The effect of chemical blockade of PKC with Gö6976 and Gö6983 on proliferation and MAPK activity in IL-6-dependent plasmacytoma cells

Propranolol Attenuates Proangiogenic Activity of Mononuclear Phagocytes: Implication in Choroidal Neovascularization

Purpose

Targeting β-adrenergic receptor signaling with propranolol has emerged as a potential candidate to counteract choroidal neovascularization (CNV). Little is known of its effect on macrophages, which play a critical role in CNV. We investigated the effect of propranolol on angiogenic response of mononuclear phagocytes (MPs).

Methods

The angiogenic effect of propranolol was evaluated in laser-induced CNV model. Mice received intraperitoneal injections of propranolol (6 mg/kg/d) or vehicle. CNV area and inflammatory cells were determined respectively by using lectin staining and an anti-IBA-1 antibody on RPE/choroid flat mounts. Inflammatory gene expression was evaluated by quantitative (q) PCR analysis. Mechanisms of propranolol was studied in MP cell lines J774 and RAW264.7 and in primary peritoneal macrophages. Expression of pro- and antiangiogenic mediators was studied. In addition, effects of propranolol treatment of MPs was assessed on choroidal explant.

Results

CNV was attenuated by propranolol and concomitantly associated with decreased inflammatory mediators IL-6 and TNFα, albeit with accumulation of (β-adrenoceptor harboring) MPs in the CNV area. Conditioned media from MPs preincubated with propranolol exerted antiangiogenic effects. Treatment of J774 confirmed the attenuation of inflammatory response to propranolol and increased cleaved caspase-3 on choroidal explant. We found that propranolol increased pigment epithelium-derived factor (PEDF) expression in MPs. Trapping of PEDF with an antibody abrogated antiangiogenic effects of propranolol. PEDF was also detected in CNV-associated MPs.

Conclusions

We hereby show that propranolol confers on MPs antiangiogenic properties by increasing PEDF expression, which complements its effects on vascular tissue resulting in inhibition of choroidal vasoproliferation in inflammatory conditions. The study supports possible use of propranolol as a therapeutic modality for CNV.

Concise Review: Lessons from Naïve Human Pluripotent Cells

The naïve state of pluripotency is actively being explored by a number of labs. There is some controversy in the field as to the true identity of naïve human pluripotent cells as they are not exact mirrors of the mouse. The various reports published, although in basic agreement, present discrepancies in the characterization of the various lines, which likely reflect the etiology of these lines. The primary lesson learned from these contributions is that a human naïve state reflecting the preimplantation human is likely to exist. The essential factors that will universally maintain the naïve state in human cells in vitro are not yet fully understood. These first need to be identified in order to describe the definitive characteristics of this state. Comparisons of naïve and primed human pluripotent cells have also highlighted consistencies between states and broadened our understanding of embryonic metabolism, epigenetic change required for development, embryonic DNA repair strategies and embryonic expression dynamics. Stem Cells 2017;35:35-41.

Thyrotropin regulates IL-6 expression in CD34+ fibrocytes: clear delineation of its cAMP-independent actions

IL-6 plays diverse roles in normal and disease-associated immunity such as that associated with Graves’ disease (GD). In that syndrome, the orbit undergoes remodeling during a process known as thyroid-associated ophthalmopathy (TAO). Recently, CD34⁺ fibrocytes were found to infiltrate the orbit in TAO where they transition into CD34⁺ orbital fibroblasts. Surprisingly, fibrocytes display high levels of functional thyrotropin receptor (TSHR), the central antigen in GD. We report here that TSH and the pathogenic anti-TSHR antibodies that drive hyperthyroidism in GD induce IL-6 expression in fibrocytes and orbital fibroblasts. Unlike TSHR signaling in thyroid epithelium, that occurring in fibrocytes is completely independent of adenylate cyclase activation and cAMP generation. Instead TSH activates PDK1 and both AKT/PKB and PKC pathways. Expression and use of PKCβII switches to that of PKCµ as fibrocytes transition to TAO orbital fibroblasts. This shift is imposed by CD34⁻ orbital fibroblasts but reverts when CD34⁺ fibroblasts are isolated. The up-regulation of IL-6 by TSH results from coordinately enhanced IL-6 gene promoter activity and increased IL-6 mRNA stability. TSH-dependent IL-6 expression requires activity at both CREB (−213 to −208 nt) and NF-κB (–78 to −62 nt) binding sites. These results provide novel insights into the molecular action of TSH and signaling downstream for TSHR in non-thyroid cells. Fibrocytes neither express adenylate cyclase nor generate cAMP and thus these findings are free from any influence of cAMP-related signaling. They identify potential therapeutic targets for TAO.

