Isoenzymes of protein kinase C: differential involvement in apoptosis and pathogenesis

Porcine reproductive and respiratory syndrome virus (PRRSV) up-regulates IL-15 through PKCβ1-TAK1-NF-κB signaling pathway

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is one of the most important infectious diseases in swine industry. IL-15 is a pleiotropic cytokine and has been shown to be essential to transform NKs, CD8 T cells, and other cells of the immune systems into functional effectors. Here, we demonstrated that the broad-spectrum or conventional PKC inhibitors repressed PRRSV-induced IL-15 expression and NF-κB activation. Subsequently, we found that the PKCβ specific inhibitor inhibited PRRSV-induced IL-15 production, which was also confirmed by knock-down of PKCβ1, suggesting that PKCβ1 is involved in the PRRSV-induced IL-15 expression. In addition, we demonstrated that PRRSV activated NF-κB through PKCβ1-induced TAK1 activation. Finally, we demonstrated that PRRSV activated PKCβ1 dependent on the participation of TRIF and MAVS. These data indicate that PRRSV up-regulates IL-15 through TRIF/MAVS-PKCβ1-TAK1-NF-κB signaling pathway. These findings will provide new insights into the molecular mechanisms of IL-15 production induced by PRRSV.

The virus-induced HSPs regulate the apoptosis of operatus APCs that result in autoimmunity, not in homeostasis

The viruses stand salient as environmental factors that trigger autoimmunity. The virus realizes its effects through induction of heat-shock proteins (HSPs) as well as by the viral IE-axis-mediated conversion of organ epithelial cells into virgin de novo professional antigen-presenting cells (APCs). The HSP is the accomplished operator in homeostasis by the logic of it being the regulator of apoptosis. By virtue of its regulation of apoptosis, the HSP is also involved in autoimmunity: (1) adornment of viral IE-axis-generated virgin de novo professional APCs with HSP-induced co-stimulatory molecules which transform these otherwise epithelial cells to competent antigen presenters, the operatus APCs, liable to apoptosis that becomes the initiator of organ damages; (2) molecular mimicry mechanism: epitopes on the HSP may be mistaken for viral peptides and be presented by operatus APCs to autoreactive TCRs resulting in the apoptosis of the operatus APCs; (3) regulation of MHC class II DR-mediated apoptosis of operatus APCS which can result in organ-specific autoimmune syndromes. We should remember, however, that Nature's intended purpose for apoptosis of the professional APCs is benevolence: as a principal regulator of immune homeostasis. But the apoptosis of our postulated operatus APCs can result in autoimmunity. The transformation of virgin de novo professional APCs to operatus APCs mirrors the maturation of DCs through their acquisition of HSP-induced costimulatory molecules. What happens to mature DCs as antigen presenters that end in homeostasis is replicated by what happens to operatus APCs that ends instead in autoimmunity.

The virus-induced HSPs regulate the apoptosis of operatus APCs that results in autoimmunity, not in homeostasis

The viruses are salient in the roles of environmental factors that trigger autoimmunity. The virus realizes its effects by the power of its induction of heat shock proteins (HSPs) as well as by the viral IE-axis-mediated conversion of organ epithelial cells into virgin de novo professional antigen-presenting cells (APCs). The HSP is the accomplished operator in homeostasis by the logic of it being the regulator of apoptosis. That HSP which regulates and controls different points in the pathways of apoptosis is rationally propitious as both HSP and apoptosis are highly conserved in multicellular organisms. By virtue of its regulation of apoptosis, the HSP is also involved in human autoimmunity and this involvement is tripartite: (i) adornment of viral IE-axis-generated virgin de novo professional APCs with HSP-induced co-stimulatory molecules which transform these otherwise epithelial cells to achieve the status of fledged competent antigen-presenters, the operatus APCs, which are liable to apoptosis that becomes the initiator of organ damages that can culminate in the autoimmune syndrome(s); apoptosis is a routine fate that befalls all APCs following their antigen presentation; (ii) molecular mimicry mechanism: epitopes on the HSP may be mistaken for viral peptides and be presented by operatus APCs to autoreactive TCRs resulting in the apoptosis of the operatus APCs; and (iii) regulation of MHC class II-DR-mediated apoptosis of operatus APCs which can ultimately consequent in organ-specific autoimmune syndromes. We should remember, however, that Nature's intended purpose for the apoptosis of the professional APCs is benevolence: as a principal regulator of homeostasis. It is only from the apoptosis of our postulated operatus APCs that the apoptotic consequence can be deleterious, an autoimmune syndrome(s). The transformation of virgin de novo professional APCs to operatus APCs mirrors the maturation of DCs, through their acquisition of HSP-induced co-stimulatory molecules; and what happens to mature DCs as antigen-presenters that ends in homeostasis is replicated by what happens to operatus APCs that ends instead in autoimmune syndromes (Fig. 1).

Protein kinase C-beta inhibition induces apoptosis and inhibits cell cycle progression in acquired immunodeficiency syndrome-related non-hodgkin lymphoma cells

INTRODUCTION

Acquired immunodeficiency syndrome (AIDS)-related non-Hodgkin lymphoma (NHL) constitutes an aggressive variety of lymphomas characterized by increased extranodal involvement, relapse rate, and resistance to chemotherapy. Protein kinase C-beta (PKCβ) targeting showed promising results in preclinical and clinical studies involving a wide variety of cancers, but studies describing the role of PKCβ in AIDS-NHL are primitive if not lacking.

METHODS

In the present study, 3 AIDS-NHL cell lines were examined: 2F7 (AIDS-Burkitt lymphoma), BCBL-1 (AIDS-primary effusion lymphoma), and UMCL01-101 (AIDS-diffuse large B-cell lymphoma).

RESULTS

Immunoblot analysis demonstrated expression of PKCβ1 and PKCβ2 in 2F7 and UMCL01-101 cells, and PKCβ1 alone in BCBL-1 cells. The viability of 2F7 and BCBL-1 cells decreased significantly in the presence of PKCβ-selective inhibitor at half-maximal inhibitory concentration of 14 and 15 μmol/L, respectively, as measured by tetrazolium dye reduction assay. In contrast, UMCL01-101 cells were relatively resistant. As determined using flow cytometric deoxynucleotidyl transferase dUTP nick-end labeling assay with propidium iodide staining, the responsiveness of sensitive cells was associated with apoptotic induction and cell cycle inhibition. Protein kinase C-beta-selective inhibition was observed not to affect AKT phosphorylation but to induce a rapid and sustained reduction in the phosphorylation of glycogen synthase kinase-3 beta, ribosomal protein S6, and mammalian target of rapamycin in sensitive cell lines.

CONCLUSIONS

The results indicate that PKCβ plays an important role in AIDS-related NHL survival and suggest that PKCβ targeting should be considered in a broader spectrum of NHL. The observations in BCBL-1 were unexpected in the absence of PKCβ2 expression and implicate PKCβ1 as a regulator in those cells.

Protein kinase C-beta inhibition induces apoptosis and inhibits cell cycle progression in acquired immunodeficiency syndrome-related non-hodgkin lymphoma cells

INTRODUCTION

Acquired immunodeficiency syndrome (AIDS)-related non-Hodgkin lymphoma (NHL) constitutes an aggressive variety of lymphomas characterized by increased extranodal involvement, relapse rate, and resistance to chemotherapy. Protein kinase C-beta (PKCβ) targeting showed promising results in preclinical and clinical studies involving a wide variety of cancers, but studies describing the role of PKCβ in AIDS-NHL are primitive if not lacking.

METHODS

In the present study, 3 AIDS-NHL cell lines were examined: 2F7 (AIDS-Burkitt lymphoma), BCBL-1 (AIDS-primary effusion lymphoma), and UMCL01-101 (AIDS-diffuse large B-cell lymphoma).

RESULTS

Immunoblot analysis demonstrated expression of PKCβ1 and PKCβ2 in 2F7 and UMCL01-101 cells, and PKCβ1 alone in BCBL-1 cells. The viability of 2F7 and BCBL-1 cells decreased significantly in the presence of PKCβ-selective inhibitor at half-maximal inhibitory concentration of 14 and 15 μmol/L, respectively, as measured by tetrazolium dye reduction assay. In contrast, UMCL01-101 cells were relatively resistant. As determined using flow cytometric deoxynucleotidyl transferase dUTP nick-end labeling assay with propidium iodide staining, the responsiveness of sensitive cells was associated with apoptotic induction and cell cycle inhibition. Protein kinase C-beta-selective inhibition was observed not to affect AKT phosphorylation but to induce a rapid and sustained reduction in the phosphorylation of glycogen synthase kinase-3 beta, ribosomal protein S6, and mammalian target of rapamycin in sensitive cell lines.

