PKCepsilon is a permissive link in integrin-dependent IFN-gamma signalling that facilitates JAK phosphorylation of STAT1

Equivocal, explicit and emergent actions of PKC isoforms in cancer

The maturing mutational landscape of cancer genomes, the development and application of clinical interventions and evolving insights into tumour-associated functions reveal unexpected features of the protein kinase C (PKC) family of serine/threonine protein kinases. These advances include recent work showing gain or loss-of-function mutations relating to driver or bystander roles, how conformational constraints and plasticity impact this class of proteins and how emergent cancer-associated properties may offer opportunities for intervention. The profound impact of the tumour microenvironment, reflected in the efficacy of immune checkpoint interventions, further prompts to incorporate PKC family actions and interventions in this ecosystem, informed by insights into the control of stromal and immune cell functions. Drugging PKC isoforms has offered much promise, but when and how is not obvious.

PKC Is Required for KRAS-Driven Lung Tumorigenesis

Non-small cell lung cancer (NSCLC) is the most frequent subtype of lung cancer and remains a highly lethal malignancy and one of the leading causes of cancer-related deaths worldwide. Mutant KRAS is the prevailing oncogenic driver of lung adenocarcinoma, the most common histologic form of NSCLC. In this study, we examined the role of PKCϵ, an oncogenic kinase highly expressed in NSCLC and other cancers, in KRAS-driven tumorigenesis. Database analysis revealed an association between PKCϵ expression and poor outcome in patients with lung adenocarcinoma specifically harboring KRAS mutations. A PKCϵ-deficient, conditionally activatable allele of oncogenic Kras (LSL-Kras^G12D ;PKCϵ^-/- mice) demonstrated the requirement of PKCϵ for Kras-driven lung tumorigenesis in vivo, which was consistent with impaired transformed growth reported in PKCϵ-deficient KRAS-dependent NSCLC cells. Moreover, PKCϵ-knockout mice were found to be less susceptible to lung tumorigenesis induced by benzo[a]pyrene, a carcinogen that induces mutations in Kras. Mechanistic analysis using RNA sequencing revealed little overlap for PKCϵ and KRAS in the control of genes and biological pathways relevant in NSCLC, suggesting that a permissive role of PKCϵ in KRAS-driven lung tumorigenesis may involve nonredundant mechanisms. Our results thus, highlight the relevance and potential of targeting PKCϵ for lung cancer therapeutics. SIGNIFICANCE: These findings demonstrate that KRAS-mediated tumorigenesis requires PKCϵ expression and highlight the potential for developing PKCϵ-targeted therapies for oncogenic RAS-driven malignancies.

Priming of microglia with IFN-γ impairs adult hippocampal neurogenesis and leads to depression-like behaviors and cognitive defects

Neuroinflammation driven by interferon-gamma (IFN-γ) and microglial activation has been linked to neurological disease. However, the effects of IFN-γ-activated microglia on hippocampal neurogenesis and behavior are unclear. In the present study, IFN-γ was administered to mice via intracerebroventricular injection. Mice received intraperitoneal injection of ruxolitinib to inhibit the JAK/STAT1 pathway or injection of minocycline to inhibit microglial activation. During a 7-day period, mice were assessed for depressive-like behaviors and cognitive impairment based on a series of behavioral analyses. Effects of the activated microglia on neural stem/precursor cells (NSPCs) were examined, as was pro-inflammatory cytokine expression by activated microglia. We showed that IFN-γ-injected animals showed long-term adult hippocampal neurogenesis reduction, behavior despair, anhedonia, and cognitive impairment. Chronic activation with IFN-γ induces reactive phenotypes in microglia associated with morphological changes, population expansion, MHC II and CD68 up-regulation, and pro-inflammatory cytokine (IL-1β, TNF-α, IL-6) and nitric oxide (NO) release. Microglia isolated from the hippocampus of IFN-γ-injected mice suppressed NSPCs proliferation and stimulated apoptosis of immature neurons. Inhibiting of the JAK/STAT1 pathway in IFN-γ-injected animals to block microglial activation suppressed microglia-mediated neuroinflammation and neurogenic injury, and alleviated depressive-like behaviors and cognitive impairment. Collectively, these findings suggested that priming of microglia with IFN-γ impairs adult hippocampal neurogenesis and leads to depression-like behaviors and cognitive defects. Targeting microglia by modulating levels of IFN-γ the brain may be a therapeutic strategy for neurodegenerative diseases and psychiatric disorders.

αvβ3-integrin regulates PD-L1 expression and is involved in cancer immune evasion

Tumors utilize a number of effective strategies, including the programmed death 1/PD ligand 1 (PD-1/PD-L1) axis, to evade immune-mediated control of their growth. PD-L1 expression is mainly induced by IFN receptor signaling or constitutively induced. Integrins are an abundantly expressed class of proteins which play multiple deleterious roles in cancer and exert proangiogenic and prosurvival activities. We asked whether αvβ3-integrin positively regulates PD-L1 expression and the anticancer immune response. We report that αvβ3-integrin regulated constitutive and IFN-induced PD-L1 expression in human and murine cancerous and noncancerous cells. αvβ3-integrin targeted STAT1 through its signaling C tail. The implantation of β3-integrin-depleted tumor cells led to a dramatic decrease in the growth of primary tumors, which exhibited reduced PD-L1 expression and became immunologically hot, with increased IFNγ content and CD8+ cell infiltration. In addition, the implantation of β3-integrin-depleted tumors elicited an abscopal immunotherapeutic effect measured as protection from the challenge tumor and durable splenocyte and serum reactivity to B16 cell antigens. These modifications to the immunosuppressive microenvironment primed cells for checkpoint (CP) blockade. When combined with anti-PD-1, β3-integrin depletion led to durable therapy and elicited an abscopal immunotherapeutic effect. We conclude that in addition to its previously known roles, αvβ3-integrin serves as a critical component of the cancer immune evasion strategy and can be an effective immunotherapy target.

Interferon-inducible cytoplasmic lncLrrc55-AS promotes antiviral innate responses by strengthening IRF3 phosphorylation

Type I interferon (IFN-I) production is efficiently induced to ensure a potent innate immune response to viral infection. How this response can be enhanced, however, remains to be explored. Here, we identify a new cytoplasmic long non-coding RNA (lncRNA), lncLrrc55-AS, that drives a positive feedback loop to promote interferon regulatory factor 3 (IRF3) signaling and IFN-I production. We show that lncLrrc55-AS is virus-induced in multiple cell types via the IFN-JAK-STAT pathway. LncLrrc55-AS-deficient mice display a weakened antiviral immune response and are more susceptible to viral challenge. Mechanistically, lncLrrc55-AS binds phosphatase methylesterase 1 (PME-1), and promotes the interaction between PME-1 and the phosphatase PP2A, an inhibitor of IRF3 signaling. LncLrrc55-AS supports PME-1-mediated demethylation and inactivation of PP2A, thereby enhancing IRF3 phosphorylation and signaling. Loss of PME-1 phenocopies lncLrrc55-AS deficiency, leading to diminished IRF3 phosphorylation and IFN-I production. We have identified an IFN-induced lncRNA as a positive regulator of IFN-I production, adding mechanistic insight into lncRNA-mediated regulation of signaling in innate immunity and inflammation.

