Protein kinase C (PKC) isoforms in cancer, tumor promotion and tumor suppression

The AGC family of serine/threonine kinases (PKA, PKG, PKC) includes more than 60 members that are critical regulators of numerous cellular functions, including cell cycle and differentiation, morphogenesis, and cell survival and death. Mutation and/or dysregulation of AGC kinases can lead to malignant cell transformation and contribute to the pathogenesis of many human diseases. Members of one subgroup of AGC kinases, the protein kinase C (PKC), have been singled out as critical players in carcinogenesis, following their identification as the intracellular receptors of phorbol esters, which exhibit tumor-promoting activities. This observation attracted the attention of researchers worldwide and led to intense investigations on the role of PKC in cell transformation and the potential use of PKC as therapeutic drug targets in cancer diseases. Studies demonstrated that many cancers had altered expression and/or mutation of specific PKC genes. However, the causal relationships between the changes in PKC gene expression and/or mutation and the direct cause of cancer remain elusive. Independent studies in normal cells demonstrated that activation of PKC is essential for the induction of cell activation and proliferation, differentiation, motility, and survival. Based on these observations and the general assumption that PKC isoforms play a positive role in cell transformation and/or cancer progression, many PKC inhibitors have entered clinical trials but the numerous attempts to target PKC in cancer has so far yielded only very limited success. More recent studies demonstrated that PKC function as tumor suppressors, and suggested that future clinical efforts should focus on restoring, rather than inhibiting, PKC activity. The present manuscript provides some historical perspectives on the tumor promoting function of PKC, reviewing some of the observations linking PKC to cancer progression, and discusses the role of PKC in the pathogenesis of cancer diseases and its potential usage as a therapeutic target.

Induction of vascular insulin resistance and endothelin-1 expression and acceleration of atherosclerosis by the overexpression of protein kinase C-β isoform in the endothelium

RATIONALE

Loss of insulin action in the endothelium can cause endothelial dysfunction and atherosclerosis. Hyperglycemia and elevated fatty acids induced by diabetes mellitus can activate protein kinase C-β isoforms and selectively inhibit insulin signaling via phosphatidylinositol 3-kinase/Akt pathway to inhibit the activation of endothelial nitric oxide synthase and metabolic actions.

OBJECTIVE

To demonstrate that overexpressing protein kinase C-β2 isoform in endothelial cells can cause selective insulin resistance and exacerbate atherosclerosis in the aorta.

METHODS AND RESULTS

Protein kinase C-β2 isoform was overexpressed in endothelial cells using a promoter of vascular endothelial cell cadherin. These mice were cross-bred with apoE-/- mice [Tg (Prkcb)apoE-/-]. On a Western diet, Tg(Prkcb)apoE-/- and apoE-/- mice did not differ in systemic insulin sensitivity, glucose tolerance, plasma lipid, or blood pressure. Insulin action in endothelial cells and femoral artery from Tg(Prkcb)apoE-/- mice was impaired by ≈40% with respect to Akt/endothelial nitric oxide synthase activation, and leukocyte-endothelial cell binding increased in cultured lung endothelial cells from Tg(Prkcb)apoE-/- mice compared with that from apoE-/- mice. Basal and angiotensin-stimulated big endothelin-1 levels were elevated in Tg(Prkcb)apoE-/- mice compared with apoE-/- mice. The severity of atherosclerosis in the aorta from Tg(Prkcb)apoE-/- mice increased by ≈70% as measured by en face fat staining and plaque content of the number of smooth muscle cells, macrophages, and extracellular matrix.

CONCLUSIONS

Specific protein kinase C-β2 activation in the endothelial cells caused dysfunction and accelerated atherosclerosis because of loss of insulin-stimulated Akt/endothelial nitric oxide synthase activation and angiotensin-induced increases in endothelin-1 expression.

Increased extracellular pressure stimulates tumor proliferation by a mechanosensitive calcium channel and PKC-β

Large tumors exhibit high interstitial pressure heightened by growth against the constraining stroma. Such pressures could stimulate tumor proliferation via a mechanosensitive ion channel. We studied the effects of 0-80 mmHg increased extracellular pressure for 24 h on proliferation of SW620, Caco-2, and CT-26 colon; MCF-7 breast; and MLL and PC3 prostate cancer cells, and delineated its mechanism in SW620 cells with specific inhibitors and siRNA. Finally, we compared NF-kB, phospho-IkB and cyclin D1 immunoreactivity in the high pressure centers and low pressure peripheries of human tumors. Pressure-stimulated proliferation in all cells. Pressure-driven SW620 proliferation required calcium influx via the T-type Ca(2+) channel Cav3.3, which stimulated PKC-β to invoke the IKK-IkB-NF-kB pathway to increase proliferation and S-phase fraction. The mitotic index and immunoreactivity of NF-kB, phospho-IkB, and cyclin D1 in the center of 28 large human colon, lung, and head and neck tumors exceeded that in tumor peripheries. Extracellular pressure increases [Ca(2+)]i via Cav3.3, driving a PKC-β- IKK- IkB-NF-kB pathway that stimulates cancer cell proliferation. Rapid proliferation in large stiff tumors may increase intratumoral pressure, activating this pathway to stimulate further proliferation in a feedback cycle that potentiates tumor growth. Targeting this pathway may inhibit proliferation in large unresectable tumors.