Upregulation of pancreatic derived factor (FAM3B) expression in pancreatic β-cells by MCP-1 (CCL2)

Pancreatic derived factor (PANDER, FAM3B) is a peptide mainly synthesized and secreted by pancreatic β-cells. PANDER is proposed to be involved in regulation of β-cell function under physiological conditions and impairment of β-cell function under pathological conditions. MCP-1 (CCL2) is expressed by normal pancreatic islets and has been implicated in inflammation related pancreatic disorders. We examined the effect of MCP-1 on PANDER expression by using murine pancreatic β-cell line MIN6 and pancreatic islets. We found that MCP-1 induced PANDER mRNA transcription and protein synthesis in MIN6 cells and islets. By using calcium chelator (EGTA); inhibitors for PKC (Go6976), MEK1/2 (PD98059) or c-Jun-N-terminal kinase (JNK) (SP600125); c-Jun dominant-negative construct; PANDER promoter luciferase constructs; and islets isolated from Fos knockout mice; we demonstrated that MCP-1 induced PANDER gene expression in β-cells through Ca(2+)-ERK1/2-AP-1 and PKC-JNK-AP-1 signaling pathways. Our findings suggest a new link between the endocrine and immune systems and provide useful information for further investigating the physiological functions of PANDER and its involvement in inflammation-related pancreatic disorders.

PKC alpha protein but not kinase activity is critical for glioma cell proliferation and survival

Protein kinase C alpha (PKCalpha) has been implicated in tumor development with high levels of PKCalpha expression being associated with various malignancies including glioblastomas and tumors of the breast and prostate. To account for its upregulation in these cancers, studies have suggested that PKCalpha plays a role in promoting cell survival. Here we show by siRNA depletion in U87MG glioma cells that a critical threshold level of PKCalpha protein expression is essential for their growth in the presence of serum and for their survival following serum deprivation. Derivation of PKCalpha wt and KO mouse embryo fibroblast cell lines confirms a role for PKCalpha in protecting cells from apoptosis induced by serum deprivation. Notably, PKCalpha was found to mediate chemo-protection in these fibroblastic cell lines. In U87MG cells PKCalpha does not confer chemoprotection though this likely reflects growth arrest associated with its depletion. To determine the requirements for catalytic function, comparison was made between distinct classes of PKC inhibitors. In contrast to loss of PKCalpha protein, inhibition of PKC kinase activity in glioma cell lines does not significantly inhibit growth or survival. Conversely, inhibition with calphostin C, which targets the regulatory domain of PKC, potently inhibits proliferation and induces apoptosis. Evidence is presented that it is the fully phosphorylated, folded form of PKCalpha that confers this activity-independent behaviour. These results indicate an essential pro-proliferative and pro-survival role for PKCalpha in glioma but question the use of ATP competitive inhibitors as therapeutics, either alone, or in combination with chemotoxic agents.

Inhibitors of protein kinase C sensitise multiple myeloma cells to common genotoxic drugs

OBJECTIVES

Despite high dose treatment regimes multiple myeloma (MM) disease is still not curable. Patients become resistant to cytotoxic drugs and die of disease progression. Therefore, besides new cytotoxic compounds drug sensitisers are urgently needed.

METHODS

The MM cell lines U266, OPM-2, RPMI-8226 and NCI-H929 were incubated with the common anti-myeloma drugs like melphalan together with protein kinase C (PKC) inhibitors. Growth inhibition was measured using the water-soluble tetrazolium salt 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1 assay), and apoptosis was determined by flow cytometry after staining with fluorescein isothiocyanate-labeled annexin V (annexin-V-FITC) and propidium iodide. Intracellular signalling was shown by western blotting.

