Genomic structure and promoter analysis of PKC-delta

PKCδ deficiency inhibits fetal development and is associated with heart elastic fiber hyperplasia and lung inflammation in adult PKCδ knockout mice

Protein kinase C-delta (PKCδ) has a caspase-3 recognition sequence in its structure, suggesting its involvement in apoptosis. In addition, PKCδ was recently reported to function as an anti-cancer factor. The generation of a PKCδ knockout mouse model indicated that PKCδ plays a role in B cell homeostasis. However, the Pkcrd gene, which is regulated through complex transcription, produces multiple proteins via alternative splicing. Since gene mutations can result in the loss of function of molecular species required for each tissue, in the present study, conditional PKCδ knockout mice lacking PKCδI, II, IV, V, VI, and VII were generated to enable tissue-specific deletion of PKCδ using a suitable Cre mouse. We generated PKCδ-null mice that lacked whole-body expression of PKCδ. PKCδ+/- parental mice gave birth to only 3.4% PKCδ-/- offsprings that deviated significantly from the expected Mendelian ratio (χ2(2) = 101.7, P < 0.001). Examination of mice on embryonic day 11.5 (E11.5) showed the proportion of PKCδ-/- mice implanted in the uterus in accordance with Mendelian rules; however, approximately 70% of the fetuses did not survive at E11.5. PKCδ-/- mice that survived until adulthood showed enlarged spleens, with some having cardiac and pulmonary abnormalities. Our findings suggest that the lack of PKCδ may have harmful effects on fetal development, and heart and lung functions after birth. Furthermore, our study provides a reference for future studies on PKCδ deficient mice that would elucidate the effects of the multiple protein variants in mice and decipher the roles of PKCδ in various diseases.

A systems biology framework integrating GWAS and RNA-seq to shed light on the molecular basis of sperm quality in swine

BACKGROUND

Genetic pressure in animal breeding is sparking the interest of breeders for selecting elite boars with higher sperm quality to optimize ejaculate doses and fertility rates. However, the molecular basis of sperm quality is not yet fully understood. Our aim was to identify candidate genes, pathways and DNA variants associated to sperm quality in swine by analysing 25 sperm-related phenotypes and integrating genome-wide association studies (GWAS) and RNA-seq under a systems biology framework.

RESULTS

By GWAS, we identified 12 quantitative trait loci (QTL) associated to the percentage of head and neck abnormalities, abnormal acrosomes and motile spermatozoa. Candidate genes included CHD2, KATNAL2, SLC14A2 and ABCA1. By RNA-seq, we identified a wide repertoire of mRNAs (e.g. PRM1, OAZ3, DNAJB8, TPPP2 and TNP1) and miRNAs (e.g. ssc-miR-30d, ssc-miR-34c, ssc-miR-30c-5p, ssc-miR-191, members of the let-7 family and ssc-miR-425-5p) with functions related to sperm biology. We detected 6128 significant correlations (P-value ≤ 0.05) between sperm traits and mRNA abundances. By expression (e)GWAS, we identified three trans-expression QTL involving the genes IQCJ, ACTR2 and HARS. Using the GWAS and RNA-seq data, we built a gene interaction network. We considered that the genes and interactions that were present in both the GWAS and RNA-seq networks had a higher probability of being actually involved in sperm quality and used them to build a robust gene interaction network. In addition, in the final network we included genes with RNA abundances correlated with more than four semen traits and miRNAs interacting with the genes on the network. The final network was enriched for genes involved in gamete generation and development, meiotic cell cycle, DNA repair or embryo implantation. Finally, we designed a panel of 73 SNPs based on the GWAS, eGWAS and final network data, that explains between 5% (for sperm cell concentration) and 36% (for percentage of neck abnormalities) of the phenotypic variance of the sperm traits.

CONCLUSIONS

By applying a systems biology approach, we identified genes that potentially affect sperm quality and constructed a SNP panel that explains a substantial part of the phenotypic variance for semen quality in our study and that should be tested in other swine populations to evaluate its relevance for the pig breeding sector.

Cell Type-Specific Roles of NF-κB Linking Inflammation and Thrombosis

The transcription factor NF-κB is a central mediator of inflammation with multiple links to thrombotic processes. In this review, we focus on the role of NF-κB signaling in cell types within the vasculature and the circulation that are involved in thrombo-inflammatory processes. All these cells express NF-κB, which mediates important functions in cellular interactions, cell survival and differentiation, as well as expression of cytokines, chemokines, and coagulation factors. Even platelets, as anucleated cells, contain NF-κB family members and their corresponding signaling molecules, which are involved in platelet activation, as well as secondary feedback circuits. The response of endothelial cells to inflammation and NF-κB activation is characterized by the induction of adhesion molecules promoting binding and transmigration of leukocytes, while simultaneously increasing their thrombogenic potential. Paracrine signaling from endothelial cells activates NF-κB in vascular smooth muscle cells and causes a phenotypic switch to a “synthetic” state associated with a decrease in contractile proteins. Monocytes react to inflammatory situations with enforced expression of tissue factor and after differentiation to macrophages with altered polarization. Neutrophils respond with an extension of their life span—and upon full activation they can expel their DNA thereby forming so-called neutrophil extracellular traps (NETs), which exert antibacterial functions, but also induce a strong coagulatory response. This may cause formation of microthrombi that are important for the immobilization of pathogens, a process designated as immunothrombosis. However, deregulation of the complex cellular links between inflammation and thrombosis by unrestrained NET formation or the loss of the endothelial layer due to mechanical rupture or erosion can result in rapid activation and aggregation of platelets and the manifestation of thrombo-inflammatory diseases. Sepsis is an important example of such a disorder caused by a dysregulated host response to infection finally leading to severe coagulopathies. NF-κB is critically involved in these pathophysiological processes as it induces both inflammatory and thrombotic responses.