KinView: a visual comparative sequence analysis tool for integrated kinome research

Multiple sequence alignments (MSAs) are a fundamental analysis tool used throughout biology to investigate relationships between protein sequence, structure, function, evolutionary history, and patterns of disease-associated variants. However, their widespread application in systems biology research is currently hindered by the lack of user-friendly tools to simultaneously visualize, manipulate and query the information conceptualized in large sequence alignments, and the challenges in integrating MSAs with multiple orthogonal data such as cancer variants and post-translational modifications, which are often stored in heterogeneous data sources and formats. Here, we present the Multiple Sequence Alignment Ontology (MSAOnt), which represents a profile or consensus alignment in an ontological format. Subsets of the alignment are easily selected through the SPARQL Protocol and RDF Query Language for downstream statistical analysis or visualization. We have also created the Kinome Viewer (KinView), an interactive integrative visualization that places eukaryotic protein kinase cancer variants in the context of natural sequence variation and experimentally determined post-translational modifications, which play central roles in the regulation of cellular signaling pathways. Using KinView, we identified differential phosphorylation patterns between tyrosine and serine/threonine kinases in the activation segment, a major kinase regulatory region that is often mutated in proliferative diseases. We discuss cancer variants that disrupt phosphorylation sites in the activation segment, and show how KinView can be used as a comparative tool to identify differences and similarities in natural variation, cancer variants and post-translational modifications between kinase groups, families and subfamilies. Based on KinView comparisons, we identify and experimentally characterize a regulatory tyrosine (Y177PLK4) in the PLK4 C-terminal activation segment region termed the P+1 loop. To further demonstrate the application of KinView in hypothesis generation and testing, we formulate and validate a hypothesis explaining a novel predicted loss-of-function variant (D523NPKCβ) in the regulatory spine of PKCβ, a recently identified tumor suppressor kinase. KinView provides a novel, extensible interface for performing comparative analyses between subsets of kinases and for integrating multiple types of residue specific annotations in user friendly formats.

Fas signaling-mediated TH9 cell differentiation favors bowel inflammation and antitumor functions

Fas induces apoptosis in activated T cell to maintain immune homeostasis, but the effects of non-apoptotic Fas signaling on T cells remain unclear. Here we show that Fas promotes TH9 cell differentiation by activating NF-κB via Ca2+-dependent PKC-β activation. In addition, PKC-β also phosphorylates p38 to inactivate NFAT1 and reduce NFAT1-NF-κB synergy to promote the Fas-induced TH9 transcription program. Fas ligation exacerbates inflammatory bowel disease by increasing TH9 cell differentiation, and promotes antitumor activity in p38 inhibitor-treated TH9 cells. Furthermore, low-dose p38 inhibitor suppresses tumor growth without inducing systemic adverse effects. In patients with tumor, relatively high TH9 cell numbers are associated with good prognosis. Our study thus implicates Fas in CD4+ T cells as a target for inflammatory bowel disease therapy. Furthermore, simultaneous Fas ligation and low-dose p38 inhibition may be an effective approach for TH9 cell induction and cancer therapy.

Targetable cellular signaling events mediate vascular pathology in vascular Ehlers-Danlos syndrome

Vascular Ehlers-Danlos syndrome (vEDS) is an autosomal-dominant connective tissue disorder caused by heterozygous mutations in the COL3A1 gene, which encodes the pro-α 1 chain of collagen III. Loss of structural integrity of the extracellular matrix is believed to drive the signs and symptoms of this condition, including spontaneous arterial dissection and/or rupture, the major cause of mortality. We created 2 mouse models of vEDS that carry heterozygous mutations in Col3a1 that encode glycine substitutions analogous to those found in patients, and we showed that signaling abnormalities in the PLC/IP3/PKC/ERK pathway (phospholipase C/inositol 1,4,5-triphosphate/protein kinase C/extracellular signal-regulated kinase) are major mediators of vascular pathology. Treatment with pharmacologic inhibitors of ERK1/2 or PKCβ prevented death due to spontaneous aortic rupture. Additionally, we found that pregnancy- and puberty-associated accentuation of vascular risk, also seen in vEDS patients, was rescued by attenuation of oxytocin and androgen signaling, respectively. Taken together, our results provide evidence that targetable signaling abnormalities contribute to the pathogenesis of vEDS, highlighting unanticipated therapeutic opportunities.

The Inhibition of Protein Kinase C β Contributes to the Pathogenesis of Preeclampsia by Activating Autophagy

Background

Preeclampsia is a devastating hypertensive disorder of pregnancy with unknown mechanism. Recent studies have considered abnormal autophagy as a new cellular mechanism for this disorder, while little is known about how autophagy is specifically involved and what factors are implicated. Here, we report a previously unrecognized preeclampsia-associated autophagic regulator, PKCβ, that is involved in placental angiogenesis.

Methods

PKCβ levels were evaluated by quantitative real-time PCR, western blotting, immunofluorescence and by the analysis of public data. The autophagy-regulating role of PKCβ inhibition in preeclampsia pathogenesis was studied in a mouse model, and in human umbilical vein endothelial cells (HUVECs) and human choriocarcinoma cells (JEG-3).

