Regulation of protein kinase C and role in cancer biology

[Calcium, Vitamin D, and Colorectal Cancer]

Colorectal cancer has a high incidence and mortality worldwide, with Westernized lifestyles and diet being significant contributing factors. Vitamin D and calcium have been known to reduce the incidence of colorectal cancer by affecting cell differentiation, proliferation, and apoptosis. Despite observational studies which have suggested that a higher serum vitamin D level can lower the risk of colorectal cancer and improve survival rates, no large-scale randomized controlled trials to establish these benefits have been conducted to date. Calcium intake has also been found to have a beneficial role in reducing the incidence and improving survival rates of colorectal cancer in several observational studies. Moreover, intervention studies have proved its effect in preventing colorectal adenomas. However, there are few intervention studies that have identified the relationship of vitamin D and calcium with colon cancer. To elucidate the impact of vitamin D and calcium supplementation on colorectal cancer, well-designed and large-scale randomized controlled trials are necessary in the future.

PKC is an indispensable factor in promoting environmental toxin chromium-mediated transformation and drug resistance

Hexavalent chromium [Cr(VI)] pollution is a serious environmental problem, due to not only its toxicity but also carcinogenesis. Although studies reveal several features of Cr(VI)-induced carcinogenesis, the underlying mechanisms of how Cr(VI) orchestrates multiple mitogenic pathways to promote tumor initiation and progression remain not fully understood. Src/Ras and other growth-related pathways are shown to be key players in Cr(VI)-initiated tumor prone actions. The role of protein kinase C (PKC, an important signal transducer) in Cr(VI)-mediated carcinogenesis has not been thoroughly investigated. In this study, using human bronchial/lung epithelial cells and keratinocytes, we demonstrate that PKC activity is increased by transient or chronic Cr(VI) exposure, which plays no role in the activation of Src/Ras signaling and ROS upregulation by this metal toxin. PKC in chronic Cr(VI)-treated cells stabilizes Bcl-2 to mitigate doxorubicin (an anti-cancer drug)-mediated apoptosis. After the suppression of this kinase by GO6976 (a PKC inhibitor), the cells chronically exposed to Cr(VI) partially regain the sensitivity to doxorubicin. However, when co-suppressed PKC and Ras, the chronic Cr(VI)-treated cells become fully responsive to doxorubicin and are unable to be transformed. Taken together, our study provides a new insight into the mechanisms, in which PKC is an indispensable player and cooperates with other mitogenic pathways to achieve Cr(VI)-induced carcinogenesis as well as to establish drug resistance. The data also suggest that active PKC can serve as a potential biomarker for early detection of health damages by Cr(VI) and therapeutic target for developing new treatments for diseases caused by Cr(VI).

Inhibitory effect of isomorellin on cholangiocarcinoma cells via suppression of NF-κB translocation, the phosphorylated p38 MAPK pathway and MMP-2 and uPA expression

Evidence indicates that most cancer deaths are caused by tumor invasion and metastasis. Cholangiocarcinoma (CCA) is a tumor of the bile duct epithelium characterized by slow growth, rapid metastasis and poor prognosis. Caged xanthones are extracted from gamboge, a dry resin exuded by Garcinia hanbury. These compounds have been reported to be cytotoxic to several types of cancer cells, without affecting normal cells. The aim of the present study was to determine the effect of isomorellin on the inhibition of CCA cell (KKU-100) viability, migration, invasion and the expression of invasion-regulated proteins. Cytotoxicity of isomorellin was evaluated using a sulforhodamine B assay. The anti-migratory and anti-invasive effects of isomorellin on KKU-100 cells were assessed using wound healing and chamber invasion assays, respectively. Furthermore, the activities of matrix metalloproteinases (MMPs)-2 and -9, and urokinase-type plasminogen activator (uPA) were also investigated. The expression levels of proteins regulating invasion were determined via western blot analysis. The cell viability of KKU-100 cells was decreased following treatment with isomorellin in a dose-dependent manner, with IC50 values at 24, 48 and 72 h of 3.46±0.19, 3.78±0.02 and 4.01±0.01 µM, respectively. Wound healing and chamber invasion assays indicated that isomorellin significantly inhibited KKU-100 cell migration and invasion in a dose-dependent manner. In addition, isomorellin significantly inhibited cancer cell migration and invasion abilities via focal adhesion kinase (FAK), protein kinase C (PKC), the phosphorylated (p)-p38 mitogen-activated protein kinase (MAPK) pathway, and nuclear factor (NF)-κB expression and translocation to the nucleus, thus resulting in downregulation of MMP-2, uPA and cyclooxygenase-2 (COX-2) expression. Therefore, inhibition of MMP-2, uPA and COX-2 expression may result in decreased CCA cell invasion ability. These data demonstrated for the first time that the suppression of KKU-100 cell viability, invasion and migration, and downregulation of NF-κB, MMP-2, uPA and the p-p38 MAPK pathway, may result in isomorellin-mediated anti-invasiveness.

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.

Protein Conformational Changes in Breast Cancer Sera Using Infrared Spectroscopic Analysis

Protein structural alterations, including misfolding and aggregation, are a hallmark of several diseases, including cancer. However, the possible clinical application of protein conformational analysis using infrared spectroscopy to detect cancer-associated structural changes in proteins has not been established yet. The present study investigates the applicability of Fourier transform infrared spectroscopy in distinguishing the sera of healthy individuals and breast cancer patients. The cancer-associated alterations in the protein structure were analyzed by fitting the amide I (1600-1700 cm-1) band of experimental curves, as well as by comparing the ratio of the absorbance values at the amide II and amide III bands, assigning those as the infrared spectral signatures. The snapshot of the breast cancer-associated alteration in circulating DNA and RNA was also evaluated by extending the spectral fitting protocol to the complex region of carbohydrates and nucleic acids, 1140-1000 cm-1. The sensitivity and specificity of these signatures, representing the ratio of the α-helix and β-pleated sheet in proteins, were both 90%. Likewise, the ratio of amides II and amide III (I1556/I1295) had a sensitivity and specificity of 100% and 80%, respectively. Thus, infrared spectroscopy can serve as a powerful tool to understand the protein structural alterations besides distinguishing breast cancer and healthy serum samples.

Genomic Analysis of Spontaneous Abortion in Holstein Heifers and Primiparous Cows

Background: The objectives of this study were to identify loci, positional candidate genes, gene-sets, and pathways associated with spontaneous abortion (SA) in cattle and compare these results with previous human SA studies to determine if cattle are a good SA model for humans. Pregnancy was determined at gestation day 35 for Holstein heifers and cows. Genotypes from 43,984 SNPs of 499 pregnant heifers and 498 pregnant cows that calved at full term (FT) were compared to 62 heifers and 28 cows experiencing SA. A genome-wide association analysis, gene-set enrichment analysis–single nucleotide polymorphism, and ingenuity pathway analysis were used to identify regions, pathways, and master regulators associated with SA in heifers, cows, and a combined population. Results: Twenty-three loci and 21 positional candidate genes were associated (p < 1 × 10⁻⁵) with SA and one of these (KIR3DS1) has been associated with SA in humans. Eight gene-sets (NES > 3.0) were enriched in SA and one was previously reported as enriched in human SA. Four master regulators (p < 0.01) were associated with SA within two populations. Conclusions: One locus associated with SA was validated and 39 positional candidate and leading-edge genes and 2 gene-sets were enriched in SA in cattle and in humans.

