Kinase Suppressor of RAS 1 (KSR1) Maintains the Transformed Phenotype of BRAFV600E Mutant Human Melanoma Cells

Kinase Suppressor of RAS 1 (KSR1) is a scaffolding protein for the RAS-RAF-MEK-ERK pathway, which is one of the most frequently altered pathways in human cancers. Previous results have shown that KSR1 has a critical role in mutant RAS-mediated transformation. Here, we examined the role of KSR1 in mutant BRAF transformation. We used CRISPR/Cas9 to knock out KSR1 in a BRAFV600E-transformed melanoma cell line. KSR1 loss produced a complex phenotype characterised by impaired proliferation, cell cycle defects, decreased transformation, decreased invasive migration, increased cellular senescence, and increased apoptosis. To decipher this phenotype, we used a combination of proteomic ERK substrate profiling, global protein expression profiling, and biochemical validation assays. The results suggest that KSR1 directs ERK to phosphorylate substrates that have a critical role in ensuring cell survival. The results further indicate that KSR1 loss induces the activation of p38 Mitogen-Activated Protein Kinase (MAPK) and subsequent cell cycle aberrations and senescence. In summary, KSR1 function plays a key role in oncogenic BRAF transformation.

KSR induces RAS-independent MAPK pathway activation and modulates the efficacy of KRAS inhibitors

The kinase suppressor of rat sarcoma (RAS) proteins (KSR1 and KSR2) have long been considered as scaffolding proteins required for optimal mitogen‐activated protein kinase (MAPK) pathway signalling. However, recent evidence suggests that they play a more complex role within this pathway. Here, we demonstrate that ectopic expression of KSR1 or KSR2 is sufficient to activate the MAPK pathway and to induce cell proliferation in the absence of RAS proteins. In contrast, the ectopic expression of KSR proteins is not sufficient to induce cell proliferation in the absence of either rapidly accelerated fibrosarcoma (RAF) or MAPK‐ERK kinase proteins, indicating that they act upstream of RAF. Indeed, KSR1 requires dimerization with at least one member of the RAF family to stimulate proliferation, an event that results in the translocation of the heterodimerized RAF protein to the cell membrane. Mutations in the conserved aspartic acid–phenylalanine–glycine motif of KSR1 that affect ATP binding impair the induction of cell proliferation. We also show that increased expression levels of KSR1 decrease the responsiveness to the KRAS^G12C inhibitor sotorasib in human cancer cell lines, thus suggesting that increased levels of expression of KSR may make tumour cells less dependent on KRAS oncogenic signalling.

Blockade of EGFR Activation Promotes TNF-Induced Lung Epithelial Cell Apoptosis and Pulmonary Injury

Pneumonitis is the leading cause of death associated with the use of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKIs) against non-small cell lung cancer (NSCLC). However, the risk factors and the mechanism underlying this toxicity have not been elucidated. Tumor necrosis factor (TNF) has been reported to transactivate EGFR in pulmonary epithelial cells. Hence, we aimed to test the hypothesis that EGFR tyrosine kinase activity regulates TNF-mediated bronchial epithelial cell survival, and that inhibition of EGFR activity increases TNF-induced lung epithelial cell apoptosis. We used surfactant protein C (SPC)-TNF transgenic (tg) mice which overexpress TNF in the lungs. In this model, gefitinib, an EGFR-TKI, enhanced lung epithelial cell apoptosis and lymphocytic inflammation, indicating that EGFR tyrosine kinase prevents TNF-induced lung injury. Furthermore, IL-17A was significantly upregulated by gefitinib in SPC-TNF tg mice and p38MAPK activation was observed, indicative of a pathway involved in lung epithelial cell apoptosis. Moreover, in lung epithelial cells, BEAS-2B, TNF stimulated EGFR transactivation via the TNF-α-converting enzyme in a manner that requires heparin binding (HB)-EGF and transforming growth factor (TGF)-α. These novel findings have significant implications in understanding the role of EGFR in maintaining human bronchial epithelial cell homeostasis and in NSCLC treatment.

Kinase suppressor of Ras 1 and Exo70 promote fatty acid-stimulated neurotensin secretion through ERK1/2 signaling

Neurotensin is a peptide hormone released from enteroendocrine cells in the small intestine in response to fat ingestion. Although the mechanisms regulating neurotensin secretion are still incompletely understood, our recent findings implicate a role for extracellular signal-regulated kinase 1 and 2 as positive regulators of free fatty acid-stimulated neurotensin secretion. Previous studies have shown that kinase suppressor of Ras 1 acts as a molecular scaffold of the Raf/MEK/extracellular signal-regulated kinase 1 and 2 kinase cascade and regulates intensity and duration of extracellular signal-regulated kinase 1 and 2 signaling. Here, we demonstrate that inhibition of kinase suppressor of Ras 1 attenuates neurotensin secretion and extracellular signal-regulated kinase 1 and 2 signaling in human endocrine cells. Conversely, we show that overexpression of kinase suppressor of Ras 1 enhances neurotensin secretion and extracellular signal-regulated kinase 1 and 2 signaling. We also show that inhibition of extracellular signal-regulated kinase 2 and exocyst complex component 70, a substrate of extracellular signal-regulated kinase 2 and mediator of secretory vesicle exocytosis, potently inhibits basal and docosahexaenoic acid-stimulated neurotensin secretion, whereas overexpression of exocyst complex component 70 enhances basal and docosahexaenoic acid-stimulated neurotensin secretion. Together, our findings demonstrate a role for kinase suppressor of Ras 1 as a positive regulator of neurotensin secretion from human endocrine cells and indicate that this effect is mediated by the extracellular signal-regulated kinase 1 and 2 signaling pathway. Moreover, we reveal a novel role for exocyst complex component 70 in regulation of neurotensin vesicle exocytosis through its interaction with the extracellular signal-regulated kinase 1 and 2 signaling pathway.

The N-terminal kinase suppressor of Ras complex has a weak nucleoside diphosphate kinase activity

INTRODUCTION

An increasing number of studies have proven that the kinase suppressor of Ras (KSR1) functions as a scaffolding protein that coordinates the assembly of a multiprotein complex containing mitogen-activated protein kinase and its upstream regulators. However, a few studies have reported that KSR1 can activate c-Raf-1. Therefore, whether KSR1 possesses a kinase activity has been an unresolved issue until now.

MATERIALS AND METHODS

pCMV-Tag2b-KSR plasmids were transfected into 293T cells. In vitro autophosphorylation was assayed by autoradiography and in vitro kinase was assayed by reversed-phase high performance liquid chromatography.

RESULTS

We observed that wild-type KSR1 (WT-KSR) and N-terminal KSR1 (N-KSR) were phosphorylated, but the C-terminal KSR1 (C-KSR) and vector proteins were not. The high performance liquid chromatography profile showed not only the adenosine diphosphate peak but also the uridine triphosphate peak in the WT-KSR and N-KSR groups; both peaks were considerably more significant in these groups than in the others. The WT-KSR and N-KSR groups exhibited transphosphorylation and autophosphorylation activities, while the other groups revealed almost no activity.

DISCUSSION

Here, we demonstrate the nucleoside diphosphate kinase activity of the KSR1 complex and that this activity can be independent of the C-terminus of KSR1. Additionally, we found the autophosphorylation activity of the KSR1 complex to be extremely weak, suggesting that the KSR1 complex possesses an extremely weak kinase activity irrespective of whether it is nucleoside diphosphate kinase activity or serine/threonine protein kinase activity. These data suggest that the kinase activity of the KSR1 complex is derived from its associated proteins.

Deciphering the RAS/ERK pathway in vivo

The RAS/ERK pathway has been intensely studied for about three decades, not least because of its role in human pathologies. ERK activation is observed in the majority of human cancers; in about one-third of them, it is driven by mutational activation of pathway components. The pathway is arguably one of the best targets for molecule-based pharmacological intervention, and several small-molecule inhibitors are in clinical use. Genetically engineered mouse models have greatly contributed to our understanding of signaling pathways in development, tissue homeostasis, and disease. In the specific case of the RAS/ERK pathway, they have revealed unique biological roles of structurally and functionally similar proteins, new kinase-independent effectors, and unsuspected relationships with other cascades. This short review summarizes the contribution of mouse models to our current understanding of the pathway.

