Paneth cell dysfunction in radiation injury and radio-mitigation by human α-defensin 5

Introduction

The mechanism underlying radiation-induced gut microbiota dysbiosis is undefined. This study examined the effect of radiation on the intestinal Paneth cell α-defensin expression and its impact on microbiota composition and mucosal tissue injury and evaluated the radio-mitigative effect of human α-defensin 5 (HD5).

Methods

Adult mice were subjected to total body irradiation, and Paneth cell α-defensin expression was evaluated by measuring α-defensin mRNA by RT-PCR and α-defensin peptide levels by mass spectrometry. Vascular-to-luminal flux of FITC-inulin was measured to evaluate intestinal mucosal permeability and endotoxemia by measuring plasma lipopolysaccharide. HD5 was administered in a liquid diet 24 hours before or after irradiation. Gut microbiota was analyzed by 16S rRNA sequencing. Intestinal epithelial junctions were analyzed by immunofluorescence confocal microscopy and mucosal inflammatory response by cytokine expression. Systemic inflammation was evaluated by measuring plasma cytokine levels.

Results

Ionizing radiation reduced the Paneth cell α-defensin expression and depleted α-defensin peptides in the intestinal lumen. α-Defensin down-regulation was associated with the time-dependent alteration of gut microbiota composition, increased gut permeability, and endotoxemia. Administration of human α-defensin 5 (HD5) in the diet 24 hours before irradiation (prophylactic) significantly blocked radiation-induced gut microbiota dysbiosis, disruption of intestinal epithelial tight junction and adherens junction, mucosal barrier dysfunction, and mucosal inflammatory response. HD5, administered 24 hours after irradiation (treatment), reversed radiation-induced microbiota dysbiosis, tight junction and adherens junction disruption, and barrier dysfunction. Furthermore, HD5 treatment also prevents and reverses radiation-induced endotoxemia and systemic inflammation.

Conclusion

These data demonstrate that radiation induces Paneth cell dysfunction in the intestine, and HD5 feeding prevents and mitigates radiation-induced intestinal mucosal injury, endotoxemia, and systemic inflammation.

E2F7 drives autotaxin/Enpp2 transcription via chromosome looping: Repression by p53 in murine but not in human carcinomas

Dysregulation of the autotaxin (ATX, Enpp2)-lysophosphatidic acid (LPA) signaling in cancerous cells contributes to tumorigenesis and therapy resistance. We previously found that ATX activity was elevated in p53-KO mice compared to wild-type (WT) mice. Here, we report that ATX expression was upregulated in mouse embryonic fibroblasts from p53-KO and p53^R172H mutant mice. ATX promoter analysis combined with yeast one-hybrid testing revealed that WT p53 directly inhibits ATX expression via E2F7. Knockdown of E2F7 reduced ATX expression and chromosome immunoprecipitation showed that E2F7 promotes Enpp2 transcription through cooperative binding to two E2F7 sites (promoter region -1393 bp and second intron 996 bp). Using chromosome conformation capture, we found that chromosome looping brings together the two E2F7 binding sites. We discovered a p53 binding site in the first intron of murine Enpp2, but not in human ENPP2. Binding of p53 disrupted the E2F7-mediated chromosomal looping and repressed Enpp2 transcription in murine cells. In contrast, we found no disruption of E2F7-mediated ENPP2 transcription via direct p53 binding in human carcinoma cells. In summary, E2F7 is a common transcription factor that upregulates ATX in human and mouse cells but is subject to steric interference by direct intronic p53 binding only in mice.

Cryptotanshinone inhibits ovarian tumor growth and metastasis by degrading c-Myc and attenuating the FAK signaling pathway