RESULTS

In this study we show that the combination of melphalan or doxorubicin with a PKC inhibitor, Gö6976 or enzastaurin, strongly increases cell toxicity. Increase of cytotoxicity is shown to be due to increased induction of apoptosis. Furthermore, we show that the protective effect of human bone marrow stromal cells (hBMSC) is abrogated by the PKC inhibitors. Finally, western blotting experiments revealed that incubation of myeloma cells with cytotoxic drugs like melphalan or doxorubicin leads to increased phosphorylation and therefore degradation of inhibitor of nuclear factor kappa B (IkappaB) and release of nuclear factor kappa B (NFkappaB). In contrast, enzastaurin inhibits phosphorylation of IkappaB.

CONCLUSIONS

We conclude that the combination of conventional drugs and PKC inhibitors might be very effective and represents a new strategy in the treatment of MM.

Interleukin-6 receptor-mediated activation of signal transducer and activator of transcription-3 (STAT3) promotes choroidal neovascularization

Interleukin (IL)-6, a potent proinflammatory cytokine, is suggested to be a risk factor for choroidal neovascularization (CNV) because of its increased levels in the serum of patients with age-related macular degeneration; however, the role of IL-6 in CNV has not been defined. The present study reveals the critical contribution of IL-6 signaling and its downstream STAT3 pathway to the murine model of laser-induced CNV. CNV induction by laser treatment stimulated IL-6 expression in the retinal pigment epithelium-choroid complex, and antibody-based blockade of IL-6 receptor or genetic ablation of IL-6 led to significant suppression of CNV. CNV generation was accompanied by STAT3 activation in choroidal endothelial cells and macrophages, and IL-6 receptor blockade resulted in selectively inhibited phosphorylation of STAT3 but not extracellular signal-regulated kinase 1/2. Consistently, pharmacological blockade of STAT3 pathway also suppressed CNV. In addition, IL-6 receptor neutralization led to significant inhibition of the in vivo and in vitro expression of inflammation-related molecules including monocyte chemotactic protein, intercellular adhesion molecule-1, and vascular endothelial growth factor, and of macrophage infiltration into CNV. These results indicate the significant involvement of IL-6 receptor-mediated activation of STAT3 inflammatory pathway in CNV generation, suggesting the possibility of IL-6 receptor blockade as a therapeutic strategy to suppress CNV associated with age-related macular degeneration.

Gö6976 is a potent inhibitor of the JAK 2 and FLT3 tyrosine kinases with significant activity in primary acute myeloid leukaemia cells

Aberrant activation of Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling is implicated in a number of haematological malignancies and effective JAK inhibitors may be therapeutically useful. We found that Gö6976, an indolocarbazole inhibitor of the calcium-dependent isozymes of protein kinase C (PKC), inhibited interleukin 3/granulocyte-macrophage colony-stimulating factor-induced signalling, proliferation and survival whereas Gö6983, a broad spectrum PKC inhibitor, had no such effects. Gö6976 was found to be a direct and potent inhibitor of JAK2 in vitro. Gö6976 also inhibited signalling, survival and proliferation in cells expressing the leukaemia-associated TEL-JAK2 fusion protein and the myeloproliferative disorder (MPD)-associated JAK2 V617F mutant. In primary acute myeloid leukaemia (AML) cells, incubation with Gö6976 reduced constitutive STAT activity in all cases studied. In addition, Akt and mitogen-activated protein kinase phosphorylation were reduced in 4/5 FLT3-internal tandem duplication (ITD) positive AML cases and 7/13 FLT3-wild-type (WT) cases. Expression of FLT3-WT, ITD and D835Y in 32D cells showed that Gö6976 is also a potent inhibitor of WT and mutant FLT3. In AML cells, Gö6976 reduced the survival to 55 +/- 5% of control in FLT3-ITD cases and to 69 +/- 5% in FLT3-WT samples. These data may help identify clinically useful compounds based on the structure of Gö6976, which can be employed for the treatment of MPDs as well as AML.

The survival of IL-6-dependent myeloma cells critically relies on their capability to transit the G1 to S phase interval of the cell cycle

Interleukin-6 (IL-6) has an essential role in the initial progression of myeloma cell tumours. IL-6 triggers proliferation of these cells via the Ras-mitogen-activated protein kinase (MAPK) cascade and is thought to promote their survival via signal transducer and activator of transcription (STAT) pathway-dependent regulation of Bcl-2 family antiapoptotic members. Using IL-6-dependent murine B9 hybridoma/plasmacytoma cells, we here report that exiting the cell cycle G1 phase is a crucial step contributing to maintain viability. We show that (1) drug-mediated reversible G1 arrest triggered apoptosis despite the presence of IL-6; (2) a short IL-6 pulse to G1-arrested cells was sufficient to induce S phase entry and prevent apoptosis; and (3) phorbol ester and related derivatives promoted S phase entry and survival of IL-6-starved cells without up-regulating bcl-XL expression. Furthermore, that the MAPK kinase (MEK) 1/2 inhibitor, U0126, blocked proliferation and induced death of B9 cells indicate that IL-6 may not exert its survival effect primarily through bcl-XL and emphasizes the key role of Ras-MAPK cascade elements in the regulation of myeloma growth/viability.

