Mechanism of PKCε regulation of cardiac GIRK channel gating.

G-protein-gated inwardly rectifying potassium (GIRK) channel activity is regulated by the membrane phospholipid, phosphatidylinositol-4,5-bisphosphate (PI 4,5P2). Constitutive activity of cardiac GIRK channels in atrial myocytes, that is implicated in atrial fibrillation (AF), is mediated via a protein kinase C-ε (PKCε)-dependent mechanism. The novel PKC isoform, PKCε, is reported to enhance the activity of cardiac GIRK channels. Here, we report that PKCε stimulation leads to activation of GIRK channels in mouse atria and in human stem cell-derived atrial cardiomyocytes (iPSCs). We identified residue GIRK4(S418) which when mutated to Ala abolished, or to Glu, mimicked the effects of PKCε on GIRK currents. PKCε strengthened the interactions of the cardiac GIRK isoforms, GIRK4 and GIRK1/4 with PIP2, an effect that was reversed in the GIRK4(S418A) mutant. This mechanistic insight into the PKCε-mediated increase in channel activity because of GIRK4(S418) phosphorylation, provides a precise druggable target to reverse AF-related pathologies due to GIRK overactivity.

The binding of PKCε and MEG2 to STAT3 regulates IL-6-mediated microglial hyperalgesia during inflammatory pain.

Studies have suggested that microglial IL-6 modulates inflammatory pain; however, the exact mechanism of action remains unclear. We therefore hypothesized that PKCε and MEG2 competitively bind to STAT3 and contribute to IL-6-mediated microglial hyperalgesia during inflammatory pain. Freund's complete adjuvant (FCA) and lipopolysaccharide (LPS) were used to induce hyperalgesia model mice and microglial inflammation. Mechanical allodynia was evaluated using von Frey tests in vivo. The interaction among PKCε, MEG2, and STAT3 was determined using ELISA and immunoprecipitation assay in vitro. The PKCε, MEG2, t-STAT3, pSTAT3Tyr705, pSTAT3Ser727, IL-6, GLUT3, and TREM2 were assessed by Western blot. IL-6 promoter activity and IL-6 concentration were examined using dual luciferase assays and ELISA. Overexpression of PKCε and MEG2 promoted and attenuated inflammatory pain, accompanied by an increase and decrease in IL-6 expression, respectively. PKCε displayed a stronger binding ability to STAT3 when competing with MEG2. STAT3Ser727 phosphorylation increased STAT3 interaction with both PKCε and MEG2. Moreover, LPS increased PKCε, MEG2, pSTAT3Tyr705, pSTAT3Ser727, IL-6, and GLUT3 levels and decreased TREM2 during microglia inflammation. IL-6 promoter activity was enhanced or inhibited by PKCε or MEG2 in the presence of STAT3 and LPS stimulation, respectively. In microglia, overexpression of PKCε and/or MEG2 resulted in the elevation of tSTAT3, pSTAT3Tyr705, pSTAT3Ser727, IL-6, and TREM2, and the reduction of GLUT3. PKCε is more potent than MEG2 when competitively binding to STAT3, displaying dual modulatory effects of IL-6 production, thus regulating the GLUT3 and TREM2 in microglia during inflammatory pain sensation.

Chemical Genetic Identification of PKC Epsilon Substrates in Mouse Brain.

PKC epsilon (PKCε) plays important roles in behavioral responses to alcohol and in anxiety-like behavior in rodents, making it a potential drug target for reducing alcohol consumption and anxiety. Identifying signals downstream of PKCε could reveal additional targets and strategies for interfering with PKCε signaling. We used a chemical genetic screen combined with mass spectrometry to identify direct substrates of PKCε in mouse brain and validated findings for 39 of them using peptide arrays and in vitro kinase assays. Prioritizing substrates with several public databases such as LINCS-L1000, STRING, GeneFriends, and GeneMAINA predicted interactions between these putative substrates and PKCε and identified substrates associated with alcohol-related behaviors, actions of benzodiazepines, and chronic stress. The 39 substrates could be broadly classified in three functional categories: cytoskeletal regulation, morphogenesis, and synaptic function. These results provide a list of brain PKCε substrates, many of which are novel, for future investigation to determine the role of PKCε signaling in alcohol responses, anxiety, responses to stress, and other related behaviors.