Cryptotanshinone (CT), a natural compound derived from Salvia miltiorrhiza Bunge that is also known as the traditional Chinese medicine Danshen, exhibits antitumor activity in various cancers. However, it remains unclear whether CT has a potential therapeutic benefit against ovarian cancers. The aim of this study was to test the efficacy of CT in ovarian cancer cells in vitro and using a xenograft model in NSG mice orthotopically implanted with HEY A8 human ovarian cancer cells and to explore the molecular mechanism(s) underlying CT’s antitumor effects. We found that CT inhibited the proliferation, migration, and invasion of OVCAR3 and HEY A8 cells, while sensitizing the cell responses to the chemotherapy drugs paclitaxel and cisplatin. CT also suppressed ovarian tumor growth and metastasis in immunocompromised mice orthotopically inoculated with HEY A8 cells. Mechanistically, CT degraded the protein encoded by the oncogene c-Myc by promoting its ubiquitination and disrupting the interaction with its partner protein Max. CT also attenuated signaling via the nuclear focal adhesion kinase (FAK) pathway and degraded FAK protein in both cell lines. Knockdown of c-Myc using lentiviral CRISPR/Cas9 nickase resulted in reduction of FAK expression, which phenocopies the effects of CT and the c-Myc/Max inhibitor 10058-F4. Taken together, our studies demonstrate that CT inhibits primary ovarian tumor growth and metastasis by degrading c-Myc and FAK and attenuating the FAK signaling pathway.

Adipose-Derived Stem Cells Facilitate Ovarian Tumor Growth and Metastasis by Promoting Epithelial to Mesenchymal Transition Through Activating the TGF-β Pathway

Adipose-derived stem cells (ADSC) are multipotent mesenchymal stem cells derived from adipose tissues and are capable of differentiating into multiple cell types in the tumor microenvironment (TME). The roles of ADSC in ovarian cancer (OC) metastasis are still not well defined. To understand whether ADSC contributes to ovarian tumor metastasis, we examined epithelial to mesenchymal transition (EMT) markers in OC cells following the treatment of the ADSC-conditioned medium (ADSC-CM). ADSC-CM promotes EMT in OC cells. Functionally, ADSC-CM promotes OC cell proliferation, survival, migration, and invasion. We further demonstrated that ADSC-CM induced EMT via TGF-β growth factor secretion from ADSC and the ensuing activation of the TGF-β pathway. ADSC-CM-induced EMT in OC cells was reversible by the TGF-β inhibitor SB431542 treatment. Using an orthotopic OC mouse model, we also provide the experimental evidence that ADSC contributes to ovarian tumor growth and metastasis by promoting EMT through activating the TGF-β pathway. Taken together, our data indicate that targeting ADSC using the TGF-β inhibitor has the therapeutic potential in blocking the EMT and OC metastasis.

A Luminacin D Analog HL142 Inhibits Ovarian Tumor Growth and Metastasis by Reversing EMT and Attenuating the TGFβ and FAK Pathways

Epithelial to mesenchymal transition (EMT) is known to contribute to tumor metastasis and chemoresistance. Reversing EMT using small molecule inhibitors to target EMT associated gene expression represents an effective strategy for cancer treatment. The purpose of this study is to test whether a new luminacin D analog HL142 reverses EMT in ovarian cancer (OC) and has the therapeutic potential for OC. We chemically synthesized HL142 and tested its functions in OC cells in vitro and its efficacy in inhibiting ovarian tumor growth and metastasis in vivo using orthotopic OC mouse models. We first demonstrate that ASAP1 is co-amplified and interacts with the focal adhesion kinase (FAK) protein in serous ovarian carcinoma. HL142 inhibits ASAP1 and its interaction protein FAK in highly invasive OVCAR8 and moderately invasive OVCAR3 cells. HL142 inhibits EMT phenotypic switch, accompanied by upregulating epithelial marker E-cadherin and cytokeratin-7 and downregulating mesenchymal markers vimentin, β-catenin, and snail2 in both cell lines. Functionally, HL142 inhibits proliferation, colony formation, migration, and invasion. HL142 also sensitizes cell responses to chemotherapy drug paclitaxel treatment and inhibits ovarian tumor growth and metastasis in orthotopic OC mouse models. We further show that HL142 attenuates the TGFβ and FAK pathways in vitro using OC cells and in vivo using orthotopic mouse models.

EIF5A2 controls ovarian tumor growth and metastasis by promoting epithelial to mesenchymal transition via the TGFβ pathway

BACKGROUND

Epithelial to mesenchymal transition (EMT) contributes to tumor metastasis and chemoresistance. Eukaryotic initiation factor 5A2 (EIF5A2) is highly expressed in a variety of human cancers but rarely expressed in normal tissues. While EIF5A2 has oncogenic activity in several cancers and contributes to tumor metastasis, its role in ovarian cancer is unknown. In this study, we investigate whether EIF5A2 contributes to ovarian tumor metastasis by promoting EMT.