CONCLUSIONS

The results indicate that PKCβ plays an important role in AIDS-related NHL survival and suggest that PKCβ targeting should be considered in a broader spectrum of NHL. The observations in BCBL-1 were unexpected in the absence of PKCβ2 expression and implicate PKCβ1 as a regulator in those cells.

Protein kinase C: an attractive target for cancer therapy

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

Apoptotic induction in B-cell acute lymphoblastic leukemia cell lines treated with a protein kinase Cβ inhibitor

B-cell acute lymphoblastic leukemia (B-ALL) in adults exhibits a 5-year disease-free survival rate of only 25-40% after currently available treatment. Protein kinase Cβ (PKCβ) is under active consideration as a rational therapeutic target in several B-cell malignancies, but studies of its possible utility in B-ALL are lacking. Expression of PKCβ1 and PKCβ2 isoforms was demonstrated in five B-ALL cell lines characterized by distinctive chromosomal translocations, and sensitivity to PKCβ-selective inhibition was examined. Inhibitor treatment resulted in a dose-dependent reduction in viability in all cell lines, although pro-B ALL with t(4;11)(q21;q23) was most sensitive. Apoptotic induction was evident after 24-48 h of treatment, and an inhibition of cell cycle progression was detected in one cell line. Treatment resulted in a rapid induction of poly(ADP-ribose) polymerase (PARP) cleavage, indicating caspase-3-mediated apoptosis, and a rapid reduction in phosphorylation of AKT and its downstream target glycogen synthase kinase 3β (GSK3β). These results indicate that PKCβ targeting should be considered as a potential treatment option in B-ALL.

Novel antileukemic compound ingenol 3-angelate inhibits T cell apoptosis by activating protein kinase Ctheta

Members of the protein kinase C (PKC) family of serine-threonine kinases are important regulators of immune cell survival. Ingenol 3-angelate (PEP005) activates a broad range of PKC isoforms and induces apoptosis in acute myeloid leukemia cells by activating the PKC isoform PKCdelta. We show here that, in contrast to its effect on leukemic cells, PEP005 provides a strong survival signal to resting and activated human T cells. The antiapoptotic effect depends upon the activation of PKC. This PKC isoform is expressed in T cells but is absent in myeloid cells. Further studies of the mechanism involved in this process showed that PEP005 inhibited activated CD8(+) T cell apoptosis through the activation of NFkappaB downstream of PKC, leading to increased expression of the antiapoptotic proteins Mcl-1 and Bcl-x(L). Transfection of CD8(+) T cells with dominant-negative PKC diminished the prosurvival effect of PEP005 significantly. Ectopic expression of PKC in the acute myeloid leukemia cell line NB4 turned their response to PEP005 from an increased to decreased rate of apoptosis. Therefore, in contrast to myeloid leukemia cells, PEP005 provides a strong survival signal to T cells, and the expression of functional PKC influences whether PKC activation leads to an anti- or proapoptotic outcome in the cell types tested.

Oral enzastaurin in prostate cancer: a two-cohort phase II trial in patients with PSA progression in the non-metastatic castrate state and following docetaxel-based chemotherapy for castrate metastatic disease

PURPOSE

Enzastaurin is an oral serine/threonine kinase inhibitor of the beta isoform of protein kinase C that may have therapeutic activity in prostate cancer. We explored the efficacy of enzastaurin on two cohorts of patients with prostate cancer progression in the castrate state.

PATIENTS AND METHODS

A two-cohort phase II trial was conducted, with both groups participating simultaneously. Cohort 1 consisted of patients with non-metastatic castrate prostate-specific antigen progressive disease. Cohort 2 consisted of patients with castrate metastatic disease with progression following docetaxel-based chemotherapy. Patients in both cohorts received 500 mg/day enzastaurin.

RESULTS

Therapy was well tolerated in both cohorts. One complete response was observed in Cohort 1, with limited activity in the majority of patients. In Cohort 2, no objective responses were seen and the median progression-free survival (11 weeks [90% confidence interval: 7.6, 11.7]) did not differ from the historical control.

CONCLUSIONS

Enzastaurin as a single agent has limited activity in castrate progressive prostate cancer. Evaluation in combination with docetaxel is ongoing.

Rac/ROS-related protein kinase C and phosphatidylinositol-3-kinase signaling are involved in a negative regulating cascade in B cell activation by antibody-mediated cross-linking of MHC class II molecules

In addition to their essential role in antigen presentation, MHC class II molecules have been widely described as receptors associated with signal transduction involved in regulating B cell function. However, their precise function and mechanism in signal transduction are not yet fully elucidated. Our previous studies demonstrated that cross-linking of MHC class II molecules led to the inhibition of resting B cell activation in which various signal molecules were involved. Especially, Rac-associated ROS-dependent MAP kinases, including ERK1/2 and p38, are involved in MHC class II-associated negative signal transduction in the phorbol 12, 13-dibutyrate (PDBU)-treated, but not LPS-treated, resting B cell line, 38B9. In this study, we further illustrated that PKC regulates downstream signal molecules, including MAP kinases and NF-kappaB in PDBU-stimulated resting B cells, together with Rac and ROS. In addition, we found that phosphatidylinositol 3-kinase (PI3K)-dependent activation of ERK/p38 MAP kinases was associated with the signaling procedure in PDBU-induced B cell activation. Collectively, Rac/ROS-related PKC and PI3K signaling are involved in a negative regulation cascade through the cross-linking of MHC class II molecules by anti-MHC class II antibodies in resting B cells.

New approaches for cancer treatment: antitumor drugs based on gene-targeted nucleic acids

Currently, the main way to fight cancer is still chemotherapy. This method of treatment is at the height of its capacity, so, setting aside the need for further improvements in traditional treatments for neoplasia, it is vital to develop now approaches toward treating malignant tumors. This paper reviews innovational experimental approaches to treating malignant malformations based on the use of gene-targeted drugs, such as antisense oligonucleotides (asON), small interfering RNA (siRNA), ribozymes, and DNAzymes, which can all inhibit oncogene expression. The target genes for these drugs are thoroughly characterized, and the main results from pre-clinical and first-step clinical trials of these drugs are presented. It is shown that the gene-targeted oligonucleotides show considerable variations in their effect on tumor tissue, depending on the target gene in question. The effects range from slowing and stopping the proliferation of tumor cells to suppressing their invasive capabilities. Despite their similarity, not all the antisense drugs targeting the same region of the mRNA of the target-gene were equally effective. The result is determined by the combination of the drug type used and the region of the target-gene mRNA that it complements.

Protein kinases C isozymes are differentially expressed in human breast carcinomas

AIMS

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

MAIN METHODS

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

KEY FINDINGS

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

SIGNIFICANCE

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

Exploitation of protein kinase C: a useful target for cancer therapy

Protein kinase C is a family of serine/threonine kinases. The PKC family is made up of at least 12 isozymes, which have a role in cell proliferation, differentiation, angiogenesis, and apoptosis. Activation of PKC isozyme is dependent on tyrosine-kinase receptors and G-protein-coupled receptors. PKC isozymes regulate multiple signaling pathways including PI3-K/Akt, MAPK, and GSK-3beta. PKC isozymes have variable roles in tumor biology which in part depend on the cell type and intracellular localization. PKC isozymes are commonly dysregulated in the cancer of the prostate, breast, colon, pancreatic, liver, and kidney. Currently, several classes of PKC inhibitors are being evaluated in clinical trials and several challenges in targeting PKC isozymes have been recently identified. In conclusion, PKC remains a promising target for cancer prevention and therapy.

Protein kinase C: a target for therapy in pancreatic cancer

OBJECTIVES

Protein kinase C (PKC) is involved in tumor growth and apoptosis and hence represents a potential target for cancer therapy. This study investigated the expression of PKC in pancreatic tumor tissue in comparison to adjacent normal tissue and determined the modulation of PKC by bryostatin-1 (BRYO) on pancreatic cancer cell lines.

METHODS

Pancreatic tissue was obtained from 18 patients who had a resection (14 with ductal adenocarcinoma and 4 with adenoma and high-grade dysplasia). Cytosolic and nuclear membrane PKCs in the paired samples were determined by immunoblotting. HPAC cells were treated with gemcitabine and BRYO and in sequential and concomitant combination. To evaluate cell viability, apoptosis, and electrophoretic mobility shift assay, 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, enzyme-linked immunosorbent assay, and nuclear factor kappaB (NF-kappaB) assays were used.

RESULTS

As compared with the adjacent normal tissue, PKC-alpha, PKC-beta1, and PKC-delta were higher in the tumor; PKC-epsilon was higher in the normal tissue. Pretreatment with gemcitabine followed by BRYO resulted in decreased cell viability, increased apoptosis, and inhibited NF-kappaB than either agent alone or BRYO followed by gemcitabine.