TLR4-mediated IRAK1 activation induces TNF-α expression via JNK-dependent NF-κB activation in human bronchial epithelial cells

The purpose of this study was to identify the mechanism of lipopolysaccharide (LPS)-induced expression of tumor necrosis factor (TNF)-α in BEAS-2B. Toll-like receptor (TLR)4-specific siRNA was found to completely abolish the LPS-induced expression of MyD88 and TNF-α. There was enhanced binding of MyD88 with IRAK1 following LPS treatment, and MyD88- or IRAK1-specific siRNAs decreased the expression of TNF-α. In addition, IRAK1 siRNA downregulated the phosphorylation of PKCα, demonstrating that PKCα is a downstream effector of IRAK1. Inhibition of PKCα completely blocked the activation of AKT, whereas inhibition of AKT with a PI3K inhibitor prevented the LPS-induced expression of TNF-α. We found that AKT activated JNK, which then stimulated phosphorylation of Iκ-Bα, resulting in NF-κB activation. As expected, inhibition of NF-κB completely inhibited the expression of TNF-α. Taken together, our results suggest that LPS induces TNF-α expression by activating NF-κB via the PKCα/PI3K/AKT/JNK pathway, which is in turn dependent on MyD88/IRAK1.

Cardiac fibroblasts as sentinel cells in cardiac tissue: Receptors, signaling pathways and cellular functions

Cardiac fibroblasts (CF) not only modulate extracellular matrix (ECM) proteins homeostasis, but also respond to chemical and mechanical signals. CF express a variety of receptors through which they modulate the proliferation/cell death, autophagy, adhesion, migration, turnover of ECM, expression of cytokines, chemokines, growth factors and differentiation into cardiac myofibroblasts (CMF). Differentiation of CF to CMF involves changes in the expression levels of various receptors, as well as, changes in cell phenotype and their associated functions. CF and CMF express the β2-adrenergic receptor, and its stimulation activates PKA and EPAC proteins, which differentially modulate the CF and CMF functions mentioned above. CF and CMF also express different levels of Angiotensin II receptors, in particular, AT1R activation increases collagen synthesis and cell proliferation, but its overexpression activates apoptosis. CF and CMF express different levels of B1 and B2 kinin receptors, whose stimulation by their respective agonists activates common signaling transduction pathways that decrease the synthesis and secretion of collagen through nitric oxide and prostacyclin I2 secretion. Besides these classical functions, CF can also participate in the inflammatory response of cardiac repair, through the expression of receptors commonly associated to immune cells such as Toll like receptor 4, NLRP3 and interferon receptor. The activation by their respective agonists modulates the cellular functions already described and the release of cytokines and chemokines. Thus, CF and CMF act as sentinel cells responding to a plethora of stimulus, modifying their own behavior, and that of neighboring cells.

Could interferon-gamma be a therapeutic target for treating heart failure?

The cytokine interferon-gamma (IFN-γ) is the only known member of the type II family of interferons, and as such, binds to its own distinct receptor. It is important in host defense against infection, as well as adaptive immune responses. While a wide array of cytokines are known to be involved in adverse remodeling of the heart and the progression to heart failure, the role of IFN-γ is unclear. Recent evidence from clinical studies, animal models of myocarditis and hypertension, as well as isolated cell studies, provide conflicting data as to whether IFN-γ is pathological or protective in the heart. Thus, it is important to highlight these discrepant findings so that areas of future investigation can be identified to more clearly determine the precise role of IFN-γ in the heart. Accordingly, this review will (1) discuss the source of IFN-γ in the diseased heart; (2) summarize the data from animal studies; (3) discuss the effects of IFN-γ on isolated cardiac fibroblasts and cardiomyocytes; (4) identify signaling mechanisms that may be invoked by IFN-γ in the heart; and (5) present the clinical evidence supporting a role for IFN-γ in heart failure.

Transcriptional regulation of oncogenic protein kinase Cϵ (PKCϵ) by STAT1 and Sp1 proteins

Overexpression of PKCϵ, a kinase associated with tumor aggressiveness and widely implicated in malignant transformation and metastasis, is a hallmark of multiple cancers, including mammary, prostate, and lung cancer. To characterize the mechanisms that control PKCϵ expression and its up-regulation in cancer, we cloned an ∼ 1.6-kb promoter segment of the human PKCϵ gene (PRKCE) that displays elevated transcriptional activity in cancer cells. A comprehensive deletional analysis established two regions rich in Sp1 and STAT1 sites located between -777 and -105 bp (region A) and -921 and -796 bp (region B), respectively, as responsible for the high transcriptional activity observed in cancer cells. A more detailed mutagenesis analysis followed by EMSA and ChIP identified Sp1 sites in positions -668/-659 and -269/-247 as well as STAT1 sites in positions -880/-869 and -793/-782 as the elements responsible for elevated promoter activity in breast cancer cells relative to normal mammary epithelial cells. RNAi silencing of Sp1 and STAT1 in breast cancer cells reduced PKCϵ mRNA and protein expression, as well as PRKCE promoter activity. Moreover, a strong correlation was found between PKCϵ and phospho-Ser-727 (active) STAT1 levels in breast cancer cells. Our results may have significant implications for the development of approaches to target PKCϵ and its effectors in cancer therapeutics.

The unique protein kinase Cη: implications for breast cancer (review)

Deregulation of key signal transduction pathways that govern important cellular processes leads to cancer. The development of effective therapeutics for cancer warrants a comprehensive understanding of the signaling pathways that are deregulated in cancer. The protein kinase C (PKC) family has served as an attractive target for cancer therapy for decades owing to its crucial roles in several cellular processes. PKCη is a novel member of the PKC family that plays critical roles in various cellular processes such as growth, proliferation, differentiation and cell death. The regulation of PKCη appears to be unique compared to other PKC isozymes, and there are conflicting reports regarding its role in cancer. This review focuses on the unique aspects of PKCη in terms of its structure, regulation and subcellular distribution and speculates on how these features could account for its distinct functions. We have also discussed the functional implications of PKCη in cancer with particular emphasis on breast cancer.

Autophagy activation by interferon-γ via the p38 mitogen-activated protein kinase signalling pathway is involved in macrophage bactericidal activity

Macrophages are involved in many essential immune functions. Their role in cell-autonomous innate immunity is reinforced by interferon-γ (IFN-γ), which is mainly secreted by proliferating type 1 T helper cells and natural killer cells. Previously, we showed that IFN-γ activates autophagy via p38 mitogen-activated protein kinase (p38 MAPK), but the biological importance of this signalling pathway has not been clear. Here, we found that macrophage bactericidal activity increased by 4 hr after IFN-γ stimulation. Inducible nitric oxide synthase (NOS2) is a major downstream effector of the Janus kinase-signal transducer and activator of transcription 1 signalling pathway that contributes to macrophage bactericidal activity via nitric oxide (NO) generation. However, no NO generation was observed after 4 hr of IFN-γ stimulation, and macrophage bactericidal activity at early stages after IFN-γ stimulation was not affected by the NOS inhibitors, NG-methyl-l-arginine acetate salt and diphenyleneiodonium chloride. These results suggest that an NOS2-independent signalling pathway is involved in IFN-γ-mediated bactericidal activity. We also found that this macrophage activity was attenuated by the addition of the p38 MAPK inhibitors, PD 169316, SB 202190, and SB 203580, or by the expression of short hairpin RNA against p38α or the essential factors for autophagy, Atg5 and Atg7. Collectively, our results suggest that the IFN-γ-mediated autophagy via p38 MAPK, without the involvement of NOS2, also contributes to the ability of macrophages to kill intracellular bacteria. These observations provide direct evidence that p38 MAPK-mediated autophagy can support IFN-γ-mediated cell-autonomous innate immunity.