Integrating virtual screening and biochemical experimental approach to identify potential anti-cancer agents from drug databank

Chemical libraries constitute a reservoir of pharmacophoric molecules to identify potent anti-cancer agents. Virtual screening of heterocyclic compound library in conjugation with the agonist-competition assay, toxicity-carcinogenicity analysis, and string-based structural searches enabled us to identify several drugs as potential anti-cancer agents targeting protein kinase C (PKC) as a target. Molecular modeling study indicates that Cinnarizine fits well within the PKC C2 domain and exhibits extensive interaction with the protein residues. Molecular dynamics simulation of PKC-Cinnarizine complex at different temperatures (300, 325, 350, 375, and 400[Formula: see text]K) confirms that Cinnarizine fits nicely into the C2 domain and forms a stable complex. The drug Cinnarizine was found to bind PKC with a dissociation constant Kd of [Formula: see text]M. The breast cancer cells stimulated with Cinnarizine causes translocation of PKC-[Formula: see text] to the plasma membrane as revealed by immunoblotting and immunofluorescence studies. Cinnarizine also dose dependently reduced the viability of MDAMB-231 and MCF-7 breast cancer cells with an IC[Formula: see text] of [Formula: see text] and [Formula: see text]g/mL, respectively. It is due to the disturbance of cell cycle of breast cancer cells with reduction of S-phase and accumulation of cells in G1-phase. It disturbs mitochondrial membrane potentials to release cytochrome C into the cytosol and activates caspase-3 to induce apoptosis in cancer cells. The cell death was due to induction of apoptosis involving mitochondrial pathway. Hence, the current study has assigned an additional role to Cinnarizine as an activator of PKC and potentials of the approach to identify new molecules for anti-cancer therapy. Thus, in silico screening along with biochemical experimentation is a robust approach to assign additional roles to the drugs present in the databank for anti-cancer therapy.

Protein kinase C beta II suppresses colorectal cancer by regulating IGF-1 mediated cell survival

Despite extensive efforts, cancer therapies directed at the Protein Kinase C (PKC) family of serine/threonine kinases have failed in clinical trials. These therapies have been directed at inhibiting PKC and have, in some cases, worsened disease outcome. Here we examine colon cancer patients and show not only that PKC Beta II is a tumour suppressor, but patients with low levels of this isozyme have significantly decreased disease free survival. Specifically, analysis of gene expression levels of all PKC genes in matched normal and cancer tissue samples from colon cancer patients revealed a striking down-regulation of the gene coding PKC Beta in the cancer tissue (n = 21). Tissue microarray analysis revealed a dramatic down-regulation of PKC Beta II protein levels in both the epithelial and stromal diseased tissue (n = 166). Of clinical significance, low levels of the protein in the normal tissue of patients is associated with a low (10%) 10 year survival compared with a much higher (60%) survival in patients with relatively high levels of the protein. Consistent with PKC Beta II levels protecting against colon cancer, overexpression of PKC Beta II in colon cancer cell lines reveals that PKC Beta II reverses transformation in cell based assays. Further to this, activation of PKC Beta II results in a dramatic downregulation of IGF-I-induced AKT, indicating a role for PKCs in regulating IGF-1 mediated cell survival. Thus, PKC Beta II is a tumour suppressor in colon cancer and low levels serve as a predictor for poor survival outcome.

Spotlight on midostaurin in the treatment of FLT3-mutated acute myeloid leukemia and systemic mastocytosis: design, development, and potential place in therapy

The Fms-like tyrosine kinase-3 (FLT3; fetal liver kinase-2; human stem cell tyrosine kinase-1; CD135) is a class III receptor tyrosine kinase that is normally involved in regulating the proliferation, differentiation, and survival of both hematopoietic cells and dendritic cells. Mutations leading it to be constitutively activated make it an oncogenic driver in ~30% of acute myeloid leukemia (AML) patients where it is associated with poor prognosis. The prevalence of oncogenic FLT3 and the dependency on its constitutively activated kinase activity for leukemia growth make this protein an attractive target for therapeutic intervention. Of the numerous small molecule inhibitors under clinical investigation for the treatment of oncogenic FLT3-positive AML, the N-benzoyl-staurosporine, midostaurin (CGP41251; PKC412; Rydapt^®; Novartis Pharma AG, Basel, Switzerland), is the first to be approved by the US Food and Drug Administration for the treatment, in combination with standard chemotherapy, of newly diagnosed adult AML patients who harbor mutations in FLT3. Here, we describe the early design of midostaurin, the preclinical discovery of its activity against oncogenic FLT3, and its subsequent clinical development as a therapeutic agent for FLT3 mutant-positive AML.

Protein kinase C β inhibits autophagy and sensitizes cervical cancer Hela cells to cisplatin

Recently, autophagy has been indicated to play an essential role in various biological events, such as the response of cervical cancer cells to chemotherapy. However, the exact signalling mechanism that regulates autophagy during chemotherapy remains unclear. In the present study, we investigated the regulation by cisplatin on protein kinase C β (PKC β), on B-cell lymphoma 2 (Bcl-2) and on apoptosis in cervical cancer Hela cells. And then we examined the regulation by cisplatin on autophagy and the role of autophagy on the chemotherapy in Hela cells. In addition, the regulation of the PKC β on the autophagy was also investigated. Our results indicated that cisplatin promoted PKC β in Hela cells. The PKC β inhibitor reduced the cisplatin-induced apoptosis, whereas increased the cisplatin-induced autophagy in Hela cells. On the other side, the PKC β overexpression aggravated the cisplatin-induced apoptosis, whereas down-regulated the cisplatin-induced autophagy. Taken together, our study firstly recognized the involvement of PKC β in the cytotoxicity of cisplatin via inhibiting autophagy in cervical cancer cells. We propose that PKC β would sensitize cervical cancer cells to chemotherapy via reducing the chemotherapy induced autophagy in cancer cells.

Final Report of the Amended Safety Assessment of Glyceryl Lau rate, Glyceryl Lau rate SE, Glyceryl Laurate/Oleate, Glyceryl Adipate, Glyceryl Alginate, Glyceryl Arachidate, Glyceryl Arachidonate, Glyceryl Behenate, Glyceryl Caprate, Glyceryl Caprylate, Glyceryl Caprylate/Caprate, Glyceryl Citrate/Lactate/Linoleate/Oleate, Glyceryl Cocoate, Glyceryl Collagenate, Glyceryl Erucate, Glyceryl Hydrogenated Rosinate, Glyceryl Hydrogenated Soyate, Glyceryl Hydroxystearate, Glyceryl Isopalmitate, Glyceryl Isostearate, Glyceryl Isostearate/Myristate, Glyceryl Isostearates, Glyceryl Lanolate, Glyceryl Linoleate, Glyceryl Linolenate, Glyceryl Montanate, Glyceryl Myristate, Glyceryl Isotridecanoate/Stearate/Adipate, Glyceryl Oleate SE, Glyceryl Oleate/Elaidate, Glyceryl Palmitate, Glyceryl Palmitate/Stearate, Glyceryl Palmitoleate, Glyceryl Pentadecanoate, Glyceryl Polyacrylate, Glyceryl Rosinate, Glyceryl Sesquioleate, Glyceryl/Sorbitol Oleate/Hydroxystearate, Glyceryl Stearate/Acetate, Glyceryl Stearate/Maleate, Glyceryl Tallowate, Glyceryl Thiopropionate, and Glyceryl Undecylenate1

