Functional role for protein kinase Cbeta as a regulator of stress-activated protein kinase activation and monocytic differentiation of myeloid leukemia cells

MAP kinase-dependent autophagy controls phorbol myristate acetate-induced macrophage differentiation of HL-60 leukemia cells

We investigated the mechanisms and the role of autophagy in the differentiation of HL-60 human acute myeloid leukemia cells induced by protein kinase C (PKC) activator phorbol myristate acetate (PMA). PMA-triggered differentiation of HL-60 cells into macrophage-like cells was confirmed by cell-cycle arrest accompanied by elevated expression of macrophage markers CD11b, CD13, CD14, CD45, EGR1, CSF1R, and IL-8. The induction of autophagy was demonstrated by the increase in intracellular acidification, accumulation/punctuation of autophagosome marker LC3-II, and the increase in autophagic flux. PMA also increased nuclear translocation of autophagy transcription factors TFEB, FOXO1, and FOXO3, as well as the expression of several autophagy-related (ATG) genes in HL-60 cells. PMA failed to activate autophagy inducer AMP-activated protein kinase (AMPK) and inhibit autophagy suppressor mechanistic target of rapamycin complex 1 (mTORC1). On the other hand, it readily stimulated the phosphorylation of mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) via a protein kinase C-dependent mechanism. Pharmacological or genetic inhibition of ERK or JNK suppressed PMA-triggered nuclear translocation of TFEB and FOXO1/3, ATG expression, dissociation of pro-autophagic beclin-1 from its inhibitor BCL2, autophagy induction, and differentiation of HL-60 cells into macrophage-like cells. Pharmacological or genetic inhibition of autophagy also blocked PMA-induced macrophage differentiation of HL-60 cells. Therefore, MAP kinases ERK and JNK control PMA-induced macrophage differentiation of HL-60 leukemia cells through AMPK/mTORC1-independent, TFEB/FOXO-mediated transcriptional and beclin-1-dependent post-translational activation of autophagy.

Taxifolin Activates the Nrf2 Anti-Oxidative Stress Pathway in Mouse Skin Epidermal JB6 P+ Cells through Epigenetic Modifications

Nuclear factor erythroid-2 related factor 2 (Nrf2) is a vital transcription factor that regulates the anti-oxidative defense system. Previous reports suggested that the expression of the Nrf2 gene can be regulated by epigenetic modifications. The potential epigenetic effect of taxifolin (TAX), a potent cancer chemopreventive agent, in skin cancer chemoprotection is unknown. In this study, we investigated how Nrf2 is epigenetically regulated by TAX in JB6 P+ cells. TAX was found to inhibit the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced colony formation of JB6 P+ cells. TAX induced antioxidant response element (ARE)-luciferase activity in HepG2-C8 cells and up-regulated mRNA and protein levels of Nrf2 and its downstream genes heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1), in JB6 P+ cells. Furthermore, bisulfite genomic sequencing revealed that TAX treatment reduces the methylation level of the first 15 CpGs sites in the Nrf2 promoter. Western blotting showed that TAX inhibits the expression levels of DNA methyltransferase (DNMT) and histone deacetylase (HDAC) proteins. In summary, our results revealed that TAX can induce expression of Nrf2 and its downstream target genes in JB6 P+ cells by CpG demethylation. These finding suggest that TAX may exhibit a skin cancer preventive effect by activating Nrf2 via an epigenetic pathway.

GPR120: A bi-potential mediator to modulate the osteogenic and adipogenic differentiation of BMMSCs

Free fatty acids display diverse effects as signalling molecules through GPCRs in addition to their involvement in cellular metabolism. GPR120, a G protein-coupled receptor for long-chain unsaturated fatty acids, has been reported to mediate adipogenesis in lipid metabolism. However, whether GPR120 also mediates osteogenesis and regulates BMMSCs remain unclear. In this study, we showed that GPR120 targeted the bi-potential differentiation of BMMSCs in a ligand dose-dependent manner. High concentrations of TUG-891 (a highly selective agonist of GPR120) promoted osteogenesis via the Ras-ERK1/2 cascade, while low concentrations elevated P38 and increased adipogenesis. The fine molecular regulation of GPR120 was implemented by up-regulating different integrin subunits (α1, α2 and β1; α5 and β3). The administration of high doses of TUG-891 rescued oestrogen-deficient bone loss in vivo, further supporting an essential role of GPR120 in bone metabolism. Our findings, for the first time, showed that GPR120-mediated cellular signalling determines the bi-potential differentiation of BMMSCs in a dose-dependent manner. Additionally, the induction of different integrin subunits was involved in the cytoplasmic regulation of a seesaw-like balance between ERK and p38 phosphorylation. These findings provide new hope for developing novel remedies to treat osteoporosis by adjusting the GPR120-mediated differentiation balance of BMMSCs.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

MAP3K1: Genomic Alterations in Cancer and Function in Promoting Cell Survival or Apoptosis

MAP3K1 is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family of serine/threonine kinases. MAP3K1 regulates JNK activation and is unique among human kinases in that it also encodes an E3 ligase domain that ubiquitylates c-Jun and ERK1/2. Full length MAP3K1 regulates cell migration and contributes to pro-survival signaling while its caspase 3-mediated cleavage generates a C-terminal kinase domain that promotes apoptosis. The critical function of MAP3K1 in cell fate decisions suggests that it may be a target for deregulation in cancer. Recent large-scale genomic studies have revealed that MAP3K1 copy number loss and somatic missense or nonsense mutations are observed in a significant number of different cancers, being most prominent in luminal breast cancer. The alteration of MAP3K1 in diverse cancer types demonstrates the importance of defining phenotypes for possible therapeutic targeting of tumor cell vulnerabilities created when MAP3K1 function is lost or gained.

Why cellular stress suppresses adipogenesis in skeletal tissue, but is ineffective in adipose tissue: control of mesenchymal cell differentiation via integrin binding sites in extracellular matrices

This Perspective addresses one of the major puzzles of adipogenesis in adipose tissue, namely its resistance to cellular stress. It introduces a concept of "density" of integrin binding sites in extracellular matrix, proposes a cellular signaling explanation for the observed effects of matrix elasticity and of cell shape on mesenchymal stem cell differentiation, and discusses how specialized integrin binding sites in collagen IV-containing matrices guard two pivotal physiological and evolutionary processes: stress-resistant adipogenesis in adipose tissues and preservation of pluripotency of mesenchymal stem-like cells in their storage niches. Finally, it proposes strategies to suppress adipogenesis in adipose tissues.

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.

Protein kinase Cbeta mediates hepatic induction of sterol-regulatory element binding protein-1c by insulin

Sterol-regulatory element binding protein-1c (SREBP-1c) is a transcription factor that controls lipogenesis in the liver. Hepatic SREBP-1c is nutritionally regulated, and its sustained activation causes hepatic steatosis and insulin resistance. Although regulation of SREBP-1c is known to occur at the transcriptional level, the precise mechanism by which insulin signaling activates SREBP-1c promoter remains to be elucidated. Here we show that protein kinase C beta (PKCbeta) is a key mediator of insulin-mediated activation of hepatic SREBP-1c and its target lipogenic genes. Activation of SREBP-1c in the liver of refed mice was suppressed by either adenoviral RNAi-mediated knockdown or dietary administration of a specific inhibitor of protein kinase C beta. The effect of PKCbeta inhibition was cancelled in insulin depletion by streptozotocin (STZ) treatment of mice. Promoter analysis indicated that PKCbeta activates SREBP-1c promoter through replacement of Sp3 by Sp1 for binding to the GC box in the sterol regulatory element (SRE) complex, a key cis-element of SREBP-1c promoter. Knockdown of Sp proteins demonstrated that Sp3 and Sp1 play reciprocally negative and positive roles in nutritional regulation of SREBP-1c, respectively. This new understanding of PKCbeta involvement in nutritional regulation of SREBP-1c activation provides a new aspect of PKCbeta inhibition as a potential therapeutic target for diabetic complications.

