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Greatwall is a protein kinase involved in the inhibition of protein phosphatase 2 (PP2A)-B55 complexes to maintain the mitotic state. Although its biochemical activity has been deeply characterized in Xenopus, its specific relevance during the progression of mitosis is not fully understood. By using a conditional knockout of the mouse ortholog, Mastl , we show here that mammalian Greatwall is essential for mouse embryonic development and cell cycle progression. Yet, Greatwall-null cells enter into mitosis with normal kinetics. However, these cells display mitotic collapse after nuclear envelope breakdown (NEB) characterized by defective chromosome condensation and prometaphase arrest. Intriguingly, Greatwall is exported from the nucleus to the cytoplasm in a CRM1-dependent manner before NEB. This export occurs after the nuclear import of cyclin B–Cdk1 complexes, requires the kinase activity of Greatwall, and is mediated by Cdk-, but not Polo-like kinase 1-dependent phosphorylation. The mitotic collapse observed in Greatwall-deficient cells is partially rescued after concomitant depletion of B55 regulatory subunits, which are mostly cytoplasmic before NEB. These data suggest that Greatwall is an essential protein in mammals required to prevent mitotic collapse after NEB.

(Background) Esophagectomy (EPG) presents high morbidity and mortality. Omega-3 fatty acids (ω-3FA) are a pharmaconutrient with benefits for postoperative morbidity. Studies of ω-3FA administered parenterally after esophagectomy are scarce. This study proposes to investigate the effect of combining fish oil lipid emulsions (LE) administered parenterally with enteral nutrition support. (Methods) Randomization was 1:1:1 in three groups: Group A received a LE mixture of 0.4 g/kg/day of fish oil and 0.4 g/kg/day of LCT/MCT 50:50, Group B received 0.8 g/kg/day of fish oil LE, and Group C received 0.8 g/kg/day of LCT/MCT 50:50. Variables were measured at recruitment time and day +1, +3, and +5. Inflammatory variables studied were Interlukin-6, C-reactive protein (CRP), tumoral necrosis factor-α (TNF-α), IL-10, IL-8 and CD25s. Safety, nutritional parameters and complications were analyzed. (Results) Administration of ω-3LE in the immediate postoperative period did not modulate the earlier inflammatory response. Statistically significant differences were found in IL-6 and CRP overall temporal evolution but were not found when studying the type of LE administered or in patients needing critical care. Administration of ω-3 resulted in safe and improved hypertriglyceridemia, depending on the dose. (Conclusions) ω-3FA has no impact on the early inflammatory postoperative response assessed for a short period but was safe. More studies for longer periods are needed.

Head and neck squamous cell carcinoma (HNSCC) remains a prevalent and aggressive malignancy, characterized by a lack of targeted therapies and limited clinical benefits. Here, we conducted an optimized whole-genome CRISPR screen across five HNSCC cell lines aimed at identifying actionable genetic vulnerabilities for rapid preclinical evaluation as novel targeted therapies. Given their critical role in cancer, cyclin-dependent kinases (CDKs) were prioritized for further investigation. Among these, CDK7 was identified as an essential and targetable gene across all five cell lines, prompting its selection for in-depth functional and molecular characterization. Genetic and pharmacological inhibition of CDK7 significantly and consistently reduced tumor cell proliferation due to generalized cell cycle arrest and apoptosis induction. Additionally, CDK7 knockout (KO) and selective inhibitors (YKL-5-124 and samuraciclib) demonstrated potent antitumor activity, effectively suppressing tumor growth in HNSCC patient-derived organoids (PDOs), as well as in both cell line- and patient-derived xenograft (PDX) mouse models with minimal toxicity. Mechanistically, CDK7 inhibition led to a broad downregulation of gene sets related to cell cycle progression and DNA repair, and significantly reduced the transcription of essential genes and untargetable vulnerabilities identified by our CRISPR screen. These findings highlight CDK7 as a promising therapeutic target for HNSCC. Our study provides strong evidence of the robust antitumor activity of CDK7-selective inhibition in disease-relevant preclinical models, strongly supporting its progression to clinical testing.

