Protein kinase C-delta (PKCδ), a marker of inflammation and tuberculosis disease progression in humans, is important for optimal macrophage killing effector functions and survival in mice

We previously demonstrated that protein kinase C-δ (PKCδ) is critical for immunity against Listeria monocytogenes, Leishmania major, and Candida albicans infection in mice. However, the functional relevance of PKCδ during Mycobacterium tuberculosis (Mtb) infection is unknown. PKCδ was significantly upregulated in whole blood of patients with active tuberculosis (TB) disease. Lung proteomics further revealed that PKCδ was highly abundant in the necrotic and cavitory regions of TB granulomas in multidrug-resistant human participants. In murine Mtb infection studies, PKCδ^-/- mice were highly susceptible to tuberculosis with increased mortality, weight loss, exacerbated lung pathology, uncontrolled proinflammatory cytokine responses, and increased mycobacterial burdens. Moreover, these mice displayed a significant reduction in alveolar macrophages, dendritic cells, and decreased accumulation of lipid bodies (lungs and macrophages) and serum fatty acids. Furthermore, a peptide inhibitor of PKCδ in wild-type mice mirrored lung inflammation identical to infected PKCδ^-/- mice. Mechanistically, increased bacterial growth in macrophages from PKCδ^-/- mice was associated with a decline in killing effector functions independent of phagosome maturation and autophagy. Taken together, these data suggest that PKCδ is a marker of inflammation during active TB disease in humans and required for optimal macrophage killing effector functions and host protection during Mtb infection in mice.

Protein kinase C-delta (PKCδ), a marker of inflammation and tuberculosis disease progression in humans, is important for optimal macrophage killing effector functions and survival in mice

This corrects the article DOI: 10.1038/mi.2017.68.

Deletion of protein kinase Cε in mice has limited effects on liver metabolite levels but alters fasting ketogenesis and gluconeogenesis

AIMS/HYPOTHESIS

Protein kinase Cε (PKCε) is emerging as a key mediator of lipid-induced insulin resistance in liver and hepatic lipid metabolism itself. We investigated whether PKCε plays a role in other metabolic processes, to further examine its suitability as a therapeutic target.

METHODS

We measured amino acid, organic acid and sugar levels by liquid and gas chromatography-mass spectrometry of liver extracts from chow and fat-fed wild-type (WT) and PKCε-deficient (Prkce(-/-)) mice. Fed and fasting glucose, ketone and fatty acid levels were measured in blood. Triacylglycerol levels and gluconeogenic and ketogenic enzyme expression were measured in liver. The effect of fasting on epididymal fat pad mass was also determined.

RESULTS

Metabolomic analysis indicated that the short-term high-fat diet affected over 20 compounds, including a 50% reduction in the glucogenic amino acid alanine. Prkce deletion resulted only in a reduction of 4-hydroxyproline and aspartate and an increase in glutamate. However, upon fasting, Prkce(-/-) mice were better able to maintain blood glucose levels and also exhibited lower levels of the ketone β-hydroxybutyrate compared with WT mice. Upon fasting, Prkce deletion also resulted in lower liver and plasma lipids and a smaller reduction in fat pad mass.

CONCLUSIONS/INTERPRETATION

Metabolomic analysis provided new insights into the effects of a high-fat diet on liver metabolite levels. Glucose homeostasis under fasting conditions is improved in Prkce(-/-) mice, which, in turn, may reduce the mobilisation of lipid from adipose tissue, reducing the availability of ketogenic substrate in the liver. Together with the protection against fat-diet-induced glucose intolerance previously observed in the fed state, these findings indicate PKCε as a unique therapeutic target for the improvement of glucose homeostasis.

Time-dependent effects of Prkce deletion on glucose homeostasis and hepatic lipid metabolism on dietary lipid oversupply in mice

AIMS/HYPOTHESIS

We examined the time-dependent effects of deletion of the gene encoding protein kinase C epsilon (Prkce) on glucose homeostasis, insulin secretion and hepatic lipid metabolism in fat-fed mice.