Collagen I matrix contributes to determination of adult human stem cell lineage via differential, structural conformation-specific elicitation of cellular stress response

Previously, we reported that the conformational transition of collagen I matrix plays, along with differentiation stimuli, a regulatory role in determination of differentiation lineage of bone marrow stromal sells via distinct signaling pathways specific for the structural state of the matrix. The present study addresses mechanisms underlying differential structural conformation-specific effects of collagen matrices on differentiation into diverse lineages. The results obtained suggest that the pivotal player in the observed matrix conformation-mediated regulation is a differential cellular stress response elicited by the exposure to native but not to denatured collagen I matrix. The stress causing such a response appears to be generated by matrix contraction and mediated by Alpha2Beta1 integrins engaged on native but not on denatured collagen I matrix. The principal facet of the observed phenomenon is not the nature of a stress but general stress response: when cells on denatured collagen I matrix are subjected to thermal stress, osteogenic pathway shifts to that seen on native collagen I matrix. Importantly, cellular stress response might be commonly involved in determination of differentiation lineage. Indeed, distinct components of cellular stress response machinery appear to regulate differentiation into diverse lineages. Thus, augmentation of Hsp90 levels enables the operation of efficient Alpha1Beta1/Alpha2Beta1 integrin-driven ERK activation pathways hence facilitating osteogenesis and suppressing adipogenesis, whereas myogenesis of satellite stem cells appears to be promoted by native collagen I matrix-elicited activation and nuclear translocation of another stress response component, Beta-catenin, shown to be essential for skeletal myogenesis, and chondrogenesis may involve stress-mediated elevation of yet another stress response constituent, Hsp70, shown to be an interactive partner of the chondrogenic transcription factor SOX9. The proposed concept of the integral role of cellular stress response in tissue generation and maintenance suggests new therapeutic approaches and indicates novel tissue engineering strategies.

Progression of human bone marrow stromal cells into both osteogenic and adipogenic lineages is differentially regulated by structural conformation of collagen I matrix via distinct signaling pathways

Adult human bone marrow stromal cells (BMSCs) containing or consisting of mesenchymal stem cells (MSCs) are an important source in tissue homeostasis and repair. Although many processes involved in their differentiation into diverse lineages have been deciphered, substantial inroads remain to be gained to synthesize a complete regulatory picture. The present study suggests that structural conformation of extracellular collagen I, the major organic matrix component in musculoskeletal tissues, plays, along with differentiation stimuli, a decisive role in the selection of differentiation lineage. It introduces a novel concept which proposes that structural transition of collagen I matrix regulates cell differentiation through distinct signaling pathways specific for the structural state of the matrix. Thus, on native collagen I matrix inefficient adipogenesis is p38-independent, whereas on its denatured counterpart, an efficient adipogenesis is primarily regulated by p38 kinase. Inversely, osteogenic differentiation occurs efficiently on native, but not on denatured collagen I matrix, with a low commencement threshold on the former and a substantially higher one on the latter. Osteogenesis on collagen I matrices in both structural conformations is fully dependent on ERK. However, whereas on native collagen I matrix osteogenic differentiation is Hsp90-dependent, on denatured collagen I matrix it is Hsp90-independent. The matrix conformation-mediated regulation appears to be one of the mechanisms determining differentiation lineage of BMSCs. It allows a novel interpretation of the bone remodeling cycle, explains the marked physiological aging-related adipogenic shift in musculoskeletal tissues, and can be a principal contributor to adipogenic shift seen in a number of clinical disorders.

Roles of protein kinase Calpha isozyme in the regulation of oxidative stress and neuropeptide Y gene expression in phenylpropanolamine-mediated appetite suppression

Hypothalamic neuropeptide Y (NPY) is an appetite stimulant in the brain. Although regulation of NPY expression has been reported to contribute to the appetite-suppressing effect of phenylpropanolamine (PPA), it is still unknown if protein kinase C (PKC) is involved in this effect. Rats were daily treated with PPA for 4 days. Changes in food intake, hypothalamic NPY, PKC, and proopiomelanocortin (POMC) mRNA levels were assessed and compared. Results showed that the NPY gene was down-regulated following PPA treatment, which was parallel with the decrease of feeding. Moreover, several isotypes of PKC mRNA level (alpha, betaI, betaII, gamma, delta, eta, lambda, epsilon, and zeta) were changed. Among these, alpha, delta, and lambda PKC were up-regulated along with POMC gene expression which coincided with down-regulation of the NPY gene. To further determine if PKCalpha was involved, infusions of antisense oligonucleotide into the cerebroventricle were performed at 1 h before daily PPA treatment in free-moving rats. Results showed that PKCalpha knock-down could modify both anorexia induced by PPA and the NPY mRNA levels. Moreover, PKCalpha knock-down could also modify superoxide dismutase (SOD) gene expression. It is suggested that PKCalpha participates in the regulation of PPA-mediated appetite suppression via the modulation of NPY and SOD gene expression.

Upregulation of myocellular DGAT1 augments triglyceride synthesis in skeletal muscle and protects against fat-induced insulin resistance

Increased fat deposition in skeletal muscle is associated with insulin resistance. However, exercise increases both intramyocellular fat stores and insulin sensitivity, a phenomenon referred to as "the athlete's paradox". In this study, we provide evidence that augmenting triglyceride synthesis in skeletal muscle is intrinsically connected with increased insulin sensitivity. Exercise increased diacylglycerol (DAG) acyltransferase (DGAT) activity in skeletal muscle. Channeling fatty acid substrates into TG resulted in decreased DAG and ceramide levels. Transgenic overexpression of DGAT1 in mouse skeletal muscle replicated these findings and protected mice against high-fat diet-induced insulin resistance. Moreover, in isolated muscle, DGAT1 deficiency exacerbated insulin resistance caused by fatty acids, whereas DGAT1 overexpression mitigated the detrimental effect of fatty acids. The heightened insulin sensitivity in the transgenic mice was associated with attenuated fat-induced activation of DAG-responsive PKCs and the stress mediator JNK1. Consistent with these changes, serine phosphorylation of insulin receptor substrate 1 was reduced, and Akt activation and glucose 4 membrane translocation were increased. In conclusion, upregulation of DGAT1 in skeletal muscle is sufficient to recreate the athlete's paradox and illustrates a mechanism of exercise-induced enhancement of muscle insulin sensitivity. Thus, increasing muscle DGAT activity may offer a new approach to prevent and treat insulin resistance and type 2 diabetes mellitus.

Role of ROS and MAPK in TPA-induced ICAM-1 expression in the myeloid ML-1 cell line

Intercellular adhesion molecule 1 (ICAM-1) has been implicated in playing a key role in the mechanism of inflammatory process initiated in response to environmental agents, and during normal hematopoietic cell differentiation. Though induction of ICAM-1 by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in myeloid cells has been reported, the molecular mechanism by which TPA upregulates ICAM-1 expression remains unclear. In the present study, we investigated the signaling mechanism associated with TPA-induced ICAM-1 expression in ML-1 cells. Herein, our microarray, flow cytometry, and Western blot analysis indicated that ICAM-1 was constitutively expressed at a low level in ML-1 cells, but its expression was further upregulated at both the mRNA and protein levels in response to TPA. ICAM-1 expression in response to TPA was inhibited by pretreatment with GF109203X [a specific inhibitor of protein kinase C (PKC)], or with PD98059 and U0126 (specific inhibitors of MEK), suggesting the importance of PKC, and Erk1/2 signaling cascades in this response. Interestingly, ICAM-1 expression in response to TPA-induced PKC activation was linked to the generation of reactive oxygen species (ROS), as pretreatment with NAC (an ROS scavenger) blocked both ErK1/2 activation and ICAM-1 expression induced by TPA. In addition, TPA-induced ICAM-1 expression was blocked by inhibition of nuclear factor-kappaB (NF-kappaB) activation following pretreatment with BAY11-7085 (a specific inhibitor of NF-kappaB activation). TPA-induced NF-kappaB activation was shown by increased degradation of IkB (NF-kappaB specific inhibitory protein). Together, these observations demonstrated that TPA, a potent activator of PKC, induces ICAM-1 expression via a ROS- and ERK1/2-dependent signaling mechanism in ML-1 cells.

Regulation of progranulin expression in myeloid cells

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34(+) progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-kappaB (NF-kappaB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cell-specific roles for NF-kappaB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-kappaB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.