How Genetics Has Helped Piece Together the MAPK Signaling Pathway

Cells respond to changes in their environment, to developmental cues, and to pathogen aggression through the action of a complex network of proteins. These networks can be decomposed into a multitude of signaling pathways that relay signals from the microenvironment to the cellular components involved in eliciting a specific response. Perturbations in these signaling processes are at the root of multiple pathologies, the most notable of these being cancer. The study of receptor tyrosine kinase (RTK) signaling led to the first description of a mechanism whereby an extracellular signal is transmitted to the nucleus to induce a transcriptional response. Genetic studies conducted in drosophila and nematodes have provided key elements to this puzzle. Here, we briefly discuss the somewhat lesser known contribution of these multicellular organisms to our understanding of what has come to be known as the prototype of signaling pathways. We also discuss the ostensibly much larger network of regulators that has emerged from recent functional genomic investigations of RTK/RAS/ERK signaling.

praja2 regulates KSR1 stability and mitogenic signaling

The kinase suppressor of Ras 1 (KSR1) has a fundamental role in mitogenic signaling by scaffolding components of the Ras/MAP kinase pathway. In response to Ras activation, KSR1 assembles a tripartite kinase complex that optimally transfers signals generated at the cell membrane to activate ERK. We describe a novel mechanism of ERK attenuation based on ubiquitin-dependent proteolysis of KSR1. Stimulation of membrane receptors by hormones or growth factors induced KSR1 polyubiquitination, which paralleled a decline of ERK1/2 signaling. We identified praja2 as the E3 ligase that ubiquitylates KSR1. We showed that praja2-dependent regulation of KSR1 is involved in the growth of cancer cells and in the maintenance of undifferentiated pluripotent state in mouse embryonic stem cells. The dynamic interplay between the ubiquitin system and the kinase scaffold of the Ras pathway shapes the activation profile of the mitogenic cascade. By controlling KSR1 levels, praja2 directly affects compartmentalized ERK activities, impacting on physiological events required for cell proliferation and maintenance of embryonic stem cell pluripotency.

Non-Hematopoietic β-Arrestin1 Confers Protection Against Experimental Colitis

β-Arrestins are multifunctional scaffolding proteins that modulate G protein-coupled receptor (GPCR)-dependent and -independent cell signaling pathways in various types of cells. We recently demonstrated that β-arrestin1 (β-arr1) deficiency strikingly attenuates dextran sodium sulfate (DSS)-induced colitis in mice. Since DSS-induced colitis is in part dependent on gut epithelial injury, we examined the role of β-arr1 in intestinal epithelial cells (IECs) using a colon epithelial cell line, SW480 cells. Surprisingly, we found that knockdown of β-arr1 in SW480 cells enhanced epithelial cell death via a caspase-3-dependent process. To understand the in vivo relevance and potential cell type-specific role of β-arr1 in colitis development, we generated bone marrow chimeras with β-arr1 deficiency in either the hematopoietic or non-hematopoietic compartment. Reconstituted chimeric mice were then subjected to DSS-induced colitis. Similar to our previous findings, β-arr1 deficiency in the hematopoietic compartment protected mice from DSS-induced colitis. However, consistent with the role of β-arr1 in epithelial apoptosis in vitro, non-hematopoietic β-arr1 deficiency led to an exacerbated colitis phenotype. To further understand signaling mechanisms, we examined the effect of β-arr1 on TNF-α-mediated NFκB and MAPK pathways. Our results demonstrate that β-arr1 has a critical role in modulating ERK, JNK and p38 MAPK pathways mediated by TNF-α in IECs. Together, our results show that β-arr1-dependent signaling in hematopoietic and non-hematopoietic cells differentially regulates colitis pathogenesis and further demonstrates that β-arr1 in epithelial cells inhibits TNF-α-induced cell death pathways.

Proteomic profile of KSR1-regulated signalling in response to genotoxic agents in breast cancer

Kinase suppressor of Ras 1 (KSR1) has been implicated in tumorigenesis in multiple cancers, including skin, pancreatic and lung carcinomas. However, our recent study revealed a role of KSR1 as a tumour suppressor in breast cancer, the expression of which is potentially correlated with chemotherapy response. Here, we aimed to further elucidate the KSR1-regulated signalling in response to genotoxic agents in breast cancer. Stable isotope labelling by amino acids in cell culture (SILAC) coupled to high-resolution mass spectrometry (MS) was implemented to globally characterise cellular protein levels induced by KSR1 in the presence of doxorubicin or etoposide. The acquired proteomic signature was compared and GO-STRING analysis was subsequently performed to illustrate the activated functional signalling networks. Furthermore, the clinical associations of KSR1 with identified targets and their relevance in chemotherapy response were examined in breast cancer patients. We reveal a comprehensive repertoire of thousands of proteins identified in each dataset and compare the unique proteomic profiles as well as functional connections modulated by KSR1 after doxorubicin (Doxo-KSR1) or etoposide (Etop-KSR1) stimulus. From the up-regulated top hits, several proteins, including STAT1, ISG15 and TAP1 are also found to be positively associated with KSR1 expression in patient samples. Moreover, high KSR1 expression, as well as high abundance of these proteins, is correlated with better survival in breast cancer patients who underwent chemotherapy. In aggregate, our data exemplify a broad functional network conferred by KSR1 with genotoxic agents and highlight its implication in predicting chemotherapy response in breast cancer.

KSR1 regulates BRCA1 degradation and inhibits breast cancer growth

Kinase suppressor of Ras-1 (KSR1) facilitates signal transduction in Ras-dependent cancers, including pancreatic and lung carcinomas but its role in breast cancer has not been well studied. Here, we demonstrate for the first time it functions as a tumor suppressor in breast cancer in contrast to data in other tumors. Breast cancer patients (n>1000) with high KSR1 showed better disease-free and overall survival, results also supported by Oncomine analyses, microarray data (n=2878) and genomic data from paired tumor and cell-free DNA samples revealing loss of heterozygosity. KSR1 expression is associated with high breast cancer 1, early onset (BRCA1), high BRCA1-associated ring domain 1 (BARD1) and checkpoint kinase 1 (Chk1) levels. Phospho-profiling of major components of the canonical Ras-RAF-mitogen-activated protein kinases pathway showed no significant changes after KSR1 overexpression or silencing. Moreover, KSR1 stably transfected cells formed fewer and smaller size colonies compared to the parental ones, while in vivo mouse model also demonstrated that the growth of xenograft tumors overexpressing KSR1 was inhibited. The tumor suppressive action of KSR1 is BRCA1 dependent shown by 3D-matrigel and soft agar assays. KSR1 stabilizes BRCA1 protein levels by reducing BRCA1 ubiquitination through increasing BARD1 abundance. These data link these proteins in a continuum with clinical relevance and position KSR1 in the major oncoprotein pathways in breast tumorigenesis.

Going for broke: targeting the human cancer pseudokinome

Protein phosphorylation lies at the heart of cell signalling, and somatic mutation(s) in kinases drives and sustains a multitude of human diseases, including cancer. The human protein kinase superfamily (the kinome) encodes approximately 50 'pseudokinases', which were initially predicted to be incapable of dynamic cell signalling when compared with canonical enzymatically active kinases. This assumption was supported by bioinformatics, which showed that amino acid changes at one or more key loci, making up the nucleotide-binding site or phosphotransferase machinery, were conserved in multiple vertebrate and non-vertebrate pseudokinase homologues. Protein kinases are highly attractive targets for drug discovery, as evidenced by the approval of almost 30 kinase inhibitors in oncology, and the successful development of the dual JAK1/2 (Janus kinase 1/2) inhibitor ruxolitinib for inflammatory indications. However, for such a large (>550) protein family, a remarkable number have still not been analysed at the molecular level, and only a surprisingly small percentage of kinases have been successfully targeted clinically. This is despite evidence that many are potential candidates for the development of new therapeutics. Indeed, several recent reports confirm that disease-associated pseudokinases can bind to nucleotide co-factors at concentrations achievable in the cell. Together, these findings suggest that drug targeting using either ATP-site or unbiased ligand-discovery approaches should now be attempted using the validation technology currently employed to evaluate their classic protein kinase counterparts. In the present review, we discuss members of the human pseudokinome repertoire, and catalogue somatic amino acid pseudokinase mutations that are emerging as the depth and clinical coverage of the human cancer pseudokinome expand.