METHODS

Prkce(-/-) and wild-type (WT) mice were fed a high-fat diet for 1 to 16 weeks and subjected to i.p. glucose tolerance tests (ipGTT) and indirect calorimetry. We also investigated gene expression and protein levels by RT-PCR, quantitative protein profiling (isobaric tag for relative and absolute quantification; iTRAQ) and immunoblotting. Lipid levels, mitochondrial oxidative capacity and lipid metabolism were assessed in liver and primary hepatocytes.

RESULTS

While fat-fed WT mice became glucose intolerant after 1 week, Prkce(-/-) mice exhibited normal glucose and insulin levels. iTRAQ suggested differences in lipid metabolism and oxidative phosphorylation between fat-fed WT and Prkce(-/-) animals. Liver triacylglycerols were increased in fat-fed Prkce(-/-) mice, resulting from altered lipid partitioning which promoted esterification of fatty acids in hepatocytes. In WT mice, fat feeding elevated oxygen consumption in vivo and in isolated liver mitochondria, but these increases were not seen in Prkce(-/-) mice. Prkce(-/-) hepatocytes also exhibited reduced production of reactive oxygen species (ROS) in the presence of palmitate. After 16 weeks of fat feeding, however, the improved glucose tolerance in fat-fed Prkce(-/-) mice was instead associated with increased insulin secretion during ipGTT, as we have previously reported.

CONCLUSIONS/INTERPRETATION

Prkce deletion ameliorates diet-induced glucose intolerance via two temporally distinct phenotypes. Protection against insulin resistance is associated with changes in hepatic lipid partitioning, which may reduce the acute inhibitory effects of fatty acid catabolism, such as ROS generation. In the longer term, enhancement of glucose-stimulated insulin secretion prevails.

Deletion of protein kinase Cδ in mice modulates stability of inflammatory genes and protects against cytokine-stimulated beta cell death in vitro and in vivo

AIMS/HYPOTHESIS

Proinflammatory cytokines contribute to beta cell destruction in type 1 diabetes, but the mechanisms are incompletely understood. The aim of the current study was to address the role of the protein kinase C (PKC) isoform PKCδ, a diverse regulator of cell death, in cytokine-stimulated apoptosis in primary beta cells.

METHODS

Islets isolated from wild-type or Prkcd(-/-) mice were treated with IL-1β, TNF-α and IFNγ and assayed for apoptosis, nitric oxide (NO) generation and insulin secretion. Activation of signalling pathways, apoptosis and endoplasmic reticulum (ER) stress were determined by immunoblotting. Stabilisation of mRNA transcripts was measured by RT-PCR following transcriptional arrest. Mice were injected with multiple low doses of streptozotocin (MLD-STZ) and fasting blood glucose monitored.

RESULTS

Deletion of Prkcd inhibited apoptosis and NO generation in islets stimulated ex vivo with cytokines. It also delayed the onset of hyperglycaemia in MLD-STZ-treated mice. Activation of ERK, p38, JNK, AKT1, the ER stress markers DDIT3 and phospho-EIF2α and the intrinsic apoptotic markers BCL2 and MCL1 was not different between genotypes. However, deletion of Prkcd destabilised mRNA transcripts for Nos2, and for multiple components of the toll-like receptor 2 (TLR2) signalling complex, which resulted in disrupted TLR2 signalling.

CONCLUSIONS/INTERPRETATION

Loss of PKCδ partially protects against hyperglycaemia in the MLD-STZ model in vivo, and against cytokine-mediated apoptosis in vitro. This is accompanied by reduced NO generation and destabilisation of Nos2 and components of the TLR2 signalling pathway. The results highlight a mechanism for regulating proinflammatory gene expression in beta cells independently of transcription.