Regulation of the mitogen-activated protein kinase p44 ERK activity during anoxia/recovery in rainbow trout hypodermal fibroblasts

It is well known from various mammalian cells that anoxia has a major impact on the mitogen-activated protein kinase ERK, but a possible similar effect in fish cells has not been investigated. Here we characterise a p44ERK-like protein in the rainbow trout cell line RTHDF and study the effect of (i) serum stimulation, (ii) sodium azide (chemical anoxia) and removal of azide (recovery) and (iii) anoxia (PO2<0.1%) and recovery. During both chemical and true anoxia p44ERK was inhibited and recovery resulted in robust reactivation of p44ERK activity, far above the initial level. The inhibition was secondary to activation of p38MAPK and the increase was MEK dependent, as SB203580 inhibited the dephosphorylation during anoxia and the presence of PD98059 inhibited phosphorylation of p44ERK during recovery. In addition, we demonstrated that the reactivation of p44ERK during recovery also was dependent on reactive oxygen species and a PP1/PP2A-like phosphatase.

Induction of heat shock proteins may combat insulin resistance

The molecular mechanism responsible for obesity-associated insulin resistance has been partially clarified: increased fatty acid levels in muscle fibers promote diacylglycerol synthesis, which activates certain isoforms of protein kinase C (PKC). This in turn triggers a kinase cascade which activates both IkappaB kinase-beta (IKK-beta) and c-Jun N-terminal kinase (JNK), each of which can phosphorylate a key serine residue in IRS-1, rendering it a poor substrate for the activated insulin receptor. Heat shock proteins Hsp27 and Hsp72 have the potential to prevent the activation of IKK-beta and JNK, respectively; this suggests that induction of heat shock proteins may blunt the adverse impact of fat overexposure on insulin function. Indeed, bimoclomol--a heat shock protein co-inducer being developed for treatment of diabetic neuropathy--and lipoic acid--suspected to be a heat shock protein inducer--have each demonstrated favorable effects on the insulin sensitivity of obese rodents, and parenteral lipoic acid is reported to improve the insulin sensitivity of type 2 diabetics. Moreover, there is reason to believe that heat shock protein induction may have a favorable impact on the microvascular complications of diabetes, and on the increased risk for macrovascular disease associated with diabetes and insulin resistance syndrome. Heat shock protein induction may also have potential for preventing or treating neurodegenerative disorders, controlling inflammation, and possibly even slowing the aging process. The possible complementarity of bimoclomol and lipoic acid for heat shock protein induction should be assessed, and further efforts to identify well-tolerated agents active in this regard are warranted.

RACK1 mediates activation of JNK by protein kinase C [corrected]

Activation of the Jun-N-terminal kinase (JNK) signaling cascade by phorbol esters (TPA) or protein kinase C (PKC) is well documented, although the underlying mechanism is not known. Here, we demonstrate that the receptor for activated C kinase 1 (RACK1) serves as an adaptor for PKC-mediated JNK activation. Phosphorylation of JNK by PKC occurs on Ser129 and requires the presence of RACK1. Ser129 phosphorylation augments JNK phosphorylation by MKK4 and/or MKK7 and is required for JNK activation by TPA, TNFalpha, UV irradiation, and PKC, but not by anisomycin or MEKK1. Inhibition of RACK1 expression by siRNA attenuates JNK activation, sensitizes melanoma cells to UV-induced apoptosis, and reduces their tumorigenicity in nude mice. In finding the role of RACK1 in activation of JNK by PKC, our study also highlights the nature of crosstalk between these two signal-transduction pathways.

Transcriptional involvement of protein kinase C-alpha isozyme in amphetamine-mediated appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. The anorectic action of AMPH has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. The molecular mechanisms behind this anorectic action of AMPH are still unclear. This study investigated the possible role of protein kinase C (PKC) isotypes in this anorectic action. Results revealed that most PKC isotypes (alpha, betaII, gamma, delta, eta, lambda and zeta), except betaI and epsilon isotypes, were stimulated during a repeated treatment of AMPH. Among these stimulated isotypes, three isotypes (alpha, delta, lambda) were activated and expressed in a similar manner, while the other isotypes were expressed differently and specifically. To determine if PKCalpha was involved in the anorectic response of AMPH, the infusions of antisense oligonucleotide into the brain were performed 1 h before daily AMPH treatment in freely moving rats, and the results showed that PKCalpha knock down could block the anorectic response and restore NPY mRNA levels in AMPH-treated rats. These results suggest that PKC isotypes- (at least the alpha isotype), related modification of NPY gene expression in hypothalamus might play an essential role in the central regulation of AMPH-mediated feeding suppression.

ERK is an anti-inflammatory signal that suppresses expression of NF-kappaB-dependent inflammatory genes by inhibiting IKK activity in endothelial cells

Unveiling of endothelial nuclear factor-kappaB (NF-kappaB) activation is pivotal for understanding the inflammatory reaction and the pathogenesis of inflammatory vascular diseases. We here report the novel function of extracellular signal-related kinase (ERK) in controlling endothelial NF-kappaB activation and inflammatory responses. In human endothelial cells, vascular endothelial growth factor (VEGF) induced NF-kappaB-dependent transcription of cell adhesion molecules (CAMs) and monocyte adhesion. These effects were prominently enhanced by either pretreatment with the MEK inhibitors, PD98059 and U0126 or overexpression of a dominant negative form of MEK, but blocked by a wild type ERK. Consistently, inhibition of ERK significantly increased IkappaB kinase (IKK) activity, IkappaBalpha phosphorylation, and nuclear translocation of NF-kappaB induced by VEGF, whereas overexpression of ERK resulted in the loss of these responses to VEGF. Using two PKC inhibitors has demonstrated that VEGF concomitantly stimulates IKK and its negative regulatory signal ERK through PKC that lies downstream of KDR/Flk-1. Strikingly, elevation of ERK in endothelial cells markedly inhibited CAM expression and NF-kappaB activation as well as monocyte adhesion induced by IL-1beta and TNF-alpha. The data collectively suggest that ERK serves as an anti-inflammatory signal that suppresses expression of NF-kappaB-dependent inflammatory genes by inhibiting IKK activity in endothelial cells. Measuring the existence of ERK activity in vascular endothelial cells may be useful for predicting the feasibility and potency of inflammatory reactions in the vasculature.

Involvement of PKC and ROS in the cytotoxic mechanism of anti-leukemic decursin and its derivatives and their structure–activity relationship in human K562 erythroleukemia and U937 myeloleukemia cells

Protein kinase C (PKC) plays an important role in the proliferation and differentiation of various cell types including normal and leukemic hematopoietic cells. Recently, various PKC modulators were used as a chemotherapeutic agent of leukemia. Decursin (1), a pyranocoumarin from Angelica gigas, exhibits the cytotoxic effects on various human cancer cell lines and in vitro PKC activation. For the development of more effective anticancer agents with PKC modulation activity, 11 decursin derivatives 2-12 were chemically synthesized and evaluated for their ability to act as a tumor-suppressing PKC activator and as an antagonist to phorbol 12-myristate 13-acetate (PMA), a tumor-promoting PKC activator. In the presence of phosphatidylserine (PS), all of 12 compounds 1-12 activated PKC (mainly alpha, beta, and gamma isozymes) but only three compounds 1-3 activated PKC even in the absence of PS. Six compounds 1-6 containing the coumarin structure were cytotoxic to human K562 erythroleukemia and U937 myeloleukemia cells. A cytotoxic mechanism of decursin and its derivatives was investigated using TUR cells, a PKC betaII-deficient variant of U937 cells. Among six compounds 1-6 with cytotoxicity to K562 and U937 leukemia cells, only three compounds 1-3 were cytotoxic to TUR cells. Therefore, compounds 1-3 and 4-6 inhibit the proliferation of leukemia cells in a PKC betaII-independent and dependent manner, respectively, indicating that the side chain of compounds determines the dependency of their cytotoxicity on PKC betaII. To further elucidate the cytotoxic mechanism of compounds 1 and 2, levels of PKC isozymes and generation of reactive oxygen species (ROS) were investigated. Compounds 1-2 induced the down-regulation of PKC alpha and betaII in K562 cells and the production of ROS in U937 cells. Thus, PKC and ROS are probably important factors in the cytotoxic mechanism of compounds 1-2. From these results, the structure-activity relationship of decursin and its derivatives is as follows: (i) the coumarin structure is required for anti-leukemic activity and (ii) the side chain is a determinant of PKC activation and the cytotoxic mechanism in leukemia cells.

