Age-specific induction of mutant p53 drives clonal hematopoiesis and acute myeloid leukemia in adult mice.

The investigation of the mechanisms behind p53 mutations in acute myeloid leukemia (AML) has been limited by the lack of suitable mouse models, which historically have resulted in lymphoma rather than leukemia. This study introduces two new AML mouse models. One model induces mutant p53 and Mdm2 haploinsufficiency in early development, showing the role of Mdm2 in myeloid-biased hematopoiesis and AML predisposition, independent of p53. The second model mimics clonal hematopoiesis by inducing mutant p53 in adult hematopoietic stem cells, demonstrating that the timing of p53 mutation determines AML vs. lymphoma development. In this context, age-related changes in hematopoietic stem cells (HSCs) collaborate with mutant p53 to predispose toward myeloid transformation rather than lymphoma development. Our study unveils new insights into the cooperative impact of HSC age, Trp53 mutations, and Mdm2 haploinsufficiency on clonal hematopoiesis and the development of myeloid malignancies.

Outcome of 3q26.2/MECOM rearrangements in chronic myeloid leukemia.

STUDY AIMS: To evaluate the outcomes of patients with 3q26.2/MECOM-rearranged chronic myeloid leukemia (CML). METHODS: We reviewed consecutive adult patients with 3q26.2/MECOM-rearranged CML between January 1, 1998 and February 16, 2023. Rearrangements of 3q26.2/MECOM were confirmed by conventional cytogenetics, and fluorescence in situ hybridization starting in 2015. RESULTS: We identified 55 patients with MECOM-rearranged CML, including 23 in chronic phase (CP) or accelerated phase (AP) and 32 in blast phase (BP). Nine patients (16%) achieved a major cytogenetic response (MCyR) or deeper. At a median follow-up of 89 months, median survival was 14 months. The 5-year survival rate was 19% overall, 23% in CML-CP/AP, and 15% in CML-BP. In the 6-month landmark analysis, the 5-year survival rate was 41% for allogeneic stem cell transplantation (allo-SCT) recipients versus 17% for non-recipients (P = 0.050). Multivariate analysis showed that the percentage of marrow blasts and achievement of MCyR or deeper could predict survival. CONCLUSION: Outcomes of 3q26.2/MECOM-rearranged CML are poor despite the availability of multiple BCR::ABL1 tyrosine kinase inhibitors (TKIs). Third-generation TKIs in combination with novel agents and possible allo-SCT could be considered given the poor outcomes and resistance to second-generation TKIs.

Population characteristics and diagnosis rate of chronic kidney disease by eGFR and proteinuria in Japanese clinical practice: an observational database study.

Chronic kidney disease (CKD) guidelines recommend early identification and intervention to delay the progression of CKD. The Kidney Disease: Improving Global Outcomes (KDIGO) heatmap is widely used for risk evaluation in CKD management; however, real-world evidence on clinical characteristics based on the KDIGO heatmap remains limited worldwide including Japan. In order to understand the management of CKD including its diagnostic rates in a Japanese clinical setting on the basis of KDIGO heatmap, we utilized a medical record database that contains estimated glomerular filtration rate (eGFR) and urine protein data. Adult individuals (≥ 18 years) with two eGFR results of < 90 mL/min/1.73 m2, 90-360 days apart, were included. Approximately half of patients (452,996/788,059) had proteinuria test results and 6.9% (54,073) had quantitative results. CKD diagnosis rate in patients without proteinuria data was 5.9%, with a lower rate (2.9%) in stage G2; the corresponding rates with quantitative test results were 43.5% and 31.3%, respectively. The most frequent comorbidities were hypertension, diabetes, and cardiovascular disease, and their prevalence increased as the eGFR and proteinuria stages progressed. This study revealed a low rate of proteinuria assessment, especially using quantitative methods, and diagnosis in individuals with suspected CKD. With emerging treatment options to prevent CKD progression and complication onset, there is a need for early evaluation and diagnosis of CKD.

Radiological findings associated with postoperative wound infection after extraction of impacted mandibular third molar: A retrospective study.

