PKCθ-regulated signalling in health and disease

Protein kinase C signaling "in" and "to" the nucleus: Master kinases in transcriptional regulation

PKC is a multifunctional family of Ser-Thr kinases widely implicated in the regulation of fundamental cellular functions, including proliferation, polarity, motility, and differentiation. Notwithstanding their primary cytoplasmic localization and stringent activation by cell surface receptors, PKC isozymes impel prominent nuclear signaling ultimately impacting gene expression. While transcriptional regulation may be wielded by nuclear PKCs, it most often relies on cytoplasmic phosphorylation events that result in nuclear shuttling of PKC downstream effectors, including transcription factors. As expected from the unique coupling of PKC isozymes to signaling effector pathways, glaring disparities in gene activation/repression are observed upon targeting individual PKC family members. Notably, specific PKCs control the expression and activation of transcription factors implicated in cell cycle/mitogenesis, epithelial-to-mesenchymal transition and immune function. Additionally, PKCs isozymes tightly regulate transcription factors involved in stepwise differentiation of pluripotent stem cells toward specific epithelial, mesenchymal, and hematopoietic cell lineages. Aberrant PKC expression and/or activation in pathological conditions, such as in cancer, leads to profound alterations in gene expression, leading to an extensive rewiring of transcriptional networks associated with mitogenesis, invasiveness, stemness, and tumor microenvironment dysregulation. In this review, we outline the current understanding of PKC signaling "in" and "to" the nucleus, with significant focus on established paradigms of PKC-mediated transcriptional control. Dissecting these complexities would allow the identification of relevant molecular targets implicated in a wide spectrum of diseases.

Expression and localization of grass carp pkc-θ (protein kinase C theta) gene after its activation

Haemorrhagic disease caused by grass carp reovirus (GCRV) can result in large-scale death of young grass carp, leading to irreparable economic losses that seriously affect large-scale breeding. Protein kinase C (PKC, also known as PRKC) represents a family of serine/threonine protein kinases that includes multiple isozymes in many species. Among these, PKC-θ (PKC theta, also written as PRKCQ) is a novel isoform, mainly expressed in T cells, that is known to be involved in immune system function in mammals. To date, no research on immunological functions of fish Pkc-θ has been reported. To address this issue, we cloned the grass carp pkc-θ gene. Phylogenetic and syntenic analysis showed that this gene is the most evolutionarily conserved relative to zebrafish. Real-time quantitative PCR (RT-qPCR) indicated that pkc-θ was expressed at high levels in the gills and spleen of healthy grass carp. Infection with GCRV down regulated pkc-θ expression in the gills and spleen. Gene products that function upstream and downstream of pkc-θ were up regulated in the gill, but were down-regulated in the spleen. These results suggest that direct or indirect targeting of pkc-θ by GCRV may help the virus evade host immune defences in the spleen. Phorbol ester (PMA) treatment of Jurkat T cells induced translocation of grass carp Pkc-θ from the cytoplasm to the plasma membrane. This response to PMA suggests evolutionary conservation of an immune response function in fish Pkc-θ, as well as conservation of its sequence and structural domains. This study expanded our knowledge of the fish PKC gene family, and explored the role of pkc-θ in function of the grass carp immune system, providing new insights which may facilitate further studies of its biological functions.

Adenosine A2A Receptor Stimulation Inhibits TCR-Induced Notch1 Activation in CD8+T-Cells

Notch receptors signaling is required for optimal T-cell activation and function. T-cell receptor (TCR) engagement can activate Notch receptors in T-cells in a ligand-independent fashion. In this study, we examined the role of adenosine A2A receptor (A2AR) signaling pathway in regulating the activity of Notch1 induced by TCR stimulation in CD8+T-cells. A selective A2AR agonist decreased Notch1 protein expression and Notch1 cleavage, and reduced transcripts of Notch1-target genes Hes1 and Myc in activated CD8+T-cells. Inhibition of TCR-induced Notch1 expression by an A2AR agonist was accompanied by increased cAMP concentration and mimicked by forskolin. This effect was associated with reduced IFN-γ and granzyme B production. The effect of an A2AR agonist was abrogated by a selective A2AR antagonist and absent in CD8+T-cells harvested from A2AR-/- mice. Stimulation of A2AR reduced Notch1 receptor levels by inhibiting upstream TCR signals, including ZAP70 phosphorylation, in turn impairing the generation of the active Notch1 intracellular domain (N1ICD). Direct activation of PKC with PMA and ionomycin bypassed A2AR-induced Notch1 inhibition. Overexpression of N1ICD in CD8+T-cells prevented the suppressive effects of an A2AR agonist on proliferation and cytokine release during activation. Our results identify the A2AR signaling pathway as an important regulator of TCR-induced Notch1 receptor activation in CD8+T-cells, and Notch as an important target of the immune suppressive effects of A2AR. We propose a mechanism whereby A2AR impairs CD8 T-cells function through inhibition of Notch1 receptor activation.