NF-κB transcription factor role in consolidation and reconsolidation of persistent memories

Transcriptional regulation is an important molecular process required for long-term neural plasticity and long-term memory (LTM) formation. Thus, one main interest in molecular neuroscience in the last decades has been the identification of transcription factors that are involved in memory processes. Among them, the nuclear factor κB (NF-κB) family of transcription factors has gained interest due to a significant body of evidence that supports a key role of these proteins in synaptic plasticity and memory. In recent years, the interest was particularly reinforced because NF-κB was characterized as an important regulator of synaptogenesis. This function may be explained by its participation in synapse to nucleus communication, as well as a possible local role at the synapse. This review provides an overview of experimental work obtained in the last years, showing the essential role of this transcription factor in memory processes in different learning tasks in mammals. We focus the review on the consolidation and reconsolidation memory phases as well as on the regulation of immediate-early and late genes by epigenetic mechanisms that determine enduring forms of memories.

Genome-wide association study for semen volume and total number of sperm in Holstein-Friesian bulls

In artificial insemination industry bulls producing high volume of semen with relatively high concentration of sperm are very desirable since they ensure stable production of commercial straws especially in case of top bulls. The aim of the study was to screen the entire bull genome to identify markers and candidate genes underlying semen volume (SV) and total number of sperm (TNS) in ejaculate produced by Holstein-Friesian bulls. Data on semen production were retrieved from records of AI center and included a population of 877 Holstein-Friesian bulls. Each bull was genotyped using the Illumina BovineSNP50 BeadChip. Genome-wide association analysis was performed with the use of GoldenHelix SVS7 software. An additive model for Linear Regression Analysis was used to estimate the effect of SNP marker for SV and TNS. After Bonferroni correction, 3 markers located on chromosome 22 reached the highest significance (rs41625599, rs41584616, rs42012507) for both traits. In the vicinity of these significant markers 3 genes are located (DCP1A, SFMBT1, TMEM110). Moreover, marker rs110109069 located on chromosome 25 was significantly associated with TNS and marker rs42438348 located on chromosome 10 has been found to be associated with SV. Some additional candidate genes were suggested to be potentially involved in analyzed traits (GALC, PRKCD, PHF7, TLR9, SPATA7). Identifying SNPs associated with the lower total number of sperm may be very useful for early recognition of a young sire as less suitable for effective semen production in artificial insemination centers.

Histone hyperacetylation up-regulates protein kinase Cδ in dopaminergic neurons to induce cell death: relevance to epigenetic mechanisms of neurodegeneration in Parkinson disease

The oxidative stress-sensitive protein kinase Cδ (PKCδ) has been implicated in dopaminergic neuronal cell death. However, little is known about the epigenetic mechanisms regulating PKCδ expression in neurons. Here, we report a novel mechanism by which the PKCδ gene can be regulated by histone acetylation. Treatment with histone deacetylase (HDAC) inhibitor sodium butyrate (NaBu) induced PKCδ expression in cultured neurons, brain slices, and animal models. Several other HDAC inhibitors also mimicked NaBu. The chromatin immunoprecipitation analysis revealed that hyperacetylation of histone H4 by NaBu is associated with the PKCδ promoter. Deletion analysis of the PKCδ promoter mapped the NaBu-responsive element to an 81-bp minimal promoter region. Detailed mutagenesis studies within this region revealed that four GC boxes conferred hyperacetylation-induced PKCδ promoter activation. Cotransfection experiments and Sp inhibitor studies demonstrated that Sp1, Sp3, and Sp4 regulated NaBu-induced PKCδ up-regulation. However, NaBu did not alter the DNA binding activities of Sp proteins or their expression. Interestingly, a one-hybrid analysis revealed that NaBu enhanced transcriptional activity of Sp1/Sp3. Overexpression of the p300/cAMP-response element-binding protein-binding protein (CBP) potentiated the NaBu-mediated transactivation potential of Sp1/Sp3, but expressing several HDACs attenuated this effect, suggesting that p300/CBP and HDACs act as coactivators or corepressors in histone acetylation-induced PKCδ up-regulation. Finally, using genetic and pharmacological approaches, we showed that NaBu up-regulation of PKCδ sensitizes neurons to cell death in a human dopaminergic cell model and brain slice cultures. Together, these results indicate that histone acetylation regulates PKCδ expression to augment nigrostriatal dopaminergic cell death, which could contribute to the progressive neuropathogenesis of Parkinson disease.

CAP37 activation of PKC promotes human corneal epithelial cell chemotaxis

PURPOSE

The objective of this study was to elucidate the signaling pathway through which cationic antimicrobial protein of 37 kDa (CAP37) mediates human corneal epithelial cell (HCEC) chemotaxis.

METHODS

Immortalized HCECs were treated with pertussis toxin (10 and 1000 ng/mL), protein kinase C (PKC) inhibitors (calphostin c, 50 nM and Ro-31-8220, 100 nM), phorbol esters (phorbol 12,13-dibutyrate, 200 nM and phorbol 12-myristate 13-acetate, 1 μM) known to deplete PKC isoforms, and siRNAs (400 nM) before a modified Boyden chamber assay was used to determine the effect of these inhibitors and siRNAs on CAP37-directed HCEC migration. PKCδ protein levels, PKCδ-Thr(505) phosphorylation, and PKCδ kinase activity was assessed in CAP37-treated HCECs using immunohistochemistry, Western blotting, and a kinase activity assay, respectively.