Influence of PRKCE non-synonymous variants on protein dynamics and functionality.

Novel protein kinase C (nPKC) family member, protein kinase C epsilon (PKCε) is an AGC kinase superfamily member. It is associated with neurological and metabolic diseases as well as human cancers. No study so far has been conducted to identify genetic variations and their effect on PKCε folding and functioning. The present study aimed to identify mutational hotspots in PKCε and disease-causing non-synonymous variants (nsSNPs) along with the investigation of nsSNP impact on protein dynamics. Twenty-nine in silico tools were applied to determine nsSNP deleteriousness, their impact on protein dynamics and disease association, along with the prediction of PKCε post-translational modification (PTM) sites. The present study's outcomes indicated that most nsSNPs were concentrated in the PKCε hinge region and C-terminal tail. Most pathogenic variants mapped to the kinase domain. Regulatory domain variants influenced PKCε interaction with molecular players whereas kinase domain variants were predicted to impact its phosphorylation pattern and protein-protein interactions. Most PTM sites were mapped to the hinge region. PKCε nsSNPs have an association with oncogenicity and its expression dysregulation is responsible for poor overall survival. Understanding nsSNP structural impact is a primary step necessary for delineating the relationship of genetic level differences with protein phenotype. The obtained knowledge can eventually help in disease diagnosis and therapy design.

Protein kinase C epsilon promotes de novo lipogenesis and tumor growth in prostate cancer cells by regulating the phosphorylation and nuclear translocation of pyruvate kinase isoform M2.

Protein kinase C epsilon (PKCε) belongs to a family of serine/threonine kinases that control cell proliferation, differentiation and survival. Aberrant PKCε activation and overexpression is a frequent feature of numerous cancers. However, its role in regulation of lipid metabolism in cancer cells remains elusive. Here we report a novel function of PKCε in regulating of prostate cancer cell proliferation by modulation of PKM2-mediated de novo lipogenesis. We show that PKCε promotes de novo lipogenesis and tumor cell proliferation via upregulation of lipogenic enzymes and lipid contents in prostate cancer cells. Mechanistically, PKCε interacts with NABD (1-388) domain of C-terminal deletion on pyruvate kinase isoform M2 (PKM2) and enhances the Tyr105 phosphorylation of PKM2, leading to its nuclear localization. Moreover, forced expression of mutant Tyr105 (Y105F) or PKM2 inhibition suppressed de novo lipogenesis and cell proliferation induced by overexpression of PKCε in prostate cancer cells. In a murine tumor model, inhibitor of PKM2 antagonizes lipogenic enzymes expression and prostate cancer growth induced by overexpression of PKCε in vivo. These data indicate that PKCε is a critical regulator of de novo lipogenesis, which may represent a potential therapeutic target for the treatment of prostate cancer.

Brain-specific serine/threonine-protein kinase 1 is a substrate of protein kinase C epsilon involved in sex-specific ethanol and anxiety phenotypes.

Protein kinase C epsilon (PKCε) regulates behavioural responses to ethanol and plays a role in anxiety-like behaviour, but knowledge is limited on downstream substrates of PKCε that contribute to these behaviours. We recently identified brain-specific serine/threonine-protein kinase 1 (BRSK1) as a substrate of PKCε. Here, we test the hypothesis that BRSK1 mediates responses to ethanol and anxiety-like behaviours that are also PKCε dependent. We used in vitro kinase assays to further validate BRSK1 as a substrate of PKCε and used Brsk1-/- mice to assess the role of BRSK1 in ethanol- and anxiety-related behaviours and in physiological responses to ethanol. We found that BRSK1 is phosphorylated by PKCε at a residue identified in a chemical genetic screen of PKCε substrates in mouse brain. Like Prkce-/- mice, male and female Brsk1-/- mice were more sensitive than wild-type to the acute sedative-hypnotic effect of alcohol. Unlike Prkce-/- mice, Brsk1-/- mice responded like wild-type to ataxic doses of ethanol. Although in Prkce-/- mice ethanol consumption and reward are reduced in both sexes, they were reduced only in female Brsk1-/- mice. Ex vivo slice electrophysiology revealed that ethanol-induced facilitation of GABA release in the central amygdala was absent in male Brsk1-/- mice similar to findings in male Prkce-/- mice. Collectively, these results indicate that BRSK1 is a target of PKCε that mediates some PKCε-dependent responses to ethanol in a sex-specific manner and plays a role distinct from PKCε in anxiety-like behaviour.