CONCLUSION

Protein kinase C is overexpressed and activated in pancreatic cancer as compared with normal tissue. Inhibition of PKC could sensitize pancreatic cancer cell lines to the effects of gemcitabine. The potentiation of gemcitabine by BRYO is sequence-dependent and mediated through inhibition of PKC-dependent activation of NF-kappaB.

Cdc42- and Rac1-mediated endothelial lumen formation requires Pak2, Pak4 and Par3, and PKC-dependent signaling

Rho GTPases regulate a diverse spectrum of cellular functions involved in vascular morphogenesis. Here, we show that Cdc42 and Rac1 play a key role in endothelial cell (EC) lumen and tube formation as well as in EC invasion in three-dimensional (3D) collagen matrices and that their regulation is mediated by various downstream effectors, including Pak2, Pak4, Par3 and Par6. RNAi-mediated or dominant-negative suppression of Pak2 or Pak4, two major regulators of cytoskeletal signaling downstream of Cdc42 or Rac1, markedly inhibits EC lumen and tube formation. Both Pak2 and Pak4 phosphorylation strongly correlate with the lumen formation process in a manner that depends on protein kinase C (PKC)-mediated signaling. We identify PKCepsilon and PKCzeta as regulators of EC lumenogenesis in 3D collagen matrices. Two polarity proteins, Par3 and Par6, are also required for EC lumen and tube formation, as they establish EC polarity through their association with Cdc42 and atypical PKC. In our model, disruption of any member in the Cdc42-Par3-Par6-PKCzeta polarity complex impairs EC lumen and tube formation in 3D collagen matrices. This work reveals novel regulators that control the signaling events mediating the crucial lumen formation step in vascular morphogenesis.

Aspirin-induced apoptosis in human gastric cancer epithelial cells: relationship with protein kinase C signaling

This study examined the relationship of protein kinase C (PKC) signaling with apoptosis induced by aspirin (ASA) in gastric surface cancer cells (AGS cell line). We found increased expression of two PKC isoforms (alpha and betaII) that translocated from the cytosol into the cell membrane fraction after ASA (40 mM) stimulation. PKC betaI expression markedly decreased in response to ASA treatment. This process was independent of caspase activation because no caspase inhibitors used (i.e., inhibitors to caspase 3, 6, 7, 8, and total caspase activity) significantly changed PKC processing, although inhibition of caspase cascade activity markedly attenuated the apoptosis induced by ASA as measured by DNA-histone complex formation. Upstream PKC signaling induced by ASA seems to play an important role in the regulation of apoptosis because PKC inhibitors significantly reduced the magnitude of DNA-histone complex formation. We conclude that ASA-induced apoptosis in gastric cancer cells is mediated, at least in part, through a PKC mechanism involving the (alpha) and (beta) isoforms and that PKC signaling operates upstream of the caspase cascade, which when activated elicits its downstream effects on DNA degradation.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Protein kinase C beta enhances growth and expression of cyclin D1 in human breast cancer cells

Although alterations in the expressions of protein kinase C (PKC) have been implicated in breast carcinogenesis, the roles of specific isoforms in this process remain elusive. In the present study, we examined the specific roles of PKCbeta1 and beta2 in growth control in human breast cancer cell lines. The PKCbeta-specific inhibitor LY379196 significantly inhibited growth of the breast cancer cell lines MCF-7, MDA-MB-231, and BT474, but not the normal mammary epithelial cell line MCF-10F. Treatment of MCF-7 cells with LY379196 caused an increase in the fraction of cells in the G(1) phase of the cell cycle. To explore the roles of PKCbeta1 and beta2, we used cDNA expression vectors that encode wild-type and constitutively activated or dominant negative mutants of these two proteins. When compared with vector controls, derivatives of MCF-7 cells that stably overexpress wild-type PKCbeta1 or PKCbeta2 displayed a slight increase in growth rate; derivatives that stably express the constitutively active mutants of PKCbeta1 or PKCbeta2 displayed a marked increase in growth rate; and derivatives that stably express a dominant negative mutant of PKCbeta1 or beta2 displayed inhibition of growth. The derivatives of MCF-7 cells that stably express the constitutively activated mutants of PKCbeta1 or beta2 were more resistant to growth inhibition by LY379196 than the vector control MCF-7 cells. Immunoblot analysis indicated that MCF-7 cells that stably overexpress wild-type or constitutively activated mutants of PKCbeta1 or beta2 had higher cellular levels of cyclin D1 than vector control cells, whereas cells that express a dominant negative mutant had decreased levels of cyclin D1. The derivatives that stably express the constitutively activated mutants of PKCbeta1 or beta2 also displayed increased cyclin D1 promoter activity in transient transfection luciferase reporter assays, and this induction of activity requires activator protein 1. Constitutively activated PKCbeta1 and beta2 also enhanced the transcription of c-fos in transient transfection luciferase reporter assays. Thus, PKCbeta1 and beta2 may play important positive roles in the growth of at least a subset of human breast cancers. Therefore, inhibitors of these isoforms may be useful in breast cancer chemoprevention or therapy.

Phase I Study of Bryostatin 1 and Gemcitabine

PURPOSE

Bryostatin 1 is a macrocyclic lactone with protein kinase C inhibitory activity. Gemcitabine is a nucleotide analogue with a broad spectrum of anticancer activity. Bryostatin 1 enhanced the activity of antitumor agents including gemcitabine in preclinical models. The primary objective of this phase I study was to determine the recommended doses for phase II trials of bryostatin 1 and gemcitabine.

EXPERIMENTAL DESIGN

Eligible patients had histologic or cytologic diagnosis of nonhematologic cancer refractory to conventional treatment; life expectancy of >3 months; normal renal, hepatic, and bone marrow function; and a Southwest Oncology Group performance status of 0 to 2. Gemcitabine was administered i.v. over 30 minutes and was followed by bryostatin 1 by i.v. infusion over 24 hours on days 1, 8, and 15 of a 28-day cycle. Bryostatin 1 (microg/m(2)) and gemcitabine (mg/m(2)) doses were escalated as follows: 25/600, 25/800, 25/1,000, 30/1,000, 35/1,000, and 45/1,000, respectively.

RESULTS

Thirty-six patients (mean age, 57 years; male/female 15:21) were treated. The median number of treatment cycles per patient was 3 (range, 0-24). Four patients developed dose limiting toxicities: myalgia, 2; myelosuppression, 1; and elevation of serum alanine aminotransferase levels, 1. Ten grade 3 toxicities were observed (anemia, 2; neutropenia, 5; thrombocytopenia, 3). No treatment-related death was seen. The recommended doses for phase II trials for bryostatin 1 and gemcitabine were 35 microg/m(2) and 1,000 mg/m(2), respectively. Two heavily pretreated patients with breast and colon cancer experienced partial responses lasting 22 and 8 months, respectively. Eight patients had stable disease.

CONCLUSION

The combination of bryostatin 1 and gemcitabine seemed to be well tolerated with limited grade 3 toxicity. The recommended dose of bryostatin 1 in combination with full doses of gemcitabine was 35 microg/m(2).

Caspases 3 and 9 are translocated to the cytoskeleton and activated by thrombin in human platelets. Evidence for the involvement of PKC and the actin filament polymerization

Platelets express, among others, initiator caspase 9 and effector caspase 3. Upon activation by physiological agonists, calcium ionophores or under shear stress they might develop apoptotic events. Although it is well known that the cytoskeletal network plays a crucial role in apoptosis, the relationship between caspases 3 and 9 and the cytoskeleton is poorly understood. Here we demonstrate that the physiological agonist thrombin is able to induce activation of caspases 3 and 9 in human platelets and significantly increases the amount in the cytoskeleton of the active forms of both caspases and the procaspases 3 and 9. After stimulation with thrombin the amount of active caspases 3 and 9 in the cytosolic and cytoskeletal fractions were significantly reduced in Ro-31-8220-treated cells, which demonstrates that caspases activation and association with the cytoskeleton needs the contribution of PKC. Inhibition of actin polymerization by cytochalasin D inhibits translocation and activation of both caspases, suggesting that thrombin stimulates caspase 3 and 9 activation and association with the reorganizing actin cytoskeleton. Finally, our results show that inhibition of thrombin-induced caspase activation has no effect on their translocation to the cytoskeleton although impairment of thrombin-evoked caspase translocation has negative effects on caspase activity, suggesting that translocation to the cytoskeleton might be important for caspase activation by thrombin in human platelets.