Redeeming an old foe: protective as well as pathophysiological roles for tumor necrosis factor in inflammatory bowel disease

Tumor necrosis factor (TNF) and its receptors TNFR1 and TNFR2 are major therapeutic targets for inflammatory bowel disease. Research advances have demonstrated that TNF produces pleiotropic responses in the gastrointestinal (GI) tract. Although in excess TNF can contribute to GI pathology, TNF is also a critical protective factor to promote GI homeostasis following injury and inflammation. Genetic studies using candidate and genome-wide association study approaches have identified variants in TNF or its receptors that are associated with Crohn's disease or ulcerative colitis in multiple populations, although the basis for these associations remains unclear. This review considers the efficacy and mechanism of anti-TNF therapies for inflammatory bowel disease to reconcile the many disparate aspects of TNF research and to consider the potential protective effects of TNF signaling in GI health.

Human intestinal epithelial cells respond to β-glucans via Dectin-1 and Syk

Intestinal epithelial cells (IECs) are the first to encounter luminal antigens and may be involved in intestinal immune responses. Fungi are important components of the intestinal microflora. The potential role of fungi, and in particular their cell wall component β-glucan, in modulating human intestinal epithelial responses is still unclear. Here we examined whether human IECs are capable of recognizing and responding to β-glucans, and the potential mechanisms of their activation. We show that human IECs freshly isolated from surgical specimens, and the human IEC lines HT-29 and SW480, express the β-glucan receptor Dectin-1. The β-glucan-consisting glycans curdlan and zymosan stimulated IL-8 and CCL2 secretion by IEC lines. This was significantly inhibited by a Dectin-1 blockade using its soluble antagonist laminarin. Spleen tyrosine kinase (Syk), a signaling mediator of Dectin-1 activation, is expressed in human IECs. β-glucans and Candida albicans induced Syk phosphorylation, and Syk inhibition significantly decreased β-glucan-induced chemokine secretion from IECs. Thus, IECs may respond to β-glucans by the secretion of pro-inflammatory chemokines in a Dectin-1- and Syk-dependent pathway, via receptors and a signaling pathway described to date only for myeloid cells. These findings highlight the importance of fungi-IEC interactions in intestinal inflammation.

Small GTPases of the Ras superfamily regulate intestinal epithelial homeostasis and barrier function via common and unique mechanisms

The intestinal epithelium forms a stable barrier protecting underlying tissues from pathogens in the gut lumen. This is achieved by specialized integral membrane structures such as tight and adherens junctions that connect neighboring cells and provide stabilizing links to the cytoskeleton. Junctions are constantly remodeled to respond to extracellular stimuli. Assembly and disassembly of junctions is regulated by interplay of actin remodeling, endocytotic recycling of junctional proteins, and various signaling pathways. Accumulating evidence implicate small G proteins of the Ras superfamily as important signaling molecules for the regulation of epithelial junctions. They function as molecular switches circling between an inactive GDP-bound and an active GTP-bound state. Once activated, they bind different effector molecules to control cellular processes required for correct junction assembly, maintenance and remodelling. Here, we review recent advances in understanding how GTPases of the Rho, Ras, Rab and Arf families contribute to intestinal epithelial homeostasis.

The dual function of KSR1: a pseudokinase and beyond

Protein kinases play a pivotal role in regulating many aspects of biological processes, including development, differentiation and cell death. Within the kinome, 48 kinases (~10%) are classified as pseudokinases owing to the fact that they lack at least one conserved catalytic residue in their kinase domain. However, emerging evidence suggest that some pseudokinases, even without the ability to phosphorylate substrates, are regulators of multiple cellular signalling pathways. Among these is KSR1 (kinase suppressor of Ras 1), which was initially identified as a novel kinase in the Ras/Raf pathway. Subsequent studies showed that KSR1 mainly functions as a platform to assemble different cellular components thereby facilitating signal transduction. In the present article, we discuss recent findings regarding KSR1, indicating that it has dual activity as an active kinase as well as a pseudokinase/scaffolding protein. Moreover, the biological functions of KSR1 in human disorders, notably in malignancies, are also reviewed.

Overview of molecular pathways in inflammatory bowel disease associated with colorectal cancer development

Patients with long-standing inflammatory bowel disease (IBD) are at a higher risk of developing colorectal cancer (CRC). This risk increases with the longer duration of colitis, greater extent of inflammation, a family history of CRC, severity of bowel inflammation, and a coexistent primary sclerosing cholangitis. The cornerstone for comprehending the development of CRC in IBD and hence early detection is based on the understanding of the molecular pathways of IBD itself. At a molecular level, the pathogenesis of CRC is related to understanding the inflammatory changes and involves multiple inter-related pathways including (i) genetic alterations (e.g. chromosomal and microsatellite instability and hypermethylation), (ii) mucosal inflammatory mediators (e.g. COX-2, interleukin-6, interleukin-23, tumor necrosis factor-α, nuclear factor-κB, and chemokines), (iii) changes in the expression of receptors on the epithelial cells, and (iv) oxidant stress, mucosal breakdown, and intestinal microbiota. The aim of this review is to provide an evidence-based approach for the role of chronic inflammatory mechanisms and the molecular basis of these mechanisms in the development of CRC. Therefore, understanding the molecular basis of CRC is an important step for the identification of new biomarkers that can help in the early detection of CRC in these patients.

The EGF receptor and HER2 participate in TNF-α-dependent MAPK activation and IL-8 secretion in intestinal epithelial cells

TNF-α activates multiple mitogen-activated protein kinase (MAPK) cascades in intestinal epithelial cells (IECs) leading to the secretion of interleukin 8 (IL-8), a neutrophil chemoattractant and an angiogenic factor with tumor promoting properties. As the epidermal growth factor receptor (EGFR) is a known transducer of proliferative signals and a potent activator of MAPKs, we hypothesized that the EGFR participates in TNF-dependent MAPK activation and IL-8 secretion by intestinal epithelial cells (IECs). We show that the EGFR is tyrosine-phosphorylated following treatment of IECs (HT-29 and IEC-6) with TNF-α. This requires EGFR autophosphorylation as it was blocked by the EGFR kinase inhibitor AG1478. Autophosphorylation was also inhibited by both a Src-kinase inhibitor and the metalloproteinase inhibitor batimastat. TNF treatment of IECs resulted in the accumulation of soluble TGF-α; treatment of IECs with batimastat suppressed TGF-α release and immunoneutralization of TGF-α resulted in decreased EGFR and ERK phosphorylations. TNF-α treatment of IECs resulted in an association between EGFR and HER2 and inhibition of HER2 using a specific inhibitor AG879 in combination with AG1478-suppressed TNF-α-dependent ERK phosphorylation and IL-8 release. Downregulation of HER2 via siRNA resulted in a significant decrease in ERK phosphorylation and a 50% reduction in IL-8 secretion.

Role of kinase suppressor of ras-1 in lipopolysaccharide-induced acute lung injury

Kinase suppressor of ras-1 (Ksr1) has been recently shown to be a central signaling molecule in the host response to Pseudomonas aeruginosa infections in the lung. Ksr1 functions to regulate the release of nitric oxide (NO)-radicals upon P. aeruginosa infections. Ksr1 also enhances Raf-1/MEK/ERK signaling and is involved in a variety of cellular responses, including cell differentiation, proliferation, and apoptosis. Here, we investigated whether Ksr1 is involved in the host immune response to lipopolysaccharide (LPS), one of the major components of gram-negative bacteria, in the lung. To this end, we induced an acute lung injury in wild type and Ksr1-deficient mice by intratracheal instillation of LPS. We found that LPS-induces acute lung injury, as characterized by cytokine expression, neutrophil infiltration and protein extrusion in wildtype mice. Ksr1-deficient mice showed a very similar reaction to LPS as the wildtype mice. In freshly isolated alveolar macrophages from wild type and Ksr1-deficient mice, LPS increased ERK activation, nuclear translocation of NFĸB and expression of inflammatory cytokines and chemokines in a similar pattern. Inhibition of Src or Raf-1 blocked LPS-induced ERK activation. Taken together, these findings indicate that Ksr1 plays a dispensable role in LPS-induced ERK activation in alveolar macrophages and does not contribute to the development of acute lung injury in the LPS model.