Findings

PKCβ was significantly downregulated in human preeclamptic placentas. In a mouse model, the selective inhibition of PKCβ by Ruboxistaurin was sufficient to induce preeclampsia-like symptoms, accompanied by excessive autophagic flux and a disruption in the balance of pro- and anti-angiogenic factors in mouse placentas. In contrast, autophagic inhibition by 3-methyladenine partially normalized hypertension, proteinuria and placental angiogenic imbalance in PKCβ-inhibited mice. Our in vitro experiments demonstrated that PKCβ inhibition activated autophagy, thus blocking VEGFA-induced HUVEC tube formation and resulting in the significant upregulation of sFLT1 and downregulation of VEGFA in JEG-3 cells.

Interpretation

These data support a novel model in which autophagic activation due to PKCβ inhibition leads to the impairment of angiogenesis and eventually results in preeclampsia.

Funding

Shanghai Key Program of Clinical Science and Technology Innovation, National Natural Science Foundation of China and Shanghai Medical Center of Key Programs for Female Reproductive Diseases.

Application of RNAi to Genomic Drug Target Validation in Schistosomes

Concerns over the possibility of resistance developing to praziquantel (PZQ), has stimulated efforts to develop new drugs for schistosomiasis. In addition to the development of improved whole organism screens, the success of RNA interference (RNAi) in schistosomes offers great promise for the identification of potential drug targets to initiate drug discovery. In this study we set out to contribute to RNAi based validation of putative drug targets. Initially a list of 24 target candidates was compiled based on the identification of putative essential genes in schistosomes orthologous of C. elegans essential genes. Knockdown of Calmodulin (Smp_026560.2) (Sm-Calm), that topped this list, produced a phenotype characterised by waves of contraction in adult worms but no phenotype in schistosomula. Knockdown of the atypical Protein Kinase C (Smp_096310) (Sm-aPKC) resulted in loss of viability in both schistosomula and adults and led us to focus our attention on other kinase genes that were identified in the above list and through whole organism screening of known kinase inhibitor sets followed by chemogenomic evaluation. RNAi knockdown of these kinase genes failed to affect adult worm viability but, like Sm-aPKC, knockdown of Polo-like kinase 1, Sm-PLK1 (Smp_009600) and p38-MAPK, Sm-MAPK p38 (Smp_133020) resulted in an increased mortality of schistosomula after 2-3 weeks, an effect more marked in the presence of human red blood cells (hRBC). For Sm-PLK-1 the same effects were seen with the specific inhibitor, BI2536, which also affected viable egg production in adult worms. For Sm-PLK-1 and Sm-aPKC the in vitro effects were reflected in lower recoveries in vivo. We conclude that the use of RNAi combined with culture with hRBC is a reliable method for evaluating genes important for larval development. However, in view of the slow manifestation of the effects of Sm-aPKC knockdown in adults and the lack of effects of Sm-PLK-1 and Sm-MAPK p38 on adult viability, these kinases may not represent suitable drug targets.

Impaired HDL function in obese adolescents: impact of lifestyle intervention and bariatric surgery

OBJECTIVE

HDL regulates endothelial function via stimulation of nitric oxide production. It is documented that endothelial function is impaired in obese adolescents, and improved by lifestyle interventions (LI).

DESIGN AND METHODS

HDL function in obese adolescents and the impact of LI or Roux-en-Y gastric bypass surgery (RYGB) was assessed. HDL was isolated from 14 adolescents with normal body mass index (HDLcontrol ), 10 obese (HDLobese ) before and after 6 month LI, and five severe obese adolescents before and one year after RYGB. HDL-mediated phosphorylation of endothelial nitric oxide synthase (eNOS)-Ser(1177) , eNOS-Thr(495) , and PKC-ßII was evaluated. In addition the HDL proteome was analyzed.

RESULTS

HDLobese -mediated eNOS-Ser(1177) phosphorylation was reduced, whereas eNOS-Thr(495) phosphorylation increased significantly when compared to HDLcontrol . No impact of obesity was observed on PKC-ßII phosphorylation. LI and RYGB had no impact on HDL-mediated phosphorylation of eNOS and PKC-ßII. A principle component plot analysis of the HDL particle separated controls and severe obese, whereas the interventions did not trigger sufficient differences to the HDL proteome to permit distinction.

CONCLUSION

These results demonstrated that HDL-function is impaired in obese adolescents, and that LI or RYGB did not correct this dysfunction. This might be an argument for developing earlier prevention strategies in obese adolescents to avoid HDL dysfunction.

Genome-wide association studies identify PRKCB as a novel genetic susceptibility locus for primary biliary cholangitis in the Japanese population

A previous genome-wide association study (GWAS) performed in 963 Japanese individuals (487 primary biliary cholangitis [PBC] cases and 476 healthy controls) identified TNFSF15 (rs4979462) and POU2AF1 (rs4938534) as strong susceptibility loci for PBC. In this study, we performed GWAS in additional 1,923 Japanese individuals (894 PBC cases and 1,029 healthy controls), and combined the results with the previous data. This GWAS, together with a subsequent replication study in an independent set of 7,024 Japanese individuals (512 PBC cases and 6,512 healthy controls), identified PRKCB (rs7404928) as a novel susceptibility locus for PBC (odds ratio [OR] = 1.26, P = 4.13 × 10-9). Furthermore, a primary functional variant of PRKCB (rs35015313) was identified by genotype imputation using a phased panel of 1,070 Japanese individuals from a prospective, general population cohort study and subsequent in vitro functional analyses. These results may lead to improved understanding of the disease pathways involved in PBC, forming a basis for prevention of PBC and development of novel therapeutics.

