Positive and negative regulation of the transcription of the human protein kinase C beta gene

Transcriptional mechanism of vascular endothelial growth factor-induced expression of protein kinase CβII in chronic lymphocytic leukaemia cells

A key feature of chronic lymphocytic leukaemia (CLL) cells is overexpressed protein kinase CβII (PKCβII), an S/T kinase important in the pathogenesis of this and other B cell malignancies. The mechanisms contributing to enhanced transcription of the gene coding for PKCβII, PRKCB, in CLL cells remain poorly described, but could be important because of potential insight into how the phenotype of these cells is regulated. Here, we show that SP1 is the major driver of PKCβII expression in CLL cells where enhanced association of this transcription factor with the PRKCB promoter is likely because of the presence of histone marks permissive of gene activation. We also show how vascular endothelial growth factor (VEGF) regulates PRKCB promoter function in CLL cells, stimulating PKCβ gene transcription via increased association of SP1 and decreased association of STAT3. Taken together, these results are the first to demonstrate a clear role for SP1 in the up regulation of PKCβII expression in CLL cells, and the first to link SP1 with the pathogenesis of this and potentially other B cell malignancies where PKCβII is overexpressed.

PROX1 overexpression inhibits protein kinase C beta II transcription through promoter DNA methylation

Prospero-related homeobox 1 (PROX1) is important for embryonic organ formation and differentiation, and changes in PROX1 activity were recently associated with cancer. To address the PROX1 roles in tumorigenesis, we established cells stably overexpressing PROX1 using the human cervical cancer cell line, HeLa. Overexpression of PROX1 reduced cell proliferation and the rate of tumor formation as compared with controls. Comparison of gene expression profiles between PROX1-overexpressing and mock-transfected cells revealed that the expression of protein kinase C βII (PRKCB2) is down-regulated in PROX1-overexpressing cells. A PRKCB inhibitor suppressed cell growth of control cells more than PROX1-expressing cells. Analysis of the 5'-promoter of PRKCB revealed that a region between -110 bp and the first exon contains two Sp1 binding sites and is important for transcriptional regulation of PRKCB. The inhibition of Sp1 transcription factor resulted in down-regulation of PRKCB2 protein levels. Treatment with a demethylating agent, 5-aza-2'-deoxycytidine, restored PRKCB2 mRNA expression in PROX1-expressing cells, suggesting that the 5'-promoter of PRKCB is methylated in these cells. Actually, it was found that a CpG island in this region, in particular a CpG site overlapping with the distal Sp1 site, was hypermethylated and direct Sp1 binding to this region was inhibited in PROX1-overexpressing cells. Thus, the suppressive effect of PROX1 on cell growth and tumor formation might be partially mediated by PRKCB2 via altered methylation of its promoter.

Vascular endothelial growth factor stimulates protein kinase CbetaII expression in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is a malignant disease of mature B lymphocytes. We have previously shown that a characteristic feature of CLL cells are high levels of expression and activity of protein kinase CbetaII (PKCbetaII), and that this might influence disease progression by modulating signaling in response to B-cell receptor engagement. The aim of the present work was to investigate the factors involved in stimulating PKCbetaII expression in CLL cells. Here we show that the activation of PKCbetaII in CLL cells stimulated with vascular endothelial growth factor (VEGF) can drive expression of the gene for PKCbeta, PRKCB1. We found that this effect of VEGF on PRKCB1 transcription is paralleled by high expression of PKCbetaII protein and therefore probably contributes to the malignant phenotype of CLL cells. Taken together, the data presented in this study demonstrate that VEGF, in addition to its role in providing prosurvival signals, also plays a role in overexpression of PKCbetaII, an enzyme with a specific pathophysiologic role in CLL.

Functional alterations in protein kinase C beta II expression in melanoma

Protein kinase C (PKC) is a heterogeneous family of serine/threonine protein kinases that have different biological effects in normal and neoplastic melanocytes (MCs). To explore the mechanism behind their differential response to PKC activation, we analyzed the expression profile of all nine PKC isoforms in normal human MCs, HPV16 E6/E7 immortalized MCs, and a panel of melanoma cell lines. We found reduced PKCbeta and increased PKCzeta and PKCiota expression at both the protein and mRNA levels in immortalized MCs and melanoma lines. We focused on PKCbeta as it has been functionally linked to melanin production and oxidative stress response. Re-expression of PKCbeta in melanoma cells inhibited colony formation in soft agar, indicating that PKCbeta loss in melanoma is important for melanoma growth. PKCbetaII, but not PKCbetaI, was localized to the mitochondria, and inhibition of PKCbeta significantly reduced UV-induced reactive oxygen species (ROS) in MCs with high PKCbeta expression. Thus alterations in PKCbeta expression in melanoma contribute to their neoplastic phenotype, possibly by reducing oxidative stress, and may constitute a selective therapeutic target.