INTRODUCTION: Studies directly relating radiological findings to the risk of postoperative wound infection (PWI) in impacted mandibular third molars (M3) are limited and poorly understood. This study aimed to clarify the radiological risk of PWI. MATERIALS AND METHODS: Twenty-six patients who developed PWI after M3 extraction were retrospectively analyzed using orthopantomography (OPG) and computed tomography (CT) before M3 extraction to determine the association between M3 impaction status and PWI. These were compared with an equal number of non-infected groups. Moreover, the possibility of assessing the same risk in OPG as in CT imaging was examined. RESULTS: Multivariate analysis identified class III and position B of the Pell and Gregory classification system as independent risk factors for PWI. On CT, an axial overlap distance (AOD) >3.5 mm was significantly associated with PWI. Furthermore, the sagittal overlap distance (SOD) and AOD of the OPG were significantly greater in group III-B. A strong positive correlation was observed between SOD and AOD. CONCLUSION: These results indicate that class III, position B, and an AOD >3.5 mm may be novel risk factors for M3 PWI. The strong correlation between SOD and AOD suggests that the risk assessment for PWI can be performed by evaluating OPG alone.

Mitochondrial regulation of GPX4 inhibition-mediated ferroptosis in acute myeloid leukemia.

Resistance to apoptosis in acute myeloid leukemia (AML) cells causes refractory or relapsed disease, associated with dismal clinical outcomes. Ferroptosis, a mode of non-apoptotic cell death triggered by iron-dependent lipid peroxidation, has been investigated as potential therapeutic modality against therapy-resistant cancers, but our knowledge of its role in AML is limited. We investigated ferroptosis in AML cells and identified its mitochondrial regulation as a therapeutic vulnerability. GPX4 knockdown induced ferroptosis in AML cells, accompanied with characteristic mitochondrial lipid peroxidation, exerting anti-AML effects in vitro and in vivo. Electron transport chains (ETC) are primary sources of coenzyme Q10 (CoQ) recycling for its function of anti-lipid peroxidation in mitochondria. We found that the mitochondria-specific CoQ potently inhibited GPX4 inhibition-mediated ferroptosis, suggesting that mitochondrial lipid redox regulates ferroptosis in AML cells. Consistently, Rho0 cells, which lack functional ETC, were more sensitive to GPX4 inhibition-mediated mitochondrial lipid peroxidation and ferroptosis than control cells. Furthermore, degradation of ETC through hyperactivation of a mitochondrial protease, caseinolytic protease P (ClpP), synergistically enhanced the anti-AML effects of GPX4 inhibition. Collectively, our findings indicate that in AML cells, GPX4 inhibition induces ferroptosis, which is regulated by mitochondrial lipid redox and ETC.

Treatment patterns and trajectories in patients after acute heart failure hospitalization.

AIMS: The trajectories of systolic function after admission for acute heart failure (HF) and their effect on clinical outcomes have not been fully elucidated. We aimed to assess changes in left ventricular ejection fraction (LVEF) between the index and 1 year after discharge and to examine their prognostic implications. METHODS AND RESULTS: We extracted data from a prospective multicentre registry of patients hospitalized for acute HF and identified 1636 patients with LVEF data at admission and 1 year after discharge. We categorized them into five groups based on LVEF changes: HF with unchanged-preserved EF [HFunc-pEF (EF ≥ 50%); N = 527, 32.2%], unchanged-mildly reduced EF [HFunc-mrEF (EF 41-49%); N = 86, 5.3%], unchanged-reduced EF [HFunc-rEF (EF ≤ 40%); N = 377, 23.0%], worsened EF (HFworEF; N = 83, 5.1%), and improved EF (HFimpEF; N = 563, 34.4%). We then evaluated the subsequent composite outcome of cardiovascular death and HF readmission. During 1 year after discharge, 53% of patients with HF with reduced EF and 67% of those with HF with mildly reduced EF (HFmrEF) transitioned to other categories, whereas 92% of those with HF with preserved EF (HFpEF) remained within the same category. Patients with HFimpEF were more likely to be younger and had relatively preserved renal function, whereas those with HFworEF were the oldest and had more comorbidities among the five groups. After multivariable adjustment, patients with HFimpEF and HFunc-pEF had a lower risk for composite outcomes when referenced to patients with HFunc-rEF [hazard ratio (95% confidence interval), P-value: 0.28 (0.16-0.49), P < 0.001, and 0.40 (0.25-0.63), P < 0.001, respectively]. Conversely, patients with HFunc-mrEF and HFworEF had a comparable risk [0.44 (0.18-1.07), P = 0.07, and 0.63 (0.29-1.39), P = 0.26, respectively]. CONCLUSIONS: A substantial number of patients with HF experienced transitions to other categories after discharge. Notably, patients with decreased EF experienced a worse prognosis, even with slight decreases (e.g. HFpEF transitioning to HFmrEF). These findings emphasize the significance of longitudinal assessments of systolic function to better manage patients following acute decompensation.

