Identification and Characterization of the Gene Responsible for the O3 Mating Type Substance in Paramecium caudatum.

The process of sexual reproduction in eukaryotes starts when gametes from two different sexes encounter each other. Paramecium, a unicellular eukaryote, undergoes conjugation and uses a gametic nucleus to enter the sexual reproductive process. The molecules responsible for recognizing mating partners, hypothetically called mating-type substances, are still unclear. We have identified an O3-type mating substance polypeptide and its gene sequence using protein chemistry, molecular genetics, immunofluorescence, RNA interference, and microinjection. The O3-type substance is a polypeptide found in the ciliary membranes, located from the head to the ventral side of cells. The O3-type substance has a kinase-like domain in its N-terminal part located outside the cell and four EF-hand motifs that bind calcium ions in its C-terminal part located inside the cell. RNA interference and immunofluorescence revealed that this polypeptide positively correlated with the expression of mating reactivity. Microinjection of an expression vector incorporating the O3Pc-MSP gene (Oms3) induced additional O3 mating type in the recipient clones of different mating types or syngen. Phylogenetic analysis indicates that this gene is widely present in eukaryotes and exhibits high homology among closely related species. The O3Pc-MSP (Oms3) gene had nine silent mutations compared to the complementary mating type of the E3 homologue gene.

Transcriptome Analysis Reveals Enhancement of Cardiogenesis-Related Signaling Pathways by S-nitroso-N-pivaloyl-D-penicillamine (SNPiP): Implications for Improved Diastolic Function and Cardiac Performance.

We previously reported a novel compound called S-nitroso-N-pivaloyl-D-penicillamine (SNPiP), which was screened from a group of nitric oxide (NO) donor compounds with a basic chemical structure of S-nitroso-N-acetylpenicillamine (SNAP), to activate the non-neuronal acetylcholine (NNA) system. SNPiP-treated mice exhibited improved cardiac output and enhanced diastolic function, without an increase in heart rate. The NNA-activating effects included increased resilience to ischemia, modulation of energy metabolism preference, and activation of angiogenesis. Here, we performed transcriptome analysis of SNPiP-treated mice ventricles to elucidate how SNPiP exerts beneficial effects on cardiac function. A time-course study (24 and 48 h after SNPiP administration) revealed that SNPiP initially induced Wnt and cGMP-protein kinase G (PKG) signaling pathways, along with upregulation of genes involved in cardiac muscle tissue development and oxytocin signaling pathway. We also observed enrichment of glycolysis-related genes in response to SNPiP treatment, resulting in a metabolic shift from oxidative phosphorylation to glycolysis, which was suggested by reduced cardiac glucose contents while maintaining ATP levels. Additionally, SNPiP significantly upregulated atrial natriuretic peptide (ANP) and sarcolipin (SLN), which play crucial roles in calcium handling and cardiac performance. These findings suggest that SNPiP may have therapeutic potential based on the pleiotropic mechanisms elucidated in this study.

Temporal inhibition of the electron transport chain attenuates stress-induced cellular senescence by prolonged disturbance of proteostasis in human fibroblasts.

We previously developed a stress-induced premature senescence (SIPS) model in which normal human fibroblast MRC-5 cells were treated with either the proteasome inhibitor MG132 or the vacuolar-type ATPase inhibitor bafilomycin A1 (BAFA1). To clarify the involvement of mitochondrial function in our SIPS model, MRC-5 cells were treated with MG132 or BAFA1 along with an inhibitor targeting either the electron transport chain complex I or complex III, or with a mitochondrial uncoupler. SIPS induced by MG132 or BAFA1 was significantly attenuated by short-term co-treatment with the complex III inhibitor, antimycin A (AA), but not the complex I inhibitor, rotenone or the mitochondrial uncoupler, carbonyl cyanide 3-chlorophenylhydrazone. By co-treatment with AA, mitochondrial and intracellular reactive oxygen species levels, accumulation of protein aggregates and mitochondrial unfolded protein responses (UPRmt ) were remarkably suppressed. Furthermore, AA co-treatment suppressed the hyperpolarization of the mitochondrial membrane and the induction of mitophagy observed in MG132-treated cells and enhanced mitochondrial biogenesis. These findings provide evidence that the temporal inhibition of mitochondrial respiration exerts protective effects against the progression of premature senescence caused by impaired proteostasis.

Prolonged disturbance of proteostasis induces cellular senescence via temporal mitochondrial dysfunction and subsequent mitochondrial accumulation in human fibroblasts.