Protein kinase C betaII plays an essential role in dendritic cell differentiation and autoregulates its own expression

Dendritic cells (DC) arise from a diverse group of hematopoietic progenitors and have marked phenotypic and functional heterogeneity. The signal transduction pathways that regulate the ability of progenitors to undergo DC differentiation, as well as the specific characteristics of the resulting DC, are only beginning to be characterized. We have found previously that activation of protein kinase C (PKC) by cytokines or phorbol esters drives normal human CD34(+) hematopoietic progenitors and myeloid leukemic blasts (KG1, K562 cell lines, and primary patient blasts) to differentiate into DC. We now report that PKC activation is also required for cytokine-driven DC differentiation from monocytes. Of the cPKC isoforms, only PKC-betaII was consistently activated by DC differentiation-inducing stimuli in normal and leukemic progenitors. Transfection of PKC-betaII into the differentiation-resistant KG1a subline restored the ability to undergo DC differentiation in a signal strength-dependent fashion as follows: 1) by development of characteristic morphology; 2) the up-regulation of DC surface markers; 3) the induction of expression of the NFkappaB family member Rel B; and 4) the potent ability to stimulate allo-T cells. Most unexpectedly, the restoration of PKC-betaII signaling in KG1a was not directly due to overexpression of the transfected classical PKC (alpha, betaII, or gamma) but rather through induction of endogenous PKC-beta gene expression by the transfected classical PKC. The mechanism of this positive autoregulation involves up-regulation of PKC-beta promoter activity by constitutive PKC signaling. These findings indicate that the regulation of PKC-betaII expression and signaling play critical roles in mediating progenitor to DC differentiation.

A role for iNOS in fasting hyperglycemia and impaired insulin signaling in the liver of obese diabetic mice

Chronic inflammation has been postulated to play an important role in the pathogenesis of insulin resistance. Inducible nitric oxide synthase (iNOS) has been implicated in many human diseases associated with inflammation. iNOS deficiency was shown to prevent high-fat diet-induced insulin resistance in skeletal muscle but not in the liver. A role for iNOS in fasting hyperglycemia and hepatic insulin resistance, however, remains to be investigated in obesity-related diabetes. To address this issue, we examined the effects of a specific inhibitor for iNOS, L-NIL, in obese diabetic (ob/ob) mice. iNOS expression was increased in the liver of ob/ob mice compared with wild-type mice. Treatment with iNOS inhibitor reversed fasting hyperglycemia with concomitant amelioration of hyperinsulinemia and improved insulin sensitivity in ob/ob mice. iNOS inhibitor also increased the protein expression of insulin receptor substrate (IRS)-1 and -2 1.5- and 2-fold, respectively, and enhanced IRS-1- and IRS-2-mediated insulin signaling in the liver of ob/ob mice. Exposure to NO donor and ectopically expressed iNOS decreased the protein expression of IRS-1 and -2 in cultured hepatocytes. These results suggest that iNOS plays a role in fasting hyperglycemia and contributes to hepatic insulin resistance in ob/ob mice.

Tetradecanoyl phorbol acetate induces expression of Toll-like receptor 2 in U937 cells: involvement of PKC, ERK, and NF-κB

Toll-like receptors (TLRs) have been identified recently as crucial signaling receptors mediating the innate immune recognition. Though induction of TLR2 or TLR4 by 12-O-tetradecanoyl phorbol 13-acetate (TPA) in leukemia cells has been reported, however, the mechanism by which TPA up-regulates TLR2 or TLR4 remains poorly understood. In this study, we investigated the effect of TPA on induction of TLR2 in U937 cells. TPA markedly induced TLR2 mRNA and protein expressions. TLR2 expression in response to TPA was attenuated by pretreatments with GF109203X and Go6976 (inhibitors of protein kinase C (PKC)) and PD98059 (an inhibitor of extracellular signal-regulated kinases (ERKs)), but not SB203580 (an inhibitor of p38s) and SP600125 (an inhibitor of c-Jun N-terminal kinases), suggesting involvement of PKC and ERKs in this response. Moreover, TPA-induced PKC activation was linked to generation of reactive oxygen species, which were dispensable for TLR2 expression in U937 cells. Pretreatments with GF109203X blocked TPA-induced phosphorylation of ERKs, suggesting activation of ERKs by PKC. In addition, TPA induced nuclear factor-kappaB (NF-kappaB) activation, which was shown by increased nuclear translocation of p65 NF-kappaB and degradation of IkappaB-alpha, a NF-kappaB inhibitory protein. Importantly, TPA-induced TLR2 expression was inhibited by blockage of NF-kappaB activation using NF-kappaB inhibitors, including MG132 and BAY11-7085. Specifically, TPA-induced nuclear translocation of NF-kappaB was effectively attenuated by GF109203X and PD98059, suggesting PKC and ERK regulation of NF-kappaB nuclear localization in response to TPA. Together, these results suggest that TPA-induced TLR2 expression in U937 cells may be at least in part mediated through activation of PKC and ERKs as well as NF-kappaB transcription factor, and that cross-talk between PKC or ERKs and NF-kappaB may exist.

Burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle

The molecular bases underlying burn- or critical illness-induced insulin resistance still remain unclarified. Muscle protein catabolism is a ubiquitous feature of critical illness. Akt/PKB plays a central role in the metabolic actions of insulin and is a pivotal regulator of hypertrophy and atrophy of skeletal muscle. We therefore examined the effects of burn injury on insulin-stimulated Akt/PKB activation in skeletal muscle. Insulin-stimulated phosphorylation of Akt/PKB was significantly attenuated in burned compared with sham-burned rats. Insulin-stimulated Akt/PKB kinase activity, as judged by immune complex kinase assay and phosphorylation status of the endogenous substrate of Akt/PKB, glycogen synthase kinase-3beta (GSK-3beta), was significantly impaired in burned rats. Furthermore, insulin consistently failed to increase the phosphorylation of p70 S6 kinase, another downstream effector of Akt/PKB, in rats with burn injury, whereas phosphorylation of p70 S6 kinase was increased by insulin in controls. The protein expression of Akt/PKB, GSK-3beta, and p70 S6 kinase was unaltered by burn injury. However, insulin-stimulated activation of ERK, a signaling pathway parallel to Akt/PKB, was not affected by burn injury. These results demonstrate that burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle and suggest that attenuated Akt/PKB activation may be involved in deranged metabolism and muscle wasting observed after burn injury.

Inducible nitric-oxide synthase and NO donor induce insulin receptor substrate-1 degradation in skeletal muscle cells

Chronic inflammation plays an important role in insulin resistance. Inducible nitric-oxide synthase (iNOS), a mediator of inflammation, has been implicated in many human diseases including insulin resistance. However, the molecular mechanisms by which iNOS mediates insulin resistance remain largely unknown. Here we demonstrate that exposure to NO donor or iNOS transfection reduced insulin receptor substrate (IRS)-1 protein expression without altering the mRNA level in cultured skeletal muscle cells. NO donor increased IRS-1 ubiquitination, and proteasome inhibitors blocked NO donor-induced reduction in IRS-1 expression in cultured skeletal muscle cells. The effect of NO donor on IRS-1 expression was cGMP-independent and accentuated by concomitant oxidative stress, suggesting an involvement of nitrosative stress. Inhibitors for phosphatidylinositol-3 kinase, mammalian target of rapamycin, and c-Jun amino-terminal kinase failed to block NO donor-induced IRS-1 reduction, whereas these inhibitors prevented insulin-stimulated IRS-1 decrease. Moreover iNOS expression was increased in skeletal muscle of diabetic (ob/ob) mice compared with lean wild-type mice. iNOS gene disruption or treatment with iNOS inhibitor ameliorated depressed IRS-1 expression in skeletal muscle of diabetic (ob/ob) mice. These findings indicate that iNOS reduces IRS-1 expression in skeletal muscle via proteasome-mediated degradation and thereby may contribute to obesity-related insulin resistance.

