Culture media composition influences patient-derived organoid ability to predict therapeutic responses in gastrointestinal cancers.

BACKGROUNDA patient-derived organoid (PDO) platform may serve as a promising tool for translational cancer research. In this study, we evaluated PDO's ability to predict clinical response to gastrointestinal (GI) cancers.METHODSWe generated PDOs from primary and metastatic lesions of patients with GI cancers, including pancreatic ductal adenocarcinoma, colorectal adenocarcinoma, and cholangiocarcinoma. We compared PDO response with the observed clinical response for donor patients to the same treatments.RESULTSWe report an approximately 80% concordance rate between PDO and donor tumor response. Importantly, we found a profound influence of culture media on PDO phenotype, where we showed a significant difference in response to standard-of-care chemotherapies, distinct morphologies, and transcriptomes between media within the same PDO cultures.CONCLUSIONWhile we demonstrate a high concordance rate between donor tumor and PDO, these studies also showed the important role of culture media when using PDOs to inform treatment selection and predict response across a spectrum of GI cancers.TRIAL REGISTRATIONNot applicable.FUNDINGThe Joan F. & Richard A. Abdoo Family Fund in Colorectal Cancer Research, GI Cancer program of the Mayo Clinic Cancer Center, Mayo Clinic SPORE in Pancreatic Cancer, Center of Individualized Medicine (Mayo Clinic), Department of Laboratory Medicine and Pathology (Mayo Clinic), Incyte Pharmaceuticals and Mayo Clinic Hepatobiliary SPORE, University of Minnesota-Mayo Clinic Partnership, and the Early Therapeutic program (Department of Oncology, Mayo Clinic).

Oncogenic gene expression and epigenetic remodeling of cis-regulatory elements in ASXL1-mutant chronic myelomonocytic leukemia.

Myeloid neoplasms are clonal hematopoietic stem cell disorders driven by the sequential acquisition of recurrent genetic lesions. Truncating mutations in the chromatin remodeler ASXL1 (ASXL1MT) are associated with a high-risk disease phenotype with increased proliferation, epigenetic therapeutic resistance, and poor survival outcomes. We performed a multi-omics interrogation to define gene expression and chromatin remodeling associated with ASXL1MT in chronic myelomonocytic leukemia (CMML). ASXL1MT are associated with a loss of repressive histone methylation and increase in permissive histone methylation and acetylation in promoter regions. ASXL1MT are further associated with de novo accessibility of distal enhancers binding ETS transcription factors, targeting important leukemogenic driver genes. Chromatin remodeling of promoters and enhancers is strongly associated with gene expression and heterogenous among overexpressed genes. These results provide a comprehensive map of the transcriptome and chromatin landscape of ASXL1MT CMML, forming an important framework for the development of novel therapeutic strategies targeting oncogenic cis interactions.

Nuclear Dynamics and Chromatin Structure: Implications for Pancreatic Cancer.

Changes in nuclear shape have been extensively associated with the dynamics and functionality of cancer cells. In most normal cells, nuclei have a regular ellipsoid shape and minimal variation in nuclear size; however, an irregular nuclear contour and abnormal nuclear size is often observed in cancer, including pancreatic cancer. Furthermore, alterations in nuclear morphology have become the 'gold standard' for tumor staging and grading. Beyond the utility of altered nuclear morphology as a diagnostic tool in cancer, the implications of altered nuclear structure for the biology and behavior of cancer cells are profound as changes in nuclear morphology could impact cellular responses to physical strain, adaptation during migration, chromatin organization, and gene expression. Here, we aim to highlight and discuss the factors that regulate nuclear dynamics and their implications for pancreatic cancer biology.

RAS mutations drive proliferative chronic myelomonocytic leukemia via a KMT2A-PLK1 axis.