Single Quantum Dot Imaging Reveals PKCβ-Dependent Alterations in Membrane Diffusion and Clustering of an Attention-Deficit Hyperactivity Disorder/Autism/Bipolar Disorder-Associated Dopamine Transporter Variant

The dopamine transporter (DAT) is a transmembrane protein that terminates dopamine signaling in the brain by driving rapid dopamine reuptake into presynaptic nerve terminals. Several lines of evidence indicate that DAT dysfunction is linked to neuropsychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD), bipolar disorder (BPD), and autism spectrum disorder (ASD). Indeed, individuals with these disorders have been found to express the rare, functional DAT coding variant Val559, which confers anomalous dopamine efflux (ADE) in vitro and in vivo. To elucidate the impact of the DAT Val559 variant on membrane diffusion dynamics, we implemented our antagonist-conjugated quantum dot (QD) labeling approach to monitor the lateral mobility of single particle-labeled transporters in transfected HEK-293 and SK-N-MC cells. Our results demonstrate significantly higher diffusion coefficients of DAT Val559 compared to those of DAT Ala559, effects likely determined by elevated N-terminal transporter phosphorylation. We also provide pharmacological evidence that PKCβ-mediated signaling supports enhanced DAT Val559 membrane diffusion rates. Additionally, our results are complimented with diffusion rates of phosphomimicked and phosphorylation-occluded DAT variants. Furthermore, we show DAT Val559 has a lower propensity for membrane clustering, which may be caused by a mutation-derived shift out of membrane microdomains leading to faster lateral membrane diffusion rates. These findings further demonstrate a functional impact of DAT Val559 and suggest that changes in transporter localization and lateral mobility may sustain ADE and contribute to alterations in dopamine signaling underlying multiple neuropsychiatric disorders.

PKCβ positively regulates RANKL-induced osteoclastogenesis by inactivating GSK-3β

Protein kinase C (PKC) family members phosphorylate a wide variety of protein targets and are known to be involved in diverse cellular signaling pathways. However, the role of PKC in receptor activator of NF-κB ligand (RANKL) signaling has remained elusive. We now demonstrate that PKCβ acts as a positive regulator which inactivates glycogen synthase kinase-3β (GSK-3β) and promotes NFATc1 induction during RANKL-induced osteoclastogenesis. Among PKCs, PKCβ expression is increased by RANKL. Pharmacological inhibition of PKCβ decreased the formation of osteoclasts which was caused by the inhibition of NFATc1 induction. Importantly, the phosphorylation of GSK-3β was decreased by PKCβ inhibition. Likewise, down-regulation of PKCβ by RNA interference suppressed osteoclast differentiation, NFATc1 induction, and GSK-3β phosphorylation. The administration of PKC inhibitor to the RANKL-injected mouse calvaria efficiently protected RANKL-induced bone destruction. Thus, the PKCβ pathway, leading to GSK-3β inactivation and NFATc1 induction, has a key role in the differentiation of osteoclasts. Our results also provide a further rationale for PKCβ's therapeutic targeting to treat inflammation-related bone diseases.

Promoter Methylation of PRKCB, ADAMTS12, and NAALAD2 Is Specific to Prostate Cancer and Predicts Biochemical Disease Recurrence

The molecular diversity of prostate cancer (PCa) has been demonstrated by recent genome-wide studies, proposing a significant number of different molecular markers. However, only a few of them have been transferred into clinical practice so far. The present study aimed to identify and validate novel DNA methylation biomarkers for PCa diagnosis and prognosis. Microarray-based methylome data of well-characterized cancerous and noncancerous prostate tissue (NPT) pairs was used for the initial screening. Ten protein-coding genes were selected for validation in a set of 151 PCa, 51 NPT, as well as 17 benign prostatic hyperplasia samples. The Prostate Cancer Dataset (PRAD) of The Cancer Genome Atlas (TCGA) was utilized for independent validation of our findings. Methylation frequencies of ADAMTS12, CCDC181, FILIP1L, NAALAD2, PRKCB, and ZMIZ1 were up to 91% in our study. PCa specific methylation of ADAMTS12, CCDC181, NAALAD2, and PRKCB was demonstrated by qualitative and quantitative means (all p < 0.05). In agreement with PRAD, promoter methylation of these four genes was associated with the transcript down-regulation in the Lithuanian cohort (all p < 0.05). Methylation of ADAMTS12, NAALAD2, and PRKCB was independently predictive for biochemical disease recurrence, while NAALAD2 and PRKCB increased the prognostic power of multivariate models (all p < 0.01). The present study identified methylation of ADAMTS12, NAALAD2, and PRKCB as novel diagnostic and prognostic PCa biomarkers that might guide treatment decisions in clinical practice.