Loss of protein kinase Cbeta function protects mice against diet-induced obesity and development of hepatic steatosis and insulin resistance

Obesity is an energy balance disorder in which intake is greater than expenditure, with most excess calories stored as triglyceride (TG). We previously reported that mice lacking the beta-isoform of protein kinase C (PKCbeta), a diacylglycerol- and phospholipid-dependent kinase, exhibit marked reduction in the whole body TG content, including white adipose tissue (WAT) mass. To investigate the role of this signaling kinase in metabolic adaptations to severe dietary stress, we studied the impact of a high-fat diet (HFD) on PKCbeta expression and the effect of PKCbeta deficiency on profound weight gain. We report herein that HFD selectively increased PKCbeta expression in obesity-prone C57BL/6J mice, specifically in WAT; the expression levels were little or unchanged in the liver, muscle, kidney, and heart. Basal PKCbeta expression was also found to be elevated in WAT of obese ob/ob mice. Remarkably, mice lacking PKCbeta were resistant to HFD-induced obesity, showing significantly reduced WAT and slightly higher core body temperatures. Unlike lean lipodystrophic mouse models, these mice did not have fatty livers, nor did they exhibit insulin resistance. Moreover, PKCbeta(-/-) mice exhibited changes in lipid metabolism gene expression, and such alterations were accompanied by significant changes in serum adipokines. These observations suggest that PKCbeta deficiency induced a unique metabolic state congruous with obesity resistance, thus raising the possibility that dysregulation of PKCbeta expression could contribute to dietary fat-induced obesity and related disorders.

Array analysis of epilepsy-associated gangliogliomas reveals expression patterns related to aberrant development of neuronal precursors

Gangliogliomas, the most frequent neoplasms in patients with pharmacoresistant focal epilepsies, are characterized by histological combinations of glial and dysplastic neuronal elements, a highly differentiated phenotype and rare gene mutations. Their molecular basis and relationship to other low-grade brain tumours are not completely understood. Systematic investigations of altered gene expression in gangliogliomas have been hampered by their cellular complexity, the lack of suitable control tissue and of sensitive expression profiling approaches. Here, we have used discrete microdissected ganglioglioma and adjacent control brain tissue obtained from the neurosurgical access to the tumour of identical patients (n = 6) carefully matched for equivalent glial and neuronal elements in an amount sufficient for oligonucleotide microarray hybridization without repetitive amplification. Multivariate statistical analysis identified a rich profile of genes with altered expression in gangliogliomas. Many differentially expressed transcripts related to intra- and intercellular signalling including protein kinase C and its target NELL2 in identical ganglioglioma cell components as determined by real-time quantitative RT-PCR (qRT-PCR) and in situ hybridization. We observed the LIM-domain-binding 2 (LDB2) transcript, critical for brain development during embryogenesis, as one of the strongest reduced mRNAs in gangliogliomas. Subsequent qRT-PCR in dysembryoplastic neuroepithelial tumours (n = 7) revealed partial expression similarities as well as marked differences from gangliogliomas. The demonstrated gene expression profile differentiates gangliogliomas from other low-grade primary brain tumours. shRNA-mediated silencing of LDB2 resulted in substantially aberrant dendritic arborization in cultured developing primary hippocampal neurons. The present data characterize novel molecular mechanisms operating in gangliogliomas that contribute to the development of dysplastic neurons and an aberrant neuronal network.