Proteolytic activity declines with age, resulting in the accumulation of aggregated proteins in aged organisms. To investigate how disturbance in proteostasis causes cellular senescence, we developed a stress-induced premature senescence (SIPS) model, in which normal human fibroblast MRC-5 cells were treated with the proteasome inhibitor MG132 or the vacuolar-type ATPase inhibitor bafilomycin A1 (BAFA1) for 5 days. Time-course studies revealed a significant increase in intracellular reactive oxygen species (ROS) and mitochondrial superoxide during and after drug treatment. Mitochondrial membrane potential initially decreased, suggesting temporal mitochondrial dysfunction during drug treatment, but was restored along with mitochondrial accumulation after drug treatment. AMP-activated protein kinase alpha was notably activated during treatment; thereafter, intracellular ATP levels significantly increased. SIPS induction by MG132 or BAFA1 was partially attenuated by co-treatment with vitamin E or rapamycin, in which the levels of ROS, mitochondrial accumulation, and protein aggregates were suppressed, implying the critical involvement of oxidative stress and mitochondrial function in SIPS progression. Rapamycin co-treatment also augmented the expression of HSP70 and activation of AKT, which could recover proteostasis and promote cell survival, respectively. Our study proposes a possible pathway from the disturbed proteostasis to cellular senescence via excess ROS production as well as functional and quantitative changes in mitochondria.

Immaturin-Nuclease as a Model System for a Gene-Programmed Sexual Development and Rejuvenescence in Paramecium Life History.

Fertilization-initiated development and adult-onset aging are standard features in the life history of eukaryotes. In Paramecium, the number of cell divisions after the birth of a new generation is an essential parameter of sexual phase transition and aging. However, the gene driving this process and its evolutionary origin have not yet been elucidated. Here we report several critical outcomes obtained by molecular genetics, immunofluorescence microscopy, transformation by microinjection, and enzymological analysis. The cloned immaturin gene induces sexual rejuvenation in both mature and senescent cells by microinjection. The immaturin gene originated from proteobacteria's glutathione-S-transferase (GST) gene. However, immaturin has been shown to lose GST activity and instead acquire nuclease activity. In vitro substrates for immaturin-nuclease are single- and double-stranded DNA, linear and circular DNA, and single-stranded viral genome RNA such as coronavirus. Anti-immaturin antibodies have shown that the subcellular localizations of immaturin are the macronucleus, cytoplasm, cell surface area, and cilia. The phase transition of sexuality is related to a decrease in the intracellular abundance of immaturin. We propose that sexual maturation and rejuvenation is a process programmed by the immaturin gene, and the sexual function of each age is defined by both the abundance and the intracellular localization mode of the immaturin-nuclease.

Anagliptin Monotherapy for Six Months in Patients With Type 2 Diabetes Mellitus and Hyper-Low-Density Lipoprotein Cholesterolemia Reduces Plasma Levels of Fasting Low-Density Lipoprotein Cholesterol and Lathosterol: A Single-Arm Intervention Trial.

BACKGROUND: Anagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, has been shown to decrease plasma low-density lipoprotein cholesterol (LDL-C) levels. The objective of our study was to elucidate the mechanisms responsible for the anagliptin-mediated improvements in high LDL-C levels (hyper-LDL cholesterolemia). METHODS: We prospectively examined the effects of anagliptin monotherapy on fasting plasma lathosterol, sitosterol, and campesterol levels in patients with type 2 diabetes mellitus and hyper-LDL cholesterolemia for 6 months. We examined 14 patients who did not use hypoglycemic or lipid-lowering drugs for 4 months before initiating the study. Plasma variables related to glucose and lipid metabolism were measured before and after 6 months of treatment and pre- and postprandially using the cookie-loading test. RESULTS: After treatment, anagliptin monotherapy (n = 14) significantly decreased fasting LDL-C (175.6 to 148.5 mg/dL, mean values before and after the treatment, respectively) and plasma lathosterol levels (3.56 to 2.49 mg/dL), whereas it did not lower fasting sitosterol or campesterol levels. Furthermore, fasting plasma lathosterol levels were negatively correlated with preprandial glucagon-like peptide-1 (GLP-1) levels after anagliptin treatment. CONCLUSIONS: Anagliptin monotherapy may have a beneficial effect on lipid metabolism, which could be mediated by the inhibition of hepatic cholesterol synthesis rather than the inhibition of intestinal lipid transport.