PP2A is a major tumor suppressor whose inactivation is frequently found in a wide spectrum of human tumors. In particular, deletion or epigenetic silencing of genes encoding the B55 family of PP2A regulatory subunits is a common feature of breast cancer cells. A key player in the regulation of PP2A/B55 phosphatase complexes is the cell cycle kinase MASTL (also known as Greatwall). During cell division, inhibition of PP2A-B55 by MASTL is required to maintain the mitotic state, whereas inactivation of MASTL and PP2A reactivation is required for mitotic exit. Despite its critical role in cell cycle progression in multiple organisms, its relevance as a therapeutic target in human cancer and its dependence of PP2A activity is mostly unknown. Here we show that MASTL overexpression predicts poor survival and shows prognostic value in breast cancer patients. MASTL knockdown or knockout using RNA interference or CRISPR/Cas9 systems impairs proliferation of a subset of breast cancer cells. The proliferative function of MASTL in these tumor cells requires its kinase activity and the presence of PP2A-B55 complexes. By using a new inducible CRISPR/Cas9 system in breast cancer cells, we show that genetic ablation of MASTL displays a significant therapeutic effect in vivo. All together, these data suggest that the PP2A inhibitory kinase MASTL may have both prognostic and therapeutic value in human breast cancer.

MASTL, a Ser/Thr kinase that inhibits PP2A-B55 complexes during mitosis, is mutated in autosomal dominant thrombocytopenia. However, the connections between the cell-cycle machinery and this human disease remain unexplored. We report here that, whereas Mastl ablation in megakaryocytes prevented proper maturation of these cells, mice carrying the thrombocytopenia-associated mutation developed thrombocytopenia as a consequence of aberrant activation and survival of platelets. Activation of mutant platelets was characterized by hyperstabilized pseudopods mimicking the effect of PP2A inhibition and actin polymerization defects. These aberrations were accompanied by abnormal hyperphosphorylation of multiple components of the actin cytoskeleton and were rescued both in vitro and in vivo by inhibiting upstream kinases such as PKA, PKC, or AMPK. These data reveal an unexpected role of Mastl in actin cytoskeletal dynamics in postmitotic cells and suggest that the thrombocytopenia-associated mutation in MASTL is a pathogenic dominant mutation that mimics decreased PP2A activity resulting in altered phosphorylation of cytoskeletal regulatory pathways.

Cancer stem cells (CSCs) play major roles in tumor initiation, progression, and resistance to cancer therapy. Several CSC markers have been studied in head and neck squamous cell carcinomas (HNSCC), including the pluripotency factors NANOG, SOX2, and OCT4; however, their clinical significance is still unclear. NANOG, SOX2, and OCT4 expression was evaluated by immunochemistry in 348 surgically-treated HNSCC, and correlated with clinicopathological parameters and patient outcomes. mRNA expression was further analyzed in 530 The Cancer Genome Atlas (TCGA) HNSCC. NANOG protein expression was detected in 250 (72%) cases, more frequently in patients with lymph node metastasis (p = 0.003), and was an independent predictor of better survival in multivariate analysis. While OCT4 expression was undetectable, SOX2 expression was observed in 105 (30%) cases, and strongly correlated with NANOG expression. Combined expression of both proteins showed the highest survival rates, and double-negative cases the worst survival. Strikingly, the impact of NANOG and SOX2 on outcome varied depending on tumor site and lymph node infiltration, specifically showing prognostic significance in pharyngeal tumors. Correlation between NANOG and SOX2 at mRNA and protein was specifically observed in node positive (N+) patients, and consistently correlated with better survival rates. According to our findings, NANOG protein expression is frequent in HNSCC, thereby emerging as an independent predictor of better prognosis in pharyngeal tumors. Moreover, this study uncovers a differential impact of NANOG and SOX2 expression on HNSCC prognosis, depending on tumor site and lymph node infiltration, which could facilitate high-risk patient stratification.