Protein kinase C involvement in deoxycholate-induced apoptosis in human gastric cells

Bile acids, such as deoxycholic acid (DC), are known to mediate some of their actions by differentially activating various protein kinase C (PKC) isoforms. This study confirms that DC induces apoptosis in gastric epithelial cells through PARP and caspase cascade activation, and examined the role of PKC in DC-induced apoptosis. We found increased activation of PKC in membrane fractions in response to DC that was concentration and time related. The PKC (beta(I)) isoform expression increased with translocation into the cell membrane fraction after DC (300 microM) stimulation. In contrast, PKCepsilon expression markedly decreased in response to DC treatment in a time- and concentration-dependent manner. In addition, this process was regulated by caspases, since the pan-caspase inhibitor z-VAD-fmk and caspase-3-, -6-, and -9-specific inhibitors prevented PKC (beta(I)) and (epsilon epsilon processing induced by DC. Treatment with the caspase-8-specific inhibitor, however, did not affect expression of either PKC isoform. No significant differences in the apoptotic response were observed when PKC (epsilon) overexpressed cells were exposed to DC in the presence of calcium-dependent conventional PKC inhibitors (Gö 6850 or Gö 6976). Our findings demonstrate that PKC is activated in gastric epithelial cells treated with DC with the PKC (beta(I)) and PKC (epsilon) isoforms being particularly involved in this process. The processing of PKC (beta(I) and epsilon) was shown to be closely regulated by caspases; however, modulations in PKC isoform concentrations by themselves have no effect on the apoptotic death of gastric mucosal cells induced by DC.

Up-regulation and increased phosphorylation of protein kinase C (PKC) delta, mu and theta in the degenerating rd1 mouse retina

The rd1 mouse serves as a model for inherited photoreceptor degeneration: retinitis pigmentosa. Microarray techniques were employed to compare the transcriptomes of rd1 and congenic wild-type retinas at postnatal day 11, when degenerative processes have started but most photoreceptors are still present. Of the several genes that were differentially expressed, focus was put on those associated with the protein kinase C (PKC) signaling pathway, in particular PKCdelta, mu and theta. Microarray identified these as being up-regulated in the rd1 retina, which was confirmed by QRT-PCR. Western blotting and immunostaining, using antibodies against either total or phosphorylated variants of the PKC isoforms, revealed increased expression and phosphorylation of PKCdelta, mu and theta in the rd1 retina at the protein level as well. Our results suggest that these PKC isoforms are involved in rd1 degeneration.

Cleavage of focal adhesion proteins and PKCdelta during lovastatin-induced apoptosis in spontaneously immortalized rat brain neuroblasts

We have previously shown that lovastatin induces apoptosis in spontaneously immortalized rat brain neuroblasts. Focal adhesion proteins and protein kinase Cdelta (PKCdelta) have been implicated in the regulation of apoptosis. We found that lovastatin exposure induced focal adhesion kinase, Crk-associated substrate (p130(Cas)), PKCdelta cleavage and caspase-3 activation in a concentration-dependent manner. Lovastatin effects were fully prevented by mevalonate. The cleavage of p130(Cas) was almost completely inhibited by z-DEVD-fmk, a specific caspase-3 inhibitor, and z-VAD-fmk, a broad spectrum caspase inhibitor, indicating that cleavage is mediated by caspase-3. In contrast, the lovastatin-induced cleavage of PKCdelta was only blocked by z-VAD-fmk suggesting that PKCdelta cleavage is caspase-dependent but caspase-3-independent. Additionally, z-VAD-fmk partially prevented lovastatin-induced neuroblast apoptosis. The present data show that lovastatin may induce neuroblast apoptosis by both caspase-dependent and independent pathways. These findings may suggest that the caspase-dependent component leading to the neuroblast cell death is likely to involve the cleavage of focal adhesion proteins and PKCdelta, which may be partially responsible for some biochemical features of neuroblast apoptosis induced by lovastatin.

Exogenous IL-7 induces Fas-mediated human neuronal apoptosis: potential effects during human immunodeficiency virus type 1 infection

The use of exogenous cytokines is part of translational immune-antiretroviral approaches to induce immune reconstitution and possibly eliminate the persistence of human immunodeficiency virus type 1 (HIV-1) in virally suppressed infected individuals on highly active antiretroviral therapy (HAART). Recently, our laboratories demonstrated that interleukin-7 (IL-7) has significant efficiency in stimulating HIV-1 replication from proviral latency in CD4+ T lymphocytes of infected patients. The authors now investigated the possible role of IL-7 in HIV-1-associated dementia (HAD). The authors demonstrated that the IL-7 receptor is expressed on both human neurons (i.e., differentiated NT2 cells) and human astrocytes, with relatively higher mRNA levels in neurons. The translational protein levels of IL-7 receptor alpha were not proportional to those of the mRNA levels in these central nervous system (CNS)-based cell types. Exogenous IL-7 was observed to only slightly down-regulate IL-7 receptor alpha expression on both neurons and astrocytes, as assayed by Western blotting. Instead of promoting survival, surprisingly, exogenous IL-7 induced neuronal apoptosis, as detected by TUNEL assays. Furthermore, IL-7 augmented neuronal apoptosis induced by HIV-1 gp120. Human apoptosis genomic microarray analyses of IL-7-treated human neurons showed up-regulated expression of proapoptotic genes: protein kinases, caspase-10, FAST kinase, tumor necrosis factor (TNF) receptor, and BCL2-antagonist of cell death. These data suggest that IL-7 leads to neuronal apoptosis by a molecular mechanism(s) that occurs via Fas-mediated activation-induced cell death. These studies may therefore not only be key in evaluating the potential use of IL-7 in vivo as a therapeutic modality, but also suggest that IL-7, which is increased endogenously in HIV-1-infected individuals late in disease, may be involved in the neuronal apoptosis demonstrated during HAD.

Suppression of protein kinase Cepsilon mediates 17beta-estradiol-induced neuroprotection in an immortalized hippocampal cell line

Although estrogens are neuroprotective in a variety of neuroprotection models, the precise underlying mechanisms are currently not well understood. Here, we examined the role of protein kinase C (PKC) in mediating estrogen-induced neuroprotection in the HT-22 immortalized hippocampal cell line. The neuroprotection model utilized calcein fluorescence to quantitate cell viability following glutamate insults. 17beta-Estradiol (betaE2) protected HT-22 cells when treatment was initiated before or after the glutamate insult. The inhibition of PKC by bis-indolylmaleimide mimicked and enhanced betaE2-induced neuroprotection. In contrast, the inhibition of specific PKC isozymes (alpha and beta) by Go6976, inhibition of 1-phosphatidylinositol 3 kinase by wortmannin, or inhibition of protein kinase A by H-89, did not alter cell viability, suggesting a specific involvement of PKC in an isozyme-dependent manner. We further examined whether estrogen interacts with PKC in a PKC isozyme-specific manner. Protein levels and activity of PKC isozymes (alpha, delta, epsilon, and zeta) were assessed by western blot analysis and radiolabeled phosphorylation assays respectively. Among the isozymes tested, betaE2 altered only PKCepsilon; it reduced the activity and membrane translocation of PKCepsilon in a manner that correlated with its protection against glutamate toxicity. Furthermore, betaE2 reversed the increased activity of membrane PKCepsilon induced by glutamate. These data suggest that the neuroprotective effects of estrogens are mediated in part by inhibition of PKCepsilon activity and membrane translocation.

PEP005, a selective small-molecule activator of protein kinase C, has potent antileukemic activity mediated via the delta isoform of PKC

Ingenol 3-angelate (PEP005) is a selective small molecule activator of protein kinase C (PKC) extracted from the plant Euphorbia peplus, whose sap has been used as a traditional medicine for the treatment of skin conditions including warts and cancer. We report here that PEP005 also has potent antileukemic effects, inducing apoptosis in myeloid leukemia cell lines and primary acute myeloid leukemia (AML) cells at nanomolar concentrations. Of importance, PEP005 did not induce apoptosis in normal CD34+ cord blood myeloblasts at up to 2-log concentrations higher than those required to induce cell death in primary AML cells. The effects of PEP005 were PKC dependent, and PEP005 efficacy correlated with expression of PKC-delta. The delta isoform of PKC plays a key role in apoptosis and is therefore a rational potential target for antileukemic therapies. Transfection of KG1a leukemia cells, which did not express PKC-delta or respond to PEP005, with enhanced green fluorescent protein (EGFP)-PKC-delta restored sensitivity to induction of apoptosis by PEP005. Our data therefore suggest that activation of PKC-delta provides a novel approach for treatment of acute myeloid leukemia and that screening for PKC-delta expression may identify patients for potential responsiveness to PEP005. (Blood. 2005;106:1362-1368)