Association between salivary proteases and protease inhibitors linked with viral infections and oral inflammatory diseases.

INTRODUCTION: Despite the role of transmembrane protease, serine 2 (TMPRSS2) in facilitating the entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the primary cause of the global COVID-19 pandemic, the interaction of extracellular and intracellular proteases in this process remains poorly elucidated. Thus, we monitored the salivary expression concentration (SEC) of TMPRSS2 and its inhibitor, alpha-1 antitrypsin (A1AT), and investigated whether oral inflammatory diseases affected the SEC of both proteins. MATERIALS AND METHODS: We collected saliva samples before and after surgical treatment of inflammatory cystic diseases (radicular and inflammatory dentigerous cysts) in 25 patients. The SEC of TMPRSS2 and A1AT was measured using enzyme-linked immunosorbent assay. SEC in multiple patient status groups and subgroups of each status were investigated. Finally, the correlation between TMPRSS2 and A1AT SEC was analyzed. RESULTS: The TMPRSS2 and A1AT SEC did not significantly change pre- or post-treatment. The TMPRSS2 SEC was significantly higher before and after treatment in patients aged >50 years, patients with radicular cysts, and patients with the basic disease. A1AT SEC was significantly decreased after treatment in the acute inflammation, large-sized, and patients without basic disease groups. No significant correlation was observed between the SEC of either protein before and after treatment. DISCUSSION: Individual-specific SEC for TMPRSS2 may be influenced by age, lesion type, and basic disease; however, oral inflammatory diseases may not have a direct effect. Moreover, the extent of oral inflammatory diseases and the presence of basic diseases may be associated with A1AT SEC. Furthermore, the SEC between the two proteins may be independent.

Molecular Mechanisms of Ferroptosis and Updates of Ferroptosis Studies in Cancers and Leukemia.

Ferroptosis is a mode of cell death regulated by iron-dependent lipid peroxidation. Growing evidence suggests ferroptosis induction as a novel anti-cancer modality that could potentially overcome therapy resistance in cancers. The molecular mechanisms involved in the regulation of ferroptosis are complex and highly dependent on context. Therefore, a comprehensive understanding of its execution and protection machinery in each tumor type is necessary for the implementation of this unique cell death mode to target individual cancers. Since most of the current evidence for ferroptosis regulation mechanisms is based on solid cancer studies, the knowledge of ferroptosis with regard to leukemia is largely lacking. In this review, we summarize the current understanding of ferroptosis-regulating mechanisms with respect to the metabolism of phospholipids and iron as well as major anti-oxidative pathways that protect cells from ferroptosis. We also highlight the diverse impact of p53, a master regulator of cell death and cellular metabolic processes, on the regulation of ferroptosis. Lastly, we discuss recent ferroptosis studies in leukemia and provide a future perspective for the development of promising anti-leukemia therapies implementing ferroptosis induction.

Evolution of sodium-glucose co-transporter 2 inhibitors from a glucose-lowering drug to a pivotal therapeutic agent for cardio-renal-metabolic syndrome.