IFNγ-mediated inhibition of cell proliferation through increased PKCδ-induced overexpression of EC-SOD

Extracellular superoxide dismutase (EC-SOD) overexpression modulates cellular responses such as tumor cell suppression and is induced by IFNγ. Therefore, we examined the role of EC-SOD in IFNγ-mediated tumor cell suppression. We observed that the dominant-negative protein kinase C delta (PKCδ) suppresses IFNγ-induced EC-SOD expression in both keratinocytes and melanoma cells. Our results also showed that PKCδ-induced ECSOD expression was reduced by pretreatment with a PKCspecific inhibitor or a siRNA against PKCδ. PKCδ-induced ECSOD expression suppressed cell proliferations by the up-regulation of p21 and Rb, and the downregulation of cyclin A and D. Finally, we demonstrated that increased expression of EC-SOD drastically suppressed lung melanoma proliferation in an EC-SOD transgenic mouse via p21 expression. In summary, our findings suggest that IFNγ-induced EC-SOD expression occurs via activation of PKCδ. Therefore, the upregulation of EC-SOD may be effective for prevention of various cancers, including melanoma, via cell cycle arrest. [BMB Reports 2012; 45(11): 659-664]

Observation of autophagosome maturation in the interferon-γ-primed and lipopolysaccharide-activated macrophages using a tandem fluorescent tagged LC3

Macrophages are engaged in many essential host functions, and their activation is a dynamic process that results in diverse functional outcomes such as the potentiation of bactericidal activity and production of chemokines, cytokines, and mediators that coordinate the inflammatory response. This pro-inflammatory response is bimodal, comprising a "prime" event, classically through interferon-γ (IFN-γ), and a "trigger," such as lipopolysaccharide (LPS). Recently, autophagy, which is one of the major degradative pathways in eukaryotic cells, has been shown to play an important role in both IFN-γ-primed and LPS-activated macrophages. In this study, we sought to characterize the mechanisms of autophagy activation in primed and activated macrophages. To this end, we established a macrophage RAW 264.7 cell line that expressed high levels of a tandem fluorescently tagged LC3 (tfLC3) autophagy marker. By using this macrophage cell line, autophagosome formation was observed in both IFN-γ- and LPS-stimulated cells. Moreover, our data demonstrated that IFN-γ, but not LPS, facilitated autophagosome maturation to autophagolysosomes, suggesting that 2 distinct mechanisms regulating autophagy exist in IFN-γ-primed and LPS-activated macrophages.

IFN-γ elicits macrophage autophagy via the p38 MAPK signaling pathway

Autophagy is a major innate immune defense pathway in both plants and animals. In mammals, this cascade can be elicited by cytokines (IFN-γ) or pattern recognition receptors (TLRs and nucleotide-binding oligomerization domain-like receptors). Many signaling components in TLR- and nucleotide-binding oligomerization domain-like receptor-induced autophagy are now known; however, those involved in activating autophagy via IFN-γ remain to be elucidated. In this study, we engineered macrophages encoding a tandem fluorescently tagged LC3b (tfLC3) autophagosome reporter along with stably integrated short hairpin RNAs to demonstrate IFN-γ-induced autophagy required JAK 1/2, PI3K, and p38 MAPK but not STAT1. Moreover, the autophagy-related guanosine triphosphatase Irgm1 proved dispensable in both stable tfLC3-expressing RAW 264.7 and tfLC3-transduced Irgm1(-/-) primary macrophages, revealing a novel p38 MAPK-dependent, STAT1-independent autophagy pathway that bypasses Irgm1. These unexpected findings have implications for understanding how IFN-γ-induced autophagy is mobilized within macrophages for inflammation and host defense.

Development of transgenic cloned pig models of skin inflammation by DNA transposon-directed ectopic expression of human β1 and α2 integrin

Integrins constitute a superfamily of transmembrane signaling receptors that play pivotal roles in cutaneous homeostasis by modulating cell growth and differentiation as well as inflammatory responses in the skin. Subrabasal expression of integrins α2 and/or β1 entails hyperproliferation and aberrant differentiation of keratinocytes and leads to dermal and epidermal influx of activated T-cells. The anatomical and physiological similarities between porcine and human skin make the pig a suitable model for human skin diseases. In efforts to generate a porcine model of cutaneous inflammation, we employed the Sleeping Beauty DNA transposon system for production of transgenic cloned Göttingen minipigs expressing human β1 or α2 integrin under the control of a promoter specific for subrabasal keratinocytes. Using pools of transgenic donor fibroblasts, cloning by somatic cell nuclear transfer was utilized to produce reconstructed embryos that were subsequently transferred to surrogate sows. The resulting pigs were all transgenic and harbored from one to six transgene integrants. Molecular analyses on skin biopsies and cultured keratinocytes showed ectopic expression of the human integrins and localization within the keratinocyte plasma membrane. Markers of perturbed skin homeostasis, including activation of the MAPK pathway, increased expression of the pro-inflammatory cytokine IL-1α, and enhanced expression of the transcription factor c-Fos, were identified in keratinocytes from β1 and α2 integrin-transgenic minipigs, suggesting the induction of a chronic inflammatory phenotype in the skin. Notably, cellular dysregulation obtained by overexpression of either β1 or α2 integrin occurred through different cellular signaling pathways. Our findings mark the creation of the first cloned pig models with molecular markers of skin inflammation. Despite the absence of an overt psoriatic phenotype, these animals may possess increased susceptibility to severe skin damage-induced inflammation and should be of great potential in studies aiming at the development and refinement of topical therapies for cutaneous inflammation including psoriasis.

PKC alpha regulates Sendai virus-mediated interferon induction through HDAC6 and β-catenin

Recognition of viral RNA by cytoplasmic retinoic acid inducible gene I (RIG-I)-like receptors initiates signals leading to the induction of type I interferon (IFN) transcription via transcription factors such as interferon regulatory factor 3 (IRF3) and nuclear factor κB (NF-κB). Here, we describe a new signalling pathway that involves protein kinase C alpha (PKCα), histone deacetylase 6 (HDAC6) and beta-catenin (β-catenin), which is essential for IFN gene induction following virus infection. Knockdown of PKCα in various human cells, including primary cells, inhibited Sendai virus (SeV)-mediated IFN induction and enhanced virus replication. In the absence of this pathway IRF3 becomes activated, but does not bind to its promoter and is thus unable to support transcription. Mechanistically, SeV infection induced the activation of PKCα, which promoted its interaction with HDAC6 and enhanced its deacetylation activity in a phosphorylation-dependent manner. Further downstream, HDAC6 caused deacetylation of β-catenin and enhanced its nuclear translocation and promoter binding. In the nucleus, β-catenin acted as a co-activator for IRF3-mediated transcription. Our findings suggest an important role of a novel signalling pathway mediated by PKCα-HDAC6-β-catenin in controlling IRF3-mediated transcription.

Cooperation between integrins and growth factor receptors in signaling and endocytosis

All multicellular animals express receptors for growth factors (GFs) and extracellular matrix (ECM) molecules. Integrin-type ECM receptors anchor cells to their surroundings and concomitantly activate intracellular signal transduction pathways. The same signaling mechanisms are regulated by GF receptors (GFRs). Recently, intensive research efforts have revealed novel mechanisms describing how the two receptor systems collaborate at many different levels. Integrins can directly bind to GFs and promote their activation. Adhesion receptors also organize signaling platforms and assist GFRs or even activate them via ligand-independent mechanisms. Furthermore, integrins can orchestrate endocytosis and recycling of GFRs. Here, we review the present knowledge about the interplay between integrins and GFRs and discuss recent ideas of how this collaboration may explain some previous controversies in integrin research.

Syndecan-1 and -4 differentially regulate oncogenic K-ras dependent cell invasion into collagen through α2β1 integrin and MT1-MMP

Syndecans function as co-receptors for integrins on different matrixes. Recently, syndecan-1 has been shown to be important for α2β1 integrin-mediated adhesion to collagen in tumor cells by regulating cell adhesion and migration on two-dimensional collagen. However, the function of syndecans in supporting α2β1 integrin interactions with three-dimensional (3D) collagen is less well studied. Using loss-of-function and overexpression experiments we show that in 3D collagen syndecan-4 supports α2β1-mediated collagen matrix contraction. Cell invasion through type I collagen containing 3D extracellular matrix (ECM) is driven by α2β1 integrin and membrane type-1 matrix metalloproteinase (MT1-MMP). Here we show that mutational activation of K-ras correlates with increased expression of α2β1 integrin, MT1-MMP, syndecan-1, and syndecan-4. While K-ras-induced α2β1 integrin and MT1-MMP are positive regulators of invasion, silencing and overexpression of syndecans demonstrate that these proteins inhibit cell invasion into collagen. Taken together, these data demonstrate the existence of a complex interplay between integrin α2β1, MT1-MMP, and syndecans in the invasion of K-ras mutant cells in 3D collagen that may represent a mechanism by which tumor cells become more invasive and metastatic.