Essential role of GATA transcriptional factors in the activation of mast cells

Mast cells are pivotal effector cells in IgE-mediated allergic reactions. GATA transcriptional factors such as GATA-1 and GATA-2 are expressed in mast cells, and recent studies have revealed that both GATA-1 and GATA-2 are required for mast cell development. However, the role of GATA transcriptional factors in differentiated mast cells has remained largely unknown. In this study, we repressed the activity of GATA-1 and GATA-2 by using three different approaches (inducible overexpression of a dominant-negative form of GATA, pharmacological inactivation, or small interfering RNA technology), and analyzed the molecular mechanisms of GATA transcriptional factors in the activation of mast cells. Surprisingly, the repression of GATA activity in differentiated mast cells led to the impairment of cell survival, IgE-induced degranulation, and cytokine production. Signal transduction and histone modification in the chromatin related to protein kinase Cbeta were defective in these cells. These results identify that GATA has a critical role in the activation of mast cell.

Identification of a common risk haplotype for diabetic nephropathy at the protein kinase C-beta1 (PRKCB1) gene locus

Abnormal activation of protein kinase C-beta isoforms in the diabetic state has been implicated in the development of diabetic nephropathy. It is thus plausible that DNA sequence differences in the protein kinase C-beta1 gene (PRKCB1), which encodes both betaI and betaII isoforms, may influence susceptibility to nephropathy. Nine single-nucleotide polymorphisms (SNP) in PRKCB1 were tested for association with diabetic nephropathy in type I diabetes mellitus, by using both case-control and family-study designs. Allele and genotype distributions of two SNP in the promoter (--1504C/T and --546C/G) differed significantly between case patients and control patients (P < 0.05). These associations were particularly strong with diabetes mellitus duration of <24 yr (P = 0.002). The risk of diabetic nephropathy was higher among carriers of the T allele of the --1504C/T SNP, compared with noncarriers (odds ratio, 2.54; 95% confidence interval, 1.39 to 4.62), and among carriers of the G allele of the --546C/G SNP (odds ratio, 2.45; 95% confidence interval, 1.37 to 4.38). Among individuals with diabetes mellitus duration of >/==" BORDER="0">24 yr, these two SNP were not associated with diabetic nephropathy. These positive findings were confirmed by using the family-based transmission disequilibrium test. The T-G haplotype, with both risk alleles, was transmitted more frequently than expected from heterozygous parents to offspring who developed diabetic nephropathy during the first 24 yr of diabetes mellitus. It is concluded that DNA sequence differences in the promoter of PRKCB1 contribute to diabetic nephropathy susceptibility in type I diabetes mellitus.

Protein kinase C isoforms in normal and transformed cells of the melanocytic lineage

Enzymes belonging to the protein kinase C (PKC) family represent one of the major mediators of signal transduction in melanocytes. To identify PKC isoforms that may be associated with the process of malignant transformation and metastasis, we investigated the expression pattern of 11 different PKC isoforms (alpha, beta I, beta II, gamma, delta, epsilon, eta, theta, zeta, lambda, and iota) in melanoma lymph node metastases, in cell lines established from these metastases, in primary cell cultures from normal melanocytes, and in permanent cell lines established from spontaneously transformed melanocytes. PKC alpha, beta I, beta II, delta, epsilon, eta, zeta, lambda and iota were found to be expressed in total lysates from melanoma metastases. In permanent cell lines established from these metastases, the expression levels of PKC beta I, beta II, delta, epsilon, and eta were lower or undetectable when compared with initial expression in tumour lysates. In normal primary melanocyte cultures, the PKC isoforms beta II, delta, epsilon, eta and iota were undetectable. PKC gamma and theta isoforms were undetectable in all melanocytic cell types examined. PKC iota was the only isoform exclusively detected in tumour lysates, in spontaneously transformed melanoma cells and melanoma cell lines, but not in normal melanocytes, and may therefore be associated with the transformed phenotype in human melanoma in vitro and in vivo.

Differential expression of protein kinase C isoform transcripts in human hematopoietic progenitors undergoing differentiation

Protein kinase C (PKC), a key component of the signaling pathways leading to proliferation and differentiation, consists of a family closely related serine/threonine protein kinases. The mRNA expression of these PKC isoforms has been characterized during hematopoietic differentiation. Using the reverse-transcriptase polymerase chain reaction technique, we have analyzed the levels of isoform transcripts in bone marrow CD34(+) hematopoietic progenitors and their progeny differentiated along erythroid, megakaryocyte, or granulocyte/monocyte lineages, upon exposure to growth factors. In contrast with isoforms alpha, beta(I), beta(II), delta, and epsilon, ubiquitously expressed, isoforms theta, eta/L, zeta, and iota/lambda exhibited a lineage-restricted expression. These qualitative changes, which allow to distinguish the erythroid and megakaryocyte phenotypes from the granulocyte/monocyte phenotype, include zeta exclusively upregulated in granulocytes/monocytes and theta, eta/L, and iota/lambda exclusively expressed in megakaryocytes and erythroblasts. In contrast, erythroblasts and megakaryocytes, which supposedly share a common bipotential progenitor, displayed only quantitative changes. These results evidence the selective expression of PKC isoforms at transcriptional and/or posttranscriptional levels in hematopoietic progenitors induced to differentiate, which may suggest a differential contribution of individual isoforms to cellular signaling.