Baicalin Inhibits Human Cervical Cancer Cells by Suppressing Protein Kinase C/Signal Transducer and Activator of Transcription (PKC/STAT3) Signaling Pathway

BACKGROUND Like other human cancers, the malignancy of cervical cancer is also characterized by abilities of proliferation, migration, and invasion. Protein kinase C-zeta (PKCζ) has been highly correlated with several human cancers. Baicalin was proven to regulate PKC. This study aimed to investigate the anti-cancer effect and involved molecular mechanisms of baicalin on human cervical cancer. MATERIAL AND METHODS Baicalin at various concentrations was used to treat 2 human cervical cancer cell lines HeLa and SiHa. The proliferation was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenylterazolium bromide (MTT) assay. The apoptosis was detected by terminal transferase UTP nick end labeling (TUNEL) assay. Wound healing assay and Transwell assay were used to evaluate the migration and invasion respectively. Western blotting was performed to assess the protein expression levels. RESULTS Baicalin administration significantly reduced the viability by facilitating the apoptosis in HeLa and SiHa cells. Baicalin treatment also significantly reduced the wound closure and cell amount invaded as measured by Transwell assay. The expression levels of PKCζ, survivin, matrix metalloproteinase (MMP)2, MMP9 as well as the phosphorylation of signal transducer and activator of transcription (STAT) 3 were reduced in baicalin administrated cervical cancer cells. CONCLUSIONS Baicalin exerted anti-cancer effects on human cervical cancer cells by targeting STAT3 regulated signaling pathways.

Identification of miR-34a-target interactions by a combined network based and experimental approach

Circulating miRNAs have been associated with numerous human diseases. The lack of understanding the functional roles of blood-born miRNAs limits, however, largely their value as disease marker. In a systems biology analysis we identified miR-34a as strongly associated with pathogenesis. Genome-wide analysis of miRNAs in blood cell fractions highlighted miR-34a as most significantly up-regulated in CD3+ cells of lung cancer patients. By our in silico analysis members of the protein kinase C family (PKC) were indicated as miR-34a target genes. Using a luciferase assay, we confirmed binding of miR-34a-5p to target sequences within the 3′UTRs of five PKC family members. To verify the biological effect, we transfected HEK 293T and Jurkat cells with miR-34a-5p causing reduced endogenous protein levels of PKC isozymes. By combining bioinformatics approaches with experimental validation, we demonstrate that one of the most relevant disease associated miRNAs has the ability to control the expression of a gene family.

Englerins: A Comprehensive Review

In the decade since the discovery of englerin A (1) and its potent activity in cancer models, this natural product and its analogues have been the subject of numerous chemical, biological, and preclinical studies by many research groups. This review summarizes published findings and proposes further research directions required for entry of an englerin analogue into clinical trials for kidney cancer and other conditions.

Pharmacological Inhibition of PKCθ Counteracts Muscle Disease in a Mouse Model of Duchenne Muscular Dystrophy

Inflammation plays a considerable role in the progression of Duchenne Muscular Dystrophy (DMD), a severe muscle disease caused by a mutation in the dystrophin gene. We previously showed that genetic ablation of Protein Kinase C θ (PKCθ) in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

Research in context

Duchenne muscular dystrophy (DMD) is a severe muscle disease affecting 1:3500 male births. DMD is caused by a mutation in dystrophin gene, coding for a protein required for skeletal and cardiac muscle integrity. Lack of a functional dystrophin is primarily responsible for the muscle eccentric contraction-induced muscle damage, observed in dystrophic muscle. However, inflammation plays a considerable role in the progression of DMD. Glucocorticoids, which have anti-inflammatory properties, are being used to treat DMD with some success; however, long term treatment with these drugs induces muscle atrophy and wasting, outweighing their benefit. The identification of specific targets for anti-inflammatory therapies is one of the ongoing therapeutic options. Although blunting inflammation would not be a “cure” for the disease, the emerging clue is that multiple strategies, addressing different aspects of the pathology, which may eventually converge, may be successful. In this context, we previously showed that genetic ablation of Protein Kinase C θ (PKCθ), an enzyme known to be involved in immune response, in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

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Immune-cell intrinsic PKCθ activity might play a hitherto unrecognized role of in the development of DMD.

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Mdx dystrophic mice were treated with the PKCθ inhibitor C20.

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C20 treatment prevents damage and inflammation in dystrophic muscle, while improving muscle regeneration.

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C20 treatment prevents drop in force and ameliorates fatigue resistance in dystrophic mice.

Unraveling the Effects of PPARβ/δ on Insulin Resistance and Cardiovascular Disease

Insulin resistance precedes dyslipidemia and type 2 diabetes mellitus (T2DM) development. Preclinical evidence suggests that peroxisome proliferator-activated receptor (PPAR) β/δ activators may prevent and treat obesity-induced insulin resistance and T2DM, while clinical trials highlight their potential utility in dyslipidemia. This review summarizes recent mechanistic insights into the antidiabetic effects of PPARβ/δ activators, including their anti-inflammatory actions, their ability to inhibit endoplasmic reticulum (ER) stress and hepatic lipogenesis, and to improve atherogenesis and insulin sensitivity, as well as their capacity to activate pathways that are also stimulated by exercise. Findings from clinical trials are also examined. Dissecting the effects of PPARβ/δ ligands on insulin sensitivity and atherogenesis may provide a basis for the development of therapies for the prevention and treatment of T2DM and cardiovascular disease (CVD).