Epidermal growth factor receptor inhibits colitis-associated cancer in mice

Inflammatory bowel disease (IBD) is a chronic illness caused by complex interactions between genetic and environmental factors that propagate inflammation and damage to the gastrointestinal epithelium. This state of chronic inflammation increases the risk for development of colitis-associated cancer in IBD patients. Thus, the development of targeted therapeutics that can disrupt the cycle of inflammation and epithelial injury is highly attractive. However, such biological therapies, including those targeting epidermal growth factor receptor pathways, pose a risk of increasing cancer rates. Using two mouse models of colitis-associated cancer, we found that epidermal growth factor receptor inactivation accelerated the incidence and progression of colorectal tumors. By modulating inflammation and epithelial regeneration, epidermal growth factor receptor optimized the response to chronic inflammation and limited subsequent tumorigenesis. These findings provide important insights into the pathogenesis of colitis-associated cancer and suggest that epidermal growth factor-based therapies for IBD may reduce long-term cancer risk.

The role of pseudokinases in cancer

Kinases play a critical role in regulating many cellular functions including development, differentiation and proliferation. To date, over 518 proteins with kinase activity, comprising ~2-3% of total cellular proteins, have been identified from within the human kinome. Interestingly, approximately 10% of kinases are categorised as pseudokinases since they lack one or more conserved catalytic residues within their kinase domain and were originally thought to have no enzymatic activity. Recently, there has been strong evidence to suggest that some pseudokinsases can not only function as scaffold proteins, but may also possess kinase activity leading to modulation of cell signalling pathways. Altered activity of these pseudokinases can result in impaired cellular function, particularly in malignancies. In this review we are discussing recent evidence that apart from a scaffolding role, pseudokinases also orchestrate cellular processes as active kinases per se in signalling pathways of malignant cells.

ErbB2 and ErbB3 regulate recovery from dextran sulfate sodium-induced colitis by promoting mouse colon epithelial cell survival

ErbB2 and ErbB3 receptor tyrosine kinases are key regulators of proliferation, migration, differentiation and cell survival; however, their roles in gastrointestinal biology remain poorly defined. We hypothesized that ErbB2 and ErbB3 promote colon epithelial cell survival in the context of the wound-healing response following colitis. In this study, mice bearing intestinal epithelial-specific deletion of ErbB2 or ErbB3 were treated with dextran sulfate sodium (DSS). Colon sections were examined for injury, cytokine expression, epithelial cell proliferation and apoptosis. Deletion of epithelial ErbB2 did not affect the extent of intestinal injury in response to DSS, whereas deletion of ErbB3 slightly increased injury. However, the roles of both receptors were more apparent during recovery from DSS colitis, in which ErbB2 or ErbB3 epithelial deletion resulted in greater inflammation and crypt damage during the early reparative period. Moreover, loss of ErbB3 prevented normal epithelial regeneration in the long term, with damage persisting for at least 6 weeks following a single round of DSS. Delayed recovery in mice with epithelial deletion of ErbB2 or ErbB3 was associated with increased colonic expression of tumor necrosis factor alpha and increased epithelial apoptosis. Furthermore, epithelial ErbB3 deletion increased apoptosis at baseline and during DSS injury. Additionally, epithelial cell hyperproliferation during recovery was exacerbated by deletion of either ErbB2 or ErbB3. These results suggest that ErbB2 and ErbB3 have important cytoprotective and reparative roles in the colonic epithelium following injury, by promoting colon epithelial cell survival.

Recent advances in underlying pathologies provide insight into interleukin-8 expression-mediated inflammation and angiogenesis

Interleukin-8 has long been recognized to have anti-inflammatory activity, which has been established in various models of infection, inflammation, and cancer. Several cell types express the receptor for the cytokine IL-8 and upon its recognition produce molecules that are active both locally and systemically. Many different types of cells, in particular monocytes, neutrophils, epithelial, fibroblast, endothelial, mesothelial, and tumor cells, secrete IL-8. Increased expression of IL-8 and/or its receptors has been characterized in many chronic inflammatory conditions, including psoriasis, ARDS, COPD, and RA as well as many cancers, and its upregulation often correlates with disease activity. IL-8 constitutes the CXC class of chemokines, a potent chemoattractant and activator of neutrophils and other immune cells. It is a proangiogenic cytokine that is overexpressed in many human cancers. Therefore, inhibiting the effects of IL-8 signaling may be a significant therapeutic intervention.

Simulating EGFR-ERK signaling control by scaffold proteins KSR and MP1 reveals differential ligand-sensitivity co-regulated by Cbl-CIN85 and endophilin

ERK activation is enhanced by the scaffolding proteins KSR and MP1, localized near the cell membrane and late endosomes respectively, but little is known about their dynamic interplay. We develop here a mathematical model with ordinary differential equations to describe the dynamic activation of EGFR-ERK signaling under a conventional pathway without scaffolds, a KSR-scaffolded pathway, and an MP1-scaffolded pathway, and their impacts were examined under the influence of the endosomal regulators, Cbl-CIN85 and Endophilin A1. This new integrated model, validated against experimental results and computational constraints, shows that changes of ERK activation and EGFR endocytosis in response to EGF concentrations (i.e ligand sensitivity) depend on these scaffold proteins and regulators. The KSR-scaffolded and the conventional pathways act synergistically and are sensitive to EGF stimulation. When the KSR level is high, the sensitivity of ERK activation from this combined pathway remains low when Cbl-CIN85 level is low. But, such sensitivity can be increased with increasing levels of Endophilin if Cbl-CIN85 level becomes high. However, reduced KSR levels already present high sensitivity independent of Endophilin levels. In contrast, ERK activation by MP1 is additive to that of KSR but it shows little ligand-sensitivity under high levels of EGF. This can be partly reversed by increasing level of Endophilin while keeping Cbl-CIN85 level low. Further analyses showed that high levels of KSR affect ligand-sensitivity of EGFR endocytosis whereas MP1 ensures the robustness of endosomal ERK activation. These simulations constitute a multi-dimensional exploration of how EGF-dependent EGFR endocytosis and ERK activation are dynamically affected by scaffolds KSR and MP1, co-regulated by Cbl-CIN85 and Endophilin A1. Together, these results provide a detailed and quantitative demonstration of how regulators and scaffolds can collaborate to fine-tune the ligand-dependent sensitivity of EGFR endocytosis and ERK activation which could underlie differences during normal physiology, disease states and drug responses.

KSR1 is overexpressed in endometrial carcinoma and regulates proliferation and TRAIL-induced apoptosis by modulating FLIP levels

The Raf/MEK/extracellular signal-regulated kinase (ERK) pathway participates in many processes altered in development and progression of cancer in human beings such as proliferation, transformation, differentiation, and apoptosis. Kinase suppressor of Ras 1 (KSR1) can interact with various kinases of the Raf/MEK/extracellular signal-regulated kinase pathway to enhance its activation. The role of KSR1 in endometrial carcinogenesis was investigated. cDNA and tissue microarrays demonstrated that expression of KSR1 was up-regulated in endometrial carcinoma. Furthermore, inhibition of KSR1 expression by specific small hairpin RNA resulted in reduction of both proliferation and anchorage-independent cell growth properties of endometrial cancer cells. Because inhibition of apoptosis has a pivotal role in endometrial carcinogenesis, the effects of KSR1 in regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis were investigated. KSR1 knock-down sensitized resistant endometrial cell lines to both TRAIL- and Fas-induced apoptosis. Sensitization to TRAIL and agonistic anti-Fas antibody was caused by down-regulation of FLIP (FLICE-inhibitory protein). Also investigated was the molecular mechanism by which KSR1 regulates FLIP protein levels. It was demonstrated that KSR1 small hairpin RNA did not affect FLIP transcription or degradation. Rather, FLIP down-regulation was caused by Fas-associated death domain protein-dependent inhibition of FLIP translation triggered after TRAIL stimulation in KSR1-silenced cells. Re-expression of heterologous KSR1 in cells with down-regulated endogenous KSR1 restored FLIP protein levels and TRAIL resistance. In conclusion, KSR1 regulates endometrial sensitivity to TRAIL by regulating FLIP levels.