RESULTS

Chemotaxis studies revealed that treatment with pertussis toxin, PKC inhibitors, phorbol esters, and siRNAs significantly inhibited CAP37-mediated chemotaxis compared with untreated controls. CAP37 treatment increased PKCδ protein levels and led to PKCδ phosphorylation on residue Thr(505). Direct activation of PKCδ by CAP37 was demonstrated using a kinase activity assay.

CONCLUSIONS

These findings lead us to conclude that CAP37 is an important regulator of corneal epithelial cell migration and mediates its effects through PKCδ.

Multiple facets of NF-κB in the heart: to be or not to NF-κB

The progression from cardiac injury to symptomatic heart failure has been intensely studied over the last decade, and is largely attributable to a loss of functional cardiac myocytes through necrosis, intrinsic and extrinsic apoptosis pathways and autophagy. Therefore, the molecular regulation of these cellular programs has been rigorously investigated in the hopes of identifying a potential cell target that could promote cell survival and/or inhibit cell death to avert, or at least prolong, the degeneration toward symptomatic heart failure. The nuclear factor (NF)-κB super family of transcription factors has been implicated in the regulation of immune cell maturation, cell survival, and inflammation in many cell types, including cardiac myocytes. Recent studies have shown that NF-κB is cardioprotective during acute hypoxia and reperfusion injury. However, prolonged activation of NF-κB appears to be detrimental and promotes heart failure by eliciting signals that trigger chronic inflammation through enhanced elaboration of cytokines including tumor necrosis factor α, interleukin-1, and interleukin-6, leading to endoplasmic reticulum stress responses and cell death. The underlying mechanisms that account for the multifaceted and differential outcomes of NF-κB on cardiac cell fate are presently unknown. Herein, we posit a novel paradigm in which the timing, duration of activation, and cellular context may explain mechanistically the differential outcomes of NF-κB signaling in the heart that may be essential for future development of novel therapeutic interventions designed to target NF-κB responses and heart failure following myocardial injury.

Transcriptional regulation of pro-apoptotic protein kinase Cdelta: implications for oxidative stress-induced neuronal cell death

We previously demonstrated that protein kinase Cδ (PKCδ; PKC delta) is an oxidative stress-sensitive kinase that plays a causal role in apoptotic cell death in neuronal cells. Although PKCδ activation has been extensively studied, relatively little is known about the molecular mechanisms controlling PKCδ expression. To characterize the regulation of PKCδ expression, we cloned an ∼2-kbp 5'-promoter segment of the mouse Prkcd gene. Deletion analysis indicated that the noncoding exon 1 region contained multiple Sp sites, including four GC boxes and one CACCC box, which directed the highest levels of transcription in neuronal cells. In addition, an upstream regulatory region containing adjacent repressive and anti-repressive elements with opposing regulatory activities was identified within the region -712 to -560. Detailed mutagenesis studies revealed that each Sp site made a positive contribution to PKCδ promoter expression. Overexpression of Sp family proteins markedly stimulated PKCδ promoter activity without any synergistic transactivating effect. Furthermore, experiments in Sp-deficient SL2 cells indicated long isoform Sp3 as the essential activator of PKCδ transcription. Importantly, both PKCδ promoter activity and endogenous PKCδ expression in NIE115 cells and primary striatal cultures were inhibited by mithramycin A. The results from chromatin immunoprecipitation and gel shift assays further confirmed the functional binding of Sp proteins to the PKCδ promoter. Additionally, we demonstrated that overexpression of p300 or CREB-binding protein increases the PKCδ promoter activity. This stimulatory effect requires intact Sp-binding sites and is independent of p300 histone acetyltransferase activity. Finally, modulation of Sp transcriptional activity or protein level profoundly altered the cell death induced by oxidative insult, demonstrating the functional significance of Sp-dependent PKCδ gene expression. Collectively, our findings may have implications for development of new translational strategies against oxidative damage.

α-Synuclein negatively regulates protein kinase Cδ expression to suppress apoptosis in dopaminergic neurons by reducing p300 histone acetyltransferase activity

We recently demonstrated that protein kinase Cδ (PKCδ), an important member of the novel PKC family, is a key oxidative stress-sensitive kinase that can be activated by caspase-3-dependent proteolytic cleavage to induce dopaminergic neuronal cell death. We now report a novel association between α-synuclein (αsyn), a protein associated with the pathogenesis of Parkinson's disease, and PKCδ, in which αsyn negatively modulates the p300- and nuclear factor-κB (NFκB)-dependent transactivation to downregulate proapoptotic kinase PKCδ expression and thereby protects against apoptosis in dopaminergic neuronal cells. Stable expression of human wild-type αsyn at physiological levels in dopaminergic neuronal cells resulted in an isoform-dependent transcriptional suppression of PKCδ expression without changes in the stability of mRNA and protein or DNA methylation. The reduction in PKCδ transcription was mediated, in part, through the suppression of constitutive NFκB activity targeted at two proximal PKCδ promoter κB sites. This occurred independently of NFκB/IκBα (inhibitor of κBα) nuclear translocation but was associated with decreased NFκB-p65 acetylation. Also, αsyn reduced p300 levels and its HAT (histone acetyltransferase) activity, thereby contributing to diminished PKCδ transactivation. Importantly, reduced PKCδ and p300 expression also were observed within nigral dopaminergic neurons in αsyn-transgenic mice. These findings expand the role of αsyn in neuroprotection by modulating the expression of the key proapoptotic kinase PKCδ in dopaminergic neurons.