Cardio-renal-metabolic (CRM) syndrome, which involves type 2 diabetes mellitus (T2DM), chronic kidney disease (CKD), and heart failure (HF), is a serious healthcare issue globally, with high morbidity and mortality. The disorders that comprise CRM syndrome are independent can mutually affect and accelerate the exacerbation of each other, thereby substantially increasing the risk of mortality and impairing quality of life. To manage CRM syndrome by preventing vicious interactions among individual disorders, a holistic treatment approach that can simultaneously address multiple disorders underpinning CRM syndrome is of great importance. Sodium-glucose co-transporter 2 inhibitors (SGLT2i) lower blood glucose levels by inhibiting glucose reabsorption in the renal proximal tubule and were first indicated for the treatment of T2DM. Several cardiovascular outcome trials have demonstrated that SGLT2i not only lower blood glucose but also reduce the risk of hospitalization for HF and worsening renal function in patients with T2DM. Results have also suggested that the observed cardiorenal benefits of SGLT2i may be independent of their blood glucose-lowering effects. Several randomized controlled trials subsequently assessed the efficacy and safety of SGLT2i in patients without T2DM, and revealed considerable benefits of SGLT2i treatment against HF and CKD, regardless of the presence of T2DM. Thus, SGLT2i have become an essential therapeutic option to prevent the onset, slow the progression, and improve the prognosis of CRM syndrome. This review assesses the evolution of SGLT2i from a glucose-lowering drug to a therapeutic agent for CRM syndrome by evaluating epoch-making clinical studies, including randomized control trials and real-world studies.

Changes in Treatment Satisfaction Over 3 Years in Patients With Type 2 Diabetes After Initiating Second-line Treatment.

CONTEXT: J-DISCOVER is a prospective observational cohort study aiming to understand the current management of patients with early-stage type 2 diabetes mellitus (T2DM) in Japan, enrolling patients initiating second-line treatment. OBJECTIVE: The current analysis examined the change in treatment satisfaction during the study period and factors affecting this change among patients in J-DISCOVER. METHODS: We used data from the J-DISCOVER study, in which 1798 patients with T2DM aged ≥ 20 years were enrolled from 142 sites across Japan. Treatment satisfaction was assessed using the Diabetes Treatment Satisfaction Questionnaire (DTSQ). RESULTS: The mean DTSQ treatment satisfaction score increased from 25.9 points at baseline to 27.3 points at 6 months, which was maintained through 36 months. Among the baseline characteristics examined, higher baseline DTSQ treatment satisfaction scores (P < 0.0001), older age (≥ 75 vs < 65 years, P = 0.0096), living alone (P = 0.0356), and type of facility (clinics vs hospitals, P = 0.0044) had a significantly negative impact on the changes in DTSQ treatment satisfaction scores. Improvement in mean glycated hemoglobin (HbA1c) from baseline (7.7%) to 36 months (7.1%) was associated with positive changes in the DTSQ treatment satisfaction score (P = 0.0003). CONCLUSION: Changes in DTSQ treatment satisfaction scores were related to HbA1c improvement, suggesting that the management strategy was appropriately planned for each patient. The results also suggest that the availability of social support for patients with T2DM who are elderly or living alone may be an important factor affecting treatment satisfaction, adherence, and clinical outcomes.

Cost-Effectiveness Analysis of Initiating Type 2 Diabetes Therapy with a Sodium-Glucose Cotransporter 2 Inhibitor Versus Conventional Therapy in Japan.

INTRODUCTION: Many patients with type 2 diabetes mellitus (T2DM) suffer from complications that impose substantial burdens on prognosis and medical costs. Accumulating evidence has demonstrated the clinical benefit of sodium-glucose cotransporter 2 inhibitors (SGLT2i) on cardiovascular and renal complications. However, the health economic impact of SGLT2i remains unclear. The aim of this study was to evaluate the cost-effectiveness of initiating antidiabetic therapy with an SGLT2i using Japanese real-world data. METHODS: We constructed a natural history model incorporating heart failure (HF), myocardial infarction, stroke, chronic kidney disease, and end-stage renal disease (ESRD) as complications. The target population comprised patients with T2DM who newly initiated their first oral glucose-lowering drugs. By using a population-based microsimulation, we estimated the 10-year medical costs in Japanese yen (JPY) and outcomes (hospitalization for/development of complications and quality-adjusted life years [QALY]) for patients who initiated antidiabetic therapy with an SGLT2i or conventional therapy. Sensitivity analyses included a probabilistic sensitivity analysis (PSA) with 1,000,000 iterations. RESULTS: In the base-case analysis, the total medical cost per person was JPY 1,638,806 versus JPY 1,825,033 and the QALYs were 8.732 versus 8.513 for the SGLT2i strategy versus the conventional strategy, respectively. Thus, initiating treatment with an SGLT2i was dominant, more effective (QALY gain), and lower cost. When treating 10,000 patients, the SGLT2i strategy would reduce all-cause deaths by 410 (552 vs 962), HF events by 201 (897 vs 1098), and ESRD events by 16 (16 vs 32) versus the conventional strategy. The PSA revealed that the probability of dominance for initiating SGLT2i therapy was 90.5%, demonstrating the robustness of the results. CONCLUSION: Our results suggest that initiating T2DM treatment with SGLT2i, aimed at managing cardiovascular and renal complications from the early stages of diabetes, can improve the clinical outcome and reduce cost burden of T2DM.