Exploring the prognostic significance of PKCε variants in cervical cancer.

BACKGROUND: Protein Kinase C-epsilon (PKCε) is a member of the novel subfamily of PKCs (nPKCs) that plays a role in cancer development. Studies have revealed that its elevated expression levels are associated with cervical cancer. Previously, we identified pathogenic variations in its different domains through various bioinformatics tools and molecular dynamic simulation. In the present study, the aim was to find the association of its variants rs1553369874 and rs1345511001 with cervical cancer and to determine the influence of these variants on the protein-protein interactions of PKCε, which can lead towards cancer development and poor survival rates. METHODS: The association of the variants with cervical cancer and its clinicopathological features was determined through genotyping analysis. Odds ratio and relative risk along with Fisher exact test were calculated to evaluate variants significance and disease risk. Protein-protein docking was performed and docked complexes were subjected to molecular dynamics simulation to gauge the variants impact on PKCε's molecular interactions. RESULTS: This study revealed that genetic variants rs1553369874 and rs1345511001 were associated with cervical cancer. Smad3 interacts with PKCε and this interaction promotes cervical cancer angiogenesis; therefore, Smad3 was selected for protein-protein docking. The analysis revealed PKCε variants promoted aberrant interactions with Smad3 that might lead to the activation of oncogenic pathways. The data obtained from this study suggested the prognostic significance of PRKCE gene variants rs1553369874 and rs1345511001. CONCLUSION: Through further in vitro and in vivo validation, these variants can be used at the clinical level as novel prognostic markers and therapeutic targets against cervical cancer.

Elucidating the role of missense SNP of protein kinase C epsilon in HCV-induced hepatocellular carcinoma.

BACKGROUND: The protein kinase C (PKC) family of serine/threonine kinases contains more than ten isozymes that are involved in multiple signaling pathways, including cell cycle regulation and carcinogenesis. The PKCε isozyme is an oncogene known to be upregulated in various signaling pathways involved in hepatitis C virus (HCV)-induced hepatocellular carcinoma (HCC). However, there is no known association of missense SNPs in PKCε with this disease, which can be a potential biomarker for early diagnosis and treatment. This research reveals a novel missense SNP in PKCε that is associated with HCV-induced HCC in the Pakistani population. METHODS: The PKCε SNP with amino acid substitution of E14K was chosen for wet lab analysis. Tetra ARMS-PCR was employed for the identification of high-risk SNP in PKCε of HCV-induced HCC patients. Liver function testing was also performed for comparison between the liver condition of the HCC patient and control group, and the viral load of HCC patient samples was evaluated to determine any alteration in the viral infectivity between different genotypes of the selected high-risk PKCε variant SNP. RESULTS: Frequency distribution of the homozygous GG genotype was found to be highest among HCV-induced HCC patients and was also found to be significantly associated with disease development and progression. The p values of comparative data obtained for the other two genotypes, heterozygous AG and homozygous AA, of the SNP also showed the significance of the data for these alleles. Still, their odds ratio and relative risk analysis did not indicate their association with HCV-induced HCC. CONCLUSION: The distribution of a genotype GG of PKCε has been found in HCV- induced HCC patients. Therefore, these PKCε SNP have the potential to be biomarkers for HCV-induced HCC. Further investigation using a larger sample size would provide additional insight into these initial data and open a new avenue for a better prognosis of this disease.