Cloning and characterization of the murine PKC alpha promoter: identification of a retinoic acid response element

Protein kinase C (PKC) is a family which consists of multiple isoforms whose distinct physiological roles within the cell are unknown. We have previously demonstrated that levels of PKC alpha mRNA, protein, and enzyme activity in B16 melanoma cells can be modulated by retinoic acid. We investigated this regulation by cloning and characterizing the promoter region of the murine PKC alpha gene. A 13 kb mouse genomic fragment containing the 5' flanking region, first exon, and first intron was isolated and sequenced. Two transcription initiation sites were identified at 919 and 925 bp upstream from the translation start site. The promoter region contained a TATA-like box at -93 bp upstream of the transcription start site, but no CAAT box. Promoter activity differed between cell lines and correlated with the levels of PKC alpha expressed in these cell lines. Reporter gene assays showed that the region between -179 and -452 bp likely contains a silencer element(s). The promoter activity of a -179 bp fragment in B16 cells was stimulated twofold by retinoic acid. Within this region (-93 to -65 bp) there is a retinoic acid response element. An oligonucleotide spanning this region specifically bound exogenous RAR-RXR heterodimers and endogenous RAR from B16 nuclear extracts. These results suggest that retinoic acid increases PKC alpha gene expression in B16 cells, at least in part, through direct transcriptional stimulation of its promoter.

Acute hyperglycemia regulates transcription and posttranscriptional stability of PKCbetaII mRNA in vascular smooth muscle cells

Acute hyperglycemia may contribute to the progression of atherosclerosis by regulating protein kinase C (PKC) isozymes and by accelerating vascular smooth muscle cell (VSMC) proliferation. We investigated acute glucose regulation of PKCbeta gene expression in A10 cells, a rat aortic smooth muscle cell line. Western blot analysis showed that PKCbetaII protein levels decreased with high glucose (25 mM) compared to normal glucose (5.5 mM), whereas PKCbetaI levels were unaltered. PKCbeta mRNA levels were depleted by 60-75% in hyperglycemic conditions. To elucidate whether high glucose regulated PKCbeta expression via the common promoter for PKCbetaI and PKCbetaII, deletion constructs of the PKCbeta promoter ligated to CAT as reporter gene were transfected into A10 cells. Construct D (-411 to +179CAT) showed quenching in high glucose (25 mM) and suggested the involvement of a carbohydrate response element in the 5' promoter region of the PKCbeta gene. In actinomycin D-treated A10 cells, a 60% decrease in PKCbeta mRNA with high glucose treatment indicated that posttranscriptional destabilization by glucose was also occurring. We have demonstrated that glucose-induced posttranscriptional destabilization of PKCbetaII message is mediated via a nuclease activity present in the cytosol. The specificity of glucose to posttranscriptionally destabilize PKCbetaII mRNA, but not the PKCbetaI mRNA, was confirmed in both A10 cells and primary cultures from human aorta.

Structure and expression of the Caenorhabditis elegans protein kinase C2 gene. Origins and regulated expression of a family of Ca2+-activated protein kinase C isoforms