Chlamydophila pneumoniae induces p44/p42 mitogen-activated protein kinase activation in human fibroblasts through Toll-like receptor 4

Chlamydophila pneumoniae, an obligately intracellular Gram-negative bacterium and a common causative agent of respiratory tract infections, has been implicated in the induction and progression of atherosclerosis and coronary artery disease. In this study, the signalling mechanism of C. pneumoniae in human fibroblasts, a prominent cell population in chronic inflammation and persistent infection, contributing to plaque formation, was investigated. C. pneumoniae elementary bodies were demonstrated to up-regulate the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK) in human fibroblasts. The effect was independent of the chlamydial lipopolysaccharide and was likely to be mediated by a heat-labile chlamydial protein. Furthermore, an anti-Toll-like receptor 4 (TLR4) antibody was shown to abolish C. pneumoniae-induced cell activation, whereas an anti-TLR2 antibody had no effect, indicating the role of TLR4 in p44/p42 MAPK activation. Ca2+/calmodulin-dependent protein kinase inhibitor KN-62 and phosphodiesterase 4 (PDE 4) inhibitor Rolipram enhanced C. pneumoniae-induced MAPK phosphorylation and attenuated C. pneumoniae infectivity in vitro. Together the results indicate that C. pneumoniae triggers rapid TLR4-mediated p44/p42 MAPK activation in human fibroblasts and chemical enhancement of MAPK phosphorylation modulates in vitro infection at the molecular level.

The protein kinase C inhibitor Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole] potentiates agonist-induced mitogen-activated protein kinase activation through tyrosine phosphorylation of the epidermal growth factor receptor

Protein kinase C (PKC) isoforms are important transducers of signals from G protein-coupled receptors (GPCRs) to diverse cellular targets, including extracellular signal-regulated kinases 1 and 2 (ERK1/2). Clone 9 rat hepatocytes (C9 cells) express receptors for angiotensin II (Ang II) type 1, lysophosphatidic acid (LPA), and epidermal growth factor (EGF), and their stimulation causes transient ERK1/2 phosphorylation through transactivation of the epidermal growth factor receptor (EGF-R). Inhibition of PKC by Go6983 [2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide], or PKC depletion by prolonged phorbol 12-myristate 13-acetate (PMA) treatment, attenuated ERK1/2 activation by Ang II and PMA, but not by LPA and EGF. In contrast, another PKC inhibitor, Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole], enhanced basal and agonist-stimulated phosphorylation of ERK1/2, which was not caused by alteration in receptor binding and internalization, stimulation of inositol phosphate production, or activation of Pyk2 and Src tyrosine kinases. However, Go6976 enhanced agonist-induced tyrosine phosphorylation of the EGF receptor, possibly through inhibition of protein tyrosine phosphatase (PTP), because the PTP inhibitor sodium orthovanadate mimicked the effects of Go6976. Selective blockade of EGF-R kinase by AG1478 [4-(3-chloroanilino)6,7-dimethoxyquinazoline] abolished the ERK1/2 activation induced by Go6976. Similar experiments were conducted in human embryonic kidney 293 cells, which express receptors for LPA and EGF but exhibit no significant cross-communication between them. Although Go6976 caused a significant increase in EGF-induced tyrosine phosphorylation of the EGF-R and subsequent ERK1/2 activation, it had no such effects on LPA-induced responses. In Chinese hamster ovary cells, which express receptors for LPA but not for EGF, Go6976 also had no significant effect on LPA-induced ERK1/2 activation. These data indicate that Go6976 potentiates agonist-induced ERK1/2 activation through stimulation of tyrosine phosphorylation of the EGF-R.