Analysis of false-negatives in exfoliative cytology in oral potentially malignant disorders: A retrospective cohort study.

INTRODUCTION: Keratinized lesions have been a conceivable false-negative (FN) factor in oral exfoliative cytology (OEC); however, other factors are poorly analyzed. In this study, we aimed to identify the factors influencing the accuracy of OEC and FNs focusing on the lesion characteristics, patient background, and surgeon factors in oral potentially malignant disorders (OPMD). MATERIAL AND METHODS: We retrospectively studied 44 patients who underwent both OEC and histopathological diagnosis. Sensitivity, specificity, FN rate, false-positive (FP) rate, and prevalence of both methods were compared. Similarly, accuracy indices were compared among clinical diagnosis groups (leukoplakia vs. other diagnosis). The association between patient and surgeon-related factors influencing FN OEC results were investigated using Fisher's exact test and a multiple logistic regression analysis. RESULTS: Overall, the sensitivity; specificity; and FN, FP, and prevalence rates of OEC were 31.8%, 82.1%, and 68.8%, 17.9%, and 36.4%, respectively. Leukoplakia was significantly more common in clinical diagnosis (P = 0.007) with sensitivity, specificity, and FN rates of 20.0%, 95.2%, and 80.0%, respectively. Contrarily, non-keratinized lesions had sensitivity, specificity, and FN of 83.3%, 85.7%, and 16.7%, respectively. In the prevalent group, leukoplakia and anucleate squamous cells were significantly associated with FN cases (P = 0.013, P = 0.050). On multivariate analysis in OEC negative patients, age ≤64 (P = 0.050) and location on the tongue (P = 0.047) was independently associated with FNs. CONCLUSION: FN of OEC was conceivable to be due to poor deep-seated cell sampling, which was associated with leukoplakia, age, and location. Therefore, these factors may be considered in the evaluation of OEC results.

Manifestation of Heart Failure and Chronic Kidney Disease are Associated with Increased Mortality Risk in Early Stages of Type 2 Diabetes Mellitus: Analysis of a Japanese Real-World Hospital Claims Database.

INTRODUCTION: To assess the initial manifestation of comorbidities and their impact on mortality risk in patients with type 2 diabetes mellitus (T2DM) without a history of cardiovascular or renal complications (i.e., in the early stages of T2DM) compared with patients without T2DM. METHODS: We performed a retrospective cohort study using a Japanese hospital claims database. The incidence rates of comorbidities (chronic kidney disease [CKD], heart failure [HF], myocardial infarction [MI], peripheral arterial disease [PAD], and stroke) and mortality risk were compared between patients with T2DM and age-/sex-matched patients without T2DM (matched 1:2). RESULTS: Among the comorbidities assessed in this study, CKD and/or HF was the most frequent initial manifestation in the patients with T2DM (n = 426,186) with an incidence rate 2.02 times greater than that in matched patients without T2DM (n = 1,018,609). The mortality risk was also greater in patients with T2DM than in patients without T2DM with a hazard ratio of 1.73. In both patients with and without T2DM, the presence of CKD or HF was associated with greater mortality risks compared with the presence of MI, PAD, or stroke. CONCLUSIONS: The high incidence of CKD or HF manifestation can contribute to the augmented mortality risk in patients in the early stages of T2DM compared with patients without T2DM. These findings highlight the importance of early interventions for preventing/treating CKD and HF to improve the prognosis of patients with T2DM.