AICAR and metformin, but not exercise, increase muscle glucose transport through AMPK-, ERK-, and PDK1-dependent activation of atypical PKC

Activators of 5'-AMP-activated protein kinase (AMPK) 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), metformin, and exercise activate atypical protein kinase C (aPKC) and ERK and stimulate glucose transport in muscle by uncertain mechanisms. Here, in cultured L6 myotubes: AICAR- and metformin-induced activation of AMPK was required for activation of aPKC and ERK; aPKC activation involved and required phosphoinositide-dependent kinase 1 (PDK1) phosphorylation of Thr410-PKC-zeta; aPKC Thr410 phosphorylation and activation also required MEK1-dependent ERK; and glucose transport effects of AICAR and metformin were inhibited by expression of dominant-negative AMPK, kinase-inactive PDK1, MEK1 inhibitors, kinase-inactive PKC-zeta, and RNA interference (RNAi)-mediated knockdown of PKC-zeta. In mice, muscle-specific aPKC (PKC-lambda) depletion by conditional gene targeting impaired AICAR-stimulated glucose disposal and stimulatory effects of both AICAR and metformin on 2-deoxyglucose/glucose uptake in muscle in vivo and AICAR stimulation of 2-[(3)H]deoxyglucose uptake in isolated extensor digitorum longus muscle; however, AMPK activation was unimpaired. In marked contrast to AICAR and metformin, treadmill exercise-induced stimulation of 2-deoxyglucose/glucose uptake was not inhibited in aPKC-knockout mice. Finally, in intact rodents, AICAR and metformin activated aPKC in muscle, but not in liver, despite activating AMPK in both tissues. The findings demonstrate that in muscle AICAR and metformin activate aPKC via sequential activation of AMPK, ERK, and PDK1 and the AMPK/ERK/PDK1/aPKC pathway is required for metformin- and AICAR-stimulated increases in glucose transport. On the other hand, although aPKC is activated by treadmill exercise, this activation is not required for exercise-induced increases in glucose transport, and therefore may be a redundant mechanism.

Diverse roles for protein kinase C delta and protein kinase C epsilon in the generation of high-fat-diet-induced glucose intolerance in mice: regulation of lipogenesis by protein kinase C delta

AIMS/HYPOTHESIS

This study aimed to determine whether protein kinase C (PKC) delta plays a role in the glucose intolerance caused by a high-fat diet, and whether it could compensate for loss of PKCepsilon in the generation of insulin resistance in skeletal muscle.

METHODS

Prkcd (-/-), Prkce (-/-) and wild-type mice were fed high-fat diets and subjected to glucose tolerance tests. Blood glucose levels and insulin responses were determined during the tests. Insulin signalling in liver and muscle was assessed after acute in vivo insulin stimulation by immunoblotting with phospho-specific antibodies. Activation of PKC isoforms in muscle from Prkce (-/-) mice was assessed by determining intracellular distribution. Tissues and plasma were assayed for triacylglycerol accumulation, and hepatic production of lipogenic enzymes was determined by immunoblotting.

RESULTS

Both Prkcd (-/-) and Prkce (-/-) mice were protected against high-fat-diet-induced glucose intolerance. In Prkce (-/-) mice this was mediated through enhanced insulin availability, while in Prkcd (-/-) mice the reversal occurred in the absence of elevated insulin. Neither the high-fat diet nor Prkcd deletion affected maximal insulin signalling. The activation of PKCdelta in muscle from fat-fed mice was enhanced by Prkce deletion. PKCdelta-deficient mice exhibited reduced liver triacylglycerol accumulation and diminished production of lipogenic enzymes.

CONCLUSIONS/INTERPRETATION

Deletion of genes encoding isoforms of PKC can improve glucose intolerance, either by enhancing insulin availability in the case of Prkce, or by reducing lipid accumulation in the case of Prkcd. The absence of PKCepsilon in muscle may be compensated by increased activation of PKCdelta in fat-fed mice, suggesting that an additional role for PKCepsilon in this tissue is masked.