All-trans retinoic acid and a novel synthetic retinoid tamibarotene (Am80) differentially regulate CD38 expression in human leukemia HL-60 cells: possible involvement of protein kinase C-delta

ATRA and a synthetic RAR agonist tamibarotene (Am80) induce granulocytic differentiation of human acute leukemia HL-60 cells and have been used in antineoplastic therapy. ATRA induces CD38 antigen during HL-60 cell differentiation, which interacts with CD31 antigen on the vascular EC surface and may induce disadvantages in the therapy. We here examined the mechanisms of the ATRA-mediated CD38 induction and compared the difference between ATRA- and tamibarotene-mediated induction. Tamibarotene-induced HL-60 cell adhesion to ECs was 38% lower than ATRA, and NB4 cell adhesion to ECs by tamibarotene was equivalent to ATRA, which induced CD38 gene transcription biphasically in HL-60 cells, the early-phase induction via DR-RARE containing intron 1, and the delayed-phase induction via RARE lacking the 5'-flanking region. In contrast to ATRA, tamibarotene induced only the early-phase induction, resulting in its lower CD38 induction than ATRA. A PKCδ inhibitor, rottlerin, and siRNA-mediated PKCδ knockdown suppressed the ATRA-induced CD38 promoter activity of the 5'-flanking region, whereas a RAR antagonist, LE540, or RAR knockdown did not affect it. Cycloheximide and rottlerin suppressed the delayed-phase induction of CD38 expression by ATRA but did not affect the early-phase induction. Moreover, ATRA, but not tamibarotene, induced PKCδ expression without affecting its mRNA stability. The diminished effect of tamibarotene on CD38-mediated HL-60 cell adhesion to ECs compared with ATRA is likely a result of the lack of its delayed-phase induction of CD38 expression, which may be advantageous in antineoplastic therapy.

Protein kinase C: an attractive target for cancer therapy

Apoptosis plays an important role during all stages of carcinogenesis and the development of chemoresistance in tumor cells may be due to their selective defects in the intracellular signaling proteins, central to apoptotic pathways. Consequently, many studies have focused on rendering the chemotherapy more effective in order to prevent chemoresistance and pre-clinical and clinical data has suggested that protein kinase C (PKC) may represent an attractive target for cancer therapy. Therefore, a complete understanding of how PKC regulates apoptosis and chemoresistance may lead to obtaining a PKC-based therapy that is able to reduce drug dosages and to prevent the development of chemoresistance.

Loss of protein kinase C delta gene expression in human squamous cell carcinomas: a laser capture microdissection study

Protein kinase C delta (PKC-delta) protein levels are frequently low in chemically and UV-induced mouse skin tumors as well as in human cutaneous squamous cell carcinomas (SCCs). Furthermore, overexpression of PKC-delta in human SCC lines and mouse epidermis is sufficient to induce apoptosis and suppress tumorigenicity, making PKC-delta a potential tumor suppressor gene for SCCs. Here we report that PKC-delta is lost in human SCCs at the transcriptional level. We used laser capture microdissection to isolate cells from three normal human epidermis and 14 human SCCs with low PKC-delta protein. Analysis by quantitative reverse transcription-PCR revealed that PKC-delta RNA was reduced an average of 90% in the SCCs tested, consistent with PKC-delta down-regulation at the protein level. Analysis of DNA from nine of the same tumors revealed that PKC-delta gene was deleted in only one tumor. In addition, Ras-transformed human keratinocytes, which have selective down-regulation of PKC-delta at both protein and mRNA levels, had significantly repressed human PKC-delta promoter activity. Together, these results indicate that PKC-delta gene expression is suppressed in human SCCs, probably via transcription repression. Our results have implications for the development of topical therapeutic strategies to trigger the re-expression of pro-apoptotic PKC-delta to induce apoptosis in SCCs.

PKCdelta regulates cortical radial migration by stabilizing the Cdk5 activator p35

Cyclin-dependent kinase 5 (Cdk5) and its activator p35 are critical for radial migration and lamination of cortical neurons. However, how this kinase is regulated by extracellular and intracellular signals during cortical morphogenesis remains unclear. Here, we show that PKCdelta, a member of novel PKC expressing in cortical neurons, could stabilize p35 by direct phosphorylation. PKCdelta attenuated the degradation of p35 but not its mutant derivative, which could not be phosphorylated by PKCdelta. Down-regulation of PKCdelta by in utero electroporation of specific small interference RNA (siRNA) severely impaired the radial migration of cortical neurons. This migration defect was similar to that caused by down-regulation of p35 and could be prevented by cotransfection with the wild-type but not the mutant p35. Furthermore, PKCdelta could be activated by the promigratory factor brain-derived neurotrophic factor (BDNF) and was required for the activation of Cdk5 by BDNF. Both PKCdelta and p35 were required for the promigratory effect of BDNF on cultured newborn neurons. Thus, PKCdelta may promote cortical radial migration through maintaining the proper level of p35 in newborn neurons.

Enhancement of Radiation-induced Apoptosis by 6-Formylpterin

Radiation-induced apoptosis and its possible enhancement in the presence of 6-formylpterin (6-FP), a metabolite of folic acid, were examined in human myelomonocytic lymphoma U937 cells. When cells were treated with 6-FP at a nontoxic concentration of 300 microM, and then exposed to X-rays at a dose of 10 Gy, significant enhancement of radiation-induced apoptosis as determined by nuclear morphological change, phosphatidylserine (PS) externalization and DNA fragmentation were observed. Flow cytometry for the detection of intracellular hydrogen peroxide (H2O2) revealed that 6-FP increased the formation of intracellular H2O2, which further increased when the cells were irradiated. Decrease of mitochondria trans-membrane potential (MMP), release of cytochrome c from mitochondria, and activation of caspase-3 were enhanced after the combined treatment. Remarkable activation of protein kinase C delta (PKC delta) and its translocation from cytosol to mitochondria were detected in combined treatment. Increase of intracellular Ca2+ concentrations ([Ca2+]i) was also observed, however, neither calpain I nor calpain II could inhibit the apoptosis. In addition, c-Jun NH2-terminal kinase (JNK) activation was not enhanced in the combined treatment. A protein involved in a caspase-independent apoptosis pathway, apoptosis inducing factor (AIF), remained unchanged even 3 h after treatment. These results indicate that intracellular H2O2 generated by 6-FP enhances radiation-induced apoptosis via the mitochondria-mediated caspase-dependent pathway, with the active involvement of PKC delta.