The molecular basis for development of proinflammatory autoantibodies to progranulin

Recently we identified in a wide spectrum of autoimmune diseases frequently occurring proinflammatory autoantibodies directed against progranulin, a direct inhibitor of TNFR1 & 2 and of DR3. In the present study we investigated the mechanisms for the breakdown of self-tolerance against progranulin. Isoelectric focusing identified a second, differentially electrically charged progranulin isoform exclusively present in progranulin-antibody-positive patients. Alkaline phosphatase treatment revealed this additional progranulin isoform to be hyperphosphorylated. Subsequently Ser81, which is located within the epitope region of progranulin-antibodies, was identified as hyperphosphorylated serine residue by site directed mutagenesis of candidate phosphorylation sites. Hyperphosphorylated progranulin was detected exclusively in progranulin-antibody-positive patients during the courses of their diseases. The occurrence of hyperphosphorylated progranulin preceded seroconversions of progranulin-antibodies, indicating adaptive immune response. Utilizing panels of kinase and phosphatase inhibitors, PKCβ1 was identified as the relevant kinase and PP1 as the relevant phosphatase for phosphorylation and dephosphorylation of Ser81. In contrast to normal progranulin, hyperphosphorylated progranulin interacted exclusively with inactivated (pThr320) PP1, suggesting inactivated PP1 to cause the detectable occurrence of phosphorylated Ser81 PGRN. Investigation of possible functional alterations of PGRN due to Ser81 phosphorylation revealed, that hyperphosphorylation prevents the interaction and thus direct inhibition of TNFR1, TNFR2 and DR3, representing an additional direct proinflammatory effect. Finally phosphorylation of Ser81 PGRN alters the conversion pattern of PGRN. In conclusion, inactivated PP1 induces hyperphosphorylation of progranulin in a wide spectrum of autoimmune diseases. This hyperphosphorylation prevents direct inhibition of TNFR1, TNFR2 and DR3 by PGRN, alters the conversion of PGRN, and is strongly associated with the occurrence of neutralizing, proinflammatory PGRN-antibodies, indicating immunogenicity of this alternative secondary modification.

Expression profiling of RNA transcripts during neuronal maturation and ischemic injury

Neuronal development is a pro-survival process that involves neurite growth, synaptogenesis, synaptic and neuronal pruning. During development, these processes can be controlled by temporal gene expression that is orchestrated by both long non-coding RNAs and microRNAs. To examine the interplay between these different components of the transcriptome during neuronal differentiation, we carried out mRNA, long non-coding RNA and microRNA expression profiling on maturing primary neurons. Subsequent gene ontology analysis revealed regulation of axonogenesis and dendritogenesis processes by these differentially expressed mRNAs and non-coding RNAs. Temporally regulated mRNAs and their associated long non-coding RNAs were significantly over-represented in proliferation and differentiation associated signalling, cell adhesion and neurotrophin signalling pathways. Verification of expression of the Axin2, Prkcb, Cntn1, Ncam1, Negr1, Nrxn1 and Sh2b3 mRNAs and their respective long non-coding RNAs in an in vitro model of ischemic-reperfusion injury showed an inverse expression profile to the maturation process, thus suggesting their role(s) in maintaining neuronal structure and function. Furthermore, we propose that expression of the cell adhesion molecules, Ncam1 and Negr1 might be tightly regulated by both long non-coding RNAs and microRNAs.

The effect of total lignans from Fructus Arctii on Streptozotocin-induced diabetic retinopathy in Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Arctii is the dried ripe fruit of Arctium lappa L. (family Asteraceae). It is a well-known Chinese Materia Medica that was included in the Chinese pharmacopoeia because of its traditional therapeutic actions, such as heat removal, detoxification, and elimination of swelling. Since ancient times Fructus Arctii has been used extensively in a number of classical drug formulas to treat type 2 diabetes mellitus. Modern pharmacological studies have shown that certain components of Fructus Arctii have multiple physiological activities on type 2 diabetes and its complications.

AIM OF THE STUDY

We have reported the inhibitory effect of total lignans from Fructus Arctii (TLFA) on aldose reductase, the key enzyme in the polyol pathway, which is considered to be closely related to the onset of diabetic retinopathy (DR). The present study aimed to observe the preventive and therapeutic effects of TLFA on DR in Streptozotocin (STZ)-induced DR rats.

MATERIALS AND METHODS

TLFA was prepared from Fructus Arctii and its content was determined using UV spectrophotometry. The DR model was induced by STZ in Wistar rats. For DR prevention, the animals were gavaged once daily for 9 weeks with TLFA (1.38, 0.69, and 0.35 g/kg/day) as soon as they were confirmed as diabetes models. Pathological changes to retinal tissues and the expression of vascular endothelial growth factor (VEGF) and protein kinase C (PKC) in the retina were detected after TLFA treatment. The effects of TLFA on blood glucose levels and body weight were also observed. For DR treatment, the animals were gavaged once daily for 12 weeks with TLFA (1.38 and 0.69 g/kg/day) at 3 months after they were confirmed as diabetes models. The therapeutic effect was studied using quantitative detection of blood-retina barrier (BRB) breakdown via an Evans Blue leakage assay.

RESULTS

For DR prevention, after 9 weeks of TLFA administration, histopathological examination of retinal tissue showed that TLFA improved the lesions in the retina. Changes to retinal microstructures such as capillaries, ganglion cells, bipolar cells, and the membrane disk examined by electron microscopy further confirmed that TLFA has a preventive effect on retinopathy. Terminal deoxynucleotidyl Transferase-mediated dUTP nick end labeling (TUNEL) detection showed that TLFA could inhibit retinal cell apoptosis in the diabetic rats, and fasting blood glucose (FBG) levels of rats in the TLFA-treated groups decreased during the experiment. For DR treatment, after 3 months of administration, the amount of dye leakage in the TLFA-administered groups was reduced by more than 50% compared with that in the model group, which indicated that TLFA has a therapeutic effect on middle and late DR. Messenger RNA (mRNA) expression of VEGF and PKCβ2 in the retina detected by real-time fluorescent quantitative reverse transcription-polymerase chain reaction (FQ-RT-PCR) showed that TLFA could inhibit the expression of them, which was consistent with the results of immunohistochemistry (IHC).