S-nitrosylation-dependent inactivation of Akt/protein kinase B in insulin resistance

Inducible nitric-oxide synthase (iNOS) has been implicated in many human diseases including insulin resistance. However, how iNOS causes or exacerbates insulin resistance remains largely unknown. Protein S-nitrosylation is now recognized as a prototype of a redox-dependent, cGMP-independent signaling component that mediates a variety of actions of nitric oxide (NO). Here we describe the mechanism of inactivation of Akt/protein kinase B (PKB) in NO donor-treated cells and diabetic (db/db) mice. NO donors induced S-nitrosylation and inactivation of Akt/PKB in vitro and in intact cells. The inhibitory effects of NO donor were independent of phosphatidylinositol 3-kinase and cGMP. In contrast, the concomitant presence of oxidative stress accelerated S-nitrosylation and inactivation of Akt/PKB. In vitro denitrosylation with reducing agent reactivated recombinant and cellular Akt/PKB from NO donor-treated cells. Mutated Akt1/PKBalpha (C224S), in which cysteine 224 was substituted by serine, was resistant to NO donor-induced S-nitrosylation and inactivation, indicating that cysteine 224 is a major S-nitrosylation acceptor site. In addition, S-nitrosylation of Akt/PKB was increased in skeletal muscle of diabetic (db/db) mice compared with wild-type mice. These data suggest that S-nitrosylation-mediated inactivation may contribute to the pathogenesis of iNOS- and/or oxidative stress-involved insulin resistance.

Cooperation between PKC-alpha and PKC-epsilon in the regulation of JNK activation in human lung cancer cells

Phorbol esters can induce activation of two mitogen-activated protein kinase (MAPK) pathways, the extracellular signal-regulated kinase (ERK) pathway and the c-Jun N-terminal kinase (JNK) pathway. Unlike ERK activation, JNK activation by phorbol esters is somehow cell-specific. However, the mechanism(s) that contribute to the cell-specific JNK activation remain elusive. In this study, we found that phorbol 12-myristate 13-acetate (PMA) induced JNK activation only in non-small cell lung cancer (NSCLC) cells, but not in small cell lung cancer (SCLC) cells, whereas ERK activation was detected in both cell types. In NSCLC cells, PMA induced JNK activation in a time- and dose-dependent manner. JNK activation was attenuated by protein kinase C (PKC) down-regulation through prolonged pre-treatment with PMA and significantly inhibited by PKC inhibitors Gö6976 and GF109203X. Subcellular localization studies demonstrated that PMA induced translocation of PKC-alpha, -betaII, and -epsilon isoforms, but not PKC-delta, from the cytosol to the membrane. Analysis of various PKC isoforms revealed that PKC-epsilon was exclusively absent in the SCLC cell lines tested. Ectopic expression of PKC-epsilon in SCLC cells restored PMA activation of JNK signaling only in the presence of PKC-alpha, suggesting that PKC-alpha and PKC-epsilon act cooperatively in regulating JNK activation in response to PMA. Furthermore, using dominant negative mutants and pharmacological inhibitors, we define that a putative Rac1/Cdc42/PKC-alpha pathway is convergent with the PKC-epsilon/MEK1/2 pathway in terms of the activation of JNK by PMA.

During human melanoma progression AP-1 binding pairs are altered with loss of c-Jun in vitro

We demonstrated previously that c-Jun, JunB and c-Fos RNA were dysregulated in metastatic melanoma cells compared with normal human melanocytes. The purpose of this study was to evaluate the distribution in composition of AP-1 dimers in human melanoma pathogenesis. We investigated AP-1 dimer pairing in radial growth phase-like (RGP) (w3211) and vertical growth phase-like (VGP) (w1205) human melanoma cells and metastatic cell lines (cloned from patients, c83-2c, c81-46A, A375, respectively) compared with melanocytes using electrophoretic mobility shift assay (EMSA), Western blot and transfection analyses. There are progressive variations in AP-1 composition in different melanoma cell lines compared with normal melanocytes, in which c-Jun, JunD and FosB were involved in AP-1 complexes. In w3211, c-Jun, JunD and Fra-1 were involved in AP-1 binding, while in w1205, overall AP-1 binding activity was decreased significantly and supershift binding was detected only with JunD antibodies. In metastatic c81-46A and A375 cells, only JunD was involved in AP-1 binding activity, but in a third (c83-2c) c-Jun, JunD and Fra-1 were present. Western blot evaluation detected c-Jun in melanocytes and w3211, but this component was decreased significantly or was not detectable in w1205, c81-46A and A375 cells. In contrast, JunD protein was elevated in c81-46A and c83-2c cells compared with melanocytes and RGP and VGP cell lines. Normal melanocytes and c83-2c cells (which have c-Jun involved in AP-1 binding), transfected with c-Jun antisense and treated with cisplatin, showed higher viability compared with untransfected cells, while in c81-46A cells (in which only JunD is detectable) no change in cell viability was observed following treatment with cisplatin and c-jun antisense transfection. A dominant-negative c-Jun mutant (TAM67) significantly increased the soft agar colony formation of w3211 and c83-2c cells. These results suggest that components of AP-1, especially c-Jun, may offer a new target for the prevention or treatment of human melanoma progression.

Increased insulin receptor substrate 1 serine phosphorylation and stress-activated protein kinase/c-Jun N-terminal kinase activation associated with vascular insulin resistance in spontaneously hypertensive rats

Insulin resistance is associated with cardiovascular disease. Impaired insulin receptor substrate (IRS)-mediated signal transduction is a major contributor to insulin resistance. Recently, IRS-1 phosphorylation at serine 307 by stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) has been highlighted as a molecular event that causes insulin resistance. We investigated IRS-1-mediated insulin signaling, IRS-1 phosphorylation at serine 307, and SAPK/JNK activation status in the aorta of spontaneously hypertensive rats (SHR) by immunoprecipitation and immunoblotting. Insulin-stimulated tyrosine phosphorylation of insulin receptor and IRS-1 in SHR was decreased to 55% (P<0.01) and 40% (P<0.01) of the levels in Wistar-Kyoto rats (WKY), respectively. Insulin-stimulated IRS-1-associated phosphatidylinositol 3-kinase activation in SHR was reduced to 28% of the level in WKY (P<0.0001). Immunoblot analysis revealed that phosphorylated IRS-1 at serine 307 in SHR was increased to 261% (P<0.001) of the level in WKY. Phosphorylated (activated) SAPK/JNK in SHR was increased to 223% of the level in WKY (P<0.01). Serine-phosphorylated IRS-1 that was immunoprecipitated from the aorta of SHR was capable of inhibiting in vitro tyrosine phosphorylation by recombinant insulin receptor compared with WKY-derived IRS-1. These findings demonstrate that insulin resistance in the aorta of SHR was associated with elevated IRS-1 phosphorylation at serine 307 and increased SAPK/JNK activation. The present study suggests that increased SAPK/JNK activation may play an important role in the pathogenesis of vascular insulin resistance via inhibitory serine phosphorylation of IRS-1.

JNK interacting protein 1 (JIP-1) protects LNCaP prostate cancer cells from growth arrest and apoptosis mediated by 12-0-tetradecanoylphorbol-13-acetate (TPA)