Competing endogenous RNA network mediated by circ_3205 in SARS-CoV-2 infected cells.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a new member of the Betacoronaviridae family, responsible for the recent pandemic outbreak of COVID-19. To start exploring the molecular events that follow host cell infection, we queried VirusCircBase and identified a circular RNA (circRNA) predicted to be synthesized by SARS-CoV-2, circ_3205, which we used to probe: (i) a training cohort comprised of two pools of cells from three nasopharyngeal swabs of SARS-CoV-2 infected (positive) or uninfected (negative, UCs) individuals; (ii) a validation cohort made up of 12 positive and 3 negative samples. The expression of circRNAs, miRNAs and miRNA targets was assayed through real-time PCR. CircRNA-miRNA interactions were predicted by TarpMiR, Analysis of Common Targets for circular RNAs (ACT), and STarMir tools. Enrichment of the biological processes and the list of predicted miRNA targets were retrieved from DIANA miRPath v3.0. Our results showed that the predicted SARS-CoV-2 circ_3205 was expressed only in positive samples and its amount positively correlated with that of SARS-CoV-2 Spike (S) mRNA and the viral load (r values = 0.80952 and 0.84867, Spearman's correlation test, respectively). Human (hsa) miR-298 was predicted to interact with circ_3205 by all three predictive tools. KCNMB4 and PRKCE were predicted as hsa-miR-298 targets. Interestingly, the function of both is correlated with blood coagulation and immune response. KCNMB4 and PRKCE mRNAs were upregulated in positive samples as compared to UCs (6 and 8.1-fold, p values = 0.049 and 0.02, Student's t test, respectively) and their expression positively correlated with that of circ_3205 (r values = 0.6 and 0.25, Spearman's correlation test, respectively). We propose that our results convincingly suggest that circ_3205 is a circRNA synthesized by SARS-CoV-2 upon host cell infection and that it may behave as a competitive endogenous RNA (ceRNA), sponging hsa-miR-298 and contributing to the upregulation of KCNMB4 and PRKCE mRNAs.

The ε-Isozyme of Protein Kinase C (PKCε) Is Impaired in ALS Motor Cortex and Its Pulse Activation by Bryostatin-1 Produces Long Term Survival in Degenerating SOD1-G93A Motor Neuron-like Cells.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and ultimately fatal neurodegenerative disease, characterized by a progressive depletion of upper and lower motor neurons (MNs) in the brain and spinal cord. The aberrant regulation of several PKC-mediated signal transduction pathways in ALS has been characterized so far, describing either impaired expression or altered activity of single PKC isozymes (α, ß, ζ and δ). Here, we detailed the distribution and cellular localization of the ε-isozyme of protein kinase C (PKCε) in human postmortem motor cortex specimens and reported a significant decrease in both PKCε mRNA (PRKCE) and protein immunoreactivity in a subset of sporadic ALS patients. We furthermore investigated the steady-state levels of both pan and phosphorylated PKCε in doxycycline-activated NSC-34 cell lines carrying the human wild-type (WT) or mutant G93A SOD1 and the biological long-term effect of its transient agonism by Bryostatin-1. The G93A-SOD1 cells showed a significant reduction of the phosphoPKCε/panPKCε ratio compared to the WT. Moreover, a brief pulse activation of PKCε by Bryostatin-1 produced long-term survival in activated G93A-SOD1 degenerating cells in two different cell death paradigms (serum starvation and chemokines-induced toxicity). Altogether, the data support the implication of PKCε in ALS pathophysiology and suggests its pharmacological modulation as a potential neuroprotective strategy, at least in a subgroup of sporadic ALS patients.

PKCε associates with the Kv3.4 channel to promote its expression in a kinase activity-dependent manner.

The voltage-gated potassium channel Kv3.4 is a crucial regulator of nociceptive signaling in the dorsal root ganglion (DRG) and the dorsal horn of the spinal cord. Moreover, Kv3.4 dysfunction has been linked to neuropathic pain. Although kinases and phosphatases can directly modulate Kv3.4 gating, the signaling mechanisms regulating the expression and stability of the Kv3.4 protein are generally unknown. We explored a potential role of PKCε and found an unexpected interaction that has a positive effect on Kv3.4 expression. Co-immunoprecipitation studies revealed a physical association between PKCε and Kv3.4 in both heterologous cells and rat DRG neurons. Furthermore, in contrast to the wild-type and constitutively active forms of PKCε, expression of a catalytically inactive form of the enzyme inhibits Kv3.4 expression and membrane localization through a dominant negative effect. Co-expression of Kv3.4 with the wild-type, constitutively active, or catalytically inactive forms of PKCε had no significant effects on Kv3.4 gating. These results suggest that a novel physical interaction of the Kv3.4 channel with functional PKCε primarily determines its stability and localization in DRG neurons. This interaction is akin to those of previously identified accessory ion channel proteins, which could be significant in neural tissues where Kv3.4 regulates electrical signaling.