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.

A feed-forward loop involving protein kinase Calpha and microRNAs regulates tumor cell cycle

Protein kinase Calpha (PKCalpha) has been implicated in cancer, but the mechanism is largely unknown. Here, we show that PKCalpha promotes head and neck squamous cell carcinoma (SCCHN) by a feed-forward network leading to cell cycle deregulation. PKCalpha inhibitors decrease proliferation in SCCHN cell lines and xenografted tumors. PKCalpha inhibition or depletion in tumor cells decreases DNA synthesis by suppressing extracellular signal-regulated kinase phosphorylation and cyclin E synthesis. Additionally, PKCalpha down-regulates miR-15a, a microRNA that directly inhibits protein synthesis of cyclin E, as well as other cell cycle regulators. Furthermore, both PKCalpha and cyclin E protein expression are increased in primary tumors, and PKCalpha inversely correlates with miR-15a expression in primary tumors. Finally, PKCalpha is associated with poor prognosis in SCCHN. These results identify PKCalpha as a key regulator of SCCHN tumor cell growth by a mechanism involving activation of mitogen-activated protein kinase, an initiator of the cell cycle, and suppression of miR-15a, an inhibitor of DNA synthesis. Although the specific components may be different, this type of feed-forward loop network, consisting of a stimulus that activates a positive signal and removes a negative brake, is likely to be a general one that enables induction of DNA synthesis by a variety of growth or oncogenic stimuli.

Systems biology-defined NF-kappaB regulons, interacting signal pathways and networks are implicated in the malignant phenotype of head and neck cancer cell lines differing in p53 status

BACKGROUND

Aberrant activation of the nuclear factor kappaB (NF-kappaB) pathway has been previously implicated as a crucial signal promoting tumorigenesis. However, how NF-kappaB acts as a key regulatory node to modulate global gene expression, and contributes to the malignant heterogeneity of head and neck cancer, is not well understood.

RESULTS

To address this question, we used a newly developed computational strategy, COGRIM (Clustering Of Gene Regulons using Integrated Modeling), to identify NF-kappaB regulons (a set of genes under regulation of the same transcription factor) for 1,265 genes differentially expressed by head and neck cancer cell lines differing in p53 status. There were 748 NF-kappaB targets predicted and individually annotated for RELA, NFkappaB1 or cREL regulation, and a prevalence of RELA related genes was observed in over-expressed clusters in a tumor subset. Using Ingenuity Pathway Analysis, the NF-kappaB targets were reverse-engineered into annotated signature networks and pathways, revealing relationships broadly altered in cancer lines (activated proinflammatory and down-regulated Wnt/beta-catenin and transforming growth factor-beta pathways), or specifically defective in cancer subsets (growth factors, cytokines, integrins, receptors and intermediate kinases). Representatives of predicted NF-kappaB target genes were experimentally validated through modulation by tumor necrosis factor-alpha or small interfering RNA for RELA or NFkappaB1.

CONCLUSION

NF-kappaB globally regulates diverse gene programs that are organized in signal networks and pathways differing in cancer subsets with distinct p53 status. The concerted alterations in gene expression patterns reflect cross-talk among NF-kappaB and other pathways, which may provide a basis for molecular classifications and targeted therapeutics for heterogeneous subsets of head and neck or other cancers.

Role of protein kinase C-delta in the age-dependent secretagogue action of bile acids in mammalian colon

The role of specific PKC isoforms in the regulation of epithelial Cl(-) secretion by Ca(2+)-dependent secretagogues remains controversial. In the developing rabbit distal colon, the bile acid taurodeoxycholate (TDC) acts via intracellular calcium to stimulate Cl(-) transport in adult, but not in young, animals, whereas the PKC activator phorbol dibutyrate (PDB) stimulates Cl(-) transport at all ages. We tested the hypothesis that specific PKC isoforms account for the age-specific effects of TDC. The effects of conventional (cPKC) and novel (nPKC) PKC-specific inhibitors on TDC- and PDB-stimulated Cl(-) transport in adult and weanling colonocytes were assessed by using 6-methoxy-quinolyl acetoethyl ester. In adult colonocytes, the cPKC inhibitor Gö-6976 inhibited PDB action but not TDC action, whereas the cPKC and nPKC inhibitor Gö-6850 blocked both TDC and PDB actions. Additionally, rottlerin and the PKC-delta-specific inhibitor peptide (deltaV1-1) inhibited TDC- and PDB-stimulated Cl(-) transport in adult colonocytes. Rottlerin also decreased TDC-stimulated short-circuit current in intact colonic epithelia. Only Gö-6976, but neither rottlerin nor deltaV1-1, inhibited PDB-stimulated transport in weanling colonocytes. Colonic lysates express PKC-alpha, -lambda, and -iota protein equally at all ages, but they do not express PKC-gamma or -theta at any age. Expression of PKC-beta and PKC-epsilon protein was newborn>adult>weanling, whereas PKC-delta was expressed in adult but not in weanling or newborn colonocytes. TDC (1.6-fold) and PDB (2.0-fold) stimulated PKC-delta enzymatic activity in adult colonocytes but failed to do so in weanling colonocytes. PKC-delta mRNA expression showed age dependence. Thus PKC-delta appears critical for the action of TDC in the adult colon, and its low expression in young animals may account for their inability to secrete in response to bile acids.