Nephrin loss in experimental diabetic nephropathy is prevented by deletion of protein kinase C alpha signaling in-vivo

Albuminuria in diabetic nephropathy is due to endothelial dysfunction, a loss of negative charges in the basement membrane, and changes a of the slit-membrane diaphragm composition. We have recently shown that protein kinase C alpha (PKCalpha)-deficient mice are protected against the development of albuminuria under diabetic conditions. We here tested the hypothesis that PKCalpha mediates the hyperglycemia-induced downregulation of the slit-diaphragm protein nephrin. After 8 weeks of streptozotocin (STZ)-induced hyperglycemia the expression of glomerular nephrin was significantly reduced. In contrast, other slit-diaphragm proteins such as podocin and CD2AP were unaltered in diabetic state. In PKCalpha-/- mice, hyperglycemia-induced downregulation of nephrin was prevented. Podocin and CD2AP remained unchanged. In addition, the nephrin messenger RNA expression was also reduced in hyperglycemic wild-type mice but remained unaltered in PKCalpha-/- mice. We postulate that the underlying mechanism of the hyperglycemia-induced regulation of various proteins of the glomerular filtration barrier is a PKCalpha-dependent regulation of the Wilms' Tumor Suppressor (WT1) which previously has been shown to act as a direct transcription factor on the nephrin promoter. Our data suggest that PKCalpha activation may be an important intracellular signaling pathway in the regulation of nephrin expression and glomerular albumin permeability in the diabetic state.

Exacerbated vein graft arteriosclerosis in protein kinase Cdelta-null mice

Smooth muscle cell (SMC) accumulation is a key event in the development of atherosclerosis, including vein bypass graft arteriosclerosis. Because members of the protein kinase C (PKC) family signal cells to undergo proliferation, differentiation, or apoptosis, we generated PKCdelta knockout mice and performed vein bypass grafts on these animals. PKCdelta(-/-) mice developed normally and were fertile. Vein segments from PKCdelta(-/-) mice isografted to carotid arteries of recipient mice of either genotype led to a more severe arteriosclerosis than was seen with PKCdelta(+/+) vein grafts. Arteriosclerotic lesions in PKCdelta(-/-) mice showed a significantly higher number of SMCs than were found in wild-type animals; this was correlated with decreased SMC death in lesions of PKCdelta(-/-) mice. SMCs derived from PKCdelta(-/-) aortae were resistant to cell death induced by any of several stimuli, but they were similar to wild-type SMCs with respect to mitogen-stimulated cell proliferation in vitro. Furthermore, pro-apoptotic treatments led to diminished caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and cytochrome c release in PKCdelta(-/-) relative to wild-type SMCs, suggesting that their apoptotic resistance involves the loss of free radical generation and mitochondrial dysfunction in response to stress stimuli. Our data indicate that PKCdelta maintains SMC homeostasis and that its function in the vessel wall per se is crucial in the development of vein graft arteriosclerosis.

Targeted disruption of the zetaPKC gene results in the impairment of the NF-kappaB pathway

Here we have addressed the role that zetaPKC plays in NF-kappaB activation using mice in which this kinase was inactivated by homologous recombination. These mice, although grossly normal, showed phenotypic alterations in secondary lymphoid organs reminiscent of those of the TNF receptor-1 and of the lymphotoxin-beta receptor gene-deficient mice. The lack of zetaPKC in embryonic fibroblasts (EFs) severely impairs kappaB-dependent transcriptional activity as well as cytokine-induced phosphorylation of p65. Also, a cytokine-inducible interaction of zetaPKC with p65 was detected which requires the previous degradation of IkappaB. Although in zetaPKC-/- EFs this kinase is not necessary for IKK activation, in lung, which abundantly expresses zetaPKC, IKK activation is inhibited.

Rottlerin-independent attenuation of pervanadate-induced tyrosine phosphorylation events by protein kinase C-delta in hemopoietic cells