The safety of 43 glyceryl monoesters listed as cosmetic ingredients was reviewed in a safety assessment completed in 2000. Additional safety test data pertaining to Glyceryl Rosinate and Glyceryl Hydrogenated Rosinate were received and served as the basis for this amended report. Glyceryl monoesters are used mostly as skin-conditioning agents—emollients and/or surfactant—emulsifying agents in cosmetics. The following 20 glyceryl monoesters are currently reported to be used in cosmetics: Glyceryl Laurate, Glyceryl Alginate, Glyceryl Arachidonate, Glyceryl Behenate, Glyceryl Caprylate, Glyceryl Caprylate/Caprate, Glyceryl Cocoate, Glyceryl Erucate, Glyceryl Hydroxystearate, Glyceryl Isostearate, Glyceryl Lanolate, Glyceryl Linoleate, Glyceryl Linolenate, Glyceryl Myristate, Glyceryl Oleate/Elaidate, Glyceryl Palmitate, Glyceryl Polyacrylate, Glyceryl Rosinate, Glyceryl Stearate/Acetate, and Glyceryl Undecylenate. Concentration of use data received from the cosmetics industry in 1999 indicate that Glyceryl Monoesters are used at concentrations up to 12 % in cosmetic products. Glyceryl Monoesters are not pure monoesters, but are mostly mixtures with mono-, di-, and tri-esters. The purity of commercial and conventional Monoglyceride (Glyceryl Monoester) is a minimum of 90%. Glyceryl Monoesters (monoglycerides) are metabolized to free fatty acids and glycerol, both of which are available for the resynthesis of triglycerides. Glyceryl Laurate enhanced the penetration of drugs through cadaverous skin and hairless rat skin in vitro and has been described as having a wide spectrum of antimicrobial activity. A low-grade irritant response was observed following inhalation of an aerosol containing 10% Glyceryl Laurate by test animals. Glyceryl monoesters have little acute or short-term toxicity in animals, and no toxicity was noted following chronic administration of a mixture consisting mostly of glyceryl di- and mono- esters. Glyceryl Laurate did have strong hemolytic activity in an in vitro assay using sheep erythrocytes. Glyceryl Laurate, Glyceryl Isostearate, or Glyceryl Citrate/Lactate/Linoleate/Oleate were not classified as ocular irritants in rabbits. Undiluted glyceryl monoesters may produce minor skin irritation, especially in abraded skin, but in general these ingredients are not irritating at concentrations used in cosmetics. Glyceryl monoesters are not sensitizers, except that Glyceryl Rosinate and Hydrogenated Glyceryl Rosinate may contain residual rosin, which can cause allergic reactions. These ingredients are not photosensitizers. Glyceryl Citrate/Lactate/Linoleate/Oleate was not mutagenic in the Ames test system. Glyceryl Laurate exhibited antitumor activity and Glyceryl Stearate was negative in a tumor promotion assay. At concentrations higher than used in cosmetics, Glyceryl Laurate did cause moderate erythema in human repeat-insult patch test (RIPT) studies, but the other glyceryl monoesters tested failed to produce any significant positive reactions. Glyceryl Rosinate was irritating to animal skin at 50%, but did not produce sensitization in clinical tests at concentrations up to 10% and covered with semioccluded patches. There is reported use of Glyceryl Rosinate at 12% in mascara, which is somewhat higher than the concentration in the clinical testing. It was reasoned that the available data do support the safety of this use because there would be minimal contact with the skin and no occlusion. The safety of Arachidonic Acid was not documented and substantiated for cosmetic product use in an earlier safety assessment and those same safety questions apply to Glyceryl Arachidonate. Based on these data, the Cosmetic Ingredient Review (CIR) Expert Panel found that these glyceryl monoesters are safe as cosmetic ingredients in the present practices of use and concentration: except that the available data are insufficient to support the safety of Glyceryl Arachidonate. Additional data needed to support the safety of Glyceryl Arachidonate include (1) dermal absorption data; and, based on the results of the absorption studies, there may be a need for (2) immunomodula-tory data; (3) carcinogenicity and photocarcinogenicity data; and (4) human irritation, sensitization, and photosensitization data.

Effects of Phorbol Dibutyrate on Cell Proliferation, Apoptosis, and Tumor Necrosis Factor-alpha Expression in Human Endometrial Adenocarcinoma Cells

OBJECTIVES

Recent evidence suggested that protein kinase C (PKC), a major cell cycle regulator in endometrial models, mimics progesterone withdrawal by inducing downstream signals. In the current study we examined the hypothesis that the PKC activator phorbol 12,13 dibutyrate (PDB) would inhibit cell proliferation and induce apoptosis in two endometrial adenocarcinoma cell (EAC) lines, HEC-1B and Ishikawa cells. We further examined whether the induction of tumor necrosis factor-alpha (TNF-alpha) might mediate these effects.

METHODS

EAC lines were cultured under standard and serum-free conditions to study the effects of PDB on cell kinetics. Cell proliferation was determined by cell count using a hemacytometer and by incorporation of (3)H thymidine into 10% trichloracetic acid-precipitable DNA. Apoptosis was determined by measuring cytoplasmic histone-associated DNA fragments. Conditioned media concentrations of TNF-alpha were measured by a commercially available enzyme-linked immunosorbent assay (ELISA). EACs were transfected with a -125-bp TNF-alpha promoter luciferase construct and treated with PDB to evaluate transcriptional activation.

RESULTS

Activation of the PKC system with PDB (10 nM) decreased cell proliferation and mitogenesis in EACs. PDB induced apoptosis in both EAC lines. EACs exhibit basal TNF-alpha gene expression and protein secretion and these were increased potently by PDB. However, neutralization of TNF-alpha by addition of anti-TNF-alpha antibodies did not prevent the suppression of mitogenesis, induction of apoptosis, or activation of TNF-alpha gene expression by PDB.

CONCLUSION

Activation of the PKC system leads to inhibition of cell proliferation, induction of apoptosis, and TNF-alpha expression in EACs. However, apoptosis in this setting does not appear to require TNF-alpha action. EACs provide an informative model to investigate aspects of endometrial epithelial remodeling that may occur under physiologic conditions of progesterone withdrawal.

Protein kinase C as a target for new anti-cancer agents

Cancer joins the category of diseases involving abnormalities in the rate of proliferation of cells and is associated with uncontrolled cell division, where cells either generate their own growth-promoting stimuli or neighboring cells or do not respond to growth inhibitory signals. Protein kinase C (PKC) is one of the key elements in the tumor growth signal transduction pathways and is found to be overexpressed in several malignant cell types. A way to control cell proliferation and cell differentiation is by influencing signal transduction pathways by modulation of PKC. PKC encloses 12 different isoenzymes, and each isoenzyme is found to have a different functional property. Because specific PKC isoenzyme types are present in different (malignant) cell species, they may be an attractive target in the development of anti-cancer agents. Classification and identification of the available PKC isoenzymes in different tumor cells could be useful in targeting specific tumors. PKC also tends to be overexpressed in association with the multidrug resistance pheno-type. This concise review deals with the role of PKC isoenzymes in (tumor) cell biology and evaluates the antineoplastic agents interacting on PKC isoenzymes.

PKCα Attenuates Jagged-1-Mediated Notch Signaling in ErbB-2-Positive Breast Cancer to Reverse Trastuzumab Resistance

PURPOSE

Breast cancer is the second leading cause of cancer mortality among women worldwide. The major problem with current treatments is tumor resistance, recurrence, and disease progression. ErbB-2-positive breast tumors are aggressive and frequently become resistant to trastuzumab or lapatinib. We showed previously that Notch-1 is required for trastuzumab resistance in ErbB-2-positive breast cancer.

EXPERIMENTAL DESIGN

Here, we sought to elucidate mechanisms by which ErbB-2 attenuates Notch signaling and how this is reversed by trastuzumab or lapatinib.

RESULTS

The current study elucidates a novel Notch inhibitory mechanism by which PKCα downstream of ErbB-2 (i) restricts the availability of Jagged-1 at the cell surface to transactivate Notch, (ii) restricts the critical interaction between Jagged-1 and Mindbomb-1, an E3 ligase that is required for Jagged-1 ubiquitinylation and subsequent Notch activation, (iii) reverses trastuzumab resistance in vivo, and (iv) predicts better outcome in women with ErbB-2-positive breast cancer.

CONCLUSIONS

The clinical impact of these studies is PKCα is potentially a good prognostic marker for low Notch activity and increased trastuzumab sensitivity in ErbB-2-positive breast cancer. Moreover, women with ErbB-2-positive breast tumors expressing high Notch activation and low PKCα expression could be the best candidates for anti-Notch therapy.

Targeting Protein Kinase C Downstream of Growth Factor and Adhesion Signalling

The signaling outputs of Receptor Tyrosine Kinases, G-protein coupled receptors and integrins converge to mediate key cell process such as cell adhesion, cell migration, cell invasion and cell proliferation. Once activated by their ligands, these cell surface proteins recruit and direct a diverse range of proteins to disseminate the appropriate response downstream of the specific environmental cues. One of the key groups of proteins required to regulate these activities is the family of serine/threonine intracellular kinases called Protein Kinase Cs. The activity and subcellular location of PKCs are mediated by a series of tightly regulated events and is dependent on several posttranslational modifications and the availability of second messengers. Protein Kinase Cs exhibit both pro- and anti-tumorigenic effects making them an interesting target for anti-cancer treatment.