Cloning and expression analysis of a protein kinase C gene, PKCmu, and its regulation of the promoter region in zebrafish

The cDNA and genomic DNA of zebrafish (Danio rerio) protein kinase Cmu (PKCmu), with its promoter region, were obtained. The 508-amino acid zebrafish PKCmu has 86.17% similarity to human PKCmu. Real-time reverse-transcription polymerase chain reaction analysis with starvation and hormonal treatment found significant differences between the control group and the experimental group after 14 days of starvation. After injecting insulin-like growth factor II (IGF-II), growth hormone (GH), insulin, or human chorionic gonadotropin, significant differences were observed between the control and experimental groups 24 h after treatment. After injecting the gonadotropin-releasing hormone or luteotropin-releasing hormone, significant differences were seen between the control and experimental groups 15 h after treatment. These results suggest that in vivo PKCmu expression is regulated by the insulin family or by the GH, but other sex hormones produced a significant expression level more quickly than the insulin family and GH. The zebrafish PKCmu gene is located on zebrafish chromosome 17 and consists of 16 exons. A 2.6 kilobase pair on the 5' flanking region displayed maximal promoter activity in the zebrafish liver (ZFL) cell line after treatment with IGF-I, IGF-II, and GH. However, a 1.6 kilobase pair on the 5' flanking region displayed maximal promoter activity in the HeLa cell line after treatment with IGF-I, IGF-II, and GH. Finally, PKCmu may have important nuclear effects on cell growth and may involve nuclear localization. By transiently transfecting ZFL cells with various zebrafish PKCmu segments, we identified a nuclear localization signal: the amino acid sequence between amino acids 206 and 209 was able to predominantly direct enhanced green fluorescence protein (EGFP) into the nucleus, whereas a deletion of this motif abrogated the nuclear localization property.

Difference in gene expression of macrophage between normal spleen and portal hypertensive spleen idendified by cDNA microarray

AIM: To identify the difference in gene expression of microphage (Mφ) between normal spleen and portal hypertensive spleen using cDNA microarrays and find new gene functions associated with hypersplenism in portal hypertension.

METHODS: The Biostar-H140s chip containing 14 112 spots of cDNAs were used to investigate the difference of the expression. The total RNA extracted from macrophages isolated from both normal spleen and portal hypertensive spleen was reversely transcribed to cDNA with the incorporation of fluorescent (cy3 and cy5) labeled dCTP to prepare the hybridization probes. After hybridization, the gene chip was scanned for the fluorescent intensity. The differentially expressed genes were screened. That was repeated three times, and only the genes which had differential expression in all three chips were considered to be associated with hypersplenism in portal hypertension.

RESULTS: Eight hundred and ninety-six, 1330 and 898 genes were identified to be differentially expressed in three chips, respectively. One hundred and twenty-one genes (0.86%) were identified to be differentially expressed in all three chips, including 21 up-regulated genes and 73 down-regulated genes. The differentially expressed genes were related to ionic channel and transport protein, cyclin, cytoskeleton, cell receptor, cell signal conduct, metabolism, immune, and so on. These genes might be related to the hypersplenism in portal hypertension.

CONCLUSION: The investigations based on cDNA microarray can screen differentially expressed genes of macrophages between normal spleen and portal hypertensive spleen, thus may provide a new idea in studying the pathogenesis of hypersplenism in portal hypertension.

PKCdelta signaling: mechanisms of DNA damage response and apoptosis

The cellular response to genotoxic stress that damages DNA includes cell cycle arrest, activation of DNA repair, and in the event of irreparable damage, induction of apoptosis. However, the signals that determine cell fate, that is, survival or apoptosis, are largely unknown. The delta isoform of protein kinase C (PKCdelta) has been implicated in many important cellular processes, including regulation of apoptotic cell death. The available information supports a model in which certain sensors of DNA lesions activate PKCdelta. This activation is triggered in part by tyrosine phosphorylation of PKCdelta by c-Abl tyrosine kinase. PKCdelta is further proteolytically activated by caspase-3. The cleaved catalytic fragment of PKCdelta translocates to the nucleus and induces apoptosis. Importantly, accumulating data have revealed the nuclear targets for PKCdelta in the induction of apoptosis. A pro-apoptotic function of activated PKCdelta is mediated by at least several downstream effectors known to be associated with the elicitation of apoptosis. Recent findings also demonstrated that PKCdelta is involved in cell cycle-specific activation and induction of apoptotic cell death. Moreover, previous studies have shown that PKCdelta regulates transcription by phosphorylating various transcription factors, including the p53 tumor suppressor that is critical for cell cycle arrest and apoptosis in response to DNA damage. These findings collectively support a pivotal role for PKCdelta in the induction of apoptosis with significant impact. This review is focused on the current views regarding the regulation of cell fate by PKCdelta signaling in response to DNA damage.

Androgens regulate protein kinase Cdelta transcription and modulate its apoptotic function in prostate cancer cells

Activation of protein kinase Cdelta (PKCdelta), a member of the novel PKC family, leads to apoptosis in several cell types. Although the molecular bases of PKCdelta activation are being unfolded, limited information is available on the mechanisms that control its expression. Here, we report that in prostate cancer cells PKCdelta is tightly regulated by androgens at the transcriptional level. Steroid depletion from the culture medium causes a pronounced down-regulation of PKCdelta protein and mRNA in androgen-sensitive LNCaP prostate cancer cells, an effect that is rescued by the androgen R1881 in an androgen receptor (AR)-dependent manner. Analysis of the PKCdelta promoter revealed a putative androgen responsive element (ARE) located 4.7 kb upstream from the transcription start site. Luciferase reporter assays show that this element is highly responsive to androgens, and mutations in key nucleotides in the AR-binding consensus abolish reporter activity. Furthermore, using chromatin immunoprecipitation assays, we determined that the AR binds in vivo to the PKCdelta ARE in response to androgen stimulation. Functional studies revealed that, notably, androgens modulate phorbol 12-myristate 13-acetate (PMA)-induced apoptosis in LNCaP cells, an effect that is dependent on PKCdelta. Indeed, androgen depletion or AR RNA interference severely impaired the apoptotic function of PKCdelta or the activation of p38, a downstream effector of PKCdelta in LNCaP cells--effects that can be rescued by restoring PKCdelta levels using an adenoviral delivery approach. Our studies identified a novel hormonal mechanism for the control of PKCdelta expression via transcriptional regulation that fine-tunes the magnitude of PKCdelta apoptotic responses.