12-0-tetradecanoylphorbol-13-acetate (TPA) stimulates protein kinase C (PKC) which mediates apoptosis in androgen-sensitive LNCaP human prostate cancer cells. The downstream signals of PKC that mediate TPA-induced apoptosis in LNCaP cells are unclear. In this study, we found that TPA activates the c-Jun NH₂-terminal kinase (JNK)/c-Jun/AP-1 pathway. To explore the possible role that the JNK/c-Jun/AP-1 signal pathway has on TPA-induced apoptosis in LNCaP cells, we stably transfected the scaffold protein, JNK interacting protein 1 (JIP-1), which binds to JNK inhibiting its ability to phosphorylate c-Jun. TPA (10⁻⁹–10⁻⁷ mol l⁻¹) caused phosphorylation of JNK in both wild-type and JIP-1-transfected (LNCaP-JIP-1) cells. It resulted in phosphorylation and upregulation of expression of c-Jun protein in the wild-type LNCaP cells, but not in the JIP-1-transfected LNCaP cells. In addition, upregulation of AP-1 reporter activity by TPA (10⁻⁹ mol l⁻¹) occurred in LNCaP cells but was abrogated in LNCaP-JIP-1 cells. Thus, TPA stimulated c-Jun through JNK, and JIP-1 effectively blocked JNK. TPA (10⁻¹²–10⁻⁸ mol l⁻¹) treatment of LNCaP cells caused their growth inhibition, cell cycle arrest, upregulation of p53 and p21^waf1, and induction of apoptosis. All of these effects were significantly attenuated when LNCaP-JIP-1 cells were similarly treated with TPA. A previous study showed that c-Jun/AP-1 blocked androgen receptor (AR) signaling by inhibiting AR binding to AR response elements (AREs) of target genes including prostate-specific antigen (PSA). Therefore, we hypothesised that TPA would not be able to disrupt the AR signal pathway in LNCaP-JIP-1 cells. Contrary to expectation, TPA (10⁻⁹–10⁻⁸ mol l⁻¹) inhibited DHT-induced AREs reporter activity and decreased levels of PSA in the LNCaP-JIP-1 cells. Taken together, TPA, probably by stimulation of PKC, phosphorylates JNK, which phosphorylates and increases expression of c-Jun leading to AP-1 activity. Growth control of prostate cancer cells can be mediated through the JNK/c-Jun pathway, but androgen responsiveness of these cells can be independent of this pathway, suggesting that androgen independence in progressive prostate cancer may not occur through activation of this pathway.

Expressions of inhibitory Smads, Smad6 and Smad7, are differentially regulated by TPA in human lung fibroblast cells

Smad6 and Smad7 are inhibitory Smads (I-Smads) with differential inhibitory effects on the regulation of the cellular signalings induced by TGF-beta superfamily. Here, we show that phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) down-regulates Smad6 mRNA expression and up-regulates Smad7 mRNA expression in IMR-90, a human lung fibroblast cell line. These regulations of I-Smads by TPA were suppressed by one PKC inhibitor (Gö6983), but not by another (Gö6976). TPA treatment had little effect on the phosphorylation of novel PKCs (PKCdelta and PKCepsilon), but specifically induced PKCmu phosphorylation, and this effect was inhibited by Gö6983, but not by Gö6976. Additionally, Gö6983 but not Gö6976 inhibited ERK- and JNK-phosphorylation as well as Smad7 promoter activity induced by TPA. MEK inhibitor U0126 inhibited the down-regulation of Smad6 mRNA expression but not the up-regulation of Smad7 mRNA expression. In contrast, JNK inhibitor SP600125 had no such effects. Luciferase reporter analysis revealed that TPA did not induce NF-kappaB activation. In addition, TPA up-regulated Smad7 expression in the presence of NF-kappaB inhibitor TLCK. These findings indicate that TPA down-regulates Smad6 expression presumably via PKCmu-ERK-dependent pathway and up-regulates Smad7 expression via PKCmu-dependent mechanism(s) which need no MAPK and NF-kappaB activation.

Microgravity modifies protein kinase C isoform translocation in the human monocytic cell line U937 and human peripheral blood T-cells

Individual protein kinase C (PKC) isoforms fulfill distinct roles in the regulation of the commitment to differentiation, cell cycle arrest, and apoptosis in both monocytes and T-cells. The human monocyte like cell line U937 and T-cells were exposed to microgravity, during spaceflight and the translocation (a critical step in PKC signaling) of individual isoforms to cell particulate fraction examined. PKC activating phorbol esters induced a rapid translocation of several PKC isoforms to the particulate fraction of U937 monocytes under terrestrial gravity (1 g) conditions in the laboratory. In microgravity, the translocation of PKC beta II, delta, and epsilon in response to phorbol esters was reduced in microgravity compared to 1 g, but was enhanced in weak hypergravity (1.4 g). All isoforms showed a net increase in particulate PKC following phorbol ester stimulation, except PKC delta which showed a net decrease in microgravity. In T-cells, phorbol ester induced translocation of PKC delta was reduced in microgravity, compared to 1 g, while PKC beta II translocation was not significantly different at the two g-levels. These data show that microgravity differentially alters the translocation of individual PKC isoforms in monocytes and T-cells, thus providing a partial explanation for the modifications previously observed in the activation of these cell types under microgravity.

Participation of protein kinase C beta in osteoclast differentiation and function

Protein kinase C (PKC) proteins have been shown to be involved in diverse cellular responses of various cell types. In experiments to identify genes regulated during osteoclast differentiation by a cDNA microarray approach, we found that the gene expression of PKC-betaII was upregulated in differentiated cells. Reverse transcription-polymerase chain reaction and Western blotting analyses also showed an increase in PKC-betaI as well as PKC-betaII during osteoclast formation in mouse bone marrow cell cultures in the presence of macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL). Use of an antisense oligonucleotide to PKC-betaII resulted in a reduction in the RANKL-driven osteoclastogenesis. Pharmacological intervention with PKC-beta activity by the specific inhibitor CG53353 suppressed cellular differentiation and fusion processes during osteoclastogenesis and inhibited bone-resorbing function of mature osteoclasts. PKC-beta inhibition abolished the ERK and MEK activation by macrophage-colony stimulating factor and RANKL in osteoclast precursor cells whereas the cytokine-induced NF-kappaB activation was not hampered by the PKC-beta inhibition. Our findings indicate that PKC-beta has a role in regulation of osteoclast formation and function potentially by participating in the ERK signaling pathway of M-CSF and RANKL.

Exercise, cachexia, and cancer therapy: a molecular rationale

Evidence from recent publications indicates that repeated exercise may enhance the quality of life of cancer patients. The lack of reported negative effects and the consistency of the observed benefits lead one to conclude that physical exercise may provide a low-risk therapy that can improve patients' capacity to perform activities of daily living and improve their quality of life. Repeated physical activity may attenuate the adverse effects of cancer therapy, prevent or reverse cachexia, and reduce risk for a second cancer through suppression of inflammatory responses or enhancement of insulin sensitivity, rates of protein synthesis, and anti-oxidant and phase II enzyme activities. These results most likely come about through the ability of physical exercise to attenuate a chronic inflammatory signaling process and to transiently activate the mitogen-activated protein kinase, c-Jun NH2-terminal kinase, c-Jun NH2-terminal kinase-mitogen-activated protein kinase, and nuclear factor-kappa B pathways and through its ability to enhance insulin sensitivity. Expanded molecular-based research into these areas may provide new insights into the biological mechanisms associated with cancer rehabilitation and endogenous risk.

Interaction of "readthrough" acetylcholinesterase with RACK1 and PKCbeta II correlates with intensified fear-induced conflict behavior

Behavioral reactions to stress are altered in numerous psychiatric and neurodegenerative syndromes, but the corresponding molecular processes and signal transduction pathways are yet unknown. Here, we report that, in mice, the stress-induced splice variant of acetylcholinesterase, AChE-R, interacts intraneuronally with the scaffold protein RACK1 and through it, with its target, protein kinase CbetaII (PKCbetaII), which is known to be involved in fear conditioning. In stress-responsive brain regions of normal FVBN mice, the mild stress of i.p. injection increased AChE and PKCbetaII levels in a manner suppressible by antisense prevention of AChE-R accumulation. Injection stress also prolonged conflict between escape and hiding in the emergence into an open field test. Moreover, transgenic FVBN mice overexpressing AChE-R displayed prolonged delay to emerge into another field (fear-induced behavioral inhibition), associated with chronically intensified neuronal colabeling of RACK1 and PKCbetaII in stress-responsive brain regions. These findings are consistent with the hypothesis that stress-associated changes in cholinergic gene expression regulate neuronal PKCbetaII functioning, promoting fear-induced conflict behavior after stress.