Neuroprotective effects of resveratrol against beta-amyloid-induced neurotoxicity in rat hippocampal neurons: involvement of protein kinase C

1. Resveratrol, an active ingredient of red wine extracts, has been shown to exhibit neuroprotective effects in several experimental models. 2. The present study evaluated the neuroprotective effects of resveratrol against amyloid beta(Abeta)-induced toxicity in cultured rat hippocampal cells and examined the role of the protein kinase C (PKC) pathway in this effect. 3. Pre-, co- and post-treatment with resveratrol significantly attenuated Abeta-induced cell death in a concentration-dependent manner, with a concentration of 25 microm being maximally effective. 4. Pretreatment (1 h) of hippocampal cells with phorbol-12-myristate-13-acetate, a PKC activator, at increasing concentrations (1-100 ng x ml(-1)), resulted in a dose-dependent reduction in Abeta-induced toxicity, whereas the inactive 4alpha-phorbol had no effect. 5. Pretreatment (30 min) of hippocampal cells with GF 109203X (1 microm), a general PKC inhibitor, significantly attenuated the neuroprotective effect of resveratrol against Abeta-induced cell death. 6. Treatment of hippocampal cells with resveratrol (20 microm) also induced the phosphorylation of various isoforms of PKC leading to activation. 7. Taken together, the present results indicate that PKC is involved in the neuroprotective action of resveratrol against Abeta-induced toxicity.

Glycoprotein Isolated fromSolanum nigrumL. Modulates the Apoptotic-Related Signals in 12-O-Tetradecanoylphorbol 13-Acetate-Stimulated MCF-7 Cells

Solanum nigrum L. (SNL) has been used in folk medicine for its anti-inflammatory activity. We isolated only the SNL glycoprotein from SNL and found that it was cytotoxic at low concentration. With respect to cytotoxicity, we investigated whether purified SNL glycoprotein is able to regulate protein kinase C (PKC) alpha activation and nuclear factor (NF)- kappaB activities in 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced tumor promotion, and whether it has an apoptosis-inducing effect in MCF-7 cells using western blot analysis. In addition, to elucidate the relationship between PKCalpha and NF-kappaB, inhibitory studies were performed with staurosporine (an inhibitor of phospholipid/calcium-dependent protein kinase) and pyrrolidine dithiocarbamate (an inhibitor of NF-kappaB activation). To verify induction of apoptosis by the SNL glycoprotein, we performed DNA fragmentation and nuclear staining assays using ethidium bromide and bisbenzamide H33342. The results in this study indicated that SNL glycoprotein induces apoptosis through modulation of PKCalpha and NF-kappaB activity in MCF-7 cells. In fact, SNL glycoprotein interfered with PKCalpha membrane translocation and inhibited NF-kappaB (p50) protein activity in MCF-7 cells stimulated with TPA (61.68 ng/mL, 100 nM) dose-dependently. Regarding the apoptotic-inducing effect, nucleosomal DNA fragmentation and nuclear staining by SNL glycoprotein in MCF-7 cells were shown. Collectively, the data demonstrate that SNL glycoprotein is a potential natural anticancer agent because of its ability to induce apoptosis in MCF-7 cells.

Erythropoietin on a tightrope: balancing neuronal and vascular protection between intrinsic and extrinsic pathways

Enthusiasm for erythropoietin (EPO) as a broad cytoprotective agent continues to increase at an almost exponential rate. The premise that EPO was required only for erythropoiesis was eventually shed by recent work demonstrating the existence of EPO and its receptor in other organs and tissues outside of the liver and the kidney, such as the brain and heart. As a result, EPO has been identified as a possible candidate in the formulation of therapeutic strategies for both cardiac and nervous system diseases. EPO has been shown to mediate an array of vital cellular functions that involve progenitor stem cell development, cellular protection, angiogenesis, DNA repair, and cellular longevity. An important requirement to achieve the goal of preventing or even reducing cellular injury by any cytoprotective agent is the ability to uncover the cellular pathways that ultimately drive a cell to its demise. We present for consideration several critical cellular pathways modulated by EPO that involve Janus kinase 2 (Jak2), the serine-threonine kinase Akt, forkhead transcription factors, glycogen synthase kinase-3beta (GSK-3beta), cellular calcium, protein kinase C, caspases, as well as the control of inflammatory microglial activation. As we continue to gain new insight into these pathways, EPO should emerge as a critical agent for the development, maturation, and survival of cells throughout the body.

Molecular mechanisms of action and prediction of response to oxaliplatin in colorectal cancer cells

The platinum compound oxaliplatin has been shown to be an effective chemotherapeutic agent for the treatment of colorectal cancer. In this study, we investigate the molecular mechanisms of action of oxaliplatin to identify means of predicting response to this agent. Exposure of colon cancer cells to oxaliplatin resulted in G2/M arrest and apoptosis. Immunofluorescent staining demonstrated that the apoptotic cascade initiated by oxaliplatin is characterised by translocation of Bax to the mitochondria and cytochrome c release into the cytosol. Oxaliplatin treatment resulted in caspase 3 activation and oxaliplatin-induced apoptosis was abrogated by inhibition of caspase activity with z-VAD-fmk, but was independent of Fas/FasL association. Targeted inactivation of Bax or p53 in HCT116 cells resulted in significantly increased resistance to oxaliplatin. However, the mutational status of p53 was unable to predict response to oxaliplatin in a panel of 30 different colorectal cancer cell lines. In contrast, the expression profile of these 30 cell lines, assessed using a 9216-sequence cDNA microarray, successfully predicted the apoptotic response to oxaliplatin. A leave-one-out cross-validation approach was used to demonstrate a significant correlation between experimentally observed and expression profile predicted apoptosis in response to clinically achievable doses of oxaliplatin (R=0.53; P=0.002). In addition, these microarray experiments identified several genes involved in control of apoptosis and DNA damage repair that were significantly correlated with response to oxaliplatin.

The phospholipid scramblase PLSCR1 increases UV induced apoptosis primarily through the augmentation of the intrinsic apoptotic pathway and independent of direct phosphorylation by protein kinase C delta

Cell death by apoptosis can be caused by the DNA mutagen UV light whose exposure causes the direct activation of both the caspase 9 regulated cell damage intrinsic pathway and the caspase 8 regulated plasma membrane extrinsic pathway. We determined that increased activity of the plasma membrane phospholipid scramblase, PLSCR1, amplified UV mediated apoptosis primarily through the activation of the intrinsic apoptotic pathway. The caspase 8 inhibitor z-IETD-fmk was not as effective an inhibitor of PLSCR1 augmented UV induced apoptosis compared to treatment with caspase 3, caspase 9, or pan-caspase inhibitors. The inability of the caspase 8 inhibitor to decrease UV induced apoptosis was dependent on PLSCR1, as UV induced apoptosis was decreased by a similar amount in the control cells in the presence of inhibitors of caspase 8, caspase 9, caspase 3, or the pan-caspase inhibitor. PKC-delta directly phosphorylates human PLSCR1 resulting in increased PLSCR1 scramblase activity. PKC-delta can also be activated by caspase mediated cleavage resulting in the release of a constitutively active kinase domain. We observed that replacing the PKC-delta phosphorylation site of PLSCR1 with an alanine did not affect the ability of PLSCR1 to enhance UV induced apoptosis implying that PKC-delta does not directly phosphorylate PLSCR1 to increase plasma membrane scramblase activity during apoptosis. Cells transfected with a PLSCR1 mutant that contained an alanine substitution at its known PKC-delta phosphorylation site underwent UV induced apoptosis at a level similar to those transfected with wild type PLSCR1. The combined results indicate that UV exposure in cells possessing PLSCR1 increases apoptosis primarily by enhancement of the intrinsic apoptotic pathway, and also imply that the increased apoptosis observed upon exposure to UV light is not through direct phosphorylation of PLSCR1 by PKC-delta.

The tamoxifen-induced suppression of telomerase activity in the human hepatoblastoma cell line HepG2: a result of post-translational regulation

PURPOSE

Patients with advanced hepatocellular carcinoma (HCC) have shown to benefit from tamoxifen treatment. The mechanisms of tamoxifen action in HCC, however, are not yet clearly understood. Results from studies on the human hepatoblastoma cell line HepG2 provide evidence that estrogen-receptor-alpha-independent antiproliferative actions of tamoxifen in HCC are mediated by the suppression of telomerase activity [5].

MATERIALS AND METHODS

We investigate the pathway of the tamoxifen-induced down-regulation of telomerase activity, using HepG2 cells incubated over 24 h or 48 h in the presence of 20 microM tamoxifen.