Transcriptome analysis on the inflammatory cell infiltration of nonalcoholic steatohepatitis in bama minipigs induced by a long-term high-fat, high-sucrose diet

Long-term adherence to a high-fat, high-calorie diet influences human health and causes obesity, metabolic syndrome and nonalcoholic steatohepatitis (NASH). Inflammation plays a key role in the development of NASH; however, the mechanism of inflammation induced by over-nutrition remains largely unknown. In this study, we fed Bama minipigs a high-fat, high-sucrose diet (HFHSD) for 23 months. The pigs exhibited characteristics of metabolic syndrome and developed steatohepatitis with greatly increased numbers of inflammatory cells, such as lymphocytes (2.27-fold, P<0.05), Kupffer cells (2.59-fold, P<0.05), eosinophils (1.42-fold, P<0.05) and neutrophils (2.77-fold, P<0.05). High-throughput RNA sequencing (RNA-seq) was performed to explore the systemic transcriptome of the pig liver during inflammation. Approximately 18.2 gigabases of raw sequence data were generated, and over 303 million high-quality reads were assembled into 21,126 unigenes. RNA-seq data analysis showed that 822 genes were differentially expressed in liver (P<0.05) between the HFHSD and control groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the process of inflammation involved the inflammatory signal transduction-related toll-like receptor, MAPK, and PPAR signaling pathways; the cytokine-related chemokine signaling, cytokine-cytokine receptor interaction, and IL2, IL4, IL6, and IL12 signaling pathways; the leukocyte receptor signaling-related T cell, B cell, and natural killer cell signaling pathways; inflammatory cell migration and invasion- related pathways; and other pathways. Moreover, we identified several differentially expressed inflammation-related genes between the two groups, including FOS, JUN, TLR7, MYC, PIK3CD, VAV3, IL2RB and IL4R, that could be potential targets for further investigation. Our study suggested that long-term HFHSD induced obesity and liver inflammation, providing basic insight into the molecular mechanism of this condition and laying the groundwork for further studies on obesity and steatohepatitis.

Protein kinase C inhibitors sensitize GNAQ mutant uveal melanoma cells to ionizing radiation

PURPOSE

Uveal melanoma (UM) tumors require large doses of radiation therapy (RT) to achieve tumor ablation, which frequently results in damage to adjacent normal tissues, leading to vision-threatening complications. Approximately 50% of UM patients present with activating somatic mutations in the gene encoding for G protein αq-subunit (GNAQ), which lead to constitutive activation of downstream pathways, including protein kinase C (PKC). In this study, we investigated the impact of small-molecule PKC inhibitors bisindolylmaleimide I (BIM) and sotrastaurin (AEB071), combined with ionizing radiation (IR), on survival in melanoma cell lines.

METHODS

Cellular radiosensitivity was determined by using a combination of proliferation, viability, and clonogenic assays. Cell-cycle effects were measured by flow cytometry. Transcriptomic and proteomic profiling were performed by quantitative real-time PCR, reverse-phase protein array analysis, and immunofluorescence.

RESULTS

We found that the PKC inhibitors combined with IR significantly decreased the viability, proliferation, and clonogenic potential of GNAQ(mt), but not GNAQ(wt)/BRAF(mt) cells, compared with IR alone. Combined treatment increased the antiproliferative and proapoptotic effects of IR in GNAQ(mt) cells through delayed DNA-damage resolution and enhanced induction of proteins involved in cell-cycle arrest, cell-growth arrest, and apoptosis.

CONCLUSIONS

Our preclinical results suggest that combined modality treatment may allow for reductions in the total RT dose and/or fraction size, which may lead to better functional organ preservation in the treatment of primary GNAQ(mt) UM. These findings suggest future clinical trials combining PKC inhibitors with RT in GNAQ(mt) UM warrant consideration.

Protein kinase C-α downregulates estrogen receptor-α by suppressing c-Jun phosphorylation in estrogen receptor-positive breast cancer cells

Protein kinase C (PKC) activity is elevated in malignant compared with that in normal human breast tissue. In the present study, we investigated the regulatory mechanism and the co-relationship between PKC-α and estrogen receptor-α (ER-α) in ER-α-positive and tamoxifen-resistant (TAMR) breast cancer cells. Our results showed that the level of ER-α expression was significantly decreased in TAMR when compared with that in tamoxifen-sensitive (TAMS) breast cancer cells. However, PKC-α phosphorylation was increased in TAMR breast cancer cells when compared to that in TAMS breast cancer cells. Additionally, ER-α expression was significantly decreased due to the overexpression of constitutively active PKC-α (CA-PKC-α). Next, we investigated the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA), a reversible activator of PKC, on ER-α expression in ER-α-positive breast cancer cells. TPA decreased the levels of ER-α expression in a time- and dose-dependent manner. In contrast, the TPA-induced downregulation of ER-α was prevented by Go6983, a specific PKC inhibitor. Notably, we found that CA-PKC-α suppressed c-JUN phosphorylation, which is a major activating protein-1 factor, and TPA-induced downregulation of ER-α was prevented by SR11302, a specific activator protein-1 inhibitor. Taken together, we demonstrated that PKC-α activity suppressed the level of ER-α expression by inhibiting c-JUN phosphorylation in ER-α-positive breast cancer cells. Therefore, we suggest that PKC-α may be a potential therapeutic target for treating ER-positive and TAMR breast cancer.

Suppression of 12-O-tetradecanoylphorbol-13-acetate-induced MCF-7 breast adenocarcinoma cells invasion/migration by α-tomatine through activating PKCα/ERK/NF-κB-dependent MMP-2/MMP-9 expressions

α-Tomatine, isolated from Lycopersicon esculentum Linn., is a naturally occurring glycoalkaloids in immature green tomatoes. Some reports demonstrated that α-tomatine had various anti-carcinogenic properties. First, the result demonstrated α-tomatine could inhibit TPA-induced the abilities of the adhesion, morphology/actin cytoskeleton arrangement, invasion, and migration by cell-matrix adhesion assay, immunofluorescence stain assay, Boyden chamber invasion assay, and wound-healing assay. Data also showed α-tomatine could inhibit the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and protein kinase C-α (PKCα) involved in the downregulation of the enzyme activities and messenger RNA levels of matrix metalloproteinase-2/9 (MMP-2/MMP-9) induced by TPA. Next, α-tomatine also strongly inhibited TPA-induced the activation of nuclear factor kappa B (NF-κB) and phospho-inhibitor of kappa Bα (phospho-IκBα). In addition, TPA-induced translocation of PKC-α from cytosol to membranes, and suppression of TPA elicited the expression of PKC-α by adding the PKC-α inhibitors, GF-109203X and Gö-6983. The treatment of specific inhibitor for ERK (U0126) to MCF-7 cells could inhibit TPA-induced MMP-2/MMP-9 and phospho-ERK along with an inhibition on cell invasion and migration. Application of α-tomatine to prevent the invasion/migration of MCF-7 cells through blocking PKCα/ERK/NF-κB activation is first demonstrated herein.