METHODS

To investigate the role of EIF5A2, we knocked out (KO) EIF5A2 using lentiviral CRISPR/Cas9 nickase in high invasive SKOV3 and OVCAR8 cells and overexpressed EIF5A2 in low invasive OVCAR3 cells using lentiviral vector. Cell proliferation, migration and invasion was examined in vitro ovarian cancer cells and tumor metastasis was evaluated in vivo using orthotopic ovarian cancer mouse models.

RESULTS

Here we report that EIF5A2 is highly expressed in ovarian cancers and associated with patient poor survival. Lentiviral CRISPR/Cas9 nickase vector mediated knockout (KO) of EIF5A2 inhibits epithelial to mesenchymal transition (EMT) in SKOV3 and OVCAR8 ovarian cancer cells that express high levels of EIF5A2. In contrast, overexpression of EIF5A2 promotes EMT in OVCAR3 epithelial adenocarcinoma cells that express relatively low EIF5A2 levels. KO of EIF5A2 in SKOV3 and OVCAR8 cells inhibits ovarian cancer cell migration and invasion, while its overexpression promotes cell migration and invasion in OVCAR3 adenocarcinoma cells. We further demonstrate that EIF5A2 promotes EMT by activating the TGFβ pathway and KO of EIF5A2 inhibits ovarian tumor growth and metastasis in orthotopic ovarian cancer mouse models.

CONCLUSION

Our results indicate that EIF5A2 is an important controller of ovarian tumor growth and metastasis by promoting EMT and activating the TGFβ pathway.

LPAR2 receptor activation attenuates radiation-induced disruption of apical junctional complexes and mucosal barrier dysfunction in mouse colon

The tight junction (TJ) and barrier function of colonic epithelium is highly sensitive to ionizing radiation. We evaluated the effect of lysophosphatidic acid (LPA) and its analog, Radioprotein-1, on γ-radiation-induced colonic epithelial barrier dysfunction using Caco-2 and m-IC_C12 cell monolayers in vitro and mice in vivo. Mice were subjected to either total body irradiation (TBI) or partial body irradiation (PBI-BM5). Intestinal barrier function was assessed by analyzing immunofluorescence localization of TJ proteins, mucosal inulin permeability, and plasma lipopolysaccharide (LPS) levels. Oxidative stress was analyzed by measuring protein thiol oxidation and antioxidant mRNA. In Caco-2 and m-IC_C12 cell monolayers, LPA attenuated radiation-induced redistribution of TJ proteins, which was blocked by a Rho-kinase inhibitor. In mice, TBI and PBI-BM5 disrupted colonic epithelial tight junction and adherens junction, increased mucosal permeability, and elevated plasma LPS; TJ disruption by TBI was more severe in Lpar2^-/- mice compared to wild-type mice. RP1, administered before or after irradiation, alleviated TBI and PBI-BM5-induced TJ disruption, barrier dysfunction, and endotoxemia accompanied by protein thiol oxidation and downregulation of antioxidant gene expression, cofilin activation, and remodeling of the actin cytoskeleton. These data demonstrate that LPAR2 receptor activation prevents and mitigates γ-irradiation-induced colonic mucosal barrier dysfunction and endotoxemia.

Osteoclast-Derived Autotaxin, a Distinguishing Factor for Inflammatory Bone Loss

OBJECTIVE

The severity of rheumatoid arthritis (RA) correlates directly with bone erosions arising from osteoclast (OC) hyperactivity. Despite the fact that inflammation may be controlled in patients with RA, those in a state of sustained clinical remission or low disease activity may continue to accrue erosions, which supports the need for treatments that would be suitable for long-lasting inhibition of OC activity without altering the physiologic function of OCs in bone remodeling. Autotaxin (ATX) contributes to inflammation, but its role in bone erosion is unknown.

METHODS

ATX was targeted by inhibitory treatment with pharmacologic drugs and also by conditional inactivation of the ATX gene Ennp2 in murine OCs (ΔATX^{C tsk} ). Arthritic and erosive diseases were studied in human tumor necrosis factor-transgenic (hTNF^+/- ) mice and mice with K/BxN serum transfer-induced arthritis. Systemic bone loss was also analyzed in mice with lipopolysaccharide (LPS)-induced inflammation and estrogen deprivation. Joint inflammation and bone erosion were assessed by histology and micro-computed tomography. The role of ATX in RA was also examined in OC differentiation and activity assays.