Effects of Pparγ1 deletion on late-stage murine embryogenesis and cells that undergo endocycle.

Peroxisome proliferator-activated receptor (PPAR) γ1, a nuclear receptor, is abundant in the murine placenta during the late stage of pregnancy (E15-E16), although its functional roles remain unclear. PPARγ1 is encoded by two splicing isoforms, namely Pparγ1canonical and Pparγ1sv, and its embryonic loss leads to early (E10) embryonic lethality. Thus, we generated knockout (KO) mice that carried only one of the isoforms to obtain a milder phenotype. Pparγ1sv-KO mice were viable and fertile, whereas Pparγ1canonical-KO mice failed to recover around the weaning age. Pparγ1canonical-KO embryos developed normally up to 15.5 dpc, followed by growth delays after that. The junctional zone of Pparγ1canonical-KO placentas severely infiltrated the labyrinth, and maternal blood sinuses were dilated. In the wild-type, PPARγ1 was highly expressed in sinusoidal trophoblast giant cells (S-TGCs), peaking at 15.5 dpc. Pparγ1canonical-KO abolished PPARγ1 expression in S-TGCs. Notably, the S-TGCs had unusually enlarged nuclei and often occupied maternal vascular spaces, disturbing the organization of the fine labyrinth structure. Gene expression analyses of Pparγ1canonical-KO placentas indicated enhanced S-phase cell cycle signatures. EdU-positive S-TGCs in Pparγ1canonical-KO placentas were greater in number than those in wild-type placentas, suggesting that the cells continued to endoreplicate in the mutant placentas. These results indicate that PPARγ1, a known cell cycle arrest mediator, is involved in the transition of TGCs undergoing endocycling to the terminal differentiation stage in the placentas. Therefore, PPARγ1 deficiency, induced through genetic manipulation, leads to placental insufficiency.

Ezetimibe impairs transcellular lipid trafficking and induces large lipid droplet formation in intestinal absorptive epithelial cells.

Ezetimibe inhibits Niemann-Pick C1-like 1 (NPC1L1) protein, which mediates intracellular cholesterol trafficking from the brush border membrane to the endoplasmic reticulum, where chylomicron assembly takes place in enterocytes or in the intestinal absorptive epithelial cells. Cholesterol is a minor lipid constituent of chylomicrons; however, whether or not a shortage of cholesterol attenuates chylomicron assembly is unknown. The aim of this study was to examine the effect of ezetimibe, a potent NPC1L1 inhibitor, on trans-epithelial lipid transport, and chylomicron assembly and secretion in enterocytes. Caco-2 cells, an absorptive epithelial model, grown onto culture inserts were given lipid micelles from the apical side, and chylomicron-like triacylglycerol-rich lipoprotein secreted basolaterally were analyzed after a 24-h incubation period in the presence of ezetimibe up to 50 µM. The secretion of lipoprotein and apolipoprotein B48 were reduced by adding ezetimibe (30% and 34%, respectively). Although ezetimibe allowed the cells to take up cholesterol normally, the esterification was abolished. Meanwhile, oleic acid esterification was unaffected. Moreover, ezetimibe activated sterol regulatory element-binding protein 2 by approximately 1.5-fold. These results suggest that ezetimibe limited cellular cholesterol mobilization required for lipoprotein assembly. In such conditions, large lipid droplet formation in Caco-2 cells and the enterocytes of mice were induced, implying that unprocessed triacylglycerol was sheltered in these compartments. Although ezetimibe did not reduce the post-prandial lipid surge appreciably in triolein-infused mice, the results of the present study indicated that pharmacological actions of ezetimibe may participate in a novel regulatory mechanism for the efficient chylomicron assembly and secretion.

Redox-dependent PPARγ/Tnpo1 complex formation enhances PPARγ nuclear localization and signaling.

The nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ has been implicated in the pathogenesis of various human diseases including fatty liver. Although nuclear translocation of PPARγ plays an important role in PPARγ signaling, details of the translocation mechanisms have not been elucidated. Here we demonstrate that PPARγ2 translocates to the nucleus and activates signal transduction through H2O2-dependent formation of a PPARγ2 and transportin (Tnpo)1 complex via redox-sensitive disulfide bonds between cysteine (Cys)176 and Cys180 of the former and Cys512 of the latter. Using hepatocyte cultures and mouse models, we show that cytosolic H2O2/Tnpo1-dependent nuclear translocation enhances the amount of DNA-bound PPARγ and downstream signaling, leading to triglyceride accumulation in hepatocytes and liver. These findings expand our understanding of the mechanism underlying the nuclear translocation of PPARγ, and suggest that the PPARγ and Tnpo1 complex and surrounding redox environment are potential therapeutic targets in the treatment of PPARγ-related diseases.