Activation of WNT/β-catenin signaling has been associated with a non-T-cell-inflamed tumor microenvironment (TME) in several cancers. The aim of this work was to investigate the relationship between β-catenin signaling and TME inflammation in head and neck squamous cell carcinomas (HNSCCs). Membrane and nuclear β-catenin expression, PD-L1 expression, and CD8+ tumor-infiltrating lymphocyte (TIL) density were jointly evaluated by immunohistochemistry in a series of 372 HPV-negative HNSCCs. Membrane β-catenin levels decreased in carcinomas compared to the normal epithelium. Positive nuclear β-catenin was detected in 50 tumors (14.3%) and was significantly associated with a low CD8+ TIL density (168 cells/mm2 versus 293 cells/mm2 in nuclear-β-catenin-negative cases; p = 0.01) and a tendency for a lower expression of PD-L1, resulting in association with a noninflamed TME (i.e., type II, immunological ignorance). Multivariate Cox analysis further demonstrated that low infiltration by CD8+ TILs (HR = 1.6, 95% CI = 1.19–2.14, p = 0.002) and nuclear β-catenin expression (HR = 1.47, 95% CI = 1.01–2.16, p = 0.04) were both independently associated with a poorer disease-specific survival. In conclusion, tumor-intrinsic nuclear β-catenin activation is associated with a non-inflamed TME phenotype and a poorer prognosis, thereby suggesting a possible implication as an immune exclusion mechanism for a subset of HNSCC patients.

Activation of the DNA‐damage checkpoint culminates in the inhibition of cyclin‐dependent kinase (Cdk) complexes to prevent cell‐cycle progression. We have shown recently that Cdk activity is required for activation of the Forkhead transcription factor FoxM1, an important regulator of gene expression in the G2 phase of the cell cycle. Here, we show that FoxM1 is transcriptionally active during a DNA‐damage‐induced G2 arrest and is essential for checkpoint recovery. Paradoxically, Cdk activity, although reduced after checkpoint activation, is required to maintain FoxM1‐dependent transcription during the arrest and for expression of pro‐mitotic targets such as cyclin A, cyclin B and Plk1. Indeed, we find that cells need to retain sufficient levels of Cdk activity during the DNA‐damage response to maintain cellular competence to recover from a DNA‐damaging insult. After DNA‐damage checkpoint activation, Cdk activity is reduced in order to arrest the cell cycle. Alvarez‐Fernández and colleagues demonstrate that during arrest, residual Cdk activity maintains FoxM1‐dependent transcription and the expression of mitotic inducers, such as cyclin B1 and Plk1, in order to allow efficient re‐entry into the cell cycle after checkpoint recovery.

Cellular reprogramming from somatic to pluripotent cells is the basis for multiple applications aimed to replace damaged tissues in regenerative medicine. However, this process is limited by intrinsic barriers that are induced in response to reprogramming factors. In this manuscript we report that miR-203, a microRNA with multiple functions in differentiation and tumor suppression, acts as an endogenous barrier to reprogramming. Genetic ablation of miR-203 results in enhanced reprogramming whereas its expression prevents the formation of pluripotent cells both in vitro and in vivo. Mechanistically, this effect correlates with the direct repression of NFATC2, a transcription factor involved in the early phases of reprogramming. Inhibition of NFATC2 mimics miR-203 effects whereas NFATC2 overexpression rescues inducible cell pluripotency in miR-203-overexpressing cultures. These data suggest that miR-203 repression may favor the efficiency of reprogramming in a variety of cellular models.

Full differentiation potential along with self-renewal capacity is a major property of pluripotent stem cells (PSCs). However, the differentiation capacity frequently decreases during expansion of PSCs in vitro. We show here that transient exposure to a single microRNA, expressed at early stages during normal development, improves the differentiation capacity of already-established murine and human PSCs. Short exposure to miR-203 in PSCs (miPSCs) results in expanded differentiation potency as well as improved efficiency in stringent assays such as tetraploid complementation and human-mouse interspecies chimerism. Mechanistically, these effects are mediated by direct repression of de novo DNA methyltransferases Dnmt3a and Dnmt3b, leading to transient and reversible erasing of DNA methylation. As a proof of concept, miR-203 improves differentiation and maturation of PSCs into cardiomyocytes in vitro as well as cardiac regeneration in vivo, after cardiac injury. These data support the use of transient exposure to miR-203 as a general and single method to reset the epigenetic memory in PSCs, and improve their use in regenerative medicine. Footnotes * Supplemental files added.