RA-inducible gene-I induction augments STAT1 activation to inhibit leukemia cell proliferation

RA-inducible gene I (RIG-I/DDX58) has been shown to activate IFN-β promoter stimulator 1 (IPS-1) on recognizing cytoplasmic viral RNAs. It is unclear how RIG-I functions within the IFN and/or RA signaling process in acute myeloid leukemia (AML) cells, however, where obvious RIG-I induction is observed. Here, we show that the RIG-I induction functionally contributes to IFN-α plus RA-triggered growth inhibition of AML cells. Interestingly, although RIG-I induction itself is under the regulation of STAT1, a major IFN intracellular signal mediator, under circumstances in which it does not stimulate IPS-1, it conversely augments STAT1 activation to induce IFN-stimulatory gene expression and inhibit leukemia cell proliferation. Thus, our results unveil a previously undescribed RIG-I activity in regulating the cellular proliferation of leukemia cells via STAT1, which is independent of its classic role of sensing viral invasion to trigger type I IFN transcription.

Functional genomic analysis of peripheral blood during early acute renal allograft rejection

BACKGROUND

Acute graft rejection is an important clinical problem in renal transplantation and an adverse predictor for long-term graft survival. Peripheral blood biomarkers that provide evidence of early graft rejection may offer an important option for posttransplant monitoring, optimize the utility of graft biopsy, and permit timely and effective therapeutic intervention to minimize the graft damage.

METHODS

In this feasibility study (n=58), we have used gene expression profiling in a case-control design to compare whole blood samples between normal subjects (n=20) and patients with (n=11) or without (n=22) biopsy-confirmed acute rejection (BCAR) or borderline changes (n=5).

RESULTS

A total of 183 probe sets representing 160 genes were differentially expressed (false discovery rate [FDR] <0.01) between subjects with or without BCAR, from which linear discriminant analysis and cross-validation identified an initial gene signature of 24 probe sets, and a more refined set of 11 probe sets found to classify subject samples correctly. Cross-validation suggested an out-of-sample sensitivity of 73% and specificity of 91% for identification of samples with or without BCAR. An increase in classifier gene expression correlated closely with acute rejection during the first 3 months posttransplant. Biological evaluation indicated that the differentially expressed genes encompassed processes related to immune response, signal transduction, and cytoskeletal reorganization.

CONCLUSION

Preliminary evidence indicates that gene expression in the peripheral blood may yield a relevant measure for the occurrence of BCAR and offer a potential tool for immunologic monitoring. These results now require confirmation in a larger cohort.

Interplay between cell adhesion and growth factor receptors: from the plasma membrane to the endosomes

The emergence of multicellular animals could only take place once evolution had produced molecular mechanisms for cell adhesion and communication. Today, all metazoans express integrin-type adhesion receptors and receptors for growth factors. Integrins recognize extracellular matrix proteins and respective receptors on other cells and, following ligand binding, can activate the same cellular signaling pathways that are regulated by growth factor receptors. Recent reports have indicated that the two receptor systems also collaborate in many other ways. Here, we review the present information concerning the role of integrins as assisting growth factor receptors and the interplay between the receptors in cell signaling and in the orchestration of receptor recycling.

Signalling cascades in mechanotransduction: cell-matrix interactions and mechanical loading

Mechanical loading of articular cartilage stimulates the metabolism of resident chondrocytes and induces the synthesis of molecules to maintain the integrity of the cartilage. Mechanical signals modulate biochemical activity and changes in cell behavior through mechanotransduction. Compression of cartilage results in complex changes within the tissue including matrix and cell deformation, hydrostatic and osmotic pressure, fluid flow, altered matrix water content, ion concentration and fixed charge density. These changes are detected by mechanoreceptors on the cell surface, which include mechanosensitive ion channels and integrins that on activation initiate intracellular signalling cascades leading to tissue remodelling. Excessive mechanical loading also influences chondrocyte metabolism but unlike physiological stimulation leads to a quantitative imbalance between anabolic and catabolic activity resulting in depletion of matrix components. In this article we focus on the role of mechanical signalling in the maintenance of articular cartilage, and discuss how alterations in normal signalling can lead to pathology.

Signal co-operation between integrins and other receptor systems

The multicellular nature of metazoans means that all cellular processes need to be tuned by adhesive interactions between cells and their local microenvironment. The spatial organization of cells within tissues requires sophisticated networks of extracellular signals to control their survival and proliferation, movements and positioning, and differentiated function. These cellular characteristics are mediated by multiple inputs from adhesion systems in combination with soluble and developmental signals. In the present review we explore how one class of adhesion receptor, the integrins, co-operate with other types of receptor to control diverse aspects of cell fate. In particular we discuss: (i) how beta3 and beta1 integrins work together with growth factors to control angiogenesis; (ii) how alpha6beta4 integrin co-operates with receptor tyrosine kinases in normal epithelial function and cancer; (iii) the interplay between beta1 integrins and EGF (epidermal growth factor) receptor; (iv) signal integration connecting integrins and cytokine receptors for interleukins, prolactin and interferons; and (v) how integrins and syndecans co-operate in cell migration.

Signal co-operation between integrins and other receptor systems

The multicellular nature of metazoans means that all cellular processes need to be tuned by adhesive interactions between cells and their local microenvironment. The spatial organization of cells within tissues requires sophisticated networks of extracellular signals to control their survival and proliferation, movements and positioning, and differentiated function. These cellular characteristics are mediated by multiple inputs from adhesion systems in combination with soluble and developmental signals. In the present review we explore how one class of adhesion receptor, the integrins, co-operate with other types of receptor to control diverse aspects of cell fate. In particular we discuss: (i) how β3 and β1 integrins work together with growth factors to control angiogenesis; (ii) how α6β4 integrin co-operates with receptor tyrosine kinases in normal epithelial function and cancer; (iii) the interplay between β1 integrins and EGF (epidermal growth factor) receptor; (iv) signal integration connecting integrins and cytokine receptors for interleukins, prolactin and interferons; and (v) how integrins and syndecans co-operate in cell migration.

Activation of protein kinase C{eta} by type I interferons

Type I interferons (IFNs) are cytokines with diverse biological properties, including antiviral, growth inhibitory, and immunomodulatory effects. Although several signaling pathways are activated during engagement of the type I IFN receptor and participate in the induction of IFN responses, the mechanisms of generation of specific signals for distinct biological effects remain to be elucidated. We provide evidence that a novel member of the protein kinase C (PKC) family of proteins is rapidly phosphorylated and activated during engagement of the type I IFN receptor. In contrast to other members of the PKC family that are also regulated by IFN receptors, PKCeta does not regulate IFN-inducible transcription of interferon-stimulated genes or generation of antiviral responses. However, its function promotes cell cycle arrest and is essential for the generation of the suppressive effects of IFNalpha on normal and leukemic human myeloid (colony-forming unit-granulocyte macrophage) bone marrow progenitors. Altogether, our studies establish PKCeta as a unique element in IFN signaling that plays a key and essential role in the generation of the regulatory effects of type I IFNs on normal and leukemic hematopoiesis.