Involvement of PKCα in insulin-induced PKCδ expression: Importance of SP-1 and NFκB transcription factors

Protein kinase C delta (PKCdelta) is a key molecule in insulin signaling essential for insulin-induced glucose transport in skeletal muscle. Recent studies in our laboratory have shown that insulin rapidly stimulates PKCdelta activity and increases PKCdelta protein and RNA levels, and that the SP-1 transcription factor is involved in insulin-induced transcription of the PKCdelta gene. Activation of SP-1 involves serine phosphorylation and translocation to the nucleus. In this study we examined the possibility that PKCalpha might be involved in serine phosphorylation and activation of SP-1. We found that insulin rapidly phosphorylates and translocates SP-1. In the cytoplasm, SP-1 was constitutively associated with PKCalpha, and insulin stimulation caused these proteins to dissociate. In contrast, in the nucleus insulin induced an increase in association between PKCalpha and SP-1. PKCalpha inhibition blocked insulin-induced serine phosphorylation of SP-1 and its association with PKCalpha in the nucleus. Inhibition of PKCalpha also reduced the insulin-induced increase in PKCdelta RNA and protein in the cytoplasmic and nuclear fractions. We also attempted to determine if another transcription factor might be involved in regulation of PKCdelta expression. We earlier showed that insulin did not affect nuclear NFkappaB levels. Inhibition of NFkappaB, however, increased insulin-induced increase in PKCdelta RNA and protein in the cytoplasmic and nuclear fractions. Surprisingly, this inhibition reduced the insulin-induced increase in cytoplasmic and nuclear PKCalpha RNA and protein. Inhibition of PKCdelta reduced IkappaBalpha phosphorylation as well as NFkappaB activation. Thus, PKCalpha regulates insulin-induced PKCdelta expression levels and this regulation involves activation of SP-1 and NFkappaB.

Activation of the nuclear transcription factor SP-1 by insulin rapidly increases the expression of protein kinase C delta in skeletal muscle

SP-1, a ubiquitous transcription factor involved in regulation of target genes participating in specific signaling pathways, is utilized by insulin for induction of gene transcription. Transcriptional activation generally occurs only after several (14-24) hours. A major element rapidly activated by insulin in skeletal muscle is PKCdelta, which plays a positive regulatory role in insulin signaling. We recently reported that insulin stimulation of skeletal muscle increases PKCdelta RNA expression and PKCdelta protein levels within 5 min. These effects were blocked by inhibitors of either translation or transcription. In this study, we investigated the possibility that SP-1 may participate in this unusually rapid effect. Studies were performed on myoblasts and myotubes of the L6 skeletal muscle cell line. Insulin rapidly increased SP-1 levels and stimulated SP-1 phosphorylation in the nuclear fraction of L6 myotubes. The increase in nuclear SP-1 was blocked by inhibition of nuclear import. Inhibition of SP-1, either pharmacologically or by suppression of SP-1 by RNAi, nearly completely abrogated insulin-induced increase in PKCdelta promoter activity. Insulin induced a rapid association of SP-1 with the PKCalpha promoter. In addition, SP-1 inhibition blocked insulin-induced increases in both PKCdelta RNA expression and PKCdelta protein levels. We conclude that insulin rapidly stimulates SP-1, which mediates the ability of this hormone to induce the rapid transcription of a major target gene utilized in the insulin signaling cascade.

Specific protein kinase C isoforms as transducers and modulators of insulin signaling

Recent studies implicate specific PKC isoforms in the insulin-signaling cascade. Insulin activates PKCs alpha, betaII, delta and zeta in several cell types. In addition, as will be documented in this review, certain members of the PKC family may also be activated and act upstream of PI3 and MAP kinases. Each of these isoforms has been shown one way or another either to mimic or to modify insulin-stimulated effects in one or all of the insulin-responsive tissues. Moreover, each of the isoforms has been shown to be activated by insulin stimulation or conditions important for effective insulin stimulation. Studies attempting to demonstrate a definitive role for any of the isoforms have been performed on different cells, ranging from appropriate model systems for skeletal muscle, liver and fat, such as primary cultures, and cell lines and even in vivo studies, including transgenic mice with selective deletion of specific PKC isoforms. In addition, studies have been done on certain expression systems such as CHO or HEK293 cells, which are far removed from the tissues themselves and serve mainly as vessels for potential protein-protein interactions. Thus, a clear picture for many of the isoforms remains elusive in spite of over two decades of intensive research. The recent intrusion of transgenic and precise molecular biology technologies into the research armamentarium has opened a wide range of additional possibilities for direct involvement of individual isoforms in the insulin signaling cascade. As we hope to discuss within the context of this review, whereas many of the long sought-after answers to specific questions are not yet clear, major advances have been made in our understanding of precise roles for individual PKC isoforms in mediation of insulin effects. In this review, in which we shall focus our attention on isoforms in the conventional and novel categories, a clear case will be made to show that these isoforms are not only expressed but are importantly involved in regulation of insulin metabolic effects.