17Beta-estradiol promotes aggressive laryngeal cancer through membrane-associated estrogen receptor-alpha 36

17β-estradiol (E2) plays a key role in tumorigenesis by enhancing cell survivability and metastasis through its cytoplasmic receptors. Recently, a variant of estrogen receptor alpha, ERα36 has been implicated as a substantial mediator of E2's proliferative and antiapoptotic effects through rapid membrane-associated signaling, and cancers previously regarded as hormone-independent due to the absence of traditional receptors, may in fact be susceptible to E2. Despite rising from a secondary sex organ and having a clear gender disposition, laryngeal cancer is not uniformly accepted as hormone dependent, even in the face of compelling evidence of E2 responsiveness. The aim of this study was to further elucidate the role of E2 in the tumorigenesis of laryngeal cancer, both in vitro and in vivo. ERα36 presence was evaluated in membranes of the laryngeal carcinoma cell line, Hep2, as well as in laryngeal tumor samples. In vitro ERα36 was found to mediate rapid activation of protein kinase C and phospholipase D by E2, leading to increased proliferation and protection against chemotherapy-induced apoptosis. Furthermore, in response to E2 activation of ERα36, an upregulation of angiogenic and metastatic factors was observed. Clinical analysis of laryngeal tumors revealed a similar association between the amount of ERα36 and VEGF and indicated a role in lymph node metastasis. These findings present compelling evidence of ERα36-dependent E2 signaling in laryngeal cancer. Thus, targeting ERα36 may reduce the deleterious effects of E2 in laryngeal cancer, ultimately suggesting the importance of antiestrogen therapy or the production of novel drugs that specifically target ERα36.

HSF1-mediated regulation of tumor cell apoptosis: a novel target for cancer therapeutics

Programmed cell death/apoptosis is a genetically conserved phenomenon involved in many biological processes including reconstruction of multicellular organisms and elimination of old or damaged cells. It is regulated by the activation/deactivation of PKC in response to exogenous and endogenous stimuli. PKC is activated under stress by a series of downstream signaling cascades, which ultimately induce HSF1 activation, which results in overexpression of heat shock proteins. Overexpression of heat shock proteins interferes in the apoptotic pathway, while their blocking results in apoptosis. Therefore, HSF1 could be a novel therapeutic target against a variety of tumors. Several pharmacological inhibitors of PKC have been demonstrated to exert inhibitory effects on the activation of HSF1 and, therefore, induce apoptosis in tumor cells. However, studies regarding the role of pharmacological inhibitors in the regulation of apoptosis and possible anti-tumor therapeutic intervention are still unknown or in their infancy. Therefore, an attempt has been made to delineate the precise role of HSF1 in the regulation of apoptosis and its prospects in cancer therapeutics.

A silk fibroin based hepatocarcinoma model and the assessment of the drug response in hyaluronan-binding protein 1 overexpressed HepG2 cells

Microenvironment around tumor cells plays an important role in its malignancy or invasiveness. Hyaluronan (HA), a major component of extracellular matrix is found to be elevated in most of cancerous niche/microenvironment and performs regulatory role in the progression of tumors and metastasis. Overexpression of the hyaladherin, hyaluronan-binding protein 1 (HABP1) in the hepatocarcinoma cells (HepG2) termed as HepR21 leads to enhanced cell proliferation with increased HA 'pool' associated with HA 'cables' indicating elevated tumorous potential under 2D culture conditions. For in vitro experimentation, scaffold based three dimensional niche modeling may have greater acceptance than conventional 2D culture condition. Thus, we have examined the influence of intrinsic properties of non-mulberry tropical tasar silk fibroin on the HepR21 cells in order to develop a 3D hepatocarcinoma construction to act as model. The scaffold of tasar silk fibroin of Antheraea mylitta when efficiently loaded with transformed hepatocarcinoma cells, HepR21; exhibits enhanced adhesiveness, viability, metabolic activity, proliferation and enlarged cellular morphology in 3D compared to its parent cell line HepG2, supporting the earlier observation made in 2D system. In addition, formation of multicellular aggregates, the indicator of tumor progression is also revealed in silk based 3D culture conditions. Further, the use of 4-MU (a hyaluronan synthase inhibitor) on HepR21 cells reduces the HA level and downregulates the expression of growth promoting factors like pAKT and PKC; while upregulating the expression of the tumor suppressor p53. Thus, 4-MU efficiently reduces the tumor potency associated with increased HA pool as well as HA cables and the effect of 4-MU doubling up as an anticancer agent in 2D and 3D are also comparable. The in vitro 3D multicellular model demonstrates the insight of hepatocarcinoma progression and offers the predictability of cellular response to transfection efficacy, drug treatment and therapeutic intervention.

Synergy between enzastaurin doxorubicin in inducing melanoma apoptosis

Melanoma is resistant to most standard chemotherapeutics. We analysed the combined effect of doxorubicin and enzastaurin on cell death of four melanoma cell lines, namely G361, SK-MEL3, A375 and SAN. Enzastaurin IC50 was calculated by measure of growth inhibition with MTS assay and corresponded to 2 μM; the half maximal cytotoxicity of doxorubicin was obtained at 3 μM dose. Evaluation of combination index showed synergism (CI > 1) or additive effect (CI = 1) with all melanoma cell lines, with enzastaurin doses ≥0.6 μM and doxorubicin doses ≥1 μM. Combination of the two drugs resulted in increase in caspase 3 and 8 activation, in comparison with activation by single agents. Caspase 8 activation was impaired by TNFR-1 blocking. Our results show doxorubicin-stimulated production of TNFα, whereas enzastaurin-stimulated TNFR-1 expression on plasma membrane. The effect on TNFR-1 appeared to be mediated by PKCζ inhibition. Taken together, our findings suggest that enzastaurin increases doxorubicin-induced apoptosis of melanoma by a mechanism involving, at least in part, activation of the TNF-α signal.

The multifaceted effects of omega-3 polyunsaturated Fatty acids on the hallmarks of cancer

Omega-3 polyunsaturated fatty acids, in particular eicosapentaenoic acid, and docosahexaenoic acid have been shown to have multiple beneficial antitumour actions that affect the essential alterations that dictate malignant growth. In this review we explore the putative mechanisms of action of omega-3 polyunsaturated fatty acid in cancer protection in relation to self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, apoptosis, limitless replicative potential, sustained angiogenesis, and tissue invasion, and how these will hopefully translate from bench to bedside.

Direct effect of chenodeoxycholic acid on differentiation of mouse embryonic stem cells cultured under feeder-free culture conditions

Chenodeoxycholic acid (CDCA), a farnesoid X receptor (FXR) ligand, is a member of the nuclear receptor family and is probably involved in regulating the cellular activities of embryonic stem (ES) cells. Recently, although it was reported that the FXR ligand can mediate differentiation, apoptosis, and/or growth arrest in several cell types, it is still not well known how CDCA mediates effects in ES cells. Therefore, we investigated the direct effect of CDCA on mES cells. Feeder-free mES cells were treated in a dose-dependent manner with CDCA (50, 100, and 200 μM) for 72 h, and then a 100 μM CDCA treatment was performed for an additional 72 h. We analyzed the morphology, cell growth, cell characteristics, immunocytochemistry, and RT-PCR. In CDCA-treated cells, we observed the disappearance of pluripotent stem cell markers including alkaline phosphatase, Oct4, and Nanog and a time- and dose-dependent increase in expression of nestin, PAX6, and α-smooth muscle actin, but not α-fetoprotein. The 100 μM CDCA-treated cells in their second passage continued this differentiation pattern similar to those in the controls. In conclusion, these results suggest that CDCA can guide mES cells by an FXR-independent pathway to differentiate into ectoderm and/or mesoderm, but not endoderm.

Network analysis of the focal adhesion to invadopodia transition identifies a PI3K-PKCα invasive signaling axis

In cancer, deregulated signaling can produce an invasive cellular phenotype. We modeled the invasive transition as a theoretical switch between two cytoskeletal structures: focal adhesions and extracellular matrix-degrading invadopodia. We constructed molecular interaction networks of each structure and identified upstream regulatory hubs through computational analyses. We compared these regulatory hubs to the status of signaling components from head and neck carcinomas, which led us to analyze phosphatidylinositol 3-kinase (PI3K) and protein kinase C α (PKCα). Consistent with previous studies, PI3K activity promoted both the formation and the activity of invadopodia. We found that PI3K induction of invadopodia was increased by overexpression of SH2 (Src homology 2) domain-containing inositol 5'-phosphatase 2 (SHIP2), which converts the phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] that is produced by PI3K activity to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], which is believed to promote invadopodia formation. Knockdown of PKCα had divergent effects on invadopodia formation, depending on the status of PI3K. Loss of PKCα inhibited invadopodia formation in cells with wild-type PI3K pathway status. Conversely, in cells with constitutively active PI3K (through activating PI3K mutants or lacking the endogenous opposing enzyme PTEN), PKCα knockdown increased invadopodia formation. Mechanistic studies revealed a negative feedback loop from PKCα that dampened PI3K activity and invasive behavior in cells with genetic hyperactivation of the PI3K pathway. These studies demonstrated the potential of network modeling as a discovery tool and identified PI3K and PKCα as interacting regulators of invasive behavior.