RESULTS

The transcriptional levels of the three telomerase core components-human telomerase RNA (hTR), human telomerase reverse transcriptase (hTERT) (all variants), and telomerase-associated protein (TP1)-did not change during tamoxifen treatment, as revealed by RT-PCR analysis. Furthermore, the hTERT splice pattern was not shifted from the active full-length variant (+alpha/+beta) to the inactive deletion variants (-alpha; -beta; -alpha/-beta) and the level of the 120 kDa hTERT full-length protein remained constant, as shown by Western blot analysis. Protein kinase C (PKC) activity has been suggested to be crucial for post-translational up-regulation of telomerase activity. In HepG2 cells, we observed a tamoxifen-induced suppression of the total protein kinase C (PKC) activity (cytosolic and membrane-bound). Inhibition of PKC with bisindolylmaleimide I resulted in a reduction of telomerase activity, as revealed by TRAP-assay. Alpha-tocopherol (vitamin E) diminished the effects of tamoxifen on PKC-activity as well as on telomerase activity.

CONCLUSIONS

We conclude that the tamoxifen-induced decrease of telomerase activity in HepG2 cells is mediated post-translationally via suppression of PKC-activity.

Antisense targeting protein kinase C alpha and beta1 inhibits gastric carcinogenesis

Protein kinase C (PKC) family, which functions through serine/threonine kinase activity, is involved in signal transduction pathways necessary for cell proliferation, differentiation, and apoptosis. Its critical role in neoplastic transformation and tumor invasion renders PKC a potential target for anticancer therapy. In this study, we investigated the effect of targeting individual PKCs on gastric carcinogenesis. We established gastric cancer cell lines stably expressing antisense PKCalpha, PKCbeta1, and PKCbeta2 cDNA. These stable transfectants were characterized by cell morphology, cell growth, apoptosis, and tumorigenicity in vitro and in vivo. PKCalpha-AS and PKCbeta1-AS transfectants showed a different morphology with flattened, long processes and decreased nuclear:cytoplasmic ratio compared with the control cells. Cell growth was markedly inhibited in PKCalpha-AS and PKCbeta1-AS transfectants. PKCalpha-AS and PKCbeta1-AS cells were more responsive to mitomycin C- or 5-fluorouracil-induced apoptosis. However, antisense targeting of PKCbeta2 did not have any significant effect on cell morphology, cell growth, or apoptosis. Furthermore, antisense inhibition of PKCalpha and PKCbeta1 markedly suppressed colony-forming efficiency in soft agar and in nude mice xenografts. Inhibition of PKCalpha or PKCbeta1 significantly suppressed transcriptional and DNA binding activity of activator protein in gastric cancer cells, suggesting that PKCalpha or PKCbeta1 exerts their effects on cell growth through regulation of activator protein activity. These data provide evidence that targeting PKCalpha and PKCbeta1 by antisense method is a promising therapy for gastric cancer.

Characterization of the Interaction of Ingenol 3-Angelate with Protein Kinase C

Ingenol 3-angelate (I3A) is one of the active ingredients in Euphorbia peplus, which has been used in traditional medicine. Here, we report the initial characterization of I3A as a protein kinase C (PKC) ligand. I3A bound to PKC-alpha in the presence of phosphatidylserine with high affinity; however, under these assay conditions, little PKC isoform selectivity was observed. PKC isoforms did show different sensitivity and selectivity for down-regulation by I3A and phorbol 12-myristate 13-acetate (PMA) in WEHI-231, HOP-92, and Colo-205 cells. In all of the three cell types, I3A inhibited cell proliferation with somewhat lower potency than did PMA. In intact CHO-K1 cells, I3A was able to translocate different green fluorescent protein-tagged PKC isoforms, visualized by confocal microscopy, with equal or higher potency than PMA. PKC-delta in particular showed a different pattern of translocation in response to I3A and PMA. I3A induced a higher level of secretion of the inflammatory cytokine interleukin 6 compared with PMA in the WEHI-231 cells and displayed a marked biphasic dose-response curve for the induction. I3A was unable to cause the same extent of association of the C1b domain of PKC-delta with lipids, compared with PMA or the physiological regulator diacylglycerol, and was able to partially block the association induced by these agents, measured by surface plasmon resonance. The in vitro kinase activity of PKC-alpha induced by I3A was lower than that induced by PMA. The novel pattern of behavior of I3A makes it of great interest for further evaluation.

Tetrandrine-induced apoptosis is mediated by activation of caspases and PKC-δ in U937 cells

Tetrandrine, which is isolated from Chinese herb Stephania tetrandrae, possesses anti-inflammatory, immunosuppressive, and cytoprotective properties. Though it was previously shown that tetrandrine causes a G1 blockade and apoptosis in various cell types, however, the mechanism by which tetrandrine initiates apoptosis remains poorly understood. In present study, we investigated the mechanisms of apoptosis induced by tetrandrine in U937 leukemia cells. Tetrandrine inhibited U937 cell growth by inducing apoptosis. After treatment of U937 cells with tetrandrine (10microM) for 24h, alteration of cell morphology, chromatin fragmentation, cytochrome c release, and caspase activation were observed. Tetrandrine also induced early oxidative stress, which resulted in activation of JNK, but not ERK and p38 MAPK. A broad-spectrum caspase inhibitor and antioxidants significantly blocked tetrandrine-induced caspase-3 activation. However, inhibition of the JNK activity with SP600125 did not block tetrandrine-induced apoptosis. Tetrandrine-induced apoptosis of U937 cells also required activity of PKC-delta, because pretreatment with a specific PKC-delta inhibitor greatly blocked tetrandrine-induced caspase-3 activation. In addition, the apoptotic response to tetrandrine was significantly attenuated in dominant-negative PKC-delta transfected MCF-7 cells, suggesting that PKC-delta plays an important role in tetrandrine-induced apoptosis and can induce caspase activation. These results suggest that tetrandrine induces oxidative stress, JNK activation, and caspase activation. However, JNK activation by ROS is not involved in the tetrandrine-induced apoptosis. In addition, tetrandrine induces caspase-dependent generation of a catalytically active fragment of PKC-delta, and this fragment also appears to play a role in the activation of caspases.

Conjugated Linoleic Acid Inhibits Proliferation and Modulates Protein Kinase C Isoforms in Human Prostate Cancer Cells

Prostate cancer is the second most common cancer in men. The disease etiology is poorly understood, but diet and lifestyle are contributory factors. Conjugated linoleic acids (CLAs), naturally occurring fatty acids in ruminant food products, have antitumor properties in animal models of cancer and antiproliferative effects on cancer cells in vitro. The cellular mechanisms by which CLAs elicit these effects are unclear, particularly for prostate cancer cells. We have previously identified protein kinase C (PKC) isoforms, alpha, delta, iota, mu, and zeta in LNCaP prostate cancer cells. The objective of this study was to determine the effects of CLAs (individual cis-9, trans-11 and trans-10, cis-12 isoforms and a 50:50 mixture) on PKC isoform abundance in LNCaP cells. Confluent cells were treated with 6, 25, and 50 microM CLA for 0.5, 6, and 24 h. Cytosol and membrane protein fractions were assayed for PKC isoforms (mainly alpha and delta but also iota, mu, and zeta) by Western blot analysis using specific antibodies. CLAs clearly modulated the abundance of these PKC isoforms, both positively and negatively, depending on the isoform, concentration of CLAs, and period of treatment. Increased PKC-delta and decreased PKC-iota membrane abundance was consistent with CLAs eliciting increased apoptosis and, in part, with their antitumor effects.

Identification of Two Distinct Pathways of Protein Kinase Cα Down-regulation in Intestinal Epithelial Cells

Signal transduction pathways are controlled by desensitization mechanisms, which can affect receptors and/or downstream signal transducers. It has long been recognized that members of the protein kinase C (PKC) family of signal transduction molecules undergo down-regulation in response to activation. Previous reports have indicated that key steps in PKCalpha desensitization include caveolar internalization, priming site dephosphorylation, ubiquitination of the dephosphorylated protein, and degradation by the proteasome. In the current study, comparative analysis of PKCalpha processing induced by the PKC agonists phorbol 12-myristate 13-acetate and bryostatin 1 in IEC-18 rat intestinal epithelial cells demonstrates that: (a) at least two pathways of PKCalpha down-regulation can co-exist within cells, and (b) a single PKC agonist can activate both pathways at the same time. Using a combined biochemical and morphological approach, we identify a novel pathway of PKCalpha desensitization that involves ubiquitination of mature, fully phosphorylated activated enzyme at the plasma membrane and subsequent down-regulation by the proteasome. The phosphatase inhibitors okadaic acid and calyculin A accelerated PKCalpha down-regulation and inhibitors of vesicular trafficking did not prevent degradation of the protein, indicating that neither internalization nor priming site dephosphorylation are requisite intermediate steps in this ubiquitin/proteasome dependent pathway of PKCalpha down-regulation. Instead, caveolar trafficking and dephosphorylation are involved in a second, proteasome-independent mechanism of PKCalpha desensitization in this system. Our findings highlight subcellular distribution and phosphorylation state as critical determinants of PKCalpha desensitization pathways.