Proliferative chronic myelomonocytic leukemia (pCMML), an aggressive CMML subtype, is associated with dismal outcomes. RAS pathway mutations, mainly NRASG12D, define the pCMML phenotype as demonstrated by our exome sequencing, progenitor colony assays and a Vav-Cre-NrasG12D mouse model. Further, these mutations promote CMML transformation to acute myeloid leukemia. Using a multiomics platform and biochemical and molecular studies we show that in pCMML RAS pathway mutations are associated with a unique gene expression profile enriched in mitotic kinases such as polo-like kinase 1 (PLK1). PLK1 transcript levels are shown to be regulated by an unmutated lysine methyl-transferase (KMT2A) resulting in increased promoter monomethylation of lysine 4 of histone 3. Pharmacologic inhibition of PLK1 in RAS mutant patient-derived xenografts, demonstrates the utility of personalized biomarker-driven therapeutics in pCMML.

A rare germline CDKN2A variant (47T>G; p16-L16R) predisposes carriers to pancreatic cancer by reducing cell cycle inhibition.

Germline mutations in CDKN2A, encoding the tumor suppressor p16, are responsible for a large proportion of familial melanoma cases and also increase risk of pancreatic cancer. We identified four families through pancreatic cancer probands that were affected by both cancers. These families bore a germline missense variant of CDKN2A (47T>G), encoding a p16-L16R mutant protein associated with high cancer occurrence. Here, we investigated the biological significance of this variant. When transfected into p16-null pancreatic cancer cells, p16-L16R was expressed at lower levels than wild-type (WT) p16. In addition, p16-L16R was unable to bind CDK4 or CDK6 compared with WT p16, as shown by coimmunoprecipitation assays and also was impaired in its ability to inhibit the cell cycle, as demonstrated by flow cytometry analyses. In silico molecular modeling predicted that the L16R mutation prevents normal protein folding, consistent with the observed reduction in expression/stability and diminished function of this mutant protein. We isolated normal dermal fibroblasts from members of the families expressing WT or L16R proteins to investigate the impact of endogenous p16-L16R mutant protein on cell growth. In culture, p16-L16R fibroblasts grew at a faster rate, and most survived until later passages than p16-WT fibroblasts. Further, western blotting demonstrated that p16 protein was detected at lower levels in p16-L16R than in p16-WT fibroblasts. Together, these results suggest that the presence of a CDKN2A (47T>G) mutant allele contributes to an increased risk of pancreatic cancer as a result of reduced p16 protein levels and diminished p16 tumor suppressor function.

GLI1/GLI2 functional interplay is required to control Hedgehog/GLI targets gene expression.

The Hedgehog-regulated transcription factors GLI1 and GLI2 play overlapping roles in development and disease; however, the mechanisms underlying their interplay remain elusive. We report for the first time that GLI1 and GLI2 physically and functionally interact in cancer cells. GLI1 and GLI2 were shown to co-immunoprecipitate in PANC1 pancreatic cancer cells and RMS13 rhabdomyosarcoma cells. Mapping analysis demonstrated that the zinc finger domains of both proteins are required for their heteromerization. RNAi knockdown of either GLI1 or GLI2 inhibited expression of many well-characterized GLI target genes (BCL2, MYCN, PTCH2, IL7 and CCND1) in PANC1 cells, whereas PTCH1 expression was only inhibited by GLI1 depletion. qPCR screening of a large set of putative canonical and non-canonical Hedgehog/GLI targets identified further genes (e.g. E2F1, BMP1, CDK2) strongly down-regulated by GLI1 and/or GLI2 depletion in PANC1 cells, and demonstrated that ANO1, AQP1 and SOCS1 are up-regulated by knockdown of either GLI1 or GLI2. Chromatin immunoprecipitation showed that GLI1 and GLI2 occupied the same regions at the BCL2, MYCN and CCND1 promoters. Furthermore, depletion of GLI1 inhibited GLI2 occupancy at these promoters, suggesting that GLI1/GLI2 interaction is required for the recruitment of GLI2 to these sites. Together, these findings indicate that GLI1 and GLI2 co-ordinately regulate the transcription of some genes, and provide mechanistic insight into the roles of GLI proteins in carcinogenesis.

Targeting of the Hedgehog/GLI and mTOR pathways in advanced pancreatic cancer, a phase 1 trial of Vismodegib and Sirolimus combination.