Lipoprotein-subclass particle numbers in children with abdominal obesity.

BACKGROUND: The lipoprotein particle number (PN) profile may be a better marker of cardiovascular risks than standard serum lipid measurements. The aim of this study was to analyze the lipoprotein PNs in Japanese children with abdominal obesity and to determine the subclass profile. METHODS: The participants included 164 Japanese children (79 boys and 85 girls) aged 9-13 years. We obtained waist-to-height ratios (WHtR) and serum lipids for all participants. The lipoprotein PNs in 12 subclasses were analyzed using high performance liquid chromatography (HPLC). RESULTS: Both boys and girls with abdominal obesity (WHtR ≧ 0.5) had significantly higher triglyceride (TG), very-low-density lipoprotein (VLDL)-PN, and all VLDL-subclass PNs compared to those without abdominal obesity. In boys with abdominal obesity, low-density lipoprotein (LDL)-PN was higher, but lipoprotein cholesterol (LDL-C) was not, and high-density lipoprotein cholesterol (HDL-C) was lower, but HDL-PN was not compared to those without abdominal obesity. In girls with abdominal obesity, LDL-C and LDL-PN were not significantly different and both HDL-C and HDL-PN were lower compared to those without abdominal obesity. Subclass analyses demonstrated that boys and girls with abdominal obesity had significantly lower very large and large HDL-PNs than those without abdominal obesity. In addition, medium, small, and very small LDL-PNs were higher in boys with abdominal obesity than those without abdominal obesity. CONCLUSIONS: This study found that Japanese children with abdominal obesity are affected by the lipoprotein-subclass PN profile, with sex differences in the LDL- and HDL-subclasses, which is different from results obtained by standard serum lipid measurements.

The enzymatic activity of inositol hexakisphosphate kinase controls circulating phosphate in mammals.

Circulating phosphate levels are tightly controlled within a narrow range in mammals. By using a novel small-molecule inhibitor, we show that the enzymatic activity of inositol hexakisphosphate kinases (IP6K) is essential for phosphate regulation in vivo. IP6K inhibition suppressed XPR1, a phosphate exporter, thereby decreasing cellular phosphate export, which resulted in increased intracellular ATP levels. The in vivo inhibition of IP6K decreased plasma phosphate levels without inhibiting gut intake or kidney reuptake of phosphate, demonstrating a pivotal role of IP6K-regulated cellular phosphate export on circulating phosphate levels. IP6K inhibition-induced decrease in intracellular inositol pyrophosphate, an enzymatic product of IP6K, was correlated with phosphate changes. Chronic IP6K inhibition alleviated hyperphosphataemia, increased kidney ATP, and improved kidney functions in chronic kidney disease rats. Our results demonstrate that the enzymatic activity of IP6K regulates circulating phosphate and intracellular ATP and suggest that IP6K inhibition is a potential novel treatment strategy against hyperphosphataemia.

Inhibition of translation initiation factor eIF4a inactivates heat shock factor 1 (HSF1) and exerts anti-leukemia activity in AML.

Eukaryotic initiation factor 4A (eIF4A), the enzymatic core of the eIF4F complex essential for translation initiation, plays a key role in the oncogenic reprogramming of protein synthesis, and thus is a putative therapeutic target in cancer. As important component of its anticancer activity, inhibition of translation initiation can alleviate oncogenic activation of HSF1, a stress-inducible transcription factor that enables cancer cell growth and survival. Here, we show that primary acute myeloid leukemia (AML) cells exhibit the highest transcript levels of eIF4A1 compared to other cancer types. eIF4A inhibition by the potent and specific compound rohinitib (RHT) inactivated HSF1 in these cells, and exerted pronounced in vitro and in vivo anti-leukemia effects against progenitor and leukemia-initiating cells, especially those with FLT3-internal tandem duplication (ITD). In addition to its own anti-leukemic activity, genetic knockdown of HSF1 also sensitized FLT3-mutant AML cells to clinical FLT3 inhibitors, and this synergy was conserved in FLT3 double-mutant cells carrying both ITD and tyrosine kinase domain mutations. Consistently, the combination of RHT and FLT3 inhibitors was highly synergistic in primary FLT3-mutated AML cells. Our results provide a novel therapeutic rationale for co-targeting eIF4A and FLT3 to address the clinical challenge of treating FLT3-mutant AML.