Salicylic acid reverses phorbol 12-myristate-13-acetate (PMA)- and tumor necrosis factor alpha (TNFalpha)-induced insulin receptor substrate 1 (IRS1) serine 307 phosphorylation and insulin resistance in human embryonic kidney 293 (HEK293) cells

Salicylates, including aspirin, have been shown to improve insulin sensitivity both in human and animal models. Although it has been suggested that salicylates sensitize insulin action by inhibiting IkappaB kinase beta (IKKbeta), the detailed mechanisms remain unclear. Protein kinase C isoforms and tumor necrosis factor alpha (TNFalpha) signaling pathways are well described mediators of insulin resistance; they are implicated in the activation of IKKbeta and the subsequent inhibition of proximal insulin signaling via insulin receptor substrate 1 (IRS1) and Akt. This study investigated the effect of salicylic acid on phorbol 12-myristate 13-acetate (PMA)- and TNFalpha-induced insulin resistance in a human embryonic kidney 293 (HEK293) cell line stably expressing recombinant human IRS1. The results showed that both PMA and TNFalpha inhibited insulin-induced Akt phosphorylation and promoted IRS1 phosphorylation on Ser-307. Salicylic acid pretreatment completely reversed the effects of PMA and TNFalpha on both Akt and IRS1. Whereas PMA activated protein kinase C isoforms and IKKbeta, TNFalpha activated neither. On the other hand, both PMA and TNFalpha activated the c-Jun N-terminal kinase (JNK), which has been reported to directly phosphorylate IRS1 Ser-307. SP600125, a JNK inhibitor, prevented PMA and TNFalpha-induced IRS1 Ser-307 phosphorylation. Finally, salicylic acid inhibited JNK activation induced by both PMA and TNFalpha. Taken together, these observations suggest that salicylic acid can reverse the inhibitory effects of TNFalpha on insulin signaling via an IKKbeta-independent mechanism(s), potentially involving the inhibition of JNK activation. The role of JNK in salicylic acid-mediated insulin sensitization, however, requires further validation because the JNK inhibitor SP600125 appears to have other nonspecific activity in addition to inhibiting JNK activity.

PKCalpha-mediated ERK, JNK and p38 activation regulates the myogenic program in human rhabdomyosarcoma cells

We have previously suggested that PKCalpha has a role in 12-O-Tetradecanoylphorbol-13-acetate (TPA)-mediated growth arrest and myogenic differentiation in human embryonal rhabdomyosarcoma cells (RD). Here, by monitoring the signalling pathways triggered by TPA, we demonstrate that PKCalpha mediates these effects by inducing transient activation of c-Jun N-terminal protein kinases (JNKs) and sustained activation of both p38 kinase and extracellular signal-regulated kinases (ERKs) (all referred to as MAPKs). Activation of MAPKs following ectopic expression of constitutively active PKCalpha, but not its dominant-negative form, is also demonstrated. We investigated the selective contribution of MAPKs to growth arrest and myogenic differentiation by monitoring the activation of MAPK pathways, as well as by dissecting MAPK pathways using MEK1/2 inhibitor (UO126), p38 inhibitor (SB203580) and JNK and p38 agonist (anisomycin) treatments. Growth-arresting signals are triggered either by transient and sustained JNK activation (by TPA and anisomycin, respectively) or by preventing both ERK and JNK activation (UO126) and are maintained, rather than induced, by p38. We therefore suggest a key role for JNK in controlling ERK-mediated mitogenic activity. Notably, sarcomeric myosin expression is induced by both TPA and UO126 but is abrogated by the p38 inhibitor. This finding indicates a pivotal role for p38 in controlling the myogenic program. Anisomycin persistently activates p38 and JNKs but prevents myosin expression induced by TPA. In accordance with this negative role, reactivation of JNKs by anisomycin, in UO126-pre-treated cells, also prevents myosin expression. This indicates that, unlike the transient JNK activation that occurs in the TPA-mediated myogenic process, long-lasting JNK activation supports the growth-arrest state but antagonises p38-mediated myosin expression. Lastly, our results with the MEK inhibitor suggest a key role of the ERK pathway in regulating myogenic-related morphology in differentiated RD cells.

Inducible nitric oxide synthase plays a role in LPS-induced hyperglycemia and insulin resistance

The molecular mechanisms underlying endotoxin-induced insulin resistance remain unclear. Endotoxin or lipopolysaccharide (LPS) injection is a potent stimulator of inducible nitric oxide synthase (iNOS). This study in rats, using the specific iNOS inhibitor aminoguanidine, investigated the role of iNOS in endotoxin-induced hyperglycemia and insulin resistance. LPS injection led to hyperglycemia, insulin resistance, and increased iNOS protein expression and activity. Aminoguanidine prevented LPS-induced hyperglycemia without affecting insulin levels or iNOS expression. Aminoguanidine attenuated the LPS-induced insulin resistance, reflected by the requirement for a higher glucose infusion rate to maintain euglycemia during a hyperinsulinemic clamp study. Aminoguanidine completely blocked the LPS-elevated hepatic glucose output and also inhibited LPS-induced increases in hepatic glycogen phosphorylase activities and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression, key enzymes for glycogenolysis and gluconeogenesis, respectively. Thus, these data demonstrate an important role for iNOS in LPS-induced insulin resistance, evidenced by the attenuation of LPS-induced hyperglycemia and reversal of increased hepatic glucose output by aminoguanidine. The protective effect of aminoguanidine on insulin resistance is probably by attenuation of hepatic glucose output via its inhibition of key enzymes for glycogenolysis and gluconeogenesis, including glycogen phosphorylase and PEPCK.

Primary acute myeloid leukaemia blasts resistant to cytokine-induced differentiation to dendritic-like leukaemia cells can be forced to differentiate by the addition of bryostatin-1

Primary acute myeloid leukaemia (AML) blasts can be induced to differentiate into dendritic-like leukaemia cells (DLLC) by culture with certain cytokine combinations. DLLC offer potential for use as autologous vaccines based on their ability to present putative leukaemia-specific antigens to T cells. It has been reported, however, that in around 30-50% of AML cases the leukaemia cells are not capable of undergoing DLLC differentiation. The purpose of this study was to identify the features that represent successful DLLC differentiation and, for those cases shown to be resistant to cytokine-induced differentiation, to use differentiating agents in an attempt to overcome the differentiation block. Leukaemia cells derived from 42 patients with AML were cultured in vitro with cytokines GM-CSF, IL-4 and TNFalpha/CD40L. In 22 cases the leukaemic cells underwent DLLC differentiation based on characteristic morphological changes and expression of costimulatory and dendritic cell-associated molecules. Four cases were not evaluable because of poor viability over the culture period. The remaining 16 cases failed to show evidence of DLLC differentiation. Many of these differentiation resistant cases were associated with poor risk karyotypic features. Nine of the resistant cases were selected for further study. Differentiating agents trichostatin (TSA), azacytidine (AZA) and bryostatin (BRYO) were used in combination with cytokines for the first 96 h of the culture period. Bryostatin (BRYO) alone was shown to be capable of overcoming differentiation resistance and allowing DLLC differentiation to proceed.

Protein kinase C-beta, fibronectin, alpha(5)beta(1)-integrin, and tumor necrosis factor-alpha are required for phorbol diester-induced apoptosis in human myeloid leukemia cells

The human myeloid HL-60 cell line and its cell variant HL-525 were used to study signaling events leading to apoptosis induction by phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC) enzymes. Unlike parental cells, HL-525 cells are PKC-beta deficient and resistant to PMA-induced apoptosis. These cells regain susceptibility to apoptosis induction after transfection with a PKC-beta expression vector. By using this vector and specific neutralizing monoclonal antibodies (mAbs), it was established that PMA-induced apoptosis also called for an interaction between cell-surface alpha(5)beta(1)-integrin and its deposited ligand fibronectin (FN), which is downstream of PKC-beta activation. Experiments with mAbs, the PKC-beta vector, and exogenous FN revealed that the next step entailed an interaction between secreted tumor necrosis factor-alpha and its type I receptor. By using a sphingomyelinase inhibitor, it was concluded that the subsequent step involved ceramide production. Moreover, a permeable ceramide was effective in inducing apoptosis in both HL-60 and HL-525 cells, and this induction was caspase-1 and/or -4 dependent because an inhibitor of these caspases abrogated the induced apoptosis. Based on these and related differentiation studies, we conclude that the above signaling events, the early ones in particular, are shared with PMA-induced macrophage differentiation in the HL-60 cells. It is likely that once these cells acquire their macrophage phenotype and perform their tasks, they become superfluous and are eliminated from the body by a self-triggered apoptotic process that involves our proposed signaling scheme.