New PKCδ family members, PKCδIV, δV, δVI, and δVII are specifically expressed in mouse testis

We isolated and characterized four new PKCdelta isoforms, PKCdeltaIV, deltaV, deltaVI, and deltaVII, specifically expressed in the mouse testis. These isoforms possess neither V1 nor C2-like domains. Moreover, PKCdeltaVI and deltaVII have a different last exon as their V5 domain. The transcription of PKCdeltaIV, deltaV, deltaVI, and deltaVII is initiated from the same site in the upstream region of exon4 of the PKCdelta gene. They are expressed exclusively in the testis in an age-dependent manner. PKCdeltaIV and deltaV are expressed in spermatids with sperm maturation stage-specific manner, and that PKCdeltaVI and deltaVII are expressed in spermatogonia and spermatocytes.

A hydrogen peroxide-generating agent, 6-formylpterin, enhances heat-induced apoptosis

The enhancement of heat-induced apoptosis by 6-formylpterin, an intra-cellular generator of hydrogen peroxide (H2O2), was examined in human myelomonocytic lymphoma U937 cells. The cells were treated with either 6-formylpterin alone at a nontoxic concentration of 300 microM (37 degrees C), heat shock (44 degrees C per 20 min) alone or a combination of the two, then incubated at 37 degrees C for 6 h. Assessments of apoptosis, mitochondrial membrane potential and caspase-3 activation were performed by flow cytometry. Moreover, caspase-8 activation and changes in the intra-cellular Ca2+ concentration ([Ca2+]i) were examined. Bax, Bcl-2, Bcl-XL, Bid, cytochrome c and PKCd were detected by Western blotting. The induction of heat-induced apoptosis evaluated by morphological observation and DNA fragmentation were promoted by the addition of 6-formylpterin. Mitochondrial membrane potential was decreased and the activation of caspase-3 and -8 was enhanced in the cells treated with the combination. A decreased-expression of Bid was noted, although no significant changes in Bax, Bcl-2 and Bcl-XL expression were observed after the combined treatment. Furthermore, both the release of cytochrome c from mitochondria to cytosol and the translocation of PKCd from cytosol to mitochondria, which were induced by heat shock, were enhanced by the addition of 6-formylpterin. The number of cells with a higher [Ca2+]i was also increased by the addition of 6-formylpterin. These findings suggest that the increase in [Ca2+]i, the activation of the mitochondria-caspase dependent pathway and the translocation of PKCd to mitochondria play principal roles in the enhancement of heat-induced apoptosis by 6-FP.

Insulin rapidly upregulates protein kinase Cdelta gene expression in skeletal muscle

Recent studies in our laboratories have shown that Protein Kinase C delta (PKCdelta) is essential for insulin-induced glucose transport in skeletal muscle, and that insulin rapidly stimulates PKCdelta activity skeletal muscle. The purpose of this study was to examine mechanisms of regulation of PKCdelta protein availability. Studies were done on several models of mammalian skeletal muscle and utilized whole cell lysates of differentiated myotubes. PKCdelta protein levels were determined by Western blotting techniques, and PKCdelta RNA levels were determined by Northern blotting, RT-PCR and Real-Time RT-PCR. Insulin stimulation increased PKCdelta protein levels in whole cell lysates. This effect was not due to an inhibition by insulin of the rate of PKCdelta protein degradation. Insulin also increased 35S-methionine incorporation into PKCdelta within 5-15 min. Pretreatment of cells with transcription or translation inhibitors abrogated the insulin-induced increase in PKCdelta protein levels. We also found that insulin rapidly increased the level of PKCdelta RNA, an effect abolished by inhibitors of transcription. The insulin-induced increase in PKCdelta expression was not reduced by inhibition of either PI3 Kinase or MAP kinase, indicating that these signaling mechanisms are not involved, consistent with insulin activation of PKCdelta. Studies on cells transfected with the PKCdelta promoter demonstrate that insulin activated the promoter within 5 min. This study indicates that the expression of PKCdelta may be regulated in a rapid manner during the course of insulin action in skeletal muscle and raise the possibility that PKCdelta may be an immediate early response gene activated by insulin.

Distinctive activation mechanisms and functions for protein kinase Cdelta

PKCdelta (protein kinase Cdelta) is a serine/threonine kinase that plays a key role in growth regulation and tissue remodelling. Traditional models of PKC activation have focused on lipid cofactors and anchoring proteins that localize the active conformation of PKCdelta to membranes, in close proximity with its target substrates. However, recent studies identify a distinct mode for PKCdelta activation involving tyrosine phosphorylation by Src family kinases. The tyrosine-phosphorylated form of PKCdelta (which accumulates in the soluble fraction of cells exposed to oxidant stress) displays lipid-independent kinase activity and is uniquely positioned to phosphorylate target substrates throughout the cell (not just on lipid membranes). This review summarizes (1) recent progress towards understanding structure-activity relationships for PKCdelta, with a particular focus on the stimuli that induce (and the distinct functional consequences that result from) tyrosine phosphorylation events in PKCdelta's regulatory, hinge and catalytic domains; (2) current concepts regarding the role of tyrosine phosphorylation as a mechanism to regulate PKCdelta localization and actions in mitochondrial and nuclear compartments; and (3) recent literature delineating distinct roles for PKCdelta (relative to other PKC isoforms) in transcriptional regulation, cell cycle progression and programmed cell death (including studies in PKCdelta-/- mice that implicate PKCdelta in immune function and cardiovascular remodelling). Collectively, these studies argue that the conventional model for PKCdelta activation must be broadened to allow for stimulus-specific differences in PKCdelta signalling during growth factor stimulation and oxidant stress.