Bacterial lipopolysaccharide induces proliferation of IL-6-dependent plasmacytoma cells by MAPK pathway activation

Mouse plasmacytomas are appropriate models to study the biology of human multiple myeloma (MM). Growth of murine interleukin-6 (IL-6)-dependent hybridoma/plasmacytoma lines can be stimulated by bacterial lipopolysaccharides (LPS). However, the molecular mechanisms of this phenomenon are still not elucidated. In this study the in vitro action of bacterial LPS on the mouse IL-6-dependent B9 hybridoma/plasmacytoma cell line and two IL-6-dependent hybridomas was investigated. The involvement of different signal transduction pathways was established using specific kinase inhibitors in proliferation assays and immunoblotting analysis of the kinase activity. Selective mitogen-activated protein kinase (MAPK) kinase inhibitor PD989059 inhibited both IL-6- and LPS-induced B9 cell proliferation. In contrast, in H187 and H188 cells, PD98059 inhibited only LPS-, but not IL-6-stimulated cell growth. The kinetics of MAPK activation in all cell lines showed that phosphorylation of p42 MAPK (encoded as ERK2) but not of p44 MAPK (ERK1), was considerably increased after treatment with LPS. We found that in H187 and H188 hybridomas IL-6 induced proliferation by a different STAT3-dependent mechanism. This study demonstrates the key role of the MAPK pathway in LPS-stimulated growth of mouse IL-6-dependent plasmacytoma cells. These findings suggest the presence of signaling mechanism in MM cells inducible by bacterial mitogens and possibly mediated by Toll-like receptors (TLR)--evolutionarily conserved molecules playing a central role in the microbial recognition and initiation of the cellular innate immune response.

Mechanisms of basal and cytokine-induced uptake of glucose in normal human eosinophils: relation to apoptosis

A link between glucose transport and apoptosis was suggested. We studied the mechanisms of glucose transport in human eosinophils by means of the uptake of the positron emitting analogue, 18Fluoro-2-Deoxyglucose (FDG) and apoptosis by means of flow cytometry. FDG uptake was inhibited by antibodies to GLUT1, 3 and 4 and by cytochalasin B. The anti-apoptotic principles IL-5, GM-CSF, IL-3 enhanced the uptake, whereas the apoptosis-inducing principles anti-CD95 (anti-Fas) and exposure to serum-coated Sephadex particles caused a reduction. Also TNF-alpha enhanced the uptake. Other cytokines such as IL-2, IL-4, IL-8, RANTES and MCP-3 had no effect on the glucose uptake. 2-Deoxyglucose, antibodies to GLUT4 and CD95 induced apoptosis. The basal FDG-uptake was unaffected by PKC inhibitors Ro-31-8220, Gö-6983 and Gö-6976, whereas the latter inhibited the IL-5-enhanced uptake possibly due to the inhibition of PKC(mu). Protein tyrosine kinase and PI-3 kinase inhibitors inhibited IL-5-enhanced FDG-uptake only. In contrast MEK inhibitors inhibited the basal uptake only. Inhibitors of p38 MAPkinase inhibited both basal and IL-5 enhanced uptake. We conclude that glucose uptake in eosinophils is governed by specific intracellular mechanisms involving mobilization of GLUTs, Ca2+ and the activation of the MAP kinase pathway and that the IL-5-enhanced uptake uniquely seems to involve PKC(mu) activity. Our results suggest a close link between apoptosis and glucose transport in human eosinophils.

KN-62 enhances Chlamydia pneumoniae-induced p44/p42 mitogen-activated protein kinase activation in murine fibroblasts and attenuates in vitro infection

Chlamydia pneumoniae elementary bodies were demonstrated to increase the proliferation of murine fibroblast cell line L-929 and rapidly activate p44/p42 mitogen-activated protein kinase (MAPK) in a protein kinase C (PKC) and protein kinase A (PKA)-independent way. Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) inhibitor KN-62 significantly enhanced C. pneumoniae-induced MAPK phosphorylation, suggesting negative control of CaM kinase pathway on the MAPK cascade. In in vitro infection assay, the upstream MAPK kinase 1/2 inhibitor U0126 increased 2.5-fold C. pneumoniae infectivity in L-929 cells, while KN-62 reduced the infection by 36%. Our findings provide insight into the molecular mechanisms of bacterium-host cell interactions and demonstrate the protective role of MAPK in murine fibroblasts, suggesting novel therapeutic approaches to the treatment and prevention of chlamydial infections.