A Sudden Onset of Severe Thrombocytopenia While Using Evolocumab.

A 72-year-old man with a 10-year history of coronary heart disease started evolocumab treatment once a month after developing excess myalgia due to therapy with a 3-hydroxy-methylglutaryl CoA reductase inhibitor. No side effects such as myalgia symptoms had been reported during the first 14 months of evolocumab treatment; however, he suddenly presented with acute severe thrombocytopenia following the 14th treatment. His platelet count continued to decrease to a nadir of 1,000/µL. His platelet-associated immunoglobulin G level had elevated to 790 ng/107 cells. He started receiving a combination of steroid therapy, high-dose immunoglobulin therapy, and platelet transfusions, but the first-line therapy was ineffective. He was subsequently treated with a thrombopoietin receptor agonist, and his platelet count recovered to 250,000/µL.

Stress-induced microglial activation occurs through ß-adrenergic receptor: noradrenaline as a key neurotransmitter in microglial activation.

BACKGROUND: The involvement of microglia in neuroinflammatory responses has been extensively demonstrated. Recent animal studies have shown that exposure to either acute or chronic stress induces robust microglial activation in the brain. In the present study, we investigated the underlying mechanism of brain microglial activation by acute stress. METHODS: We first looked at the spatial distribution of the noradrenaline (NA)-synthesizing enzyme, DBH (dopamine ß-hydroxylase), in comparison with NA receptors-ß1, ß2, and ß3 adrenergic receptors (ß1-AR, ß2-AR, and ß3-AR)-after which we examined the effects of the ß-blocker propranolol and α-blockers prazosin and yohimbine on stress-induced microglial activation. Finally, we compared stress-induced microglial activation between wild-type (WT) mice and double-knockout (DKO) mice lacking ß1-AR and ß2-AR. RESULTS: The results demonstrated that (1) microglial activation occurred in most studied brain regions, including the hippocampus (HC), thalamus (TM), and hypothalamus (HT); (2) within these three brain regions, the NA-synthesizing enzyme DBH was densely stained in the neuronal fibers; (3) ß1-AR and ß2-AR, but not ß3-AR, are detected in the whole brain, and ß1-AR and ß2-AR are co-localized with microglial cells, as observed by laser scanning microscopy; (4) ß-blocker treatment inhibited microglial activation in terms of morphology and count through the whole brain; α-blockers did not show such effect; (5) unlike WT mice, DKO mice exhibited substantial inhibition of stress-induced microglial activation in the brain. CONCLUSIONS: We demonstrate that neurons/microglia may interact with NA via ß1-AR and ß2-AR.

Luminal plant sterol promotes brush border membrane-to-lumen cholesterol efflux in the small intestine.

Plant sterols are used as food additives to reduce intestinal cholesterol absorption. They also increase fecal neutral sterol (FNS) excretion irrespective of the absorption inhibition. Intestine-mediated reverse cholesterol transport, or trans-intestinal cholesterol efflux (TICE), provides the major part of the increase of FNS excretion. However, it is unknown whether plant sterols stimulate TICE or not. We have shown previously that TICE can be evaluated by brush border membrane (BBM)-to-lumen cholesterol efflux. Thus, we examined whether luminal plant sterols stimulate BBM-to-lumen cholesterol efflux in the intestinal tract or not in mice. Cannulated upper jejunum that had been pre-labeled with orally given 3H-cholesterol, was flushed and perfused to collect 3H-cholesterol effluxed back into the lumen from the BBM to estimate the efflux efficiency. Adding 0.5 mg/ml of plant sterols, but not cholesterol, in the perfusion solution doubled the efflux. Plant sterols enter the BBM and are effluxed back to the lumen rapidly, in which process cholesterol transporters in the BBM are involved. We thus speculate that phytosterols alter cholesterol flux in the BBM; thereby, increases BBM-to-lumen cholesterol efflux, resulting in the increased TICE.

Evaluation of Teneligliptin Effects on Transcriptional Activity of PPARγ in Cell-Based Assays.