The ups and downs of MEK kinase interactions

MEK kinases (MEKKs) comprise a family of related serine-threonine protein kinases that regulate mitogen-activated protein kinase (MAPK) signalling pathways leading to c-Jun NH2-terminal kinase (JNK) and p38 activation, induced by cellular stress (e.g., UV and gamma irradiation, osmotic stress, heat shock, protein synthesis inhibitors), inflammatory cytokines (e.g., tumour necrosis factor alpha, TNFalpha, and interleukin-1, IL1) and G protein-coupled receptor agonists (e.g., thrombin). These stress-activated kinases have been implicated in apoptosis, oncogenic transformation, and inflammatory responses in various cell types. At present, the signalling events involving MEKKs are not well understood. This review summarises our current knowledge concerning the regulation and function of MEKK family members, with particular emphasis on those factors capable of directly interacting with distinct MEKK isoforms.

Pyridinyl imidazole inhibitor SB203580 activates p44/42 mitogen-activated protein kinase and induces the differentiation of human myeloid leukemia cells

Various inhibitors of protein kinases regulate the growth and differentiation of human leukemic cell lines. The pyridinyl imidazole inhibitor SB203580 has been widely used to elucidate the role of p38 kinase in a wide array of biological systems. In the present investigation, we found that SB203580 effectively induced the granulocytic differentiation of human promyelocytic HL-60 cells. In addition to morphological differentiation, it also induced NBT-reduction, lysozyme activity and growth-inhibition. It also induced the differentiation of human myeloid leukemia HT93 and ML-1 cells, but not of other cell lines, such as NB4, U937, THP-1, K562 and HEL. This differentiation was not associated with the inhibition of p38 kinase activity, but was closely associated with the activation of extracellular signal-regulated kinase. These results demonstrate a new activity for this drug.

Activation of c-Jun amino-terminal kinase is required for retinoic acid-induced neural differentiation of P19 embryonal carcinoma cells

P19 embryonal carcinoma cells are known to differentiate into neurons and glia when treated with relatively high concentrations (>100 nM) of retinoic acid (RA). Concomitant with this RA-induced neural differentiation, we observed an activation of the c-Jun amino-terminal kinase (JNK). JNK was required for the RA-induced neural differentiation, because dominant-negative JNK blocked the differentiation. Studies using protein phosphatase inhibitors and protein kinase inhibitors suggested that both okadaic acid-sensitive protein phosphatase(s) and protein kinase C participate in the RA-induced activation of JNK.

Mitochondrial targeting of JNK/SAPK in the phorbol ester response of myeloid leukemia cells

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with activation of the stress-activated protein kinase (SAPK) and induction of terminal monocytic differentiation. The present studies demonstrate that TPA targets SAPK to mitochondria by a mechanism dependent on activation of protein kinase C (PKC) beta. Translocation of SAPK to mitochondria in response to TPA is associated with release of cytochrome c, caspase-3 activation and induction of apoptosis. The results show that TPA induces the association of SAPK with the mitochondrial anti-apoptotic Bcl-x(L) protein. Overexpression of Bcl-x(L) attenuated the apoptotic response to TPA treatment. Moreover, expression of Bcl-x(L) mutated at sites of SAPK phosphorylation (Thr-47, -115) was more effective than wild-type Bcl-x(L) in abrogating TPA-induced cytochrome c release and apoptosis. By contrast, expression of Bcl-x(L) had little effect on induction of the monocytic phenotype. These findings indicate that myeloid leukemia cells respond to TPA with targeting of SAPK to mitochondria and that this response contributes to terminal differentiation through the release of cytochrome c and induction of apoptosis.

Protein kinase C-associated kinase (PKK), a novel membrane-associated, ankyrin repeat-containing protein kinase

A novel murine membrane-associated protein kinase, PKK (protein kinase C-associated kinase), was cloned on the basis of its physical association with protein kinase Cbeta (PKCbeta). The regulated expression of PKK in mouse embryos is consistent with a role for this kinase in early embryogenesis. The human homolog of PKK has over 90% identity to its murine counterpart, has been localized to chromosome 21q22.3, and is identical to the PKCdelta-interacting kinase, DIK (Bahr, C., Rohwer, A., Stempka, L., Rincke, G., Marks, F., and Gschwendt, M. (2000) J. Biol. Chem. 275, 36350-36357). PKK comprises an N-terminal kinase domain and a C-terminal region containing 11 ankyrin repeats. PKK exhibits protein kinase activity in vitro and associates with cellular membranes. PKK exists in three discernible forms at steady state: an underphosphorylated form of 100 kDa; a soluble, cytosolic, phosphorylated form of 110 kDa; and a phosphorylated, detergent-insoluble form of 112 kDa. PKK is initially synthesized as an underphosphorylated soluble 100-kDa protein that is quantitatively converted to a detergent-soluble 110-kDa form. This conversion requires an active catalytic domain. Although PKK physically associates with PKCbeta, it does not phosphorylate this PKC isoform. However, PKK itself may be phosphorylated by PKCbeta. PKK represents a developmentally regulated protein kinase that can associate with membranes. The functional significance of its association with PKCbeta remains to be ascertained.

Granulocyte colony-stimulating factor induces ERK5 activation, which is differentially regulated by protein-tyrosine kinases and protein kinase C. Regulation of cell proliferation and survival

Granulocyte colony-stimulating factor (G-CSF) plays a major role in the regulation of granulopoiesis. Treatment of cells with G-CSF has been shown to activate multiple signal transduction pathways. We show here that Erk5, a novel member of the MAPK family, and its specific upstream activator MEK5 were activated in response to incubation of cells with G-CSF. Different from other members of the MAPK family including Erk1/2, JNK, and p38, maximal activation of Erk5 by G-CSF required the C-terminal region of the G-CSF receptor. Genistein, a specific inhibitor of protein-tyrosine kinases, blocked G-CSF-induced Erk5 activation. In contrast, inhibition of protein kinase C activity increased G-CSF-mediated activation of Erk5 and MEK5, whereas stimulation of protein kinase C activity inhibited activation of the two kinases by G-CSF. The proliferation of BAF3 cells in response to G-CSF was inhibited by expression of a dominant-negative MEK5 but potentiated by expression of a constitutively active MEK5. Expression of the constitutively active MEK5 also increased the survival of BAF3 cells cultured in the absence of or in low concentrations of G-CSF. Together, these data implicate Erk5 as an important signaling component in the biological actions of G-CSF.

Expression of macrophage asialoglycoprotein-binding protein is induced through MAPK classical pathway

Macrophage asialoglycoprotein-binding protein (M-ASGP-BP) is a Gal/GalNAc-specific lectin, which functions as an endocytosis receptor. We found that the expression of M-ASGP-BP mRNA in bone marrow cells was induced during the differentiation into macrophages. To investigate the mechanism by which M-ASGP-BP mRNA expression is induced, we used U937 cells as a model. Treatment of U937 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in M-ASGP-BP mRNA expression within 6 h. This induction was completely inhibited by PKC inhibitors, calphostin C, and staurosporine. Furthermore, MAP kinase inhibitors PD98059, but not SB202190, blocked M-ASGP-BP mRNA expression. These data indicate that M-ASGP-BP mRNA expression occurs through the activation of PKC and the MAPK classical pathway in the course of cell differentiation into macrophages.

Phorbol ester-induced generation of reactive oxygen species is protein kinase cbeta -dependent and required for SAPK activation

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with protein kinase C (PKC) betaII-mediated activation of the stress-activated protein kinase (SAPK) pathway. The present studies demonstrate that the TPA response of U-937 cells includes the generation of reactive oxygen species (ROS). By contrast, the TPA-resistant U-937 cell variant (TUR), which is deficient in PKCbetaII expression, failed to respond to TPA with the induction of ROS. Moreover, we show that TPA-induced ROS production is restored in TUR cells stably transfected to express PKCbetaII. The results also demonstrate that TPA-induced ROS production is required for activation of the MEK kinase-1 (MEKK-1)--> SAPK pathway. In concert with this observation, treatment of U-937 with H(2)O(2) as a source of ROS is associated with activation of the MEKK-1-->SAPK cascade. These findings indicate that PKCbetaII is required for TPA-induced ROS production and that the MEKK-1-->SAPK pathway is activated by a ROS-mediated mechanism.