Lycopene enhances antioxidant enzyme activities and immunity function in N-methyl-N'-nitro-N-nitrosoguanidine-enduced gastric cancer rats

To investigate anticancer effect of lycopene, we examined the effects of lycopene on the oxidative injury and immunity activities of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced gastric cancer rats. The animals were divided into five groups. Group I served as the normal control and was given corn oil orally for 20 weeks. Group II were induced with MNNG 200 mg/kg body weight by oral gavage at days 0 and 14, and saturated NaCl (1 mL per rats) was given once every three days for four weeks until the end of the experimental period. Group III, IV and V were posttreated with lycopene (50, 100 and 150 mg/kg body weight, dissolved in corn oil) from the sixth week of MNNG (as in group II) induction up to the end of the experimental period. In the presence of MNNG, MDA and immunity levels were significantly increased, whereas enzymatic (SOD, CAT, and GPx) antioxidant activities were decreased in the treated rats compared with normal control rats. Administration of lycopene to gastric carcinoma-induced rats largely up-regulated the redox status and immunity activities to decrease the risk of cancer compared to group II. We conclude that up-regulation of antioxidants and immunity by lycopene treatment might be responsible for the anticancer effect in gastric carcinoma.

In vivo systems analysis identifies spatial and temporal aspects of the modulation of TNF-α-induced apoptosis and proliferation by MAPKs

Cellular responses to external stimuli depend on dynamic features of multipathway network signaling; thus, cell behavior is influenced in a complex manner by the environment and by intrinsic properties. Methods of multivariate systems analysis have provided an understanding of these convoluted effects, but only for relatively simplified examples in vitro. To determine whether such approaches could be successfully used in vivo, we analyzed the signaling network that determines the response of intestinal epithelial cells to tumor necrosis factor-α (TNF-α). We built data-driven, partial least-squares discriminant analysis (PLSDA) models based on signaling, apoptotic, and proliferative responses in the mouse small intestinal epithelium after systemic exposure to TNF-α. The extracellular signal-regulated kinase (ERK) signaling axis was a critical modulator of the temporal variation in apoptosis at different doses of TNF-α and of the spatial variation in proliferation in distinct intestinal regions. Inhibition of MEK, a mitogen-activated protein kinase kinase upstream of ERK, altered the signaling network and changed the temporal and spatial phenotypes consistent with model predictions. Our results demonstrate the dynamic, adaptive nature of in vivo signaling networks and identify natural, tissue-level variation in responses that can be deconvoluted only with quantitative, multivariate computational modeling. This study lays a foundation for the use of systems-based approaches to understand how dysregulation of the cellular network state underlies complex diseases.

KSR1 protects from interleukin-10 deficiency-induced colitis in mice by suppressing T-lymphocyte interferon-γ production

BACKGROUND & AIMS

Immunological disorders of the gastrointestinal tract such as inflammatory bowel disease often result in recurrent and persistently elevated levels of proinflammatory cytokines. Kinase suppressor of Ras 1 (KSR1) is involved in tumor necrosis factor-mediated colon epithelial cell survival, yet its role in chronic inflammation has not been defined. In this study, we tested the hypothesis that KSR1 is protective against spontaneous experimental colitis.

METHODS

KSR1(-/-)Interleukin-10 (Il10)(-/-) mice were generated and histolopathologic parameters of intestinal inflammation were scored. Bone marrow transplants performed on wild-type and KSR1(-/-)Il10(-/-) mice determined the contribution of KSR1 in hematopoietic lineages. Mucosal T helper (Th) 1 and Th17 cytokine were also examined. In vitro Th1 and Th17 polarization assays were conducted and interleukin (IL)-17A and interferon-γ (IFN-γ) production analyzed by flow cytometry. Neutralizing antibodies against IgG, IL-17A, or IFN-γ were administered to 3-week-old KSR1(-/-)Il10(-/-) mice for 3 weeks and scored for colitis.

RESULTS

KSR1(-/-)Il10(-/-) mice developed accelerated and severe spontaneous colitis by 4 weeks of age. KSR1 expression in hematopoietic lineages was protective against colitis. Both IFN-γ and IL-17A transcripts were elevated in colons of KSR1(-/-) and KSR1(-/-)Il10(-/-) mice. IFN-γ production was increased in lamina propria T cells isolated from KSR1(-/-) and KSR1(-/-)Il10(-/-) mice. Additionally, in vitro Th1 polarization was increased while Th17 polarization was impaired in KSR1-deficient naïve T cells. Finally, administration of IFN-γ neutralizing antibodies attenuated colitis in KSR1(-/-)Il10(-/-) mice.

CONCLUSIONS

Mice lacking both KSR1 and IL-10 develop exacerbated colitis due to dysregulated IFN-γ production in T lymphocytes.

Kinase suppressor of Ras transphosphorylates c-Raf-1

Whether kinase suppressor of Ras1 (KSR1) is an active kinase that phosphorylates c-Raf-1 or a scaffold that coordinates signaling along the Ras/ERK1 signaling module is actively debated. In this study, we generated a monoclonal antibody against a c-Raf-1 peptide containing phosphorylated Thr(269), the putative target for KSR1 kinase activity. We show that this antibody detects Thr(269)-phosphorylated c-Raf-1 in A431 cells upon epidermal growth factor (EGF) stimulation, preceding MEK1 activation. Furthermore, this antibody detects in vitro phosphorylation of FLAG-c-Raf-1 and kinase-dead FLAG-c-Raf-1(K375M) by immunopurified KSR1, but fails to detect phosphorylation of FLAG-c-Raf-1(K375M/T269V), engineered with a Thr(269) to valine substitution. To provide unequivocal evidence that KSR1 is a legitimate kinase, we purified KSR1 to homogeneity, confirmed by mass spectrometry, renatured it in-gel, and demonstrated that it phosphorylates BSA-conjugated c-Raf-1 peptide at Thr(269). These studies add to emerging data validating KSR1 as a kinase that phosphorylates c-Raf-1.

Epidermal growth factor receptor activation protects gastric epithelial cells from Helicobacter pylori-induced apoptosis

BACKGROUND & AIMS

Helicobacter pylori infection disrupts the balance between gastric epithelial cell proliferation and apoptosis, which is likely to lower the threshold for the development of gastric adenocarcinoma. H pylori infection is associated with epidermal growth factor (EGF) receptor (EGFR) activation through metalloproteinase-dependent release of EGFR ligands in gastric epithelial cells. Because EGFR signaling regulates cell survival, we investigated whether activation of EGFR following H pylori infection promotes gastric epithelial survival.

METHODS

Mouse conditionally immortalized stomach epithelial cells (ImSt) and a human gastric epithelial cell line, AGS cells, as well as wild-type and kinase-defective EGFR (EGFRwa2) mice, were infected with the H pylori cag+ strain 7.13. Apoptosis, caspase activity, EGFR activation (phosphorylation), and EGFR downstream targets were analyzed.

RESULTS

Inhibiting EGFR kinase activity or decreasing EGFR expression significantly increased H pylori-induced apoptosis in ImSt. Blocking H pylori-induced EGFR activation with a heparin-binding (HB)-EGF neutralizing antibody or abrogating a disintegrin and matrix metalloproteinase-17 (ADAM-17) expression increased apoptosis of H pylori-infected AGS and ImSt, respectively. Conversely, pretreatment of ImSt with HB-EGF completely blocked H pylori-induced apoptosis. H pylori infection stimulated gastric epithelial cell apoptosis in EGFRwa2 but not in wild-type mice. Furthermore, H pylori-induced EGFR phosphorylation stimulated phosphotidylinositol-3'-kinase-dependent activation of the antiapoptotic factor Akt, increased expression of the antiapoptotic factor Bcl-2, and decreased expression of the proapoptotic factor Bax.