BACKGROUND/OBJECTIVES: Preclinical data indicated a functional and molecular interaction between Hedgehog (HH)/GLI and PI3K-AKT-mTOR pathways promoting pancreatic ductal adenocarcinoma (PDAC). A phase I study was conducted of Vismodegib and Sirolimus combination to evaluate maximum tolerated dose (MTD) and preliminary anti-tumor efficacy. METHODS: Cohort I included advanced solid tumors patients following a traditional 3 + 3 design. Vismodegib was orally administered at 150 mg daily with Sirolimus starting at 3 mg daily, increasing to 6 mg daily at dose level 2. Cohort II included only metastatic PDAC patients. Anti-tumor efficacy was evaluated every two cycles and target assessment at pre-treatment and after a single cycle. RESULTS: Nine patient were enrolled in cohort I and 22 patients in cohort II. Twenty-eight patients were evaluated for dose-limiting toxicities (DLTs). One DLT was observed in each cohort, consisting of grade 2 mucositis and grade 3 thrombocytopenia. The MTD for Vismodegib and Sirolimus were 150 mg daily and 6 mg daily, respectively. The most common grade 3-4 toxicities were fatigue, thrombocytopenia, dehydration, and infections. A total of 6 patients had stable disease. No partial or complete responses were observed. Paired biopsy analysis before and after the first cycle in cohort II consistently demonstrated reduced GLI1 expression. Conversely, GLI and mTOR downstream targets were not significantly affected. CONCLUSIONS: The combination of Vismodegib and Sirolimus was well tolerated. Clinical benefit was limited to stable disease in a subgroup of patients. Targeting efficacy demonstrated consistent partial decreases in HH/GLI signaling with limited impact on mTOR signaling. These findings conflict with pre-clinical models and warrant further investigations.

TFII-I-mediated polymerase pausing antagonizes GLI2 induction by TGFß.

The modulation of GLI2, an oncogenic transcription factor commonly upregulated in cancer, is in many cases not due to genetic defects, suggesting dysregulation through alternative mechanisms. The identity of these molecular events remains for the most part unknown. Here, we identified TFII-I as a novel repressor of GLI2 expression. Mapping experiments suggest that the INR region of the GLI2 promoter is necessary for GLI2 repression. ChIP studies showed that TFII-I binds to this INR. TFII-I knockdown decreased the binding of NELF-A, a component of the promoter-proximal pausing complex at this site, and enriched phosphorylated RNAPII serine 2 in the GLI2 gene body. Immunoprecipitation studies demonstrate TFII-I interaction with SPT5, another pausing complex component. TFII-I overexpression antagonized GLI2 induction by TGFß, a known activator of GLI2 in cancer cells. TGFß reduced endogenous TFII-I binding to the INR and increased RNAPII SerP2 in the gene body. We demonstrate that this regulatory mechanism is not exclusive of GLI2. TGFß-induced genes CCR7, TGFß1 and EGR3 showed similar decreased TFII-I and NELF-A INR binding and increased RNAPII SerP2 in the gene body post-TGFß treatment. Together these results identify TFII-I as a novel repressor of a subset of TGFß-responsive genes through the regulation of RNAPII pausing.

The transcription factor GLI1 cooperates with the chromatin remodeler SMARCA2 to regulate chromatin accessibility at distal DNA regulatory elements.