The molecular and cellular basis for concerted Ca2+/lipid signaling in Caenorhabditis elegans was investigated. A unique gene (pkc-2) and cognate cDNAs that encode six Ca2+/diacylglycerol-stimulated PKC2 isoenzymes were characterized. PKC2 polypeptides (680-717 amino acid residues) share identical catalytic, Ca2+-binding, diacylglycerol-activation and pseudosubstrate domains. However, sequences of the N- and C-terminal regions of the kinases diverge. PKC2 diversity is partly due to differential activation of transcription by distinct promoters. Each promoter precedes an adjacent exon that encodes 5'-untranslated RNA, an initiator AUG codon and a unique open reading frame. PKC2 mRNAs also incorporate one of two 3'-terminal exons via alternative splicing. Cells that are capable of receiving and propagating signals carried by Ca2+/diacylglycerol were identified by assessing activities of pkc-2 gene promoters in transgenic C. elegans and visualizing the distribution of PKC2 polypeptides via immunofluorescence. Highly-selective expression of certain PKC2 isoforms was observed in distinct subsets of neurons, intestinal and muscle cells. A low level of PKC2 isoforms is observed in embryos. When L1 larvae hatch and interact with the external environment PKC2 content increases 10-fold. Although 77- and 78-kDa PKC2 isoforms are evident throughout post-embryonic development, an 81-kDa isoform appears to be adapted for function in L1 and L2 larvae.

Protein kinase C-delta mRNA is down-regulated transcriptionally and post-transcriptionally by 12-O-tetradecanoylphorbol-13-acetate

Activation of protein kinase C-delta (PKC-delta) by 12-O-tetradecanoylphorbol-13-acetate (TPA) is followed by a gradual decrease in detectable protein 12-24 h later in the mouse B lymphoma cell line A20. Down-regulation is associated with TPA-induced proteolysis and a 50-86% decrease in PKC-delta mRNA 0.5-24 h post-treatment which is due to both a 50% decrease in transcription and accelerated degradation of PKC-delta mRNA as determined using the pulse-chase method. Destabilization of PKC-delta mRNA is also observed when actinomycin D is added to cells pretreated with TPA for 2 h; however, addition of actinomycin D or cycloheximide prior to TPA treatment blocks destabilization. Addition of PKC inhibitors to TPA-treated cells also blocks destabilization of PKC-delta mRNA. Cells treated with TPA for 4 h contain an activity not found in control cells which destabilizes PKC-delta mRNA but not glyceraldehyde-3-phosphate dehydrogenase mRNA in vitro. Addition of TPA to control extracts fails to increase degradation of PKC-delta mRNA in vitro, suggesting that treatment of intact cells is required to induce the synthesis of a factor(s) that destabilizes PKC-delta mRNA. This factor(s) then acts along with transcriptional and post-translational regulatory mechanisms to down-regulate PKC-delta.

Upregulation of PKC delta- and downregulation of PKC alpha-mRNA and protein by phorbol ester in human T84 cells

Protein kinase C (PKC) family members are downregulated by chronic activation at the protein level in most cell types. In T84 human epithelia] cells 12-O-tetradecanoyl phorbol 13-acetate (TPA) caused persistent translocation of PKC delta to the membrane compartment and a 400% increase of PKC delta-mRNA after 24 h. In contrast, PKC alpha protein was completely downregulated and its mRNA was decreased to 60% of control levels after 24 h. This is the first report of PKC delta-mRNA upregulation by TPA which was previously only shown for PKCbeta. In view of the antimitogenic actions of PKC delta this pattern of regulation may serve to preserve growth control even in the presence of chronic cell activation.

Autoregulation of cloned human protein kinase C beta and gamma gene promoters in U937 cells

Protein kinase C (PKC) serine/threonine kinases transduce cellular signals initiated by phospholipase C activation and diacylglycerol production. Human gene sequences from the beta and gamma isoforms were cloned and sequenced, and transcriptional regulation was studied. The major PKC beta transcription initiation site was identified by primer extension and S1 nuclease protection. Additional transcription initiation sites were located within a CpG-rich region proximal to the ATG. The transcription initiation site of the PKC gamma gene was identified by primed cDNA synthesis. In transfection experiments, the PKC gamma promoter was expressed at high level in U937 and HL60 cells but not in COS-1 cells. A sequence motif (AnAGATTCanAGAGnCa), reiterated over at least 1 kb, was located approximately 1.5 kb 5' of the PKC gamma translation initiation codon. This repetitive motif is abundant in run-on RNA in the hematopoietic and epithelial cell lines tested. Analysis of promoter deletion constructs by transient transcription assays in U937, IM9, and COS-1 cells showed negative regulation of the PKC beta promoter by sequences located between -3,000 and -690. although no homology between PKC beta and PKC-gamma 5'-flanking sequences was observed, both PKC beta and PKC gamma promoters were potently induced by 12-phorbol 13-myristate in transfected U937 cells.