CONCLUSION

TLFA has a preventive and therapeutic effect on DR. Its mechanism of action on DR is related to inhibiting PKC activation and blocking VEGF elevation.

Protein kinase C is a calcium sensor for presynaptic short-term plasticity

In presynaptic boutons, calcium (Ca(2+)) triggers both neurotransmitter release and short-term synaptic plasticity. Whereas synaptotagmins are known to mediate vesicle fusion through binding of high local Ca(2+) to their C2 domains, the proteins that sense smaller global Ca(2+) increases to produce short-term plasticity have remained elusive. Here, we identify a Ca(2+) sensor for post-tetanic potentiation (PTP), a form of plasticity thought to underlie short-term memory. We find that at the functionally mature calyx of Held synapse the Ca(2+)-dependent protein kinase C isoforms α and β are necessary for PTP, and the expression of PKCβ in PKCαβ double knockout mice rescues PTP. Disruption of Ca(2+) binding to the PKCβ C2 domain specifically prevents PTP without impairing other PKCβ-dependent forms of synaptic enhancement. We conclude that different C2-domain-containing presynaptic proteins are engaged by different Ca(2+) signals, and that Ca(2+) increases evoked by tetanic stimulation are sensed by PKCβ to produce PTP.DOI: http://dx.doi.org/10.7554/eLife.03011.001.

High glucose/lysophosphatidylcholine levels stimulate extracellular matrix deposition in diabetic nephropathy via platelet‑activating factor receptor

Platelet-activating factor (PAF), protein kinase C (PKC)βI, transforming growth factor (TGF)‑β1 and aberrant extracellular matrix (ECM) deposition have been associated with diabetic nephropathy (DN). However, the mechanistic basis underlying this association remains to be elucidated. The present study investigated the association among the aforementioned factors in a DN model consisting of human mesangial cells (HMCs) exposed to high glucose (HG) and lysophosphatidylcholine (LPC) treatments. HMCs were divided into the following treatment groups: Control; PAF; PAF+PKCβI inhibitor LY333531; HG + LPC; PAF + HG + LPC; and PAF + HG + LPC + LY333531. Cells were cultured for 24 h, and PKCβI and TGF‑β1 expression was determined using the reverse transcription‑quantitative polymerase chain reaction and western blotting. The expression levels of the ECM‑associated molecules collagen IV and fibronectin in the supernatant were detected using ELISA analysis. Subcellular localization of PKCβI was assessed using immunocytochemistry. PKCβI and TGF‑β1 expression was increased in the PAF + HG + LPC group compared with the other groups (P<0.05); however, this effect was abolished in the presence of LY333531 (P<0.05). Supernatant fibronectin and collagen IV levels were increased in the PAF + HG + LPC group compared with the others (P<0.05); this was reversed by treatment with LY333531 (P<0.05). In cells treated with PAF, HG and LPC, PKCβI was translocated from the cytosol to the nucleus, an effect which was blocked when PKCβI expression was inhibited (P<0.05). The findings of the present study demonstrated that PAF stimulated ECM deposition in HMCs via activation of the PKC‑TGF‑β1 axis in a DN model.

Role of the PKCβII/JNK signaling pathway in acute glucose fluctuation-induced apoptosis of rat vascular endothelial cells

AIMS

The purpose of this study was to investigate the mechanism of vascular endothelial cell apoptosis induced by acute blood glucose fluctuation.

METHODS

Thirty rats were assigned to three groups: normal saline (SAL group), constant high glucose (CHG group) and acute blood glucose fluctuation (AFG) group. Other forty rats were assigned to SAL group, AFG group, LY group (PKCβ inhibitor LY333531 was injected intragastrically to the rats who were under acute blood glucose fluctuation) and SP group (JNK inhibitor SP600125 was injected intraperitoneally to the rats who were under acute blood glucose fluctuation). Oxidative stress and inflammatory cytokines were detected. TUNEL was performed to detect apoptosis. Pro-caspase-3, caspase-3 p17, JNK, PKC-βII and insulin signaling-related protein expression were tested by Western blotting.

RESULTS

After administration of LY333531, AFG-induced membrane translocation of PKCβII protein was inhibited, but SP600125 failed to affect AFG-induced PKCβII membrane translocation. After administration of LY333531, the AFG-induced increase in JNK activity was significantly compromised. LY333531 inhibited AFG-induced oxidative stress. However, SP600125 only slightly inhibited AFG-induced oxidative stress reaction (P > 0.05). Both LY333531 and SP600125 can reverse AFG-induced endothelial cell apoptosis increase, inflammatory cytokines levels rise and insulin signaling impairment.

CONCLUSIONS

It is necessary to actively control blood glucose and avoid significant glucose fluctuation. PKCβII/JNK may serve as a target, and inhibitors of PKCβII/JNK may be used to help prevent cardiovascular diseases in patients with poor glucose control or significant glucose fluctuation.