The transcription factor GLI1 (GLI family zinc finger 1) plays a key role in the development and progression of multiple malignancies. To date, regulation of transcriptional activity at target gene promoters is the only molecular event known to underlie the oncogenic function of GLI1. Here, we provide evidence that GLI1 controls chromatin accessibility at distal regulatory regions by modulating the recruitment of SMARCA2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 2) to these elements. We demonstrate that SMARCA2 endogenously interacts with GLI1 and enhances its transcriptional activity. Mapping experiments indicated that the C-terminal transcriptional activation domain of GLI1 and SMARCA2's central domains, including its ATPase motif, are required for this interaction. Interestingly, similar to SMARCA2, GLI1 overexpression increased chromatin accessibility, as indicated by results of the micrococcal nuclease assay. Further, results of assays for transposase-accessible chromatin with sequencing (ATAC-seq) after GLI1 knockdown supported these findings, revealing that GLI1 regulates chromatin accessibility at several regions distal to gene promoters. Integrated RNA-seq and ATAC-seq data analyses identified a subset of differentially expressed genes located in cis to these regulated chromatin sites. Finally, using the GLI1-regulated gene HHIP (Hedgehog-interacting protein) as a model, we demonstrate that GLI1 and SMARCA2 co-occupy a distal chromatin peak and that SMARCA2 recruitment to this HHIP putative enhancer requires intact GLI1. These findings provide insights into how GLI1 controls gene expression in cancer cells and may inform approaches targeting this oncogenic transcription factor to manage malignancies.

Phase 1 trial of Vismodegib and Erlotinib combination in metastatic pancreatic cancer.

BACKGROUND/OBJECTIVES: Interplay between the Hedgehog (HH) and epidermal growth factor receptor (EGFR) pathways modulating the outcome of their signaling activity have been reported in various cancers including pancreatic ductal adenocarcinoma (PDAC). Therefore, simultaneous targeting of these pathways may be clinically beneficial. This Phase I study combined HH and EGFR inhibition in metastatic PDAC patients. METHODS: Combined effects of HH and EGFR inhibition using Vismodegib and Erlotinib with or without gemcitabine in metastatic solid tumors were assessed by CT. Another cohort of patients with metastatic PDAC was evaluated by FDG-PET and tumor biopsies-derived biomarkers. RESULTS: Treatment was well tolerated with the maximum tolerated dose cohort experiencing no grade 4 toxicities though 25% experienced grade 3 adverse effects. Recommended phase II dose of Vismodegib and Erlotinib were each 150 mg daily. No tumor responses were observed although 16 patients achieved stable disease for 2-7 cycles. Paired biopsy analysis before and after first cycle of therapy in PDAC patients showed reduced GLI1 mRNA, phospho-GLI1 and associated HH target genes in all cases. However, only half of the cases showed reduced levels of desmoplasia or changes in fibroblast markers. Most patients had decreased phospho-EGFR levels. CONCLUSIONS: Vismodegib and Erlotinib combination was well-tolerated although overall outcome in patients with metastatic PDAC was not significantly impacted by combination treatment. Biomarker analysis suggests direct targets inhibition without significantly affecting the stromal compartment. These findings conflict with pre-clinical mouse models, and thus warrant further investigation into how upstream inhibition of these pathways is circumvented in PDAC.

Epigenetics of gastrointestinal diseases: notes from a workshop.

International experts gathered at the Mayo Clinic (Rochester MN, USA) on February 27th-28th, 2017 for a meeting entitled 'Basic and Translational Facets of the Epigenetics of GI Diseases'. This workshop summarized recent advances on the role of epigenetics in the pathobiology of gastrointestinal (GI) diseases. Highlights of the meeting included recent advances on the involvement of different epigenetic mechanisms in malignant and nonmalignant GI disorders and the epigenetic heterogeneity exhibited in these diseases. The translational value of epigenetic drugs, as well as the current and future use of epigenetic changes (i.e., DNA methylation patterns) as biomarkers for early detection tools or disease stratification were also important topics of discussion.

Molecular Modeling and Functional Analysis of Exome Sequencing-Derived Variants of Unknown Significance Identify a Novel, Constitutively Active FGFR2 Mutant in Cholangiocarcinoma.