Roles of phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase in the regulation of protein kinase C-alpha activation in interferon-gamma-stimulated macrophages

Members of the protein kinase C (PKC) family are activated by interferon-gamma (IFN-gamma) and modulate IFN-gamma-induced cellular responses by regulating the activity of transcription factors. We previously reported that PKC-alpha enhances the ability of IFN regulatory factor-1 to transactivate the class II transactivator (CIITA) promoter IV in IFN-gamma-stimulated macrophages. In addition, we showed that IFN-gamma induces the nuclear translocation of PKC-alpha but the mechanisms for this remain to be elucidated. In this study, we sought to identify signalling pathways involved in IFN-gamma-induced activation of PKC-alpha and to characterize their potential roles in modulating IFN-gamma-induced responses in macrophages. IFN-gamma-mediated nuclear translocation of PKC-alpha was a Janus activated kinase 2 (JAK2)-independent process, which required phosphatidylinositol 3-kinase (PI3K) and p38 mitogen-activated protein kinase (MAPK). However, PKC-alpha phosphorylation was independent of PI3K and p38 MAPK, indicating that IFN-gamma-induced phosphorylation and nuclear translocation of PKC-alpha are mediated by distinct mechanisms. In addition, inhibition of PI3K, but not of p38 MAPK, strongly impaired IFN-gamma-induced CIITA and MHC II gene expression. Finally, PKC-alpha associated with signal transducer and activator of transcription 1 (STAT1) and was required for the phosphorylation of STAT1 on serine 727 in IFN-gamma-stimulated macrophages. Taken together, our data indicate that PI3K and p38 MAPK modulate IFN-gamma-stimulated PKC-alpha nuclear translocation independently of JAK2 activity and that both PI3K and PKC-alpha are required for type IV CIITA and MHC II gene expression in IFN-gamma-stimulated macrophages.

Timing and Expression Level of Protein Kinase Cε Regulate the Megakaryocytic Differentiation of Human CD34 Cells

Protein kinase C (PKC)-mediated intracellular signaling participates in several key steps of hematopoietic cell differentiation. The epsilon isoform of PKC has been associated with erythroid differentiation as well as with the early phases of megakaryocytic (MK) lineage commitment. Here, we worked on the hypothesis that PKCepsilon expression levels might be modulated during MK differentiation, with a specific role in the early as well as in the late phases of thrombopoiesis. We demonstrate that--at variance with the erythroid lineage development--PKCepsilon is completely downmodulated in TPO-induced CD34 cells from day 6 onward. The forced expression of PKCepsilon in the late phases of MK differentiation delays the phenotypic differentiation of progenitors likely via Bcl-xL upregulation. Moreover, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), known as a negative regulator of early erythroid expansion, is not apoptogenic for thrombopoietin-induced CD34 cells, but rather accelerates their maturation. However, PKCepsilon levels negatively interfere also with the effects of TRAIL in MK differentiation. PKCepsilon can therefore be considered a signaling intermediate whose expression levels are finely tuned, with a virtually opposite kinetic, in erythroid versus megakaryocytic lineages, to adequately respond to the signaling requirements of the specific hematopoietic lineage.

Loss of protein kinase Cϵ results in impaired cutaneous wound closure and myofibroblast function

Cutaneous wound repair requires the de novo induction of a specialized form of fibroblast, the α-smooth muscle actin (α-SMA)-expressing myofibroblast, which migrates into the wound where it adheres to and contracts extracellular matrix (ECM), resulting in wound closure. Persistence of the myofibroblast results in scarring and fibrotic disease. In this report, we show that, compared with wild-type littermates, PKCϵ-/- mice display delayed impaired cutaneous wound closure and a reduction in myofibroblasts. Moreover, both in the presence and absence of TGFβ, dermal fibroblasts from PKCϵ-/- mice cultured on fibronectin show impaired abilities to form `supermature' focal adhesions and α-SMA stress fibers, and reduced pro-fibrotic gene expression. Smad3 phosphorylation in response to TGFβ1 was impaired in PKCϵ-/- fibroblasts. PKCϵ-/- fibroblasts show reduced FAK and Rac activation, and adhesive, contractile and migratory abilities. Overexpressing constitutively active Rac1 rescues the defective FAK phosphorylation, cell migration, adhesion and stress fiber formation of these PKCϵ-/- fibroblasts, indicating that Rac1 operates downstream of PKCϵ, yet upstream of FAK. These results suggest that loss of PKCϵ severely impairs myofibroblast formation and function, and that targeting PKCϵ may be beneficial in selectively modulating wound healing and fibrotic responses in vivo.

Midkine promotes tetraspanin-integrin interaction and induces FAK-Stat1alpha pathway contributing to migration/invasiveness of human head and neck squamous cell carcinoma cells

The heparin-binding growth factor, MK, promoting tumorigenesis and survival was found to associate with alpha6beta1 integrins. We showed for the first time that MK interacted with TSPAN1 and facilitated the association between TSPAN1 and integrin alpha6beta1 proteins in head and neck squamous cell carcinoma (HNSCC) cells. We found that MK mediated an integrin-dependent tyrosine phosphorylation of FAK and activation of paxillin and Stat1alpha pathways. As result, downstream target genes implicated in cell migration and invasiveness (e.g. MMP-2 and MMP-26) were overexpressed. We observed that RNAi silencing of the critical signaling intermediates led to decrease of MK-induced migration/invasiveness of HNSCC cells. The major finding of this study is a novel MK-triggered signaling mechanism implicated in migration and invasiveness of HNSCC cells.

Mouse vanin-1 is cytoprotective for islet beta cells and regulates the development of type 1 diabetes

AIMS/HYPOTHESIS

Islet cell death is a key initiating and perpetuating event in type 1 diabetes and involves both immune-mediated and endogenous mechanisms. The epithelial pantetheinase vanin-1 is proinflammatory and cytoprotective via cysteamine release in some tissues. We investigated the impact of a vanin-1 deficiency on islet death and type 1 diabetes incidence.

METHODS

Vanin-1-deficient mice were produced and tested in drug-induced and autoimmune diabetes models. The contribution of vanin-1 to islet survival versus immune responses was evaluated using lymphocyte transfer and islet culture experiments.

RESULTS

The vanin-1/cysteamine pathway contributes to the protection of islet beta cells from streptozotocin-induced death in vitro and in vivo. Furthermore, vanin-1-deficient NOD mice showed a significant aggravation of diabetes, which depended upon loss of vanin-1 expression by host tissues. This increased islet fragility was accompanied by greater CD4+ insulitis without impairment of regulatory cells. Addition of cystamine, the product of pantetheinase activity, protected islets in vitro and compensated for vanin-1 deficiency in vivo.

CONCLUSIONS/INTERPRETATION

This study unravels a major cytoprotective role of cysteamine for islet cells and suggests that modulation of pantetheinase activity may offer alternative strategies to maintain islet cell homeostasis.