The understanding and control of many pathophysiological conditions is based on knowledge of subtly regulated intracellular signaling networks. We have found that in pervanadate (PV)-treated J558L myeloma cells, amongst other signaling proteins, protein kinase C (PKC)-delta and src homology 2-containing inositol phosphatase (SHIP) are tyrosine phosphorylated on expression of the B cell receptor, suggesting a role for these proteins in the preformed B cell receptor transducer complex. Rottlerin, a widely used PKC-delta-specific inhibitor, efficiently blocks these PV-induced tyrosine phosphorylation events. Furthermore, PV treatment of bone marrow-derived mast cells (BMMC) also results in tyrosine phosphorylation of PKC-delta, SHIP, and additional proteins. Rottlerin also inhibits these responses, indicating that PKC-delta might play an important enhancing role in the propagation of phosphotyrosine signals in B cells and mast cells and hence in the regulation of function of both cell types. Therefore, BMMC from PKC-delta -/- mice were generated by in vitro differentiation and assayed for tyrosine phosphorylation events in response to PV. Intriguingly, and opposite to the Rottlerin data, PKC-delta -/- BMMC show a stronger response to PV than wild-type cells, suggesting an attenuating role for PKC-delta. This response can be inhibited equally well by Rottlerin, indicating clearly that Rottlerin is not specific for PKC-delta in vivo. A comparison between Rottlerin and the panspecific PKC inhibitor bisindolylmaleimide suggests that Rottlerin also targets kinases beyond the PKC family. Moreover, Ser473 phosphorylation of protein kinase B (PKB) after PV treatment is blocked by Rottlerin as efficiently as by the phosphatidylinositol 3-kinase inhibitor LY294002. In this report, we provide evidence that PKC-delta constitutes a crucial attenuating factor in B cell and mast cell signal transduction and suggest that PKC-delta is important for the regulation of physiological B and mast cell functions as well as for their pathophysiology. Furthermore, dominant PKC-delta-independent effects of Rottlerin are presented, indicating restrictions of this inhibitor for use in signal transduction research.

PKC-beta is not necessary for cardiac hypertrophy

Studies in human and rodent models have shown that activation of protein kinase C-beta (PKC-beta) is associated with the development of pathological hypertrophy, suggesting that ablation of the PKC-beta pathway might prevent or reverse cardiac hypertrophy. To explore this, we studied mice with targeted disruption of the PKC-beta gene (knockout, KO). There were no detectable differences in expression or distribution of other PKC isoforms between the KO and control hearts as determined by Western blot analysis. Baseline hemodynamics were measured using a closed-chest preparation and there were no differences in heart rate and arterial or left ventricular pressure. Mice were subjected to two independent hypertrophic stimuli: phenylephrine (Phe) at 20 mg x kg(-1) x day(-1) sq infusion for 3 days, and aortic banding (AoB) for 7 days. KO animals demonstrated an increase in heart weight-to-body weight ratio (Phe, 4.3 +/- 0.6 to 6.1 +/- 0.4; AoB, 4.0 +/- 0.1 to 5.8 +/- 0.7) as well as ventricular upregulation of atrial natriuretic factor mRNA analogous to those seen in control animals. These results demonstrate that PKC-beta expression is not necessary for the development of cardiac hypertrophy nor does its absence attenuate the hypertrophic response.

T cell expressed PKCtheta demonstrates cell-type selective function

T lymphocyte stimulation leading to interleukin-2 (IL-2) expression requires activation of protein kinase C (PKC); however, the relevant PKC isoform(s) have not yet been systematically defined. Here we examine seven major T cell expressed PKC isoforms (PKCalpha, delta, epsilon, zeta, nu, theta and iota) and identify PKCtheta to be essential for IL-2 expression (via the critical NF-AT and NF-kappaB enhancer) in Jurkat T cells. Employing a conditionally activated PKCtheta estrogen-receptor fusion mutant, a de novo synthesis-independent transactivation of JNK2 was established. Based on mRNA in situ hybridization to mouse whole body sections, PKCtheta was found to be highly expressed in lymphoid organs but also skeletal muscle and the nervous system. PKCtheta function appears to be cell-type specific, since its isoenzyme-selective function was not observed in ectopic expression studies, employing COS-1 or NIH3T3 cells. These results confirm PKCtheta to be the prime target for the activating effect of phorbol ester in T cell signaling and suggest that gene expression as well as gene function of PKCtheta is strictly controlled by the cell type.