Co-ordinated control of the Aurora B abscission checkpoint by PKCε complex assembly, midbody recruitment and retention.

A requirement for PKCε in exiting from the Aurora B dependent abscission checkpoint is associated with events at the midbody, however, the recruitment, retention and action of PKCε in this compartment are poorly understood. Here, the prerequisite for 14-3-3 complex assembly in this pathway is directly linked to the phosphorylation of Aurora B S227 at the midbody. However, while essential for PKCε control of Aurora B, 14-3-3 association is shown to be unnecessary for the activity-dependent enrichment of PKCε at the midbody. This localisation is demonstrated to be an autonomous property of the inactive PKCε D532N mutant, consistent with activity-dependent dissociation. The C1A and C1B domains are necessary for this localisation, while the C2 domain and inter-C1 domain (IC1D) are necessary for retention at the midbody. Furthermore, it is shown that while the IC1D mutant retains 14-3-3 complex proficiency, it does not support Aurora B phosphorylation, nor rescues division failure observed with knockdown of endogenous PKCε. It is concluded that the concerted action of multiple independent events facilitates PKCε phosphorylation of Aurora B at the midbody to control exit from the abscission checkpoint.

Silencing P2X7R Alleviates Diabetic Neuropathic Pain Involving TRPV1 via PKCε/P38MAPK/NF-κB Signaling Pathway in Rats.

Transient receptor potential vanillic acid 1 (TRPV1) is an ion channel activated by heat and inflammatory factors involved in the development of various types of pain. The P2X7 receptor is in the P2X family and is associated with pain mediated by satellite glial cells. There might be some connection between the P2X7 receptor and TRPV1 in neuropathic pain in diabetic rats. A type 2 diabetic neuropathic pain rat model was induced using high glucose and high-fat diet for 4 weeks and low-dose streptozocin (35 mg/kg) intraperitoneal injection to destroy islet B cells. Male Sprague Dawley rats were administrated by intrathecal injection of P2X7 shRNA and p38 inhibitor, and we recorded abnormal mechanical and thermal pain and nociceptive hyperalgesia. One week later, the dorsal root ganglia from the L4-L6 segment of the spinal cord were harvested for subsequent experiments. We measured pro-inflammatory cytokines, examined the relationship between TRPV1 on neurons and P2X7 receptor on satellite glial cells by measuring protein and transcription levels of P2X7 receptor and TRPV1, and measured protein expression in the PKCε/P38 MAPK/NF-κB signaling pathway after intrathecal injection. P2X7 shRNA and p38 inhibitor relieved hyperalgesia in diabetic neuropathic pain rats and modulated inflammatory factors in vivo. P2X7 shRNA and P38 inhibitors significantly reduced TRPV1 expression by downregulating the PKCε/P38 MAPK/NF-κB signaling pathway and inflammatory factors in dorsal root ganglia. Intrathecal injection of P2X7 shRNA alleviates nociceptive reactions in rats with diabetic neuropathic pain involving TRPV1 via PKCε/P38 MAPK/NF-κB signaling pathway.

Aberration of the modulatory functions of intronic microRNA hsa-miR-933 on its host gene ATF2 results in type II diabetes mellitus and neurodegenerative disease development.

BACKGROUND: MicroRNAs are ~ 22-nucleotide-long biological modifiers that act as the post-transcriptional modulator of gene expression. Some of them are identified to be embedded within the introns of protein-coding genes, these miRNAs are called the intronic miRNAs. Previous findings state that these intronic miRNAs are co-expressed with their host genes. This co-expression is necessary to maintain the robustness of the biological system. Till to date, only a few experiments are performed discretely to elucidate the functional relationship between few co-expressed intronic miRNAs and their associated host genes. RESULTS: In this study, we have interpreted the underlying modulatory mechanisms of intronic miRNA hsa-miR-933 on its target host gene ATF2 and found that aberration can lead to several disease conditions. A protein-protein interaction network-based approach was adopted, and functional enrichment analysis was performed to elucidate the significantly over-represented biological functions and pathways of the common targets. Our approach delineated that hsa-miR-933 might control the hyperglycemic condition and hyperinsulinism by regulating ATF2 target genes MAP4K4, PRKCE, PEA15, BDNF, PRKACB, and GNAS which can otherwise lead to the development of type II diabetes mellitus. Moreover, we showed that hsa-miR-933 can regulate a target of ATF2, brain-derived neurotrophic factor (BDNF), to modulate the optimal expression of ATF2 in neuron cells to render neuroprotection for the inhibition of neurodegenerative diseases. CONCLUSIONS: Our in silico model provides interesting resources for experimentations in a model organism or cell line for further validation. These findings may extend the common perception of gene expression analysis with new regulatory functionality.

