aPKC and DOC2b in glucose transport

Aims/introduction: Double C2 domain protein b (DOC2b), one of the synaptotagmins, has been shown to translocate to the plasma membrane, and to initiate membrane-fusion processes of vesicles containing glucose transporter 4 proteins on insulin stimulation. However, the mechanism by which DOC2b is regulated remains unclear. Herein, we identified the upstream regulatory factors of DOC2b in insulin signal transduction. We also examined the role of DOC2b on systemic homeostasis using DOC2b knockout (KO) mice. Materials and Methods: We first identified DOC2b binding proteins by immunoprecipitation and mutagenesis experiments. Then, DOC2b KO mice were generated by disrupting the first exon of the DOC2b gene. In addition to the histological examination, glucose metabolism was assessed by measuring parameters on glucose/insulin tolerance tests. Insulin-stimulated glucose uptake was also measured using isolated soleus muscle and epididymal adipose tissue. Results: We identified an isoform of atypical protein kinase C (protein kinase C iota) that can bind to DOC2b and phosphorylates one of the serine residues of DOC2b (S34). This phosphorylation is essential for DOC2b translocation. DOC2b KO mice showed insulin resistance and impaired oral glucose tolerance on insulin and glucose tolerance tests, respectively. Insulin-stimulated glucose uptake was impaired in isolated soleus muscle and epididymal adipose tissues from DOC2b KO mice. Conclusions: We propose a novel insulin signaling mechanism by which protein kinase C iota phosphorylates DOC2b, leading to glucose transporter 4 vesicle translocation, fusion and facilitation of glucose uptake in response to insulin. The present results also showed DOC2b to play important roles in systemic glucose homeostasis

Myosin motor Myo1c and its receptor NEMO/IKK-γ promote TNF-α–induced serine307 phosphorylation of IRS-1

Tumor necrosis factor-α (TNF-α) signaling through the IκB kinase (IKK) complex attenuates insulin action via the phosphorylation of insulin receptor substrate 1 (IRS-1) at Ser307. However, the precise molecular mechanism by which the IKK complex phosphorylates IRS-1 is unknown. In this study, we report nuclear factor κB essential modulator (NEMO)/IKK-γ subunit accumulation in membrane ruffles followed by an interaction with IRS-1. This intracellular trafficking of NEMO requires insulin, an intact actin cytoskeletal network, and the motor protein Myo1c. Increased Myo1c expression enhanced the NEMO–IRS-1 interaction, which is essential for TNF-α– induced phosphorylation of Ser307–IRS-1. In contrast, dominant inhibitory Myo1c cargo domain expression diminished this interaction and inhibited IRS-1 phosphorylation. NEMO expression also enhanced TNF-α–induced Ser307–IRS-1 phosphorylation and inhibited glucose uptake. In contrast, a deletion mutant of NEMO lacking the IKK-β–binding domain or silencing NEMO blocked the TNF-α signal. Thus, motor protein Myo1c and its receptor protein NEMO act cooperatively to form the IKK–IRS-1 complex and function in TNF-α–induced insulin resistance

Infectious cerebral thromboembolism in a patient with lung cancer during long-term administration of gefitinib: a case report

Introduction　Gefitinib is a molecularly targeted drug for oral administration, a selective epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI). It is effective for patients with lung cancer who have EGFR mutation and enables long-term survival of patients with advanced disease.Case presentation　An 84-year-old Asian female with lung cancer (adenocarcinoma, cT4N3M1b stage IV PUL BRA OSS ADR) was treated by gefitinib for two years. The primary tumor was markedly reduced, and bone metastasis had almost disappeared. However, the patient became unconsciousness with general edema and died two days after falling unconsciousness. In the autopsy, it was diagnosed as infectious cerebral thromboembolism due to infectious endocarditis. The cause of death was cardiac tamponade.Conclusions　While long-term survival can be expected in patients with advanced lung cancer by molecular-targeted agents, cautious management is warranted for complications, the same as for the primary disease

再灌流後急性心筋梗塞患者におけるリバースリモデリングと非造影T1低信号梗塞コア

Background: Non-contrast T1 hypointense infarct cores (ICs) within infarcted myocardium detected using cardiac magnetic resonance imaging (CMR) T1 mapping may help assess the severity of left ventricular (LV) injury. However, because the relationship of ICs with chronic LV reverse remodeling (LVRR) is unknown, this study aimed to clarify it. Methods and Results: We enrolled patients with reperfused AMI who underwent baseline CMR on day-7 post-primary percutaneous coronary intervention (n=109) and 12-month follow-up CMR (n=94). Correlations between ICs and chronic LVRR (end-systolic volume decrease ≥15% at 12-month follow-up from baseline CMR) were investigated. We detected 52 (47.7%) ICs on baseline CMR by non-contrast-T1 mapping. LVRR was found in 52.1% of patients with reperfused AMI at 12-month follow-up. Patients with ICs demonstrated higher peak creatine kinase levels, higher B-type natriuretic peptide levels at discharge, lower LV ejection fraction at discharge, and lower incidence of LVRR than those without ICs (26.5% vs. 73.3%, P<0.001) at follow-up. Multivariate logistic regression analysis showed that the presence of ICs was an independent and the strongest negative predictor for LVRR at 12-month followup (hazard ratio: 0.087, 95% confidence interval: 0.017–0.459, P=0.004). Peak creatine kinase levels, native T1 values at myocardial edema, and myocardial salvaged indices also correlated with ICs. Conclusions: ICs detected by non-contrast-T1 mapping with 3.0-T CMR were an independent negative predictor of LVRR in patients with reperfused AMI.博士（医学）・乙第1529号・令和5年3月15

Cleavage of a model DNA replication fork by a methyl-specific endonuclease

Epigenetic DNA methylation is involved in many biological processes. An epigenetic status can be altered by gain or loss of a DNA methyltransferase gene or its activity. Repair of DNA damage can also remove DNA methylation. In response to such alterations, DNA endonucleases that sense DNA methylation can act and may cause cell death. Here, we explored the possibility that McrBC, a methylation-dependent DNase of Escherichia coli, cleaves DNA at a replication fork. First, we found that in vivo restriction by McrBC of bacteriophage carrying a foreign DNA methyltransferase gene is increased in the absence of homologous recombination. This suggests that some cleavage events are repaired by recombination and must take place during or after replication. Next, we demonstrated that the enzyme can cleave a model DNA replication fork in vitro. Cleavage of a fork required methylation on both arms and removed one, the other or both of the arms. Most cleavage events removed the methylated sites from the fork. This result suggests that acquisition of even rarely occurring modification patterns will be recognized and rejected efficiently by modification-dependent restriction systems that recognize two sites. This process might serve to maintain an epigenetic status along the genome through programmed cell death