A role for the beta isoform of protein kinase C in fear conditioning

The protein kinase C family of enzymes has been implicated in synaptic plasticity and memory in a wide range of animal species, but to date little information has been available concerning specific roles for individual isoforms of this category of kinases. To investigate the role of the beta isoform of PKC in mammalian learning, we characterized mice deficient in the PKC beta gene using anatomical, biochemical, physiological, and behavioral approaches. In our studies we observed that PKC beta was predominantly expressed in the neocortex, in area CA1 of the hippocampus, and in the basolateral nucleus of the amygdala. Mice deficient in PKC beta showed normal brain anatomy and normal hippocampal synaptic transmission, paired pulse facilitation, and long-term potentiation and normal sensory and motor responses. The PKC beta knock-out animals exhibited a loss of learning, however; they suffered deficits in both cued and contextual fear conditioning. The PKC expression pattern and behavioral phenotype in the PKC beta knock-out animals indicate a critical role for the beta isoform of PKC in learning-related signal transduction mechanisms, potentially in the basolateral nucleus of the amygdala.

A sensitized genetic system for the analysis of murine B lymphocyte signal transduction pathways dependent on Bruton's tyrosine kinase

Modifier screens have been powerful genetic tools to define signaling pathways in lower organisms. The identification of modifier loci in mice has begun to allow a similar dissection of mammalian signaling pathways. Transgenic mice (Btk(lo)) expressing 25% of endogenous levels of Bruton's tyrosine kinase (Btk) have B cell functional responses between those of wild-type and Btk(-/-) mice. We asked whether reduced dosage or complete deficiency of genes previously implicated as Btk regulators would modify the Btk(lo) phenotype. We used two independent assays of Btk-dependent B cell function. Proliferative response to B cell antigen receptor cross-linking in vitro was chosen as an example of a relatively simple, well-defined signaling system. In vivo response to type II T-independent antigens (TI-II) measures complex interactions among multiple cell types over time and may identify additional Btk pathways. All modifiers identified differentially affected these two assays, indicating that Btk mediates these processes via distinct mechanisms. Loss of Lyn, PTEN (phosphatase and tensin homolog), or SH2-containing inositol phosphatase suppressed the Btk(lo) phenotype in vitro but not in vivo, whereas CD19 and the p85alpha form of phosphoinositide 3-kinase behaved as Btk(lo) enhancers in vivo but not in vitro. Effects of Lyn, PTEN, or p85alpha haploinsufficiency were observed. Haploinsufficiency or complete deficiency of protein kinase C beta, Fyn, CD22, Galphaq, or Galpha11 had no detectable effect on the function of Btk(lo) B cells. A transgenic system creating a reduction in dosage of Btk can therefore be used to identify modifier loci that affect B cell responses and quantitatively rank their contribution to Btk-mediated processes.

The paired homeobox gene Uncx4.1 specifies pedicles, transverse processes and proximal ribs of the vertebral column

The axial skeleton develops from the sclerotome, a mesenchymal cell mass derived from the ventral halves of the somites, segmentally repeated units located on either side of the neural tube. Cells from the medial part of the sclerotome form the axial perichondral tube, which gives rise to vertebral bodies and intervertebral discs; the lateral regions of the sclerotome will form the vertebral arches and ribs. Mesenchymal sclerotome cells condense and differentiate into chondrocytes to form a cartilaginous pre-skeleton that is later replaced by bone tissue. Uncx4.1 is a paired type homeodomain transcription factor expressed in a dynamic pattern in the somite and sclerotome. Here we show that mice homozygous for a targeted mutation of the Uncx4.1 gene die perinatally and exhibit severe malformations of the axial skeleton. Pedicles, transverse processes and proximal ribs, elements derived from the lateral sclerotome, are lacking along the entire length of the vertebral column. The mesenchymal anlagen for these elements are formed initially, but condensation and chondrogenesis do not occur. Hence, Uncx4.1 is required for the maintenance and differentiation of particular elements of the axial skeleton.