The expression and role of non-canonical (PKC) signaling in nucleus pulposus cell metabolism

Canonical Wnt/β-catenin (hereafter Wnt) signaling regulates the proliferation and differentiation of various cell types. However, the role of non-canonical signaling including protein kinase C (PKC) signaling has not been investigated in intervertebral disc (IVD) cells. The aim of this study was to elucidate whether the activation of PKC signaling act to modulate Wnt signaling in IVD cells. We performed several reporter assays, real-time reverse transcription polymerase chain reaction (RT-PCR), immunohistochemical and immunofluorescence analyses, and western blot analyses using rat nucleus pulposus (NP) cells. We also examined the cell proliferation and cell cycle distribution under phorbol 12-myristate 13-acetate (PMA) stimulation, a known activator of PKC signaling. We found that NP cells exhibited decreased β-catenin mRNA and protein levels upon stimulation with PMA. PMA treatment promoted proliferation and cell cycle progression in a time- and dose-dependent manner. In addition, activation of the PKC signaling also regulated the expression of aggrecan. Finally, activation by PMA induced the expression of several PKC isoforms in NP cells. It is concluded that activation of PKC signaling might lead to an increase in matrix synthesis and cell proliferation, thereby inhibiting IVD degeneration. Crosstalk in these signaling pathways plays an important role in the regulation of IVD homeostasis.

Targeting sphingosine kinase 1 in carcinoma cells decreases proliferation and survival by compromising PKC activity and cytokinesis

Sphingosine kinases (SK) catalyze the phosphorylation of proapoptotic sphingosine to the prosurvival factor sphingosine 1-phosphate (S1P), thereby promoting oncogenic processes. Breast (MDA-MB-231), lung (NCI-H358), and colon (HCT 116) carcinoma cells were transduced with shRNA to downregulate SK-1 expression or treated with a pharmacologic SK-1 inhibitor. The effects of SK-1 targeting were investigated by measuring the level of intracellular sphingosine, the activity of protein kinase C (PKC) and cell cycle regulators, and the mitotic index. Functional assays included measurement of cell proliferation, colony formation, apoptosis, and cell cycle analysis. Downregulation of SK-1 or its pharmacologic inhibition increased intracellular sphingosine and decreased PKC activity as shown by reduced phosphorylation of PKC substrates. In MDA-MB-231 cells this effect was most pronounced and reduced cell proliferation and colony formation, which could be mimicked using exogenous sphingosine or the PKC inhibitor RO 31-8220. SK-1 downregulation in MDA-MB-231 cells increased the number of cells with 4N and 8N DNA content, and similar effects were observed upon treatment with sphingosine or inhibitors of SK-1 or PKC. Examination of cell cycle regulators unveiled decreased cdc2 activity and expression of Chk1, which may compromise spindle checkpoint function and cytokinesis. Indeed, SK-1 kd cells entered mitosis but failed to divide, and in the presence of taxol also failed to sustain mitotic arrest, resulting in further increased endoreduplication and apoptosis. Our findings delineate an intriguing link between SK-1, PKC and components of the cell cycle machinery, which underlines the significance of SK-1 as a target for cancer therapy.

Regulation of ADP-ribosylation factor 4 expression by small leucine zipper protein and involvement in breast cancer cell migration

ADP-ribosylation factor 4 (ARF4) is a member of the Ras superfamily of small guanine nucleotide-binding proteins. ARF4 is known to interact with the epidermal growth factor receptor (EGFR) and mediates the EGF-dependent signal pathway, and has an anti-apoptotic function in human glioblastoma-derived U373MG cells. Although ARF4 plays a role in cancer cells, the molecular mechanism underlying regulation of its expression and its exact functions in breast cancer are unknown. In this study, we investigated the regulatory mechanism of ARF4 expression and its involvement in breast cancer cell migration. Our results show that phorbol 12-myristate 13-acetate (PMA) treatment increases ARF4 expression at both the transcriptional and translational levels. We found that the novel transcription factor small leucine zipper protein (sLZIP) binds directly to the CRE motif of the -43 to -35 region in the ARF4 promoter and regulates PMA-induced ARF4 expression. We also found that PMA-stimulated ARF4 expression increases AP-1 promoter activity, leading to induction of breast cancer cell migration. These results indicate that sLZIP-regulated ARF4 expression in response to PMA is involved in breast cancer cell migration, and sLZIP and ARF4 are potential therapeutic target molecules for treating breast cancer invasion and metastasis.

Paracrine and endocrine effects of adipose tissue on cancer development and progression

The past few years have provided substantial evidence for the vital role of the local tumor microenvironment for various aspects of tumor progression. With obesity and its pathophysiological sequelae still on the rise, the adipocyte is increasingly moving center stage in the context of tumor stroma-related studies. To date, we have limited insight into how the systemic metabolic changes associated with obesity and the concomitant modification of the paracrine and endocrine panel of stromal adipocyte-derived secretory products ("adipokines") influence the incidence and progression of obesity-related cancers. Here, we discuss the role of adipocyte dysfunction associated with obesity and its potential impact on cancer biology.

PKC activator therapeutic for mild traumatic brain injury in mice

Traumatic brain injury (TBI) is a frequent consequence of vehicle, sport and war related injuries. More than 90% of TBI patients suffer mild injury (mTBI). However, the pathologies underlying the disease are poorly understood and treatment modalities are limited. We report here that in mice, the potent PKC activator bryostatin1 protects against mTBI induced learning and memory deficits and reduction in pre-synaptic synaptophysin and post-synaptic spinophylin immunostaining. An effective treatment has to start within the first 8h after injury, and includes 5 × i.p. injections over a period of 14 days. The treatment is dose dependent. Exploring the effects of the repeated bryostatin1 treatment on the processing of the amyloid precursor protein, we found that the treatment induced an increase in the putative α-secretase ADAM10 and a reduction in β-secretase activities. Both these effects could contribute towards a reduction in β-amyloid production. These results suggest that bryostatin1 protects against mTBI cognitive and synaptic sequela by rescuing synapses, which is possibly mediated by an increase in ADAM10 and a decrease in BACE1 activity. Since bryostatin1 has already been extensively used in clinical trials as an anti-cancer drug, its potential as a remedy for the short- and long-term TBI sequelae is quite promising.

24R,25-Dihydroxyvitamin D3, lysophosphatidic acid, and p53: a signaling axis in the inhibition of phosphate-induced chondrocyte apoptosis

Maintenance of the pool of chondrocytes in the resting zone of the growth plate in the presence of the physiological apoptogen inorganic phosphate (Pi) is crucial for skeletal development. Costochondral resting zone chondrocytes are regulated by the vitamin D metabolite 24R,25-dihydroxyvitamin D3 [24R,25(OH)(2)D(3)], with increased production of sulfated glycosaminoglycan-rich extracellular matrix, and reduced matrix metalloproteinase activity. The effects of 24R,25(OH)(2)D(3) are mediated by activation of phospholipase D (PLD), resulting in increased production of lysophosphatidic acid (LPA) and LPA-mediated proliferation, maturation, inhibition of Pi-induced apoptosis, and reduction of p53. However, the exact mechanism by which 24R,25(OH)(2)D(3) and LPA exert their effects is not fully understood. It was found that both 24R,25(OH)(2)D(3) and LPA attenuate Pi-induced caspase-3 activity. The actions of 24R,25(OH)(2)D(3) and LPA were dependent upon G(αi), LPA receptor(s) 1 and/or 3, PLD, phospholipase C (PLC), and intracellular calcium, phosphoinositide 3-kinase (PI(3)K) signaling, and nuclear export. 24R,25(OH)(2)D(3) decreased both p53 abundance and p53-medaited transcription and inhibited Pi-induced cytochrome c translocation. Moreover, LPA induced increased mdm2 phosphorylation, a negative regulator of p53. Taken together, these data show that 24R,25(OH)(2)D(3) inhibits Pi-induced apoptosis through Ca(2+), PLD, and PLC signaling and through LPA-LPA1/3-G(αi)-PI(3)K-mdm2-mediated p53 degradation, resulting in decreased cytochrome c translocation and caspase-3 activity.

