12.1, may contribute to the neurodevelopmental defects associated with 16p11.2-p12.2 microdeletions and microduplications in children with developmental delay and dysmorphic features.

A Preclinical and Phase Ib Study of Palbociclib plus Nab-Paclitaxel in Patients with Metastatic Adenocarcinoma of the Pancreas.

Purpose: To assess the preclinical efficacy, clinical safety and efficacy, and MTD of palbociclib plus nab-paclitaxel in patients with advanced pancreatic ductal adenocarcinoma (PDAC). Experimental Design: Preclinical activity was tested in patient-derived xenograft (PDX) models of PDAC. In the open-label, phase I clinical study, the dose-escalation cohort received oral palbociclib initially at 75 mg/day (range, 50‒125 mg/day; modified 3+3 design; 3/1 schedule); intravenous nab-paclitaxel was administered weekly for 3 weeks/28-day cycle at 100‒125 mg/m2. The modified dose-regimen cohorts received palbociclib 75 mg/day (3/1 schedule or continuously) plus nab-paclitaxel (biweekly 125 or 100 mg/m2, respectively). The prespecified efficacy threshold was 12-month survival probability of ≥65% at the MTD. Results: Palbociclib plus nab-paclitaxel was more effective than gemcitabine plus nab-paclitaxel in three of four PDX models tested; the combination was not inferior to paclitaxel plus gemcitabine. In the clinical trial, 76 patients (80% received prior treatment for advanced disease) were enrolled. Four dose-limiting toxicities were observed [mucositis (n = 1), neutropenia (n = 2), febrile neutropenia (n = 1)]. The MTD was palbociclib 100 mg for 21 of every 28 days and nab-paclitaxel 125 mg/m2 weekly for 3 weeks in a 28-day cycle. Among all patients, the most common all-causality any-grade adverse events were neutropenia (76.3%), asthenia/fatigue (52.6%), nausea (42.1%), and anemia (40.8%). At the MTD (n = 27), the 12-month survival probability was 50% (95% confidence interval, 29.9-67.2). Conclusions: This study showed the tolerability and antitumor activity of palbociclib plus nab-paclitaxel treatment in patients with PDAC; however, the prespecified efficacy threshold was not met. Trial Registration: Pfizer Inc (NCT02501902). Significance: In this article, the combination of palbociclib, a CDK4/6 inhibitor, and nab-paclitaxel in advanced pancreatic cancer evaluates an important drug combination using translational science. In addition, the work presented combines preclinical and clinical data along with pharmacokinetic and pharmacodynamic assessments to find alternative treatments for this patient population.

Expanding the Differentiation Potential of Already-Established Pluripotent Stem Cells.

Pluripotent stem cells (PSCs) have proven to be an essential tool in many research fields including basic cell biology, development, or human disease. In addition, we are only starting to see their potential in regenerative medicine. Manipulation and culture of PSCs, however, imposes limitations in the quality of these cells and their ability to differentiate into functional cells with physiological function. Here we propose a novel and simple technique based on the transient expression of a single microRNA molecule to expand the differentiation potency of a wide range of PSCs including induced PSCs (iPSCs) as well as embryonic stem cells (ESCs). This method requires no genetic modification of PSCs and achieves stable improvement of the differentiation potential of these cells through several cell passages both in vitro and in vivo.