Bidirectional sex-dependent regulation of α6 and ß3 nicotinic acetylcholine receptors by protein kinase Cε.

Nicotine and alcohol are the most commonly abused substances worldwide and are frequently coabused. Nicotinic acetylcholine receptors (nAChRs) containing the α6 and ß3 subunits are expressed in neural reward circuits and are critical for nicotine and alcohol reward. nAChRs are dynamically regulated by signaling molecules such as protein kinase C epsilon (PKCε), which impact transcription of α6 and ß3 subunit mRNA (Chrna6 and Chrnb3, respectively). Previous work found decreased expression of Chrna6 and Chrnb3 transcripts in the ventral midbrain of male PKCε-/- mice, who also consume less nicotine and alcohol compared with wild-type (WT) littermates. Using RT-qPCR, we show that female PKCε-/- mice have higher expression of Chrna6 and Chrnb3 transcripts in the ventral midbrain, which functionally impacts nAChR-dependent behavior as female but not male PKCε-/- mice exhibit locomotor hypersensitivity to low-dose (0.25 mg/kg i.p.) nicotine. Female PKCε-/- mice show no differences in alcohol-induced sedation in the loss-of-righting reflex assay (4.0 g/kg i.p.) compared with WT littermates, whereas male PKCε-/- mice have enhanced sedation compared with WT mice. Female PKCε-/- mice also show reduced immobility time in response to varenicline (1.0 mg/kg i.p.) compared with WT littermates in the tail suspension test, and this effect was absent in male mice. Additionally, we found that female PKCε-/- mice show altered alcohol and nicotine consumption patterns in chronic voluntary two-bottle choice assays. Our data reveal a bidirectional effect of sex in the transcriptional regulation of nicotinic receptors by PKCε, highlighting the importance of studying both sexes in preclinical animal models.

PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling.

Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat-fed, and high-fat-fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.

Impact of Maturation on Myocardial Response to Ischemia and the Effectiveness of Remote Preconditioning in Male Rats.

Aging attenuates cardiac tolerance to ischemia/reperfusion (I/R) associated with defects in protective cell signaling, however, the onset of this phenotype has not been completely investigated. This study aimed to compare changes in response to I/R and the effects of remote ischemic preconditioning (RIPC) in the hearts of younger adult (3 months) and mature adult (6 months) male Wistar rats, with changes in selected proteins of protective signaling. Langendorff-perfused hearts were exposed to 30 min I/120 min R without or with prior three cycles of RIPC (pressure cuff inflation/deflation on the hind limb). Infarct size (IS), incidence of ventricular arrhythmias and recovery of contractile function (LVDP) served as the end points. In both age groups, left ventricular tissue samples were collected prior to ischemia (baseline) and after I/R, in non-RIPC controls and in RIPC groups to detect selected pro-survival proteins (Western blot). Maturation did not affect post-ischemic recovery of heart function (Left Ventricular Developed Pressure, LVDP), however, it increased IS and arrhythmogenesis accompanied by decreased levels and activity of several pro-survival proteins and by higher levels of pro-apoptotic proteins in the hearts of elder animals. RIPC reduced the occurrence of reperfusion-induced ventricular arrhythmias, IS and contractile dysfunction in younger animals, and this was preserved in the mature adults. RIPC did not increase phosphorylated protein kinase B (p-Akt)/total Akt ratio, endothelial nitric oxide synthase (eNOS) and protein kinase Cε (PKCε) prior to ischemia but only after I/R, while phosphorylated glycogen synthase kinase-3ß (GSK3ß) was increased (inactivated) before and after ischemia in both age groups coupled with decreased levels of pro-apoptotic markers. We assume that resistance of rat heart to I/R injury starts to already decline during maturation, and that RIPC may represent a clinically relevant cardioprotective intervention in the elder population.