CONCLUSIONS

EGFR activation by H pylori infection has an antiapoptotic effect in gastric epithelial cells that appears to involve Akt signaling and Bcl family members. These findings provide important insights into the mechanisms of H pylori-associated tumorigenesis.

KSR1 is required for cell cycle reinitiation following DNA damage

KSR1 (kinase suppressor of Ras 1) is a molecular scaffold and positive regulator of the Raf/MEK/ERK phosphorylation cascade. KSR1 is required for maximal ERK activation induced by growth factors and by some cytotoxic agents. We show here that KSR1 is also required for maximal ERK activation induced by UV light, ionizing radiation, or the DNA interstrand cross-linking agent mitomycin C (MMC). We further demonstrate a role for KSR1 in the reinitiation of the cell cycle and proliferation following cell cycle arrest induced by MMC. Cells lacking KSR1 underwent but did not recover from MMC-induced G(2)/M arrest. Expression of KSR1 allowed KSR1(-/-) cells to re-enter the cell cycle following MMC treatment. However, cells expressing a mutated form of KSR1 unable to bind ERK did not recover from MMC-induced cell cycle arrest, demonstrating the requirement for the KSR1-ERK interaction. In addition, constitutive activation of ERK was not sufficient to promote cell cycle reinitiation in MMC-treated KSR1(-/-) cells. Only cells expressing KSR1 recovered from MMC-induced cell cycle arrest. Importantly, MMC-induced DNA damage was repaired in KSR1(-/-) cells, as determined by resolution of gamma-H2AX-containing foci. These data indicate that cell cycle reinitiation is not actively signaled in the absence of KSR1, even when DNA damage has been resolved. These data reveal a specific role for the molecular scaffold KSR1 and KSR1-mediated ERK signaling in the cellular response to DNA interstrand cross-links.

Positive impact of blocking tumor necrosis factor alpha on the nutritional status in pediatric Crohn's disease patients

BACKGROUND

TNFalpha seems to contribute to inflammation and malnutrition in Crohn's disease (CD) patients. In CD patients, the comparative effects on nutritional status of infliximab and traditional therapy have not yet been determined. The aim of our study was to assess the effects of infliximab as compared with those of standard therapy on nutritional status, disease activity, resting energy expenditure (REE), and food intake in CD children and adolescents.

METHODS

From September 1999 to September 2005, all CD patients treated with infliximab (group A) were reviewed and matched with CD patients treated with traditional therapy (mesalazine and azathioprine) (group B).

RESULTS

Fourteen CD patients from group A and 14 from group B were included; median interval before follow-up investigation was 10 months. Baseline and final values of weight, height, body mass index (BMI), pediatric CD activity index (pCDAI), REE, and food intake were studied. In treated patients, but not in control group, mean baseline weight (kg) and BMI values, 39.7 +/- 13.1 and 17.9 +/- 3.3, respectively, were significantly lower than their final values 42.6 +/- 13.2 and 18.9 +/- 3.1, and median pCDAI values 23.5 were significantly higher than their final values 10 (P < 0.05). Significant changes in height, REE, and food intake were not found in either group.

CONCLUSIONS

In pediatric CD patients, infliximab seems to impact positively on the nutritional status as demonstrated by the improvement in weight and BMI, but not in linear growth; effects on nutritional status seem to be due to amelioration of disease activity, rather than to REE reduction or food intake increase.

The ErbB4 growth factor receptor is required for colon epithelial cell survival in the presence of TNF

BACKGROUND & AIMS

The ErbB4 receptor tyrosine kinase regulates cell growth, survival, and differentiation in several tissues, but its role in the gastrointestinal tract has not been reported. We tested the hypothesis that ErbB4 promotes intestinal cell survival and restitution following injury or inflammation.

METHODS

ErbB4 expression in human inflammatory bowel disease was determined by immunohistochemistry. Mice were subjected to dextran sulfate sodium (DSS, 3%) colitis or injected with tumor necrosis factor (TNF), and ErbB4 expression was quantified by immunohistochemistry and Western blot. Cultured young adult mouse colon (YAMC) cells were exposed to TNF, and ErbB4 messenger RNA, protein, and phosphorylation levels were measured. Cells transfected with ErbB4 small interfering RNA (siRNA), or over expressing ErbB4, were subjected to wound healing and apoptosis assays.

RESULTS

ErbB4 levels increased in Crohn's colitis and the colon epithelium of mice with DSS colitis or injected with TNF. In YAMC cells, TNF induced ErbB4 messenger RNA, protein, and phosphorylation; nuclear factor kappaB activation also stimulated ErbB4 accumulation. ErbB4 siRNA sensitized cells to TNF-stimulated apoptosis, while over expression blocked apoptosis induced by TNF plus cycloheximide. Additionally, ErbB4 siRNA decreased YAMC cell wound healing. ErbB4 knockdown attenuated, while over expression elevated, phosphorylation of Akt in response to TNF. Inhibition of the phosphatidylinositol 3-kinase/Akt signaling cascade reversed the ability of ErbB4 over expression to protect from cytokine-induced apoptosis.

CONCLUSIONS

ErbB4 expression and signaling are key elements for TNF responses in vivo and in cell culture, protecting intestinal epithelial cells from apoptosis in the inflammatory environment, possibly through Akt activation.

hKSR-2, a vitamin D-regulated gene, inhibits apoptosis in arabinocytosine-treated HL60 leukemia cells

Ras signaling can be modulated by the scaffolding activity of kinase suppressor of Ras-1 (KSR-1) and by the hKSR-2 protein, resulting in diverse phenotypic outcomes. The mitogen-activated protein kinase cascade downstream from Ras and KSRs includes Raf-1 and extracellular signal-regulated kinase 1/2 kinases, known to enhance survival potential of a range of cell types. Because the molecular events that increase survival of HL60 cells induced to differentiate toward monocytic phenotype by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] are not known, we investigated if KSR proteins provide a survival function in these cells. We found that whereas kinase suppressor of Ras-1 had no detectable effect on cell survival in the system studied here, 1,25-(OH)2D3-induced up-regulation of hKSR-2 enhanced the resistance of HL60 cells to arabinocytosine. Knockdown of hKSR-2 by either small interfering RNA or antisense oligonucleotides increased arabinocytosine-induced apoptosis, which was accompanied by reduced Bcl-2/Bax and Bcl-2/Bad ratios, and increased caspase-3 activating cleavage. In contrast, up-regulation of Mcl-1 was not abrogated by anti-sense (AS) AS-hKSR-2, pointing to a specific role of Bcl-2 in control of 1,25-(OH)2D3-induced increased cell survival. These findings are consistent with the previously shown lack of fully differentiated monocytic cells in HL60 cultures exposed to 1,25-(OH)2D3 in which hKSR-2 was knocked down, suggesting that optimal differentiation of these cells requires enhanced antiapoptotic mechanisms provided, at least in part, by hKSR-2. Collectively, these results suggest that hKSR-2 may offer a new target for novel therapies of acute myelogenous leukemia.

Nuclear factor-kappaB is a critical mediator of Ste20-like proline-/alanine-rich kinase regulation in intestinal inflammation

Inflammatory bowel disease (IBD) is thought to result from commensal flora, aberrant cellular stress, and genetic factors. Here we show that the expression of colonic Ste20-like proline-/alanine-rich kinase (SPAK) that lacks a PAPA box and an F-alpha helix loop is increased in patients with IBD. The same effects were observed in a mouse model of dextran sodium sulfate-induced colitis and in Caco2-BBE cells treated with the pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha. The 5'-flanking region of the SPAK gene contains two transcriptional start sites, three transcription factor Sp1-binding sites, and one transcription factor nuclear factor (NF)-kappaB-binding site, but no TATA elements. The NF-kappaB-binding site was essential for stimulated SPAK promoter activity by TNF-alpha, whereas the Sp1-binding sites were important for basal promoter activity. siRNA-induced knockdown of NF-kappaB, but not of Sp1, reduced TNF-alpha-induced SPAK expression. Nuclear run-on and mRNA decay assays demonstrated that TNF-alpha directly increased SPAK mRNA transcription without affecting SPAK mRNA stability. Furthermore, up-regulation of NF-kappaB expression and demethylation of the CpG islands induced by TNF-alpha also played roles in the up-regulation of SPAK expression. In conclusion, our data indicate that during inflammatory conditions, TNF-alpha is a key regulator of SPAK expression. The development of compounds that can either modulate or disrupt the activity of SPAK-mediated pathways is therefore important for the control and attenuation of downstream pathological responses, particularly in IBD.