PURPOSE: Genomic testing has increased the quantity of information available to oncologists. Unfortunately, many identified sequence alterations are variants of unknown significance (VUSs), which thus limit the clinician's ability to use these findings to inform treatment. We applied a combination of in silico prediction and molecular modeling tools and laboratory techniques to rapidly define actionable VUSs. MATERIALS AND METHODS: Exome sequencing was conducted on 308 tumors from various origins. Most single nucleotide alterations within gene coding regions were VUSs. These VUSs were filtered to identify a subset of therapeutically targetable genes that were predicted with in silico tools to be altered in function by their variant sequence. A subset of receptor tyrosine kinase VUSs was characterized by laboratory comparison of each VUS versus its wild-type counterpart in terms of expression and signaling activity. RESULTS: The study identified 4,327 point mutations of which 3,833 were VUSs. Filtering for mutations in genes that were therapeutically targetable and predicted to affect protein function reduced these to 522VUSs of interest, including a large number of kinases. Ten receptortyrosine kinase VUSs were selected to explore in the laboratory. Of these, seven were found to be functionally altered. Three VUSs (FGFR2 F276C, FGFR4 R78H, and KDR G539R) showed increased basal or ligand-stimulated ERK phosphorylation compared with their wild-type counterparts, which suggests that they support transformation. Treatment of a patient who carried FGFR2 F276C with an FGFR inhibitor resulted in significant and sustained tumor response with clinical benefit. CONCLUSION: The findings demonstrate the feasibility of rapid identification of the biologic relevance of somatic mutations, which thus advances clinicians' ability to make informed treatment decisions.

Pancreatic Cancer, A Mis-interpreter of the Epigenetic Language.

Pancreatic cancer is the third leading cause of cancer mortality in the U.S. with close to 40,000 deaths per year. Pancreatic ductal adenocarcinoma (PDAC) represents approximately 90 percent of all pancreatic cancer cases and is the most lethal form of the disease. Current therapies for PDAC are ineffective and most patients cannot be treated by surgical resection. Most research efforts have primarily focused on how genetic alterations cause, alter progression, contribute to diagnosis, and influence PDAC management. Over the past two decades, a model has been advanced of PDAC initiation and progression as a multi-step process driven by the acquisition of mutations leading to loss of tumor suppressors and activation of oncogenes. The recognition of the essential roles of these genetic alterations in the development of PDAC has revolutionized our knowledge of this disease. However, none of these findings have turned into effective treatment for this dismal malignancy. In recent years, studies in the areas of chromatin modifications, and non-coding RNAs have uncovered mechanisms for regulating gene expression which occur independently of genetic alterations. Chromatin-based mechanisms are interwoven with microRNA-driven regulation of protein translation to create an integrated epigenetic language, which is grossly dysregulated in PDAC. Thus in PDAC, key tumor suppressors that are well established to play a role in PDAC may be repressed, and oncogenes can be upregulated secondary to epigenetic alterations. Unlike mutations, epigenetic changes are potentially reversible. Given this feature of epigenetic mechanisms, it is conceivable that targeting epigenetic-based events promoting and maintaining PDAC could serve as foundation for the development of new therapeutic and diagnostic approaches for this disease.

Epigenetic control of the tumor microenvironment.

Stromal cells of the tumor microenvironment have been shown to play important roles in both supporting and limiting cancer growth. The altered phenotype of tumor-associated stromal cells (fibroblasts, immune cells, endothelial cells etc.) is proposed to be mainly due to epigenetic dysregulation of gene expression; however, only limited studies have probed the roles of epigenetic mechanisms in the regulation of stromal cell function. We review recent studies demonstrating how specific epigenetic mechanisms (DNA methylation and histone post-translational modification-based gene expression regulation, and miRNA-mediated translational regulation) drive aspects of stromal cell phenotype, and discuss the implications of these findings for treatment of malignancies. We also summarize the effects of epigenetic mechanism-targeted drugs on stromal cells and discuss the consideration of the microenvironment response in attempts to use these drugs for cancer treatment.

Inhibition of Rab prenylation by statins induces cellular glycosphingolipid remodeling.