EGFR-induced and PKCε monoubiquitylation-dependent NF-κB activation upregulates PKM2 expression and promotes tumorigenesis.

Many types of human tumor cells have overexpressed pyruvate kinase M2 (PKM2). However, the mechanism underlying this increased PKM2 expression remains to be defined. We demonstrate here that EGFR activation induces PLCγ1-dependent PKCε monoubiquitylation at Lys321 mediated by RINCK1 ubiquitin ligase. Monoubiquitylated PKCε interacts with a ubiquitin-binding domain in NEMO zinc finger and recruits the cytosolic IKK complex to the plasma membrane, where PKCε phosphorylates IKKß at Ser177 and activates IKKß. Activated RelA interacts with HIF1α, which is required for RelA to bind the PKM promoter. PKCε- and NF-κB-dependent PKM2 upregulation is required for EGFR-promoted glycolysis and tumorigenesis. In addition, PKM2 expression correlates with EGFR and IKKß activity in human glioblastoma specimens and with grade of glioma malignancy. These findings highlight the distinct regulation of NF-κB by EGF, in contrast to TNF-α, and the importance of the metabolic cooperation between the EGFR and NF-κB pathways in PKM2 upregulation and tumorigenesis.

Mechanism by which arylamine N-acetyltransferase 1 ablation causes insulin resistance in mice.

A single-nucleotide polymorphism in the human arylamine N-acetyltransferase 2 (Nat2) gene has recently been identified as associated with insulin resistance in humans. To understand the cellular and molecular mechanisms by which alterations in Nat2 activity might cause insulin resistance, we examined murine ortholog Nat1 knockout (KO) mice. Nat1 KO mice manifested whole-body insulin resistance, which could be attributed to reduced muscle, liver, and adipose tissue insulin sensitivity. Hepatic and muscle insulin resistance were associated with marked increases in both liver and muscle triglyceride (TAG) and diacylglycerol (DAG) content, which was associated with increased PKCε activation in liver and increased PKCθ activation in skeletal muscle. Nat1 KO mice also displayed reduced whole-body energy expenditure and reduced mitochondrial oxygen consumption in white adipose tissue, brown adipose tissue, and hepatocytes. Taken together, these studies demonstrate that Nat1 deletion promotes reduced mitochondrial activity and is associated with ectopic lipid-induced insulin resistance. These results provide a potential genetic link among mitochondrial dysfunction with increased ectopic lipid deposition, insulin resistance, and type 2 diabetes.

Regulation of Autophagy by Protein Kinase C-ε in Breast Cancer Cells.

Protein kinase C-ε (PKCε), an anti-apoptotic protein, plays critical roles in breast cancer development and progression. Although autophagy is an important survival mechanism, it is not known if PKCε regulates autophagy in breast cancer cells. We have shown that silencing of PKCε by siRNA inhibited basal and starvation-induced autophagy in T47D breast cancer cells as determined by the decrease in LC3-II, increase in p62, and decrease in autophagy puncta both in the presence and absence of bafilomycin A1. The mechanistic target of rapamycin (mTOR) associates with Raptor or Rictor to form complex-1 (mTORC1) or complex-2 (mTORC2), respectively. Knockdown of PKCε attenuated an increase in autophagy caused by the depletion of Raptor and Rictor. Overexpression of PKCε in MCF-7 cells caused activation of mTORC1 and an increase in LC3-I, LC3-II, and p62. The mTORC1 inhibitor rapamycin abolished the increase in LC3-I and p62. Knockdown of mTOR and Rictor or starvation enhanced autophagy in PKCε overexpressing cells. While overexpression of PKCε in MCF-7 cells inhibited apoptosis, it induced autophagy in response to tumor necrosis factor-α. However, inhibition of autophagy by Atg5 knockdown restored apoptosis in PKCε-overexpressing cells. Thus, PKCε promotes breast cancer cell survival not only by inhibiting apoptosis but also by inducing autophagy.