Inhibition of neutrophil apoptosis by type 1 IFN depends on cross-talk between phosphoinositol 3-kinase, protein kinase C-delta, and NF-kappa B signaling pathways

Neutrophils are abundant, short-lived leukocytes with a key role in the defense against rapidly dividing bacteria. They enter apoptosis spontaneously within 24-48 h of leaving the bone marrow. However, their life span can be extended during inflammatory responses by several proinflammatory cytokines. Inappropriate survival of neutrophils contributes to chronic inflammation and tissue damage associated with diseases such as rheumatoid arthritis. We have previously reported that type I IFNs can inhibit both cytokine deprivation and Fas-induced apoptosis in activated T cells. IFN-beta locally produced by hyperplastic fibroblasts within the pannus tissue of patients with rheumatoid arthritis contributes to the inappropriately extended life span of infiltrating T cells. Type I IFNs are equally effective at delaying spontaneous apoptosis in human neutrophils. In the work presented here we investigated the signaling pathways involved in mediating this effect. The antiapoptotic actions of IFN-beta were targeted at an early stage of neutrophil apoptosis, occurring upstream of mitochondrial permeability transition, and were phosphatidylinositol 3-kinase (PI3K) dependent, as they were blocked by the PI3K inhibitor LY294002. Analysis of signaling pathways downstream of PI3K revealed that the antiapoptotic effect of type 1 IFN was inhibited by rottlerin, SN50, and cycloheximide, indicating requirements for activation of protein kinase C-delta, NF-kappaB, and de novo protein synthesis, respectively. Moreover, EMSA was used to show that the activation of NF-kappaB occurred downstream of PI3K and protein kinase C-delta activation. We conclude that type I IFNs inhibit neutrophil apoptosis in a PI3K-dependent manner, which requires activation of protein kinase C-delta and induction of NF-kappaB-regulated genes.

Survival pathways regulating the apoptosis induced by tumour necrosis factor-alpha in primary cultured bovine endothelial cells

The aim of the present study was to identify biochemical pathways driving the resistance of endothelial cells to apoptosis induced by tumour necrosis factor-alpha (TNF). (1) Although nuclear factor-kappa B (NF-kappaB) was activated by TNF, its inhibition by MG-132 failed to sensitize these cells. (2) The activation of protein kinase C (PKC) by phorbol ester completely abolished the TNF-induced cell death. (3) The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin (Wo) triggered apoptosis and enhanced the TNF-induced cell death. (4) The MEK inhibitor PD98059 did not affect the TNF-induced apoptotic process. (5) The p38 is activated by TNF and its inhibition by SB203580 sensitized the cells to TNF. This is correlated with the inhibition of phosphorylation of heat-shock protein of 27 kDa (HSP27). These results indicate that TNF activates NF-kappaB, which does not drive any anti-apoptotic response, and p38, which plays an anti-apoptotic function probably through HSP27 phosphorylation. Moreover, PKC and PI3K are involved in the control of survival pathways.

Opposing effects of butyrate and bile acids on apoptosis of human colon adenoma cells: differential activation of PKC and MAP kinases

Butyrate, produced in the colon by fermentation of dietary fibre, induces apoptosis in colon adenoma and cancer cell lines, which may contribute to protection against colorectal cancer. However, butyrate is present in the colon along with other dietary factors, including unconjugated bile acids, which are tumour promoters. We have shown previously that the proapoptotic effects of butyrate on AA/C1 human adenoma cells were reduced in the presence of bile acids. To determine the cellular basis of this interaction, we examined the effects of butyrate and the secondary bile acid ursodeoxycholic acid (UDCA) on signalling pathways known to regulate apoptosis using AA/C1 cells. Butyrate activated PKC-delta and p38 MAP (mitogen-activated protein) kinase, whereas UDCA activated PKC-alpha and p42/44 MAP kinase. Butyrate treatment also resulted in the caspase-3-mediated proteolysis of PKC-delta. Butyrate-induced apoptosis was reduced by inhibitors of PKC-delta (Rottlerin), p38 MAP kinase (SB202190) and caspase 3 (DEVD-fmk), whereas the proliferative/survival effects of UDCA were blocked by inhibitors of PKC-alpha (Gö6976) and MEK 1 (PD98059). The effects of butyrate and bile acids are therefore mediated by the differential activation of signalling pathways that are known to regulate apoptosis.

Estrogen activates protein kinase C in neurons: role in neuroprotection

It has been previously demonstrated that estrogen can protect neurons from a variety of insults, including beta-amyloid (Abeta). Recent studies have shown that estrogen can rapidly modulate intracellular signaling pathways involved in cell survival. In particular, estrogen activates protein kinase C (PKC) in a variety of cell types. This enzyme plays a key role in many cellular events, including regulation of apoptosis. In this study, we show that 17beta-estradiol (E2) rapidly increases PKC activity in primary cultures of rat cerebrocortical neurons. A 1 h pre-treatment with E2 or phorbol-12-myristate-13-acetate (PMA), a potent activator of PKC, protects neurons against Abeta toxicity. Protection afforded by both PMA and E2 is blocked by pharmacological inhibitors of PKC. Further, depletion of PKC levels resulting from prolonged PMA exposure prevents subsequent E2 or PMA protection. Our results indicate that E2 activates PKC in neurons, and that PKC activation is an important step in estrogen protection against Abeta. These data provide new understanding into the mechanism(s) underlying estrogen neuroprotection, an action with therapeutic relevance to Alzheimer's disease and other age-related neurodegenerative disorders.

Synthesis of a simplified bryostatin C-ring analogue that binds to the CRD2 of human PKC-alpha and construction of a novel BC-analogue by an unusual Julia olefination process

[structure: see text] The synthesis of two truncated bryostatin analogues 2 and 3 is described. High-field NMR measurements on the C-ring analogue 3 in C(2)H(3)CN containing 25% (2)H(2)O have shown that it binds to the CRD2 of human PKC-alpha at virtually the same position as phorbol-13-acetate (PA) and bryostatin 1 (1). NMR titration studies have also revealed that 3 binds to the CRD2 with a potency similar in magnitude to PA but much less potently than 1.

Characterization of p21Ras-mediated apoptosis induced by protein kinase C inhibition and application to human tumor cell lines

Suppression of PKC activity can selectively induce apoptosis in cells expressing a constitutively activated p21Ras protein. We demonstrate that continued expression of p21Ras activity is required in PKC-mediated apoptosis because farnesyltransferase inhibitors abrogated the loss of viability in p21Ras-transformed cells occurring following PKC inhibition. Studies utilizing gene transfer or viral vectors demonstrate that transient expression of oncogenic p21Ras activity is sufficient for induction of apoptosis by PKC inhibition, whereas physiologic activation of p21Ras by growth factor is not sufficient to induce apoptosis. Mechanistically, the p21Ras-mediated apoptosis induced by PKC inhibition is dependent upon mitochondrial dysregulation, with a concurrent loss of mitochondrial membrane potential (psim). Cyclosporine A, which prevented the loss of psim, also inhibited HMG-induced DNA fragmentation in cells expressing an activated p21Ras. Induction of apoptosis by PKC inhibition in human tumors with oncogenic p21Ras mutations was demonstrated. Inhibition of PKC caused increased apoptosis in MIA-PaCa-2, a human pancreatic tumor line containing a mutated Ki-ras allele, when compared to HS766T, a human pancreatic tumor line with normal Ki-ras alleles. Furthermore, PKC inhibition induced apoptosis in HCT116, a human colorectal tumor line containing an oncogenic Ki-ras allele but not in a subline (Hke3) in which the mutated Ki-ras allele had been disrupted. The PKC inhibitor 1-O-hexadecyl-2-O-methyl-rac-glycerol (HMG), significantly reduced p21Ras-mediated tumor growth in vivo in a nude mouse MIA-PaCa-2 xenograft model. Collectively these studies suggest the therapeutic feasibility of targeting PKC activity in tumors expressing an activated p21Ras oncoprotein.