A Protein Kinase Cε-Anti-apoptotic Kinase Signaling Complex Protects Human Vascular Endothelial Cells against Apoptosis through Induction of Bcl-2

Endothelial cell apoptosis is associated with vascular injury and predisposes to atherogenesis. Endothelial cells express anti-apoptotic genes including Bcl-2, Bcl-XL and survivin, which also contribute to angiogenesis and vascular remodeling. We report a central role for protein kinase Cepsilon (PKCepsilon) in the regulation of Bcl-2 expression and cytoprotection of human vascular endothelium against apoptosis. Using myristoylated inhibitory peptides, a predominant role for PKCepsilon in vascular endothelial growth factor-mediated endothelial resistance to apoptosis was revealed. Immunoblotting of endothelial cells infected with an adenovirus expressing a constitutively active form of PKCepsilon (Adv-PKCepsilon-CA) or control Adv-beta-galactosidase demonstrated a 3-fold, PKCepsilon-dependent increase in Bcl-2 expression, with no significant change in Bcl-XL, Bad, Bak, or Bax. The induction of Bcl-2 inhibited apoptosis induced by serum starvation or etoposide, and PKCepsilon activation attenuated etoposide-induced caspase-3 cleavage. The functional role of Bcl-2 was confirmed with Bcl-2 antagonist HA-14-1. Inhibition of phosphoinositide 3-kinase attenuated vascular endothelial growth factor-induced protection against apoptosis, and this was rescued by overexpression of constitutively active PKCepsilon, suggesting PKCepsilon acts downstream of phosphoinositide 3-kinase. Co-immunoprecipitation studies demonstrated a physical interaction between PKCepsilon and Akt, which resulted in formation of a signaling complex, leading to optimal induction of Bcl-2. This study reveals a pivotal role for PKCepsilon in endothelial cell cytoprotection against apoptosis. We demonstrate that PKCepsilon forms a signaling complex and acts co-operatively with Akt to protect human vascular endothelial cells against apoptosis through induction of the anti-apoptotic protein Bcl-2 and inhibition of caspase-3 cleavage.

Phosphatidylinositol 3'-kinase is a critical mediator of interferon-gamma-induced increases in enteric epithelial permeability

The epithelial lining of mucosal surfaces acts as a barrier to regulate the entry of antigen and pathogens. Nowhere is this function of the contiguous epithelium more important than in the gut, which is continually exposed to a huge antigenic load and, in the colon, an immense commensal microbiota. We assessed the intracellular signaling events that underlie interferon (IFN) gamma-induced increases in epithelial permeability using monolayers of the human colonic T84 epithelial cell line. Confluent epithelial monolayers on semipermeable supports were treated with IFNgamma (20 ng/ml), and barrier function was assessed 48 h later by measuring transepithelial electrical resistance (TER: reflects passive ion flux), fluxes of (51)Cr-EDTA and horseradish peroxidase (HRP), and transcytosis of noninvasive, nonpathogenic Escherichia coli (strain HB101). Exposure to IFNgamma decreased barrier function as assessed by all four markers. The phosphatidylinositol 3'-kinase (PI-3K) inhibitors, LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride] and wortmannin, did not affect baseline permeability characteristics but completely blocked the drop in TER, increased fluxes of (51)Cr-EDTA and HRP, and significantly reduced E. coli transcytosis evoked by IFNgamma. In addition, use of the pan-protein kinase C (PKC) inhibitor, bisindolylmaleimide I (5 muM), but not rottlerin (blocks PKCdelta), partially ameliorated the drop in TER and inhibited increased E. coli transcytosis. Addition of the PI-3K and PKC inhibitors to epithelia 6 h after IFNgamma exposure still prevented the increase in paracellular permeability but not E. coli transcytosis. Thus, IFNgamma-induced increases in epithelial paracellular and transcellular permeability are critically dependent on PI-3K activity, which may represent an epithelial-specific target to treat immune-mediated loss of barrier function.

PI 3 kinase-dependent Akt kinase and PKCε independently regulate interferon-γ-induced STAT1α serine phosphorylation to induce monocyte chemotactic protein-1 expression

Monocyte chemotactic protein-1 (MCP-1) recruits activated phagocytes to the site of tissue injury. Interferon-gamma (IFN-gamma) present in the microenvironment of glomerulus acts on mesangial cells to induce local production of MCP-1. The mechanism by which IFN-gamma stimulates expression of MCP-1 is not clear. We therefore examined the role of PI 3 kinase signaling in regulating the IFN-gamma-induced MCP-1 expression in mesangial cells. Blocking PI 3 kinase activity with Ly294002 attenuated IFN-gamma-induced MCP-1 protein and mRNA expression. IFN-gamma increased Akt kinase activity in a PI 3 kinase-dependent manner. Expression of dominant negative Akt kinase inhibited serine phosphorylation of STAT1alpha, without any effect on its tyrosine phosphorylation, and decreased IFN-gamma-induced expression of MCP-1. These data for the first time indicate a role for PI 3 kinase-dependent Akt kinase in MCP-1 expression. We have recently shown that along with Akt, PKCepsilon is a downstream target of PI 3 kinase in IFN-gamma signaling. Similar to dominant negative Akt kinase, dominant negative PKCepsilon also inhibited serine phosphorylation of STAT1alpha without any effect on tyrosine phosphorylation. Dominant negative PKCepsilon also abrogated MAPK activity, resulting in decrease in IFN-gamma-induced MCP-1 expression. Furthermore, Akt and PKCepsilon are present together in a signaling complex. IFN-gamma had no effect on this complex formation, but did increase PKCepsilon-associated Akt kinase activity. PKCepsilon did not regulate IFN-gamma-induced Akt kinase. Finally, expression of dominant negative Akt kinase blocked IFN-gamma-stimulated MAPK activation. These data provide the first evidence that PI 3 kinase-dependent Akt and PKCepsilon activation independently regulate MAPK activity and serine phosphorylation of STAT1alpha to increase expression of MCP-1.

A spatiotemporally coordinated cascade of protein kinase C activation controls isoform-selective translocation

In pituitary GH3B6 cells, signaling involving the protein kinase C (PKC) multigene family can self-organize into a spatiotemporally coordinated cascade of isoform activation. Indeed, thyrotropin-releasing hormone (TRH) receptor activation sequentially activated green fluorescent protein (GFP)-tagged or endogenous PKCbeta1, PKCalpha, PKCepsilon, and PKCdelta, resulting in their accumulation at the entire plasma membrane (PKCbeta and -delta) or selectively at the cell-cell contacts (PKCalpha and -epsilon). The duration of activation ranged from 20 s for PKCalpha to 20 min for PKCepsilon. PKCalpha and -epsilon selective localization was lost in the presence of Gö6976, suggesting that accumulation at cell-cell contacts is dependent on the activity of a conventional PKC. Constitutively active, dominant-negative PKCs and small interfering RNAs showed that PKCalpha localization is controlled by PKCbeta1 activity and is calcium independent, while PKCepsilon localization is dependent on PKCalpha activity. PKCdelta was independent of the cascade linking PKCbeta1, -alpha, and -epsilon. Furthermore, PKCalpha, but not PKCepsilon, is involved in the TRH-induced beta-catenin relocation at cell-cell contacts, suggesting that PKCepsilon is not the unique functional effector of the cascade. Thus, TRH receptor activation results in PKCbeta1 activation, which in turn initiates a calcium-independent but PKCbeta1 activity-dependent sequential translocation of PKCalpha and -epsilon. These results challenge the current understanding of PKC signaling and raise the question of a functional dependence between isoforms.

PKCϵ controls protection against TRAIL in erythroid progenitors

Apoptosis plays a central role in the regulation of the size of the hematopoietic stem cell pool as well as in the processes of cell differentiation along the various hematopoietic lineages. TRAIL is a member of the TNF family of cytokines with a known apoptogenic role against a variety of malignant cells and an emerging role in the modulation of normal hematopoiesis. Here we worked on the hypothesis that PKCϵ could act as a switch of the cellular response to TRAIL during erythropoiesis. We demonstrate that EPO-induced erythroid CD34 cells are insensitive to the apoptogenic effect of TRAIL at day 0 due to the lack of specific receptor expression. From day 3 onward, erythroid cells express surface death receptors and become sensitive to TRAIL up to day 7/8 when, notwithstanding death-receptor expression, the EPO-driven up-regulation of PKCϵ intracellular levels renders differentiating erythroid cells resistant to TRAIL likely via Bcl-2 up-regulation. Our conclusion is that in human CD34 cells, EPO promotes a series of events that, being finely regulated in their kinetics, restricts the sensitivity of these cells to TRAIL to a specific period of time, which therefore represents the “TRAIL window” for the negative regulation of erythroid-cell numbers.