BACKGROUND: The antidiabetic drug teneligliptin is a novel dipeptidyl peptidase-4 (DPP-4) inhibitor with a thiazolidine-specific structure. This study aimed to investigate whether teneligliptin can activate PPARγ directly and/or indirectly in cell-based assays. METHODS: Promoter assays using the reporter construct driven under the control of the SV40 promoter and the PPAR response element (PPRE) were performed. Luciferase activity was measured after a 3-day incubation of vector-transduced cells with various concentrations of teneligliptin. RESULTS: Treatment of the cells with 50 µM teneligliptin significantly transactivated a reporter gene. The presence of the PPARγ antagonist, GW9662, did not affect the activation of PPRE-reporter expression by teneligliptin. CONCLUSION: We found that teneligliptin could increase PPARγ activity in cell-based assays irrespective of the PPARγ ligand-binding domain.

Characterization of CoPK02, a Ca2+/calmodulin-dependent protein kinase in mushroom Coprinopsis cinerea.

We surveyed genome sequences from the basidiomycetous mushroom Coprinopsis cinerea and isolated a cDNA homologous to CMKA, a calmodulin-dependent protein kinase (CaMK) in Aspergillus nidulans. We designated this sequence, encoding 580 amino acids with a molecular weight of 63,987, as CoPK02. CoPK02 possessed twelve subdomains specific to protein kinases and exhibited 43, 35, 40% identity with rat CaMKI, CaMKII, CaMKIV, respectively, and 40% identity with CoPK12, one of the CaMK orthologs in C. cinerea. CoPK02 showed significant autophosphorylation activity and phosphorylated exogenous proteins in the presence of Ca2+/CaM. By the CaM-overlay assay we confirmed that the C-terminal sequence (Trp346-Arg358) was the calmodulin-binding site, and that the binding of Ca2+/CaM to CoPK02 was reduced by the autophosphorylation of CoPK02. Since CoPK02 evolved in a different clade from CoPK12, and showed different gene expression compared to that of CoPK32, which is homologous to mitogen-activated protein kinase-activated protein kinase, CoPK02 and CoPK12 might cooperatively regulate Ca2+-signaling in C. cinerea.

Feminizing Adrenocortical Carcinoma with Distinct Histopathological Findings.

We herein present a 60-year-old man with adrenocortical carcinoma who had gynecomastia. An endocrinological examination revealed increased levels of serum estradiol and dehydroepiandrosterone-sulfate (DHEA-S) and reduced levels of free testosterone. Magnetic resonance imaging showed an adrenal tumor with heterogeneous intensity. Iodine-131 adosterol scintigraphy showed an increased uptake at the same site. Because feminizing adrenocortical carcinoma was suspected, right adrenalectomy was performed; the pathological diagnosis was adrenocortical carcinoma. The results of immunostaining indicated a virilizing tumor. Aromatase activity was identified on RT-PCR. As disorganized steroidogenesis is pathologically present in adrenocortical carcinoma, this diagnosis should be made with caution.

Molecular Cloning of Secreted Luciferases from Marine Planktonic Copepods.

Secreted luciferases isolated from copepod crustaceans are frequently used for nondisruptive reporter-gene assays, such as the continuous, automated and/or high-throughput monitoring of gene expression in living cells. All known copepod luciferases share highly conserved amino acid residues in two similar, repeated domains in the sequence. The similarity in the domains are ideal nature for designing PCR primers to amplify cDNA fragments of unidentified copepod luciferases from bioluminescent copepod crustaceans. Here, we introduce how to establish a cDNA encoding novel copepod luciferases from a copepod specimen by PCR with degenerated primers.

Ezetimibe Promotes Brush Border Membrane-to-Lumen Cholesterol Efflux in the Small Intestine.