Genetic signatures of heroin addiction

Heroin addiction is a complex psychiatric disorder with a chronic course and a high relapse rate, which results from the interaction between genetic and environmental factors. Heroin addiction has a substantial heritability in its etiology; hence, identification of individuals with a high genetic propensity to heroin addiction may help prevent the occurrence and relapse of heroin addiction and its complications. The study aimed to identify a small set of genetic signatures that may reliably predict the individuals with a high genetic propensity to heroin addiction. We first measured the transcript level of 13 genes (RASA1, PRKCB, PDK1, JUN, CEBPG, CD74, CEBPB, AUTS2, ENO2, IMPDH2, HAT1, MBD1, and RGS3) in lymphoblastoid cell lines in a sample of 124 male heroin addicts and 124 male control subjects using real-time quantitative PCR. Seven genes (PRKCB, PDK1, JUN, CEBPG, CEBPB, ENO2, and HAT1) showed significant differential expression between the 2 groups. Further analysis using 3 statistical methods including logistic regression analysis, support vector machine learning analysis, and a computer software BIASLESS revealed that a set of 4 genes (JUN, CEBPB, PRKCB, ENO2, or CEBPG) could predict the diagnosis of heroin addiction with the accuracy rate around 85% in our dataset. Our findings support the idea that it is possible to identify genetic signatures of heroin addiction using a small set of expressed genes. However, the study can only be considered as a proof-of-concept study. As the establishment of lymphoblastoid cell line is a laborious and lengthy process, it would be more practical in clinical settings to identify genetic signatures for heroin addiction directly from peripheral blood cells in the future study.

Genetic variants of the peroxisome proliferator-activated receptor (PPAR) signaling pathway genes and risk of pancreatic cancer

Because the peroxisome proliferator-activated receptor (PPAR) signaling pathway is involved in development and progression of pancreatic cancer, we investigated associations between genetic variants of the PPAR pathway genes and pancreatic cancer risk by using three published genome-wide association study datasets including 8477 cases and 6946 controls of European ancestry. Expression quantitative trait loci (eQTL) analysis was also performed for correlations between genotypes of the identified genetic variants and messenger RNA (mRNA) expression levels of their genes by using available databases of the 1000 Genomes, TCGA, and GTEx projects. In the single-locus logistic regression analysis, we identified 1141 out of 17 532 significant single-nucleotide polymorphisms (SNPs) in 112 PPAR pathway genes. Further multivariate logistic regression analysis identified three independent, potentially functional loci (rs12947620 in MED1, rs11079651 in PRKCA, and rs34367566 in PRKCB) for pancreatic cancer risk (odds ratio [OR] = 1.11, 95% confidence interval [CI], [1.06-1.17], P = 5.46 × 10-5 ; OR = 1.10, 95% CI, [1.04-1.15], P = 1.99 × 10-4 ; and OR = 1.09, 95% CI, [1.04-1.14], P = 3.16 × 10-4 , respectively) among 65 SNPs that passed multiple comparison correction by false discovery rate (< 0.2). When risk genotypes of these three SNPs were combined, carriers with 2 to 3 unfavorable genotypes (NUGs) had a higher risk of pancreatic cancer than those with 0 to 1 NUGs. The eQTL analysis showed that rs34367566 A>AG was associated with decreased expression levels of PRKCB mRNA in 373 lymphoblastoid cell lines. Our findings indicate that genetic variants of the PPAR pathway genes, particularly MED1, PRKCA, and PRKCB, may contribute to susceptibility to pancreatic cancer.

Hepatocyte-specific PKCβ deficiency protects against high-fat diet-induced nonalcoholic hepatic steatosis

OBJECTIVE

Nonalcoholic hepatic steatosis, also known as fatty liver, is a uniform response of the liver to hyperlipidic-hypercaloric diet intake. However, the post-ingestive signals and mechanistic processes driving hepatic steatosis are not well understood. Emerging data demonstrate that protein kinase C beta (PKCβ), a lipid-sensitive kinase, plays a critical role in energy metabolism and adaptation to environmental and nutritional stimuli. Despite its powerful effect on glucose and lipid metabolism, knowledge of the physiological roles of hepatic PKCβ in energy homeostasis is limited.

METHODS

The floxed-PKCβ and hepatocyte-specific PKCβ-deficient mouse models were generated to study the in vivo role of hepatocyte PKCβ on diet-induced hepatic steatosis, lipid metabolism, and mitochondrial function.

RESULTS

We report that hepatocyte-specific PKCβ deficiency protects mice from development of hepatic steatosis induced by high-fat diet, without affecting body weight gain. This protection is associated with attenuation of SREBP-1c transactivation and improved hepatic mitochondrial respiratory chain. Lipidomic analysis identified significant increases in the critical mitochondrial inner membrane lipid, cardiolipin, in PKCβ-deficient livers compared to control. Moreover, hepatocyte PKCβ deficiency had no significant effect on either hepatic or whole-body insulin sensitivity supporting dissociation between hepatic steatosis and insulin resistance.

CONCLUSIONS

The above data indicate that hepatocyte PKCβ is a key focus of dietary lipid perception and is essential for efficient storage of dietary lipids in liver largely through coordinating energy utilization and lipogenesis during post-prandial period. These results highlight the importance of hepatic PKCβ as a drug target for obesity-associated nonalcoholic hepatic steatosis.