Novel changes in NF-{kappa}B activity during progression and regression phases of hyperplasia: role of MEK, ERK, and p38

Utilizing the Citrobacter rodentium-induced transmissible murine colonic hyperplasia (TMCH) model, we measured hyperplasia and NF-κB activation during progression (days 6 and 12 post-infection) and regression (days 20-34 post-infection) phases of TMCH. NF-κB activity increased at progression in conjunction with bacterial attachment and translocation to the colonic crypts and decreased 40% by day 20. NF-κB activity at days 27 and 34, however, remained 2-3-fold higher than uninfected control. Expression of the downstream target gene CXCL-1/KC in the crypts correlated with NF-κB activation kinetics. Phosphorylation of cellular IκBα kinase (IKK)α/β (Ser(176/180)) was elevated during progression and regression of TMCH. Phosphorylation (Ser(32/36)) and degradation of IκBα, however, contributed to NF-κB activation only from days 6 to 20 but not at later time points. Phosphorylation of MEK1/2 (Ser(217/221)), ERK1/2 (Thr(202)/Tyr(204)), and p38 (Thr(180)/Tyr(182)) paralleled IKKα/β kinetics at days 6 and 12 without declining with regressing hyperplasia. siRNAs to MEK, ERK, and p38 significantly blocked NF-κB activity in vitro, whereas MEK1/2-inhibitor (PD98059) also blocked increases in MEK1/2, ERK1/2, and IKKα/β thereby inhibiting NF-κB activity in vivo. Cellular and nuclear levels of Ser(536)-phosphorylated (p65(536)) and Lys(310)-acetylated p65 subunit accompanied functional NF-κB activation during TMCH. RSK-1 phosphorylation at Thr(359)/Ser(363) in cellular/nuclear extracts and co-immunoprecipitation with cellular p65-NF-κB overlapped with p65(536) kinetics. Dietary pectin (6%) blocked NF-κB activity by blocking increases in p65 abundance and nuclear translocation thereby down-regulating CXCL-1/KC expression in the crypts. Thus, NF-κB activation persisted despite the lack of bacterial attachment to colonic mucosa beyond peak hyperplasia. The MEK/ERK/p38 pathway therefore seems to modulate sustained activation of NF-κB in colonic crypts in response to C. rodentium infection.

Oleic acid promotes MMP-9 secretion and invasion in breast cancer cells

Epidemiological and animal studies suggest an association between dietary fatty acids and an increase risk of developing breast cancer. Obesity, which is characterized by hyperlipidemia and an elevation of circulating free fatty acids (FFAs), is also associated with enhanced cancer risk. In breast cancer cells, the FFA oleic acid (OA) induces migration, proliferation, prolong survival, invasion, an increase in cellular Ca(2+) concentration, MEK1/2, ERK1/2, FAK and Src activation. However, the role of OA on MMP-9 secretion and invasion has not been studied in detail. We demonstrate here that stimulation of MDA-MB-231 breast cancer cells with 200 μM OA induces an increase on MMP-9 secretion through a PKC, Src, and EGFR-dependent pathway, as revealed by gelatin zymography assays. Furthermore, microtubule network mediates MMP-9 secretion induced by OA. In contrast, OA does not induce an increase on MMP-9 secretion in MCF10A cells, whereas it does not induce MMP-9 secretion in MCF12A mammary non-tumorigenic epithelial cells. In addition, OA induces invasion through an EGFR, Gi/Go proteins, MMPs, PKC and Src-dependent pathway, but it is not able to promote invasion in non-invasive MCF-7 breast cancer cells. In summary, our findings demonstrate that OA promotes an increase on MMP-9 secretion and invasion through a PKC, Src, and EGFR-dependent pathway in breast cancer cells.

Polyphenol-rich extracts from Solanum nigrum attenuated PKC alpha-mediated migration and invasion of hepatocellular carcinoma cells

Solanum nigrum L. (SN) has exhibited multiple biological effects such as anti-inflammation and antiproliferation. Protein kinase C (PKC) regulates cellular functions including proliferation, migration, and invasion. In the present investigation, we demonstrated that 12-o-tetradecanoylphobor-13-acetate (TPA) and constitutively activated PKC alpha significantly increased migration and invasion of HepG2 cells, while treatment with water or polyphenol extracts of SN (SNWE or SNPE) attenuated TPA-induced migration and invasion. SNWE and SNPE reduced TPA-elicited PKC alpha expression in a dose-dependent manner and obviously inhibited TPA-induced phosphorylation of p38 and ERK, respectively. Constitutively activated PKC alpha (caPKC alpha) significantly reversed the inhibitory effects of SNWE and SNPE on ERK and p38 activation. However, the antimigration effect of SNWE and SNPE could not be abrogated by caPKC alpha. Our results revealed the antimigration and anti-invasion effects of both extracts derived from SN, which may act as a promising therapeutic agent for the treatment of hepatocellular carcinoma.

Adhesion of renal carcinoma cells to endothelial cells depends on PKCmu

Background

The formation of metastases includes the separation of tumor cells from the primary tumor, cell migration into subendothelial tissue and cell proliferation in secondary organ. In this process, cell adhesion of tumor cells to the endothelium is an essential requirement for formation of metastases. Protein kinase C (PKC) regulates adhesion and proliferation. To identify a relation between PKC isoforms and tumor progression in renal cell carcinoma (RCC), the influence of PKC isoforms on cell adhesion and proliferation, and possible influences of integrins were analyzed in RCC cells.

Methods

The experiments were performed in the RCC cell lines CCF-RC1 and CCF-RC2 after pre-incubation (16 h) with the PKC inhibitors GF109203X (inhibits PKCα, βI, βII, γ, δ and ε), GÖ6976 (inhibits PKCα, βI and μ), RO31-8220 (inhibits PKCα, βI, βII, γ and ε) and rottlerin (inhibits PKCδ). Cell adhesion was assessed through adherence of RCC cells to an endothelial monolayer. Cell proliferation was analyzed by a BrdU incorporation assay. The expression of β1 integrins was analyzed by flow cytometry.

Results

In CCF-RC1 cells, cell adhesion was significantly reduced by GÖ6976 to 55% and by RO31-8220 to 45% of control. In CCF-RC2 cells, only GÖ6976 induced a significant reduction of cell adhesion to 50% of control levels. Proliferation of both cell lines was reduced by rottlerin to 39% and 45% of control, respectively. The β1 integrin expression on the cell surface of CCF-RC1 and CCR-RC2 cells was decreased by RO31-8220 to 8% and 7% of control, respectively. β2 and β3 integrins were undetectable in both cell lines.

Conclusions

The combination of the PKC inhibitors leads to the assumption that PKCμ influences cell adhesion in CCF-RC1 and CCF-RC2 cells, whereas in CCF-RC1 cells PKCε also seems to be involved in this process. The expression of β1 integrins appears to be regulated in particular by PKCε. Cell proliferation was inhibited by rottlerin, so that PKCδ might be involved in cell proliferation in these cells.