TNFR1 promotes tumor necrosis factor-mediated mouse colon epithelial cell survival through RAF activation of NF-kappaB

Tumor necrosis factor (TNF) is a therapeutic target in the treatment of inflammatory bowel disease; however, the exact role of TNF signaling in the colon epithelium remains unclear. We demonstrate that TNF activation of TNF receptor (R)1 stimulates both pro- and anti-apoptotic signaling pathways in the colon epithelium; however, TNFR1 protects against colon epithelial cell apoptosis following TNF exposure. To investigate anti-apoptotic signaling pathways downstream of TNFR1, we generated an intestinal epithelium-specific Raf knock-out mouse and identified Raf kinase as a key regulator of colon epithelial cell survival in response to TNF. Surprisingly, Raf promotes NF-kappaB p65 phosphorylation, independent of MEK signaling, to support cell survival. Taken together, these data demonstrate a novel pathway in which Raf promotes colon epithelial cell survival through NF-kappaB downstream of TNFR1 activation. Thus, further understanding of colon epithelial cell-specific TNFR signaling may result in the identification of new targets for inflammatory bowel disease treatment and define novel mediators of colitis-associated cancer.

Enterocyte-derived TAK1 signaling prevents epithelium apoptosis and the development of ileitis and colitis

Recent studies have revealed that TAK1 kinase is an essential intermediate in several innate immune signaling pathways. In this study, we investigated the role of TAK1 signaling in maintaining intestinal homeostasis by generating enterocyte-specific constitutive and inducible gene-deleted TAK1 mice. We found that enterocyte-specific constitutive TAK1-deleted mice spontaneously developed intestinal inflammation as observed by histological analysis and enhanced expression of IL-1beta, MIP-2, and IL-6 around the time of birth, which was accompanied by significant enterocyte apoptosis. When TAK1 was deleted in the intestinal epithelium of 4-wk-old mice using an inducible knockout system, enterocytes underwent apoptosis and intestinal inflammation developed within 2-3 days following the initiation of gene deletion. We found that enterocyte apoptosis and intestinal inflammation were strongly attenuated when enterocyte-specific constitutive TAK1-deleted mice were crossed to TNF receptor 1(-/-) mice. However, these mice later (>14 days) developed ileitis and colitis. Thus, TAK1 signaling in enterocytes is essential for preventing TNF-dependent epithelium apoptosis and the TNF-independent development of ileitis and colitis. We propose that aberration in TAK1 signaling might disrupt intestinal homeostasis and favor the development of inflammatory disease.

Raf protects against colitis by promoting mouse colon epithelial cell survival through NF-kappaB

BACKGROUND & AIMS

Raf-1 kinase is a key regulator of a number of cellular processes, which promote the maintenance of a healthy colon epithelium. This study addresses the role of Raf in epithelial cell survival in response to dextran sulfate sodium (DSS)-induced injury and inflammation.

METHODS

Inducible intestinal epithelium-specific Raf knockout mice were generated and subjected to acute colitis followed by a short recovery period. Colon sections were analyzed by in situ oligo ligation or immunostaining for Ki67, phospho-extracellular signal regulated kinase, and nuclear factor-kappaB p65. Western blot analysis and terminal deoxynucleotidyl transferase nick-end labeling assays were performed on Raf small interfering RNA-transfected young adult mouse colon cells following DSS treatment.

RESULTS

We report that Raf protects against epithelial injury and inflammation and promotes recovery from acute DSS-induced colitis by both MAPK/ERK kinase (MEK)-dependent and -independent pathways. Furthermore, we demonstrate that Raf induces novel cell survival responses through activating nuclear factor-kappaB in a MEK-independent manner.

CONCLUSIONS

These novel findings indicate a protective role for Raf in colon epithelium following ulcerative damage through inhibiting cell apoptosis and promoting proliferation with important implications for responses such as inflammation-associated carcinogenesis.

Genetic ablation of M3 muscarinic receptors attenuates murine colon epithelial cell proliferation and neoplasia

Colon epithelial cells express and most colon cancers overexpress M(3) muscarinic receptors (M(3)R). In human colon cancer cells, post-M(3)R signaling stimulates proliferation. To explore the importance of M(3)R expression in vivo, we used the azoxymethane-induced colon neoplasia model. Mice treated with weekly i.p. injection of saline [10 wild-type (WT) mice] or azoxymethane (22 WT and 16 M(3)R(-/-) mice) for 6 weeks were euthanized at 20 weeks. At week 20, azoxymethane-treated WT mice weighed approximately 16% more than M(3)R(-/-) mice (33.4 grams +/- 1.0 grams versus 27.9 grams +/- 0.5 grams; mean +/- SE, P < 0.001). In azoxymethane-treated M(3)R(-/-) mice, cell proliferation (BrdUrd staining) was reduced 43% compared with azoxymethane-treated WT mice (P < 0.05). Whereas control mice (both WT and M(3)R(-/-)) had no colon tumors, azoxymethane-treated WT mice had 5.3 +/- 0.5 tumors per animal. Strikingly, azoxymethane-treated M(3)R(-/-) mice had only 3.2 +/- 0.3 tumors per mouse (P < 0.05), a 40% reduction. Tumor volume in azoxymethane-treated M(3)R(-/-) mice was reduced 60% compared with azoxymethane-treated WT mice (8.1 mm(3) +/- 1.5 mm(3) versus 20.3 mm(3) +/- 4.1 mm(3); P < 0.05). Compared with WT, fewer M(3)R(-/-) mice had adenomas (6% versus 36%; P = 0.05), and M(3)R(-/-) mice had fewer adenocarcinomas per mouse (0.6 +/- 0.1 versus 1.7 +/- 0.4; P < 0.05). Eleven of 22 WT but no M(3)R(-/-) mice had multiple adenocarcinomas (P < 0.001). Compared with WT, azoxymethane-treated M(3)R-deficient mice have attenuated epithelial cell proliferation, tumor number, and size. M(3)R and post-M(3)R signaling are novel therapeutic targets for colon cancer.

p21 Ras/impedes mitogenic signal propagation regulates cytokine production and migration in CD4 T cells

The propensity of T cells to generate coordinated cytokine responses is critical for the host to develop resistance to pathogens while maintaining the state of immunotolerance to self-antigens. The exact mechanisms responsible for preventing the overproduction of proinflammatory cytokines including interferon (IFN)-gamma are not fully understood, however. In this study, we examined the role of a recently described Ras GTPase effector and repressor of the Raf/MEK/ERK cascade called impedes mitogenic signal propagation (Imp) in limiting the induction of T-cell cytokines. We found that stimulation of the T cell receptor complex leads to the rapid development of a physical association between Ras and Imp. Consistent with the hypothesis that Imp inhibits signal transduction, we also found that disengagement of this molecule by the Ras(V12G37) effector loop mutant or RNA interference markedly enhances the activation of the NFAT transcription factor and IFN-gamma secretion. A strong output of IFN-gamma is responsible for the distinct lymphocyte traffic pattern observed in vivo because the transgenic or retroviral expression of Ras(V12G37) caused T cells to accumulate preferentially in the lymph nodes and delayed their escape from the lymphoid tissue, respectively. Together, our results describe a hitherto unrecognized negative regulatory role for Imp in the production of IFN-gamma in T cells and point to Ras-Imp binding as an attractive target for therapeutic interventions in conditions involving the production of this inflammatory cytokine.