MPL overexpression induces a high level of mutant-CALR/MPL complex: a novel mechanism of ruxolitinib resistance in myeloproliferative neoplasms with CALR mutations.

Ruxolitinib (RUX), a JAK1/2-inhibitor, is effective for myeloproliferative neoplasm (MPN) with both JAK2V617 F and calreticulin (CALR) mutations. However, many MPN patients develop resistance to RUX. Although mechanisms of RUX-resistance in cells with JAK2V617 F have already been characterized, those in cells with CALR mutations remain to be elucidated. In this study, we established RUX-resistant human cell lines with CALR mutations and characterized mechanisms of RUX-resistance. Here, we found that RUX-resistant cells had high levels of MPL transcripts, overexpression of both MPL and JAK2, and increased phosphorylation of JAK2 and STAT5. We also found that mature MPL proteins were more stable in RUX-resistant cells. Knockdown of MPL in RUX-resistant cells by shRNAs decreased JAK/STAT signaling. Immunoprecipitation assays showed that binding of mutant CALR to MPL was increased in RUX-resistant cells. Reduction of mutated CALR decreased proliferation of the resistant cells. When resistant cells were cultured in the absence of RUX, the RUX-resistance was reversed, with reduction of the mutant-CALR/MPL complex. In conclusion, MPL overexpression induces higher levels of a mutant-CALR/MPL complex, which may cause RUX-resistance in cells with CALR mutations. This mechanism may be a new therapeutic target to overcome RUX-resistance.

Drp1 SUMO/deSUMOylation by Senp5 isoforms influences ER tubulation and mitochondrial dynamics to regulate brain development.

Brain development is a highly orchestrated process requiring spatiotemporally regulated mitochondrial dynamics. Drp1, a key molecule in the mitochondrial fission machinery, undergoes various post-translational modifications including conjugation to the small ubiquitin-like modifier (SUMO). However, the functional significance of SUMOylation/deSUMOylation on Drp1 remains controversial. SUMO-specific protease 5 (Senp5L) catalyzes the deSUMOylation of Drp1. We revealed that a splicing variant of Senp5L, Senp5S, which lacks peptidase activity, prevents deSUMOylation of Drp1 by competing against other Senps. The altered SUMOylation level of Drp1 induced by Senp5L/5S affects mitochondrial morphology probably through controlling Drp1 ubiquitination and tubulation of the endoplasmic reticulum. A dynamic SUMOylation/deSUMOylation balance controls neuronal polarization and migration during the development of the cerebral cortex. These findings suggest a novel role of post-translational modification, in which deSUMOylation enzyme isoforms competitively regulate mitochondrial dynamics via Drp1 SUMOylation levels, in a tightly controlled process of neuronal differentiation and corticogenesis.

Inositol 1,4,5-Trisphosphate Receptor Type 3 Regulates Neuronal Growth Cone Sensitivity to Guidance Signals.

During neurodevelopment, the growth cone deciphers directional information from extracellular guidance cues presented as shallow concentration gradients via signal amplification. However, it remains unclear how the growth cone controls this amplification process during its navigation through an environment in which basal cue concentrations vary widely. Here, we identified inositol 1,4,5-trisphosphate (IP3) receptor type 3 as a regulator of axonal sensitivity to guidance cues in vitro and in vivo. Growth cones lacking the type 3 subunit are hypersensitive to nerve growth factor (NGF), an IP3-dependent attractive cue, and incapable of turning toward normal concentration ranges of NGF to which wild-type growth cones respond. This is due to globally, but not asymmetrically, activated Ca2+ signaling in the hypersensitive growth cones. Remarkably, lower NGF concentrations can polarize growth cones for turning if IP3 receptor type 3 is deficient. These data suggest a subtype-specific IP3 receptor function in sensitivity adjustment during axon navigation.