Protein kinase C-beta and oxygen deprivation. A novel Egr-1-dependent pathway for fibrin deposition in hypoxemic vasculature

Fibrin deposition is a salient feature of hypoxemic vasculature and results from induction of tissue factor. Such tissue factor expression in an oxygen deficient environment is driven by the transcription factor Early Growth Response (Egr)-1. Using homozygous null mice for the protein kinase C beta-isoform gene (PKCbeta null), PKCbeta is shown to be upstream of Egr-1 in this oxygen deprivation-mediated pathway for triggering procoagulant events. Whereas wild-type mice exposed to hypoxia (6%) displayed a robust increase in tissue factor transcripts and antigen, and vascular fibrin deposition, PKCbeta null animals showed a markedly blunted response. Consistent with a central role for Egr-1 in hypoxia-induced expression of tissue factor, PKCbeta null mice subjected to oxygen deprivation displayed at most a minor elevation in Egr-1 transcripts, antigen, and intensity of the gel shift band by electrophoretic mobility shift assay, compared with normoxic animals. These data firmly establish PKCbeta as a trigger for events leading to induction of Egr-1 and tissue factor under hypoxic conditions, and provide insight into a biologic cascade whereby oxygen deprivation recruits targets of PKCbeta and Egr-1, thereby amplifying the cellular response.

Protein kinase C-beta contributes to NADPH oxidase activation in neutrophils

We have analysed the involvement of the beta isotype of the protein kinase C (PKC) family in the activation of NADPH oxidase in primary neutrophils. Using immunofluorescence and cell fractionation, PKC-beta is shown to be recruited to the plasma membrane upon stimulation with phorbol ester and to the phagosomal membrane upon phagocytosis of IgG-coated particles (Fcgamma-receptor stimulus). The time course of recruitment is similar to that of NADPH oxidase activation by these stimuli. The PKC-beta specific inhibitor 379196 inhibits the response to PMA as well as to IgG-coated bacteria. Partial inhibition occurs between 10 and 100 nM of inhibitor, the concentration at which PKC-beta, but not other PKC isotypes, is targeted. Neutrophils isolated from a mouse that lacks PKC-beta also showed an inhibition of NADPH oxidase activation by PMA and IgG-coated particles. The level of inhibition is comparable to that achieved with 379196 in human neutrophils. Thus the PKC-beta isotype mediates activation of NADPH oxidase by PMA and by stimulation of Fcgamma receptors in neutrophils.

Inhibition of degranulation and interleukin-6 production in mast cells derived from mice deficient in protein kinase Cbeta

The antigen-mediated activation of mast cells by means of IgE antibodies bound to the cell surface leads to direct interactions between FcepsilonRI receptor cytoplasmic domains and various intracellular proteins. These interactions initiate diverse signal-transduction pathways, and the activation of these pathways results in the immediate release of proinflammatory agents. A delayed response also occurs and includes the release of various cytokines. It is clear that the activation of kinases is a requirement for the exocytosis observed in mast cells. In addition to the tyrosine phosphorylation of the affected system by soluble tyrosine kinases, activity of protein kinase C (PKC) results in serine or threonine phosphorylation of multiple protein substrates. In this study, we found that mast cells derived from PKCbeta-deficient mice produce less interleukin 6 in response to IgE-Ag. The inhibition of exocytosis in the PKCbeta-deficient mast cells occurred whether the stimuli were due to the aggregation of the mast cell surface FcepsilonRI or to the calcium ionophore, ionomycin. However, no significant changes were observed in the proliferative response of the mast cells to interleukin 3 (IL-3) or in their apoptotic rate after IL-3 depletion. (Blood. 2000;95:1752-1757)

Effects of knockout of the protein kinase C beta gene on glucose transport and glucose homeostasis