Cell adhesion regulates Ser/Thr phosphorylation and proteasomal degradation of HEF1

Human enhancer of filamentation 1 (HEF1), a multifunctional docking protein of the Cas family, participates in integrin and growth factor signaling pathways that regulate global cellular processes including growth, motility and apoptosis. HEF1 consists of two isoforms, p105 and p115, the larger molecular weight form resulting from Ser/Thr phosphorylation of p105HEF1. The molecular mechanisms that regulate the interconversion of the two HEF1 species as well as the function of HEF1 Ser/Thr phosphorylation are unknown. Our study reveals that cell adhesion and detachment regulate the interconversion of the two HEF1 isoforms. Experiments using various inhibitors of cytoskeletal organization indicated that disruption of actin microfilaments but not intermediate filaments or microtubules resulted in a complete conversion of p115HEF1 to p105HEF1. The conversion of p115HEF1 to p105HEF1 was prevented by inhibition of protein phosphatase 2A (PP2A), suggesting that cytoskeletal regulation of PP2A activity controlled the dephosphorylation of p115HEF1. Degradation of endogenous HEF1 was dependent on proteasomes with the p115 species of HEF1 being preferentially targeted for turnover. Dephosphorylation of HEF1 by suspending cells or disrupting actin filaments protected HEF1 from degradation. These results suggest that the adhesion-dependent actin organization regulates proteasomal turnover of HEF1 through the activity of PP2A.

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.

A novel protein kinase C (PKCepsilon) is required for fMet-Leu-Phe-induced activation of NF-kappaB in human peripheral blood monocytes

We have reported that the chemoattractant, fMet-Leu-Phe (fMLP), induces the activation of NF-kappaB in human peripheral blood monocytes and that this requires the activity of small GTPase, RhoA (Huang, S., Chen, L.-Y., Zuraw, B. L., Ye, R. D., and Pan, Z. K. (2001) J. Biol. Chem. 276, 40977-40981). Here we showed that the novel protein kinase C isozyme, PKCepsilon, associates functionally with RhoA in fMLP-stimulated monocytes and that PKCepsilon acted as a signaling component downstream of the GTPase RhoA during fMLP-induced activation of NF-kappaB. Stimulation of monocytes with fMLP resulted in activation of both PKCepsilon and NF-kappaB. This latter activation was largely blocked by specific inhibitors of PKCepsilon by transient expression of a dominant-negative form of PKCepsilon and by PKCepsilon-specific short interfering RNA. These findings demonstrate, for the first time, that fMLP-induced activation of NF-kappaB utilizes a signaling pathway, which requires activity of PKCepsilon, and that PKCepsilon acts as a signaling component downstream of RhoA in cytokine gene transcription stimulated by a chemoattractant. The specificity of this response suggests an important role for the Rho GTPase-PKCepsilon-NF-kappaB pathway in host defense and represents a novel and potentially important mechanism through which fMLP not only attracts leukocytes but may also contribute directly to inflammation.

JAK-STAT signaling involved in phorbol 12-myristate 13-acetate- and dimethyl sulfoxide-induced 2'-5' oligoadenylate synthetase expression in human HL-60 leukemia cells

The JAK-STAT signal transduction cascade participates in various cellular processes, including immune response, cell replication, differentiation and oncogenesis. Here, we report that this cascade is induced in two human myeloid HL-60 leukemia cell variants by the granulocyte differentiation inducer dimethyl sulfoxide (DMSO) and macrophage differentiation inducer phorbol 12-myristate 13-acetate (PMA). DMSO and PMA also induced the expression and catalytic activity of 2'-5' oligoadenylate synthetase (2-5A synthetase), a known interferon (IFN) inducible enzyme. The HL-60 cell variants included HL-205, which is susceptible to DMSO- and PMA-induced differentiation, and HL-525, which is susceptible to DMSO- but not to PMA-induced differentiation. Treatment of HL-205 and HL-525 cells with DMSO and HL-205 cells with PMA-induced JAK1 phosphorylation, JAK1/STAT1 association, formation of STAT1-STAT2 heterodimers, and the binding of the active IFN stimulating growth factor 3 (ISGF3) to the IFN-stimulated response element (ISRE) fragment isolated from the 2-5A synthetase promoter. These events were either reduced or absent in the resistant HL-525 cells treated with PMA. Taken together, our data implicate the above signaling cascade in DMSO- and PMA-induced 2-5A synthetase expression and catalytic activity in the HL-60 cell system.

Negative regulation of EGFR signalling through integrin-α1β1-mediated activation of protein tyrosine phosphatase TCPTP

Integrin-mediated cell adhesion regulates a multitude of cellular responses, including proliferation, survival and cross-talk between different cellular signalling pathways. So far, integrins have been mainly shown to convey permissive signals enabling anchorage-dependent receptor tyrosine kinase signalling. Here we show that a collagen-binding integrin alpha(1)beta(1) functions as a negative regulator of epidermal growth factor receptor (EGFR) signalling through the activation of a protein tyrosine phosphatase. The cytoplasmic tail of alpha(1) integrin selectively interacts with a ubiquitously expressed protein tyrosine phosphatase TCPTP (T-cell protein tyrosine phosphatase) and activates it after cell adhesion to collagen. The activation results in reduced EGFR phosphorylation after EGF stimulation. Introduction of the alpha(1) cytoplasmic domain peptide into cells induces phosphatase activation and inhibits EGF-induced cell proliferation and anchorage-independent growth of malignant cells. These data are the first demonstration of the regulation of TCPTP activity in vivo and represent a new molecular paradigm of integrin-mediated negative regulation of receptor tyrosine kinase signalling.

Conventional protein kinase C inhibition prevents alpha interferon-mediated hepatitis C virus replicon clearance by impairing STAT activation

Hepatitis C virus (HCV) has evolved complex strategies to evade host immune responses and establish chronic infection. The only treatment available for HCV infections, alpha interferon (IFN-alpha), is effective in a limited percentage of patients. The mechanisms by which IFN-alpha interferes with the HCV life cycle and the reasons for limited effectiveness of IFN-alpha therapy have not yet been fully elucidated. Using a cell-based HCV replication system and specific kinase inhibitors, we examined the role played by various signaling pathways in the IFN-alpha-mediated HCV clearance. We reported that conventional protein kinase C (cPKC) activity is important for the effectiveness of IFN-alpha treatment. In cells treated with a cPKC-specific inhibitor, IFN-alpha failed to induce an efficient HCV RNA degradation. The lack of cPKC activity leads to a broad reduction of IFN-alpha-stimulated gene expression due to a significant impairment of STAT1 and STAT3 tyrosine phosphorylation. Thus, modulation of cPKC function by either host or viral factors could influence the positive outcome of IFN-alpha-mediated antiviral therapies.

Integrin signaling links protein kinase Cepsilon to the protein kinase B/Akt survival pathway in recurrent prostate cancer cells

Failure of hormone therapy often involves an outgrowth of protein kinase Cepsilon (PKCepsilon)-positive cells in recurrent prostate cancer. Our previous investigations have uncovered evidence of a complex signaling network operating downstream of this oncogenic protein kinase to actively advance the survival and proliferation of prostate cancer cells. In this study, we present evidence of a functional interplay among integrin receptors, PKCepsilon, and protein kinase B (PKB/Akt) in recurrent CWR-R1 prostate cancer cells. Flow cytometry and confocal microscopy provided evidence that PKCepsilon signaling promoted the assembly of matrix adhesions containing an abundance of colocalized actin filaments and beta1 integrins that exhibited an exposed activation epitope on the surface of live CWR-R1 cells. Reciprocal coimmunoprecipitations provided evidence of signaling complexes containing PKCepsilon, beta1 integrins, Src, and PKB/Akt in CWR-R1 cell cultures. An investigation into the functional significance of these interactions, and of their positive influence on beta1 integrins, demonstrated that PKCepsilon and several key components of the PKB/Akt signaling pathway remain constitutively phosphorylated/activated in adherent but not suspension cultures of PTEN-positive CWR-R1 cells. Gene transfer, antisense and pharmacological experiments provided additional support for the hypothesis that a mutually reinforcing signaling loop sustains the activation of beta1 integrins, PKCepsilon, and PKB/Akt in adherent prostate cancer cells.