RESULTS

OCs present at sites of inflammation overexpressed ATX. Pharmacologic inhibition of ATX in hTNF^+/- mice, as compared to vehicle-treated controls, significantly mitigated focal bone erosion (36% decrease; P < 0.05) and systemic bone loss (43% decrease; P < 0.05), without affecting synovial inflammation. OC-derived ATX was revealed to be instrumental in OC bone resorptive activity and was up-regulated by the inflammation elicited in the presence of TNF or LPS. Specific loss of ATX in OCs from mice subjected to ovariectomy significantly protected against the systemic bone loss and erosion that had been induced with LPS and K/BxN serum treatments (30% reversal of systemic bone loss [P < 0.01]; 55% reversal of erosion [P < 0.001]), without conferring bone-protective properties.

CONCLUSION

Our results identify ATX as a novel OC factor that specifically controls inflammation-induced bone erosions and systemic bone loss. Therefore, ATX inhibition offers a novel therapeutic approach for potentially preventing bone erosion in patients with RA.

LPA5 Is an Inhibitory Receptor That Suppresses CD8 T-Cell Cytotoxic Function via Disruption of Early TCR Signaling

Persistent T cell antigen receptor (TCR) signaling by CD8 T cells is a feature of cancer and chronic infections and results in the sustained expression of, and signaling by, inhibitory receptors, which ultimately impair cytotoxic activity via poorly characterized mechanisms. We have previously determined that the LPA₅ GPCR expressed by CD8 T cells, upon engaging the lysophosphatidic acid (LPA) bioactive serum lipid, functions as an inhibitory receptor able to negatively regulate TCR signaling. Notably, the levels of LPA and autotaxin (ATX), the phospholipase D enzyme that produces LPA, are often increased in chronic inflammatory disorders such as chronic infections, autoimmune diseases, obesity, and cancer. In this report, we demonstrate that LPA engagement selectively by LPA₅ on human and mouse CD8 T cells leads to the inhibition of several early TCR signaling events including intracellular calcium mobilization and ERK activation. We further show that, as a consequence of LPA₅ suppression of TCR signaling, the exocytosis of perforin-containing granules is significantly impaired and reflected by repressed in vitro and in vivo CD8 T cell cytolytic activity. Thus, these data not only document LPA₅ as a novel inhibitory receptor but also determine the molecular and biochemical mechanisms by which a naturally occurring serum lipid that is elevated under settings of chronic inflammation signals to suppress CD8 T cell killing activity in both human and murine cells. As diverse tumors have repeatedly been shown to aberrantly produce LPA that acts in an autocrine manner to promote tumorigenesis, our findings further implicate LPA in activating a novel inhibitory receptor whose signaling may be therapeutically silenced to promote CD8 T cell immunity.

Novel Inhibitory Effect of a Lysophosphatidic Acid 2 Agonist on Allergen-Driven Airway Inflammation

Lysophosphatidic acid (LPA) is a pleiotropic lipid signaling molecule associated with asthma pathobiology. LPA elicits its effects by binding to at least six known cell surface G protein-coupled receptors (LPA1-6) that are expressed in the lung in a cell type-specific manner. LPA2 in particular has emerged as an attractive therapeutic target in asthma because it appears to transduce inhibitory or cell-protective signals. We studied a novel and specific small molecule LPA2 agonist (2-[4-(1,3-dioxo-1H,3H-benzoisoquinolin-2-yl)butylsulfamoyl] benzoic acid [DBIBB]) in a mouse model of house dust mite-induced allergic airway inflammation. Mice injected with DBIBB developed significantly less airway and lung inflammation compared with vehicle-treated controls. Levels of lung Th2 cytokines were also significantly attenuated by DBIBB. We conclude that pharmacologic activation of LPA2 attenuates Th2-driven allergic airway inflammation in a mouse model of asthma. Targeting LPA receptor signaling holds therapeutic promise in allergic asthma.

Rapid disruption of intestinal epithelial tight junction and barrier dysfunction by ionizing radiation in mouse colon in vivo: protection by N-acetyl-l-cysteine

The goals of this study were to evaluate the effects of ionizing radiation on apical junctions in colonic epithelium and mucosal barrier function in mice in vivo. Adult mice were subjected to total body irradiation (4 Gy