The beta-isoform of protein kinase C (PKC) has paradoxically been suggested to be important for both insulin action and insulin resistance as well as for contributing to the pathogenesis of diabetic complications. Presently, we evaluated the effects of knockout of the PKCbeta gene on overall glucose homeostasis and insulin regulation of glucose transport. To evaluate subtle differences in glucose homeostasis in vivo, knockout mice were extensively backcrossed in C57BL/6 mice to diminish genetic differences other than the absence of the PKCbeta gene. PKCbeta-/- knockout offspring obtained through this backcrossing had 10% lower blood glucose levels than those observed in PKCbeta+/+ wild-type offspring in both the fasting state and 30 min after i.p. injection of glucose despite having similar or slightly lower serum insulin levels. Also, compared with commercially obtained C57BL/6-129/SV hybrid control mice, serum glucose levels were similar, and serum insulin levels were similar or slightly lower, in C57BL/6-129/SV hybrid PKCbeta knockout mice in fasting and fed states and after i.p. glucose administration. In keeping with a tendency for slightly lower serum glucose and/or insulin levels in PKCbeta knockout mice, insulin-stimulated 2-deoxyglucose (2-DOG) uptake was enhanced by 50-100% in isolated adipocytes; basal and insulin-stimulated epitope-tagged GLUT4 translocations in adipocytes were increased by 41% and 27%, respectively; and basal 2-DOG uptake was mildly increased by 20-25% in soleus muscles incubated in vitro. The reason for increased 2-DOG uptake and/or GLUT4 translocation in these tissues was uncertain, as there were no significant alterations in phosphatidylinositol 3-kinase activity or activation or in levels of GLUT1 or GLUT4 glucose transporters or other PKC isoforms. On the other hand, increases in 2-DOG uptake may have been partly caused by the loss of PKCbeta1, rather than PKCbeta2, as transient expression of PKCbeta1 selectively inhibited insulin-stimulated translocation of epitope-tagged GLUT4 in adipocytes prepared from PKCbeta knockout mice. Our findings suggest that 1) PKCbeta is not required for insulin-stimulated glucose transport; 2) overall glucose homeostasis in vivo is mildly enhanced by knockout of the PKCbeta gene; 3) glucose transport is increased in some tissues in PKCbeta knockout mice; and 4) increased glucose transport may be partly due to loss of PKCbeta1, which negatively modulates insulin-stimulated GLUT4 translocation.

PACSIN, a brain protein that is upregulated upon differentiation into neuronal cells

To identify genes that are differentially expressed during self-repair processes in mouse brain, we screened a subtracted cDNA library enriched for brain-specific clones. One of these clones, H74, detected a 4.4-kb mRNA predominantly expressed in brain and dorsal root ganglia neurons. Expression increased continuously during the lifespan and the state of differentiation, but decreased after entorhinal-cortex lesion. A full-length cDNA clone was isolated from a cerebellum cDNA library and characterized. Sequence analysis and database search revealed high sequence similarity to FAP52, a protein expressed in focal-adhesion contacts, and uncharacterized Echinococcus and Caenorhabditis elegans gene products. Furthermore, peptide sequences derived from human cDNA fragments showed up to 65% sequence identity at the amino acid level. The presence of a C-terminal src homology 3 (SH3) domain and its phosphorylation by casein kinase 2 (CK2) and protein kinase C (PKC) imply a role in signaling. Here we demonstrate that the gene encodes a phosphoprotein, referred to as PACSIN, with a restricted spatial and temporal expression pattern.

The molecular mechanism of B cell activation by toll-like receptor protein RP-105

The B cell-specific transmembrane protein RP-105 belongs to the family of Drosophila toll-like proteins which are likely to trigger innate immune responses in mice and man. Here we demonstrate that the Src-family protein tyrosine kinase Lyn, protein kinase C beta I/II (PKCbetaI/II), and Erk2-specific mitogen-activated protein (MAP) kinase kinase (MEK) are essential and probably functionally connected elements of the RP-105-mediated signaling cascade in B cells. We also find that negative regulation of RP-105-mediated activation of MAP kinases by membrane immunoglobulin may account for the phenomenon of antigen receptor-mediated arrest of RP-105-mediated B cell proliferation.

Immunodeficiency in protein kinase cbeta-deficient mice

Cross-linking of the antigen receptor on lymphocytes by antigens or antibodies to the receptor results in activation of enzymes of the protein kinase C (PKC) family. Mice homozygous for a targeted disruption of the gene encoding the PKC-betaI and PKC-betaII isoforms develop an immunodeficiency characterized by impaired humoral immune responses and reduced cellular responses of B cells, which is similar to X-linked immunodeficiency in mice. Thus PKC-betaI and PKC-betaII play an important role in B cell activation and may be functionally linked to Bruton's tyrosine kinase in antigen receptor-mediated signal transduction.