Ezetimibe inhibits Niemann-Pick C1-like 1 (NPC1L1), an apical membrane cholesterol transporter of enterocytes, thereby reduces intestinal cholesterol absorption. This treatment also increases extrahepatic reverse cholesterol transport via an undefined mechanism. To explore this, we employed a trans-intestinal cholesterol efflux (TICE) assay, which directly detects circulation-to-intestinal lumen 3H-cholesterol transit in a cannulated jejunal segment, and found an increase of TICE by 45%. To examine whether such increase in efflux occurs at the intestinal brush border membrane(BBM)-level, we performed luminal perfusion assays, similar to TICE but the jejunal wall was labelled with orally-given 3H-cholesterol, and determined elevated BBM-to-lumen cholesterol efflux by 3.5-fold with ezetimibe. Such increased efflux probably promotes circulation-to-lumen cholesterol transit eventually; thus increases TICE. Next, we wondered how inhibition of NPC1L1, an influx transporter, resulted in increased efflux. When we traced orally-given 3H-cholesterol in mice, we found that lumen-to-BBM 3H-cholesterol transit was rapid and less sensitive to ezetimibe treatment. Comparison of the efflux and fractional cholesterol absorption revealed an inverse correlation, indicating the efflux as an opposite-regulatory factor for cholesterol absorption efficiency and counteracting to the naturally-occurring rapid cholesterol influx to the BBM. These suggest that the ezetimibe-stimulated increased efflux is crucial in reducing cholesterol absorption. Ezetimibe-induced increase in cholesterol efflux was approximately 2.5-fold greater in mice having endogenous ATP-binding cassette G5/G8 heterodimer, the major sterol efflux transporter of enterocytes, than the knockout counterparts, suggesting that the heterodimer confers additional rapid BBM-to-lumen cholesterol efflux in response to NPC1L1 inhibition. The observed framework for intestinal cholesterol fluxes may provide ways to modulate the flux to dispose of endogenous cholesterol efficiently for therapeutic purposes.

Identification of two nickel ion-induced genes, NCI16 and PcGST1, in Paramecium caudatum.

Here, we describe the isolation of two nickel-induced genes in Paramecium caudatum, NCI16 and PcGST1, by subtractive hybridization. NCI16 encoded a predicted four-transmembrane domain protein (∼16 kDa) of unknown function, and PcGST1 encoded glutathione S-transferase (GST; ∼25 kDa) with GST and glutathione peroxidase (GPx) activities. Exposing cells to cobalt chloride also caused the moderate upregulation of NCI16 and PcGST1 mRNAs. Both nickel sulfate and cobalt chloride dose dependently induced NCI16 and PcGST1 mRNAs, but with different profiles. Nickel treatment caused a continuous increase in PcGST1 and NCI16 mRNA levels for up to 3 and 6 days, respectively, and a notable increase in H2O2 concentrations in P. caudatum. NCI16 expression was significantly enhanced by incubating cells with H2O2, implying that NCI16 induction in the presence of nickel ions is caused by reactive oxygen species (ROS). On the other hand, PcGST1 was highly induced by the antioxidant tert-butylhydroquinone (tBHQ) but not by H2O2, suggesting that different mechanisms mediate the induction of NCI16 and PcGST1. We introduced a luciferase reporter vector with an ∼0.42-kb putative PcGST1 promoter into cells and then exposed the transformants to nickel sulfate. This resulted in significant luciferase upregulation, indicating that the putative PcGST1 promoter contains a nickel-responsive element. Our nickel-inducible system also may be applicable to the efficient expression of proteins that are toxic to host cells or require temporal control.

An active C-terminally truncated form of Ca (2+) /calmodulin-dependent protein kinase phosphatase-N (CaMKP-N/PPM1E).

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) and its nuclear homolog CaMKP-N (PPM1E) are Ser/Thr protein phosphatases that belong to the PPM family. CaMKP-N is expressed in the brain and undergoes proteolytic processing to yield a C-terminally truncated form. The physiological significance of this processing, however, is not fully understood. Using a wheat-embryo cell-free protein expression system, we prepared human CaMKP-N (hCaMKP-N(WT)) and the truncated form, hCaMKP-N(1-559), to compare their enzymatic properties using a phosphopeptide substrate. The hCaMKP-N(1-559) exhibited a much higher V(max) value than the hCaMKP-N(WT) did, suggesting that the processing may be a regulatory mechanism to generate a more active species. The active form, hCaMKP-N(1-559), showed Mn(2+) or Mg(2+)-dependent phosphatase activity with a strong preference for phospho-Thr residues and was severely inhibited by NaF, but not by okadaic acid, calyculin A, or 1-amino-8-naphthol-2,4-disulfonic acid, a specific inhibitor of CaMKP. It could bind to postsynaptic density and dephosphorylate the autophosphorylated Ca(2+)/calmodulin-dependent protein kinase II. Furthermore, it was inactivated by H2O2 treatment, and the inactivation was completely reversed by treatment with DTT, implying that this process is reversibly regulated by oxidation/reduction. The truncated CaMKP-N may play an important physiological role in neuronal cells.