Caspase-dependent cleavage disrupts the ERK cascade scaffolding function of KSR1

Kinase suppressor of Ras 1 (KSR1) is a protein scaffold that facilitates ERK cascade activation at the plasma membrane, a critical step in the signal transduction process that allows cells to respond to survival, proliferative, and differentiative cues. Here, we report that KSR1 undergoes caspase-dependent cleavage in apoptotic cells and that cleavage destroys the scaffolding function of the full-length KSR1 protein and generates a stable C-terminal fragment that can inhibit ERK activation. KSR1 is cleaved in response to multiple apoptotic stimuli and occurs in vivo during the involution of mouse mammary tissues, a morphogenic process requiring cellular apoptosis. In addition, we find that in comparison with KSR1(-/-) mouse embryonic fibroblasts expressing wild type KSR1 (WT-KSR1), cells expressing a cleavage-resistant KSR1 protein (DEVA-KSR1) exhibit reduced apoptotic signaling in response to tumor necrosis factor-alpha/cycloheximide treatment. The effect of DEVA-KSR1 expression was found to correlate with increased levels of active phosphoERK and could be significantly reversed by treating cells with the MEK inhibitor U0126. In contrast, reduced phosphoERK levels and enhanced apoptotic signaling were observed in cells constitutively expressing the C-terminal KSR1 fragment (CTF-KSR1). Moreover, we find that cleavage of WT-KSR1 correlates with a dramatic reduction in active phosphoERK levels. These findings identify KSR1 as a caspase target and suggest that cleavage of the KSR1 scaffold represents another mechanism whereby caspases down-regulate ERK survival signaling to promote cellular apoptosis.

Soluble proteins produced by probiotic bacteria regulate intestinal epithelial cell survival and growth

BACKGROUND & AIMS

Increased inflammatory cytokine levels and intestinal epithelial cell apoptosis leading to disruption of epithelial integrity are major pathologic factors in inflammatory bowel diseases. The probiotic bacterium Lactobacillus rhamnosus GG (LGG) and factors recovered from LGG broth culture supernatant (LGG-s) prevent cytokine-induced apoptosis in human and mouse intestinal epithelial cells by regulating signaling pathways. Here, we purify and characterize 2 secreted LGG proteins that regulate intestinal epithelial cell antiapoptotic and proliferation responses.

METHODS

LGG proteins were purified from LGG-s, analyzed, and used to generate polyclonal antibodies for immunodepletion of respective proteins from LGG-conditioned cell culture media (CM). Mouse colon epithelial cells and cultured colon explants were treated with purified proteins in the absence or presence of tumor necrosis factor (TNF). Akt activation, proliferation, tissue injury, apoptosis, and caspase-3 activation were determined.

RESULTS

We purified 2 novel proteins, p75 (75 kilodaltons) and p40 (40 kilodaltons), from LGG-s. Each of these purified protein preparations activated Akt, inhibited cytokine-induced epithelial cell apoptosis, and promoted cell growth in human and mouse colon epithelial cells and cultured mouse colon explants. TNF-induced colon epithelial damage was significantly reduced by p75 and p40. Immunodepletion of p75 and p40 from LGG-CM reversed LGG-CM activation of Akt and its inhibitory effects on cytokine-induced apoptosis and loss of intestinal epithelial cells.

CONCLUSIONS

p75 and p40 are the first probiotic bacterial proteins demonstrated to promote intestinal epithelial homeostasis through specific signaling pathways. These findings suggest that probiotic bacterial components may be useful for preventing cytokine-mediated gastrointestinal diseases.

CK2 Is a component of the KSR1 scaffold complex that contributes to Raf kinase activation

Kinase Suppressor of Ras (KSR) is a molecular scaffold that interacts with the core kinase components of the ERK cascade, Raf, MEK, and ERK and provides spatial and temporal regulation of Ras-dependent ERK cascade signaling. In this report, we identify the heterotetrameric protein kinase, casein kinase 2 (CK2), as a new KSR1-binding partner. Moreover, we find that the KSR1/CK2 interaction is required for KSR1 to maximally facilitate ERK cascade signaling and contributes to the regulation of Raf kinase activity. Binding of the CK2 holoenzyme is constitutive and requires the basic surface region of the KSR1 atypical C1 domain. Loss of CK2 binding does not alter the membrane translocation of KSR1 or its interaction with ERK cascade components; however, disruption of the KSR1/CK2 interaction or inhibition of CK2 activity significantly reduces the growth-factor-induced phosphorylation of C-Raf and B-Raf on the activating serine site in the negative-charge regulatory region (N-region). This decrease in Raf N-region phosphorylation further correlates with impaired Raf, MEK, and ERK activation. These findings identify CK2 as a novel component of the KSR1 scaffolding complex that facilitates ERK cascade signaling by functioning as a Raf family N-Region kinase.

A mouse model of hereditary pancreatitis generated by transgenic expression of R122H trypsinogen

BACKGROUND & AIMS

Missense mutations in human cationic trypsinogen PRSS1 are frequently detected in patients with hereditary pancreatitis, a rare genetic disease of the pancreas characterized by autodigestive necrosis, chronic inflammation, and fibrosis. To examine the link between PRSS1 mutations and the initiation and progression of hereditary pancreatitis, we have sought to generate a transgenic mouse that carries a missense mutation in the PRSS1 that is most frequently observed in patients.

METHODS

A transgenic mouse was generated in which the expression of the mouse PRSS1 mutant R122H (R122H_mPRSS1) is targeted to pancreatic acinar cells by fusion to the elastase promoter. The expression of the mutant trypsinogen was assessed by immunohistochemical staining and real-time reverse transcription polymerase chain reaction analysis. The relationship between transgene expression and inflammation was analyzed by morphologic assessment of H&E-stained tissue sections, responsiveness to cerulein-induced pancreatitis, and immunohistochemical identification of cellular and biochemical components of the inflammatory response.

RESULTS

Pancreata from transgenic mice display early-onset acinar cell injury and inflammatory cell infiltration. With progressing age, the transgenic mice develop pancreatic fibrosis and display acinar cell dedifferentiation. Moreover, the expression of R122H_mPRSS1 transgene is associated with enhanced response to cerulein-induced pancreatitis. Finally, cell-specific activation of the inflammation-associated signaling pathways, c-jun-N-terminal kinase and extracellular signal-regulated kinase, was observed in response to expression of R122H_mPRSS1.

CONCLUSIONS

These results underscore the importance of PRSS1 mutations as pathogenic mediators of hereditary pancreatitis and indicate that persistent pancreatic injury might be causally linked to chronic pancreatitis.

Deletion of Mtgr1 sensitizes the colonic epithelium to dextran sodium sulfate-induced colitis

BACKGROUND & AIMS

The disruption of homeostasis between proliferation and apoptosis in the colonic epithelium contributes to the pathogenesis of human ulcerative colitis. Mice lacking the transcriptional corepressor myeloid translocation gene related-1 (Mtgr1) display impaired secretory cell lineage development in the small intestine and an increase in proliferation in the crypts of both the small and large intestines. Despite the increase in proliferating cells, the colons of Mtgr1-null mice have a normal cell lineage distribution and normal architecture. To uncover colonic phenotypes in Mtgr1(-/-) mice, we stressed the colonic epithelium with low-molecular-weight dextran sodium sulfate (DSS), which is a well-studied model of murine ulcerative colitis.

METHODS

Mtgr1-null mice were given 3% DSS in their drinking water for 4 days and the colons examined at various times thereafter for ulceration and for changes in proliferation and apoptosis.

RESULTS

Treatment with DSS resulted in severe colitis in Mtgr1(-/-) mice, at least partially due to increased epithelial apoptosis rates. Transplantation of wild-type and Mtgr1-null bone marrow into irradiated wild-type mice demonstrated that the severe DSS-induced ulceration seen in Mtgr1-null mice was due to a colonic, rather than a hematologic, defect. Importantly, the epithelium of DSS-treated Mtgr1-null mice failed to completely regenerate, showing changes consistent with chronic colitis, even 10 weeks after a single DSS treatment.

CONCLUSIONS

These findings suggest that Mtgr1 has an important role in crypt survival and regeneration after colonic epithelial ulceration.