Novel target for induction of apoptosis by cyclo-oxygenase-2 inhibitor SC-236 through a protein kinase C-beta(1)-dependent pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of gastrointestinal cancers. Recently, a similar protective effect has been demonstrated by the specific cyclo-oxygenase-2 (COX-2) inhibitors. However, the exact mechanism that accounts for the anti-proliferative effect of specific COX-2 inhibitors is still not fully understood, and it is still controversial whether these protective effects are predominantly mediated through the inhibition of COX-2 activity and prostaglandin synthesis. Identification of molecular targets regulated by COX-2 inhibitors could lead to a better understanding of their pro-apoptotic and anti-neoplastic activities. In the present study, we investigated the effect and the possible molecular target of a COX-2-specific inhibitor SC-236 on gastric cancer. We showed that SC-236 induced apoptosis in gastric cancer cells. However, this effect was not dependent on COX-2 inhibition. SC-236 down-regulated the protein expression and kinase activity of PKC-beta(1), increased the expression of PKCdelta and PKCeta, but did not alter the expression of other PKC isoforms in AGS cells. Moreover, exogenous prostaglandins or PGE(2) receptor antagonists could not reverse the inhibition effect on PKCbeta(1) by SC-236, which suggested that this effect occurred through a mechanism independent of cyclo-oxygenase activity and prostaglandin synthesis. Overexpression of PKCbeta(1) attenuated the apoptotic response of AGS cells to SC-236 and was associated with overexpression of p21(waf1/cip1). Inhibition of PKCbeta(1)-mediated overexpression of p21(waf1/cip1) partially reduced the anti-apoptotic effect of PKCbeta(1). The down-regulation of PKCbeta(1) provides an explanation for COX-independent apoptotic effects of specific COX-2 inhibitor in cultured gastric cancer cells. We also suggest that PKCbeta(1) act as survival mediator in gastric cancer, and its down-regulation by COX-2 inhibitor SC-236 may provide new target for future treatment of gastric cancer.

Involvement of protein kinase C activation and cell survival/ cell cycle genes in green tea polyphenol (-)-epigallocatechin 3-gallate neuroprotective action

Studies from our laboratory have demonstrated that the major green tea polyphenol, (-)-epigallocatechin 3-gallate (EGCG), exerts potent neuroprotective actions in the mice model of Parkinson's disease. These studies were extended to neuronal cell culture employing the parkinsonism-inducing neurotoxin, 6-hydroxydopamine (6-OHDA). Pretreatment with EGCG (0.1-10 microm) attenuated human neuroblastoma (NB) SH-SY5Y cell death, induced by a 24-h exposure to 6-OHDA (50 microm). Potential cell signaling candidates involved in this neuroprotective effect were further examined. EGCG restored the reduced protein kinase C (PKC) and extracellular signal-regulated kinases (ERK1/2) activities caused by 6-OHDA toxicity. However, the neuroprotective effect of EGCG on cell survival was abolished by pretreatment with PKC inhibitor GF 109203X (1 microm). Because EGCG increased phosphorylated PKC, we suggest that PKC isoenzymes are involved in the neuroprotective action of EGCG against 6-OHDA. In addition, gene expression analysis revealed that EGCG prevented both the 6-OHDA-induced expression of several mRNAs, such as Bax, Bad, and Mdm2, and the decrease in Bcl-2, Bcl-w, and Bcl-x(L). These results suggest that the neuroprotective mechanism of EGCG against oxidative stress-induced cell death includes stimulation of PKC and modulation of cell survival/cell cycle genes.

Increase in glutamate-induced neurotoxicity by activated astrocytes involves stimulation of protein kinase C

Activation of astrocytes is a common feature of neurological disorders, but the importance of this phenomenon for neuronal outcome is not fully understood. Treatment of mixed hippocampal cultures of neurones and astrocytes from day 2-4 in vitro (DIV 2-4) with 1 micro m cytosine arabinofuranoside (AraC) caused an activation of astrocytes as detected by a stellate morphology and a 10-fold increase in glial fibrillary acidic protein (GFAP) level compared with vehicle-treated cultures. After DIV 12, we determined 43% and 97% damaged neurones 18 h after the exposure to glutamate (1 mm, 1 h) in cultures treated with vehicle and AraC, respectively. Dose-response curves were different with a higher sensitivity to glutamate in cultures treated with AraC (EC50 = 0.01 mm) than with vehicle (EC50 = 0.12 mm). The susceptibility of neurones to 1 mm glutamate did not correlate with the percentage of astrocytes and was insensitive to an inhibition of glutamate uptake. In cultures treated with vehicle and AraC, glutamate-induced neurotoxicity was mediated through stimulation of the NR1-NR2B subtype of NMDA receptors, because it was blocked by the NMDA receptor antagonist MK-801 and the NR1-NR2B selective receptor antagonist ifenprodil. Protein levels of the NR2A and NR2B subunits of NMDA receptor were similar in cultures treated with vehicle or AraC. AraC-induced changes in glutamate-induced neurotoxicity were mimicked by activation of protein kinase C (PKC), whereas neuronal susceptibility to glutamate was reduced in cultures depleted of PKC and treated with AraC suggesting that the increase in glutamate toxicity by activated astrocytes involves activation of PKC.

Complestatin antagonizes the AMPA/kainate-induced neurotoxicity in cultured chick telencephalic neurons

Excitatory amino acids are known to induce considerable neurotoxicity in central nervous system. In the present study, the neurotoxicity was induced by application of kainate or AMPA in chick telencephalic neuron, and neuroprotective activity was tested with complestatin that was isolated from streptomyces species. In cultured telencephalic neurons exposed to 500 microM kainate for 2 days, the AMPA/kainate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX, 5 microM) completely blocked kainate-induced neurotoxicity. Also, complestatin (0.5 microM) completely blocked kainate-induced neuronal injury at a concentration lower than that required for prototype AMPA/kainate receptor antagonist DNQX. In addition, complestatin blocked AMPA-induced neurotoxicity when the neurons were pretreated with cyclothiazide, a desensitization blocker of AMPA receptor. Surprisingly, when the onset of the treatment was delayed for 6 hours, complestatin led to a reduction in kainate-induced neuronal injury. While inhibition of protein kinase C (PKC) by staurosporin induced neurotoxicity, that was blocked by complestatin. Activation of PKC by phorbol dibutyrate partially inhibited the kainate-induced neurotoxicity. These results suggest that complestatin may be used as an anti-excitotoxic agent and involved in the PKC activation contributing to inhibition of neurotoxicity.

Phorbol esters inhibit fibroblast growth factor-2-stimulated fibroblast proliferation by a p38 MAP kinase dependent pathway

Treatment of fibroblasts with the phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate (TPA), specifically inhibits fibroblast growth factor-2 (FGF-2) induced proliferation. TPA treatment has little or no effect on FGF receptor activation but specifically inhibits the activation of p38 MAPK but not other downstream signaling pathways implicated in cell proliferation. p38 MAPK was recently shown to be required for the FGF-2-stimulated proliferation of fibroblasts. The effect of TPA on both p38 MAPK activation and cell proliferation can be reversed by treatment with the PKC inhibitor Go6983. The TPA-mediated inhibition of p38 MAPK activation requires phosphatase activity and is at least partially mediated by ERKs since it is reduced by treatment with the MEK inhibitor PD98059. In contrast, the FGF-2-stimulated differentiation of PC12 cells, which express the same FGF receptor as Swiss 3T3 fibroblasts, is not affected by TPA treatment, consistent with a lack of involvement of p38 MAPK activity in this process. These data indicate that the effects of TPA treatment on cellular function are not only cell type but also stimulus specific and are dependent upon the distinct pathways activated downstream of each stimulus.

Possible involvement of PKC isoforms in signalling placental apoptosis in intrauterine growth retardation

Apoptosis contributes to uteroplacental dsyfunction in intrauterine growth retardation (IUGR). Specific protein kinase C (PKC) isoforms regulate apoptosis in other cell types. PKC isoforms thought to be anti-apoptotic include the conventional PKC isoforms (cPKC-alpha, -beta I and -beta II), whereas the novel PKC isoforms nPKC-delta and nPKC-epsilon may be apoptotic. Dexamethasone administration during the last third of pregnancy in the rat leads to IUGR. We used the dexamethasone model to test the hypothesis that adverse changes in fetal growth might be associated with a modified placental PKC isoform profile. Dexamethasone administered from day 15 of gestation via subcutaneous infusion (osmotic minipump; 100 or 200 microg dexamethasone/kg maternal body wt. per day) induced a dose-dependent decline in placental and fetal body weights at day 21 of gestation. Placental protein expression of all three cPKC isoforms was downregulated by maternal dexamethasone exposure, whereas placental nPKC-epsilon protein expression and activity was significantly upregulated in a dose-dependent manner. These data indicate that IUGR induced by excessive glucocorticoid exposure late in pregnancy leads to changes in the placental PKC isoform profile consistent with the concept that members of the PKC family participate in apoptosis signalling in the placenta.