Polar 3-alkylidene-5-pivaloyloxymethyl-5'-hydroxymethyl-gamma-lactones as protein kinase C ligands and antitumor agents

A series of DAG-lactones with polar 3-alkylidene substituents have been investigated as PKC-alpha ligands and antitumor agents. Extensive analysis of structure-activity relationships for the 3-alkylidene chain revealed that polar groups such as ether, hydroxyl, aldehyde, ester, acyloxy, and amido were tolerated with similar binding affinities and reduced lipophilicities compared to the corresponding unsubstituted alkylidene chain. Among the derivatives, compounds 5, 6 and 8 with an ether type of side chain showed high binding affinities in range of K(i)= 3-5 nM and excellent antitumor profiles, particularly against the colo205 colon cancer and the K562 leukemia cell lines.

Plasma protein kinase C (PKC)alpha as a biomarker for the diagnosis of cancers

Protein kinase C (PKC)alpha plays a key role in the differentiation, proliferation and apoptosis of cancer cells, and its activity is higher in cancer cells than in normal cells. In the present study, we investigated the existence of activated PKCalpha in plasma and its possibility for cancer diagnosis. Plasma samples were prepared from xenograft mouse models of cancer and from normal mice. Phosphorylation ratios for a PKCalpha-specific peptide substrate (Alphatomega) were analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and activated PKCalpha was identified by western blot analysis. Increased levels of activated PKCalpha were found in the plasma of cancer-bearing mice (U87, A549, A431, HuH-7 and B16 melanoma) compared with the levels found in control mice. Phosphorylation ratios for peptide substrate increased with an increase in tumor size. Moreover, the addition of Ro-31-7549, a highly specific inhibitor of PKCalpha, produced a concentration-dependent reduction of phosphorylation ratios, whereas the non-PKCalpha inhibitors, rottlerin and H-89, did not significantly effect phosphorylation ratios. In addition, the level of activated PKCalpha decreased after cancer resection but increased if the cancer recurred. From these results, we suggest that (i) activated PKCalpha in plasma can be a useful biomarker for the diagnosis of cancers and (ii) the level of activated PKCalpha can be monitored to assess the recurrence of cancer after surgical removal. To our knowledge, this is the first report demonstrating the existence of activated PKCalpha in plasma and its possibility for cancer diagnosis.

Tamoxifen inhibits tumor cell invasion and metastasis in mouse melanoma through suppression of PKC/MEK/ERK and PKC/PI3K/Akt pathways

In melanoma, several signaling pathways are constitutively activated. Among these, the protein kinase C (PKC) signaling pathways are activated through multiple signal transduction molecules and appear to play major roles in melanoma progression. Recently, it has been reported that tamoxifen, an anti-estrogen reagent, inhibits PKC signaling in estrogen-negative and estrogen-independent cancer cell lines. Thus, we investigated whether tamoxifen inhibited tumor cell invasion and metastasis in mouse melanoma cell line B16BL6. Tamoxifen significantly inhibited lung metastasis, cell migration, and invasion at concentrations that did not show anti-proliferative effects on B16BL6 cells. Tamoxifen also inhibited the mRNA expressions and protein activities of matrix metalloproteinases (MMPs). Furthermore, tamoxifen suppressed phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt through the inhibition of PKCalpha and PKCdelta phosphorylation. However, other signal transduction factor, such as p38 mitogen-activated protein kinase (p38MAPK) was unaffected. The results indicate that tamoxifen suppresses the PKC/mitogen-activated protein kinase kinase (MEK)/ERK and PKC/phosphatidylinositol-3 kinase (PI3K)/Akt pathways, thereby inhibiting B16BL6 cell migration, invasion, and metastasis. Moreover, tamoxifen markedly inhibited not only developing but also clinically evident metastasis. These findings suggest that tamoxifen has potential clinical applications for the treatment of tumor cell metastasis.

Transcription of the protein kinase C-delta gene is activated by JNK through c-Jun and ATF2 in response to the anticancer agent doxorubicin

Expression of protein kinase C-delta (PKCdelta) is up-regulated by apoptosis-inducing stimuli. However, very little is known about the signaling pathways that control PKCdelta gene transcription. In the present study, we demonstrate that JNK stimulates PKCdelta gene expression via c-Jun and ATF2 in response to the anticancer agent doxorubicin (DXR) in mouse lymphocytic leukemia L1210 cells. Luciferase reporter assays showed that DXR-induced activation of the PKCdelta promoter was enhanced by ectopic expression of JNK1, c-Jun, or ATF2, whereas it was strongly reduced by expression of dominant negative JNK1 or by treatment with the JNK inhibitor SP600125. Furthermore, point mutations in the core sequence of the c-Jun/ATF2 binding site suppressed DXR-induced activation of the PKCdelta promoter. Our results suggest an additional role for a JNK signaling cascade in DXR-induced PKCdelta gene expression.

Protein kinases C isozymes are differentially expressed in human breast carcinomas

AIMS

The protein kinase C (PKC) family of enzymes has been implicated in cellular proliferation, differentiation, and apoptosis. However, the distribution of specific PKC isoforms with varying functions in normal and malignant human tissues remains to be determined. The objective of this study was to investigate the expression of certain PKC isoforms (alpha, betaI, betaII, epsilon) in human breast cancer specimens relative to adjacent uninvolved tissue (n=24) and in the normal breast tissue obtained from patients undergoing reduction mammoplasty (n=12).

MAIN METHODS

Western blot analysis using PKC isoform specific antibodies was performed on tissue extracts from breast tumors, adjacent uninvolved tissues, and reduction mammoplasty tissues.

KEY FINDINGS

Mean levels of cytosolic and membrane PKC-alpha, PKC-betaI, and PKC-betaII were significantly higher in the cancer specimens than in the adjacent uninvolved breast tissues (Wilcoxon signed-ranks test; P<0.05 for each, after adjustment for multiple comparisons). There was a notably higher mean level of membrane PKC-betaII isozyme in Her-2 positive and in poorly differentiated tumors. No significant differences were observed when normal tissue adjacent to tumor was compared to breast tissue obtained from reduction mammoplasty specimens.

SIGNIFICANCE

Higher level of PKC-alpha, PKC-betaI, and PKC-betaII in cancer specimens and higher level of PKC-betaII in Her-2 positive tumors require further exploration of the intracellular pathways involving PKC-alpha and -beta isoforms in breast cancer because both could be specific targets for the development of new therapies and for the prevention and treatment of this disease.

PKCalpha activation downregulates ATM and radio-sensitizes androgen-sensitive human prostate cancer cells in vitro and in vivo

We previously demonstrated that treatment of human androgen-responsive prostate cancer cell lines LNCaP and CWR22-Rv1 with 12-O-tetradecanoylphorbol 13-acetate (TPA), a known protein kinase C (PKC) activator, decreases ATM protein levels, thus de-repressing the enzyme ceramide synthase (CS) and promoting apoptosis as well as radio-sensitizing these cells.(1) Here we show that PKCalpha mediates the TPA effect on ATM expression, since ATM suppression and apoptosis induced by either TPA or diacylglycerol-lactone (DAG-lactone), both inducing PKCalpha activation,(2) are abrogated in LNCaP cells following transfection of a kinase-dead PKCalpha mutant (KD-PKCalpha). Similarly, KD-PKCalpha blocks the apoptotic response elicited by combination of TPA and radiation, whereas expression of constitutively active PKCalpha is sufficient to sensitize cells to radiation alone, without a need to pre-treat the cells with TPA. These findings identify CS activation as a downstream event of PKCalpha activity in LNCaP cells. Similar results were obtained in CWR22-Rv1 cells with DAG-lactone treatment. Using the LNCaP orthotopic prostate model it is shown that treatment with TPA or DAG-lactone induces significant reduction in tumor ATM levels coupled with tumor growth delay. Furthermore, while fractionated radiation alone produces significant tumor growth delay, pretreatment with TPA or DAG-lactone significantly potentiates tumor cure. These findings support a model in which activation of PKCalpha downregulates ATM, thus relieving CS repression by ATM and enhancing apoptosis via ceramide generation. This model may provide a basis for the design of new therapies in prostate cancer.