Regulation of outside-in signaling in platelets by integrin-associated protein kinase C beta

Studies with inhibitors have implicated protein kinase C (PKC) in the adhesive functions of integrin alpha(IIb)beta(3) in platelets, but the responsible PKC isoforms and mechanisms are unknown. Alpha(IIb)beta(3) interacts directly with tyrosine kinases c-Src and Syk. Therefore, we asked whether alpha(IIb)beta(3) might also interact with PKC. Of the several PKC isoforms expressed in platelets, only PKC beta co-immunoprecipitated with alpha(IIb)beta(3) in response to the interaction of platelets with soluble or immobilized fibrinogen. PKC beta recruitment to alpha(IIb)beta(3) was accompanied by a 9-fold increase in PKC activity in alpha(IIb)beta(3) immunoprecipitates. RACK1, an intracellular adapter for activated PKC beta, also co-immunoprecipitated with alpha(IIb)beta(3), but in this case, the interaction was constitutive. Broad spectrum PKC inhibitors blocked both PKC beta recruitment to alpha(IIb)beta(3) and the spread of platelets on fibrinogen. Similarly, mouse platelets that are genetically deficient in PKC beta spread poorly on fibrinogen, despite normal agonist-induced fibrinogen binding. In a Chinese hamster ovary cell model system, adhesion to fibrinogen caused green fluorescent protein-PKC beta I to associate with alpha(IIb)beta(3) and to co-localize with it at lamellipodial edges. These responses, as well as Chinese hamster ovary cell migration on fibrinogen, were blocked by the deletion of the beta(3) cytoplasmic tail or by co-expression of a RACK1 mutant incapable of binding to beta(3). These studies demonstrate that the interaction of alpha(IIb)beta(3) with activated PKC beta is regulated by integrin occupancy and can be mediated by RACK1 and that the interaction is required for platelet spreading triggered through alpha(IIb)beta(3). Furthermore, the studies extend the concept of alpha(IIb)beta(3) as a scaffold for multiple protein kinases that regulate the platelet actin cytoskeleton.

Signal transduction pathways implicated in the decrease in CYP1A1, 1A2 and 3A6 activity produced by serum from rabbits and humans with an inflammatory reaction

Incubation of serum from rabbits with a turpentine-induced inflammatory reaction and from humans with an upper respiratory viral infection with hepatocytes from rabbits with a turpentine-induced inflammatory reaction for 4h reduces total cytochrome P450 content and activity of cytochrome P450 isoforms CYP1A1/1A2 and 3A6 without affecting the expression of these proteins. To document the signal transduction pathways implicated in the decrease in CYP1A1/1A2 and 3A6 activity, hepatocytes from rabbits with a turpentine-induced inflammatory reaction were incubated with serum from rabbits with a turpentine-induced inflammatory reaction, serum from individuals with a viral infection and interleukin-6 for 4h in presence of inhibitors of protein kinases. The sera-induced decrease in CYP1A1/1A2 and 3A6 activity was partially prevented by the inhibition of Janus-associated protein tyrosine kinase, double-stranded RNA-dependent protein kinase, protein kinase C, and p42/44 mitogen-activated protein kinase. The serum from rabbits with a turpentine-induced inflammatory reaction increased the phosphorylation of Erk1/2, effect prevented by PD98059 but not by bis-indolylmaleimide, a specific inhibitor of protein kinase C. The results demonstrated that the decrease in total cytochrome P450 content and in CYP1A1/1A2 and 3A6 activity by sera and interleukin-6 involves the activation of protein tyrosine kinases, p42/44 mitogen-activated protein kinase and protein kinase C. Indirect evidence supported that nitric oxide is implicated in the decrease in activity of these enzymes.

A role for the cytoskeleton in prolactin-dependent mammary epithelial cell differentiation

The function of exocrine glands depends on signals within the extracellular environment. In the mammary gland, integrin-mediated adhesion to the extracellular matrix protein laminin co-operates with soluble factors such as prolactin to regulate tissue-specific gene expression. The mechanism of matrix and prolactin crosstalk and the activation of downstream signals are not fully understood. Because integrins organize the cytoskeleton, we analysed the contribution of the cytoskeleton to prolactin receptor activation and the resultant stimulation of milk protein gene expression. We show that the proximal signalling events initiated by prolactin (i.e. tyrosine phosphorylation of receptor and the associated kinase Jak2) do not depend on an intact actin cytoskeleton. However, actin networks and microtubules are both necessary for continued mammary cell differentiation, because cytoskeletal integrity is required to transduce the signals between prolactin receptor and Stat5, a transcription factor necessary for milk protein gene transcription. The two different cytoskeletal scaffolds regulate prolactin signalling through separate mechanisms that are specific to cellular differentiation but do not affect the general profile of protein synthesis.

A linear signal transduction pathway involving phosphatidylinositol 3-kinase, protein kinase Cepsilon, and MAPK in mesangial cells regulates interferon-gamma-induced STAT1alpha transcriptional activation

Interferon-gamma (IFN-gamma) exerts an pleiotropic effect in mesangial cells in inflammatory glomerular diseases. The biologic effect of IFN-gamma is mediated by STAT1alpha. The precise mechanism by which IFN-gamma stimulates the transcriptional activity of STAT1alpha is poorly understood. I investigated the role of protein kinase C (PKC) epsilon in regulating the transcriptional activation of STAT1alpha in mesangial cells. IFN-gamma increased PKCepsilon activity in a time-dependent manner with a concomitant increase in STAT1alpha transcriptional activity. Expression of constitutively active PKCepsilon mimicked the effect of IFN-gamma on STAT1alpha-dependent transcription. Expression of dominant negative PKCepsilon inhibited IFN-gamma-induced STAT1alpha-dependent transcription. Ly294002, a pharmacological inhibitor of phosphatidylinositol (PI) 3-kinase, blocked IFN-gamma-induced PKCepsilon activity and resulted in inhibition of STAT1alpha transcriptional activity but had no effect on STAT1alpha tyrosine phosphorylation and STAT1alpha-DNA complex formation. A PKC inhibitor, H7, also had no effect on STAT1alpha tyrosine phosphorylation and DNA binding. However, Ly294002 and H7 blocked IFN-gamma-induced serine phosphorylation of STAT1alpha. These data indicate that PI 3 kinase-dependent PKCepsilon regulates STAT1alpha transcriptional activity in the absence of any effect on its DNA binding capability. In addition to activating PKCepsilon, IFN-gamma increased MAPK activity, resulting in transcriptional activation of Elk-1, a nuclear target of MAPK. Ly294002 or a dominant negative PI 3-kinase significantly blocked IFN-gamma-induced MAPK activity. On the other hand, ectopic expression of constitutively active PKCepsilon significantly increased MAPK activity. IFN-gamma-stimulated MAPK phosphorylated STAT1alpha in vitro. Inhibition of MAPK activity blocked IFN-gamma-induced serine phosphorylation of STAT1alpha; but its tyrosine phosphorylation and DNA binding were partially inhibited. Finally, expression of dominant negative MAPK significantly inhibited IFN-gamma-induced STAT1alpha-dependent transcription. These data provide the first evidence that IFN-gamma stimulates PKCepsilon in a PI 3-kinase-sensitive manner to activate MAPK, which regulates STAT1alpha transcriptional activity.