Statins, which specifically inhibit HMG Co-A reductase, the rate-limiting step of cholesterol biosynthesis, are widely prescribed to reduce serum cholesterol and cardiac risk, but many other effects are seen. We now show an effect of these drugs to induce profound changes in the step-wise synthesis of glycosphingolipids (GSLs) in the Golgi. Glucosylceramide (GlcCer) was increased several-fold in all cell lines tested, demonstrating a widespread effect. Additionally, de novo or elevated lactotriaosylceramide (Lc3Cer; GlcNAcß1-3Galß1-4GlcCer) synthesis was observed in 70%. Western blot showed that GlcCer synthase (GCS) was elevated by statins, and GCS and Lc3Cer synthase (Lc3S) activities were increased; however, transcript was elevated for Lc3S only. Supplementation with the isoprenoid precursor, geranylgeranyl pyrophosphate (GGPP), a downstream product of HMG Co-A reductase, reversed statin-induced glycosyltransferase and GSL elevation. The Rab geranylgeranyl transferase inhibitor 3-PEHPC, but not specific inhibitors of farnesyl transferase, or geranylgeranyl transferase I, was sufficient to replicate statin-induced GlcCer and Lc3Cer synthesis, supporting a Rab prenylation-dependent mechanism. While total cholesterol was unaffected, the trans-Golgi network (TGN) cholesterol pool was dissipated and medial Golgi GCS partially relocated by statins. GSL-dependent vesicular retrograde transport of Verotoxin and cholera toxin to the Golgi/endoplasmic reticulum were blocked after statin or 3-PEHPC treatment, suggesting aberrant, prenylation-dependent vesicular traffic as a basis of glycosyltransferase increase and GSL remodeling. These in vitro studies indicate a previously unreported link between Rab prenylation and regulation of GCS activity and GlcCer metabolism.

Nuclear Factor of Activated T Cells-dependent Down-regulation of the Transcription Factor Glioma-associated Protein 1 (GLI1) Underlies the Growth Inhibitory Properties of Arachidonic Acid.

Numerous reports have demonstrated a tumor inhibitory effect of polyunsaturated fatty acids (PUFAs). However, the molecular mechanisms modulating this phenomenon are in part poorly understood. Here, we provide evidence of a novel antitumoral mechanism of the PUFA arachidonic acid (AA). In vivo and in vitro experiments showed that AA treatment decreased tumor growth and metastasis and increased apoptosis. Molecular analysis of this effect showed significantly reduced expression of a subset of antiapoptotic proteins, including BCL2, BFL1/A1, and 4-1BB, in AA-treated cells. We demonstrated that down-regulation of the transcription factor glioma-associated protein 1 (GLI1) in AA-treated cells is the underlying mechanism controlling BCL2, BFL1/A1, and 4-1BB expression. Using luciferase reporters, chromatin immunoprecipitation, and expression studies, we found that GLI1 binds to the promoter of these antiapoptotic molecules and regulates their expression and promoter activity. We provide evidence that AA-induced apoptosis and down-regulation of antiapoptotic genes can be inhibited by overexpressing GLI1 in AA-sensitive cells. Conversely, inhibition of GLI1 mimics AA treatments, leading to decreased tumor growth, cell viability, and expression of antiapoptotic molecules. Further characterization showed that AA represses GLI1 expression by stimulating nuclear translocation of NFATc1, which then binds the GLI1 promoter and represses its transcription. AA was shown to increase reactive oxygen species. Treatment with antioxidants impaired the AA-induced apoptosis and down-regulation of GLI1 and NFATc1 activation, indicating that NFATc1 activation and GLI1 repression require the generation of reactive oxygen species. Collectively, these results define a novel mechanism underlying AA antitumoral functions that may serve as a foundation for future PUFA-based therapeutic approaches.

The transcription factor GLI1 interacts with SMAD proteins to modulate transforming growth factor ß-induced gene expression in a p300/CREB-binding protein-associated factor (PCAF)-dependent manner.