Down-regulation of PRKCB1 expression in Han Chinese patients with subsyndromal symptomatic depression

BACKGROUND

Subsyndromal symptomatic depression (SSD) is a common disease with significant social dysfunction. However, SSD is still not well understood and the pathophysiology of it remains unclear.

METHODS

We classified 48 candidate genes for SSD according to our previous study into clusters and pathways using DAVID Bioinformatics Functional Annotation Tool. We further replicated the result by using real-time Quantitative PCR (qPCR) studies to examine the expression of identified genes (i.e., STAT5b, PKCB1, ABL1 and NRAS) in another group of Han Chinese patients with SSD (n = 50). We further validated the result by examining PRKCB1 expression collected from MDD patients (n = 20). To test whether a deficit in PRKCB1 expression leads to dysregulation in PRKCB1 dependent transcript networks, we tested mRNA expression levels for the remaining 44 genes out of 48 genes in SSD patients. Finally, the power of discovery was improved by incorporating information from Quantitative Trait (eQTL) analysis.

RESULTS

The results showed that the PRCKB1 gene expression in peripheral blood mononuclear cells (PBMC) was 33.3% down-regulated in SSD patients (n = 48, t = 3.202, p = 0.002), and a more dramatic (n = 17, 49%) down-regulation in MDD patients than control (n = 49, t = 2.114, p = 0.001). We also identified 37 genes that displayed a strong correlation with PRKCB1 mRNA expression levels in SSD patients. The expression of PRKCB1 was regulated by multiple single nucleotide polymorphisms (SNPs) both at the transcript level and exon level.

CONCLUSIONS

In conclusion, we first found a significant decrease of PRCKB1 mRNA expression in SSD, suggesting PRKCB1 might be the candidate gene and biomarker for SSD.

Activation of Coronary Arteriolar PKCβ2 Impairs Endothelial NO-Mediated Vasodilation: Role of JNK/Rho Kinase Signaling and Xanthine Oxidase Activation

Protein kinase C (PKC) activation can evoke vasoconstriction and contribute to coronary disease. However, it is unclear whether PKC activation, without activating the contractile machinery, can lead to coronary arteriolar dysfunction. The vasoconstriction induced by the PKC activator phorbol 12,13-dibutyrate (PDBu) was examined in isolated porcine coronary arterioles. The PDBu-evoked vasoconstriction was sensitive to a broad-spectrum PKC inhibitor but not affected by inhibiting PKCβ2 or Rho kinase. After exposure of the vessels to a sub-vasomotor concentration of PDBu (1 nmol/L, 60 min), the endothelium-dependent nitric oxide (NO)-mediated dilations in response to serotonin and adenosine were compromised but the dilation induced by the NO donor sodium nitroprusside was unaltered. PDBu elevated superoxide production, which was blocked by the superoxide scavenger Tempol. The impaired NO-mediated vasodilations were reversed by Tempol or inhibition of PKCβ2, xanthine oxidase, c-Jun N-terminal kinase (JNK) and Rho kinase but were not affected by a hydrogen peroxide scavenger or inhibitors of NAD(P)H oxidase and p38 kinase. The PKCβ2 protein was detected in the arteriolar wall and co-localized with endothelial NO synthase. In conclusion, activation of PKCβ2 appears to compromise NO-mediated vasodilation via Rho kinase-mediated JNK signaling and superoxide production from xanthine oxidase, independent of the activation of the smooth muscle contractile machinery.

Thrombin impairs the angiogenic activity of extravillous trophoblast cells via monocyte chemotactic protein-1 (MCP-1): A possible link with preeclampsia

Cytokines' secretion from the decidua and trophoblast cells has been known to regulate trophoblast cell functions, such as Extravillous trophoblasts (EVTs) cell migration and invasion and remodeling of spiral arteries. Defective angiogenesis and spiral arteries transformation are mainly caused by proinflammatory cytokines and excessive thrombin generation during preeclampsia. Monocyte chemotactic protein-1 (MCP-1), a crucial cytokine, has a role in maintaining normal pregnancy. In this study, we explored whether thrombin regulates the secretion of MCP-1 in HTR-8/SVneo cells; if yes, what is its function? We used HTR-8/SVneo cells, developed from first trimester villous explants of early pregnancy, as the model of EVTs. MCP-1 gene silencing was performed using gene-specific siRNA. qPCR and ELISA were performed to estimate the expression and secretion of MCP-1. Here, we found that thrombin enhanced the secretion of MCP-1 in HTR-8/SVneo cells. Proteinase-activated receptor-1 (PAR-1) was found as the primary receptor, regulating MCP-1 secretion in these cells. Furthermore, MCP-1 secretion is modulated via protein kinase C (PKC) α, β, and Rho/Rho-kinase-dependent pathways. Thrombin negatively regulates HTR-8/SVneo cells' ability to mimic tube formation in an MCP-1 dependent manner. In conclusion, we propose that thrombin-controlled MCP-1 secretion may play an essential role in normal placental development and successful pregnancy maintenance. Improper thrombin production and MCP-1 secretion during pregnancy might cause inadequate vascular formation and transformation of spiral arteries, which may contribute to pregnancy disorders, such as preeclampsia.