The biological role of the transcription factor GLI1 in the regulation of tumor growth is well established; however, the molecular events modulating this phenomenon remain elusive. Here, we demonstrate a novel mechanism underlying the role of GLI1 as an effector of TGFß signaling in the regulation of gene expression in cancer cells. TGFß stimulates GLI1 activity in cancer cells and requires its transcriptional activity to induce BCL2 expression. Analysis of the mechanism regulating this interplay identified a new transcriptional complex including GLI1 and the TGFß-regulated transcription factor, SMAD4. We demonstrate that SMAD4 physically interacts with GLI1 for concerted regulation of gene expression and cellular survival. Activation of the TGFß pathway induces GLI1-SMAD4 complex binding to the BCL2 promoter whereas disruption of the complex through SMAD4 RNAi depletion impairs GLI1-mediated transcription of BCL2 and cellular survival. Further characterization demonstrated that SMAD2 and the histone acetyltransferase, PCAF, participate in this regulatory mechanism. Both proteins bind to the BCL2 promoter and are required for TGFß- and GLI1-stimulated gene expression. Moreover, SMAD2/4 RNAi experiments showed that these factors are required for the recruitment of GLI1 to the BCL2 promoter. Finally, we determined whether this novel GLI1 transcriptional pathway could regulate other TGFß targets. We found that two additional TGFß-stimulated genes, INTERLEUKIN-7 and CYCLIN D1, are dependent upon the intact GLI1-SMAD-PCAF complex for transcriptional activation. Collectively, these results define a novel epigenetic mechanism that uses the transcription factor GLI1 and its associated complex as a central effector to regulate gene expression in cancer cells.

Reduced GM1 ganglioside in CFTR-deficient human airway cells results in decreased ß1-integrin signaling and delayed wound repair.

Loss of cystic fibrosis transmembrane conductance regulator (CFTR) function reduces chloride secretion and increases sodium uptake, but it is not clear why CFTR mutation also results in progressive lung inflammation and infection. We previously demonstrated that CFTR-silenced airway cells migrate more slowly during wound repair than CFTR-expressing controls. In addition, CFTR-deficient cells and mouse models have been reported to have altered sphingolipid levels. Here, we investigated the hypothesis that reduced migration in CFTR-deficient airway epithelial cells results from altered sphingolipid composition. We used cell lines derived from a human airway epithelial cell line (Calu-3) stably transfected with CFTR short hairpin RNA (CFTR-silenced) or nontargeting short hairpin RNA (controls). Cell migration was measured by electric cell substrate impedance sensing (ECIS). Lipid analyses, addition of exogenous glycosphingolipids, and immunoblotting were performed. We found that levels of the glycosphingolipid, GM1 ganglioside, were ~60% lower in CFTR-silenced cells than in controls. CFTR-silenced cells exhibited reduced levels of activated ß1-integrin, phosphorylated tyrosine 576 of focal adhesion kinase (pFAK), and phosphorylation of Crk-associated substrate (pCAS). Addition of GM1 (but not GM3) ganglioside to CFTR-silenced cells restored activated ß1-integrin, pFAK, and pCAS to near control levels and partially restored (~40%) cell migration. Our results suggest that decreased GM1 in CFTR-silenced cells depresses ß1-integrin signaling, which contributes to the delayed wound repair observed in these cells. These findings have implications for the pathology of cystic fibrosis, where altered sphingolipid levels in airway epithelial cells could result in a diminished capacity for wound repair after injury.

Internalization of Clostridium perfringens α-toxin leads to ERK activation and is involved on its cytotoxic effect.

Clostridium perfringens phospholipase C (CpPLC), also called α-toxin, plays a key role in the pathogenesis of gas gangrene. CpPLC may lead to cell lysis at concentrations that cause extensive degradation of plasma membrane phospholipids. However, at sublytic concentrations it induces cytotoxicity without inducing evident membrane damage. The results of this work demonstrate that CpPLC becomes internalized in cells by a dynamin-dependent mechanism and in a time progressive process: first, CpPLC colocalizes with caveolin both at the plasma membrane and in vesicles, and later it colocalizes with early and late endosomes and lysosomes. Lysosomal damage in the target cells is evident 9 h after CpPLC exposure. Our previous work demonstrated that CpPLCinduces ERK1/2 activation, which is involved in its cytotoxic effect. In this work we found that cholesterol sequestration, dynamin inhibition, as well as inhibition of actin polymerization, prevent CpPLC internalization and ERK1/2 activation, involving endocytosis in the signalling events required for CpPLC cytotoxic effect at sublytic concentrations. These results provide new insights about the mode of action of this bacterial phospholipase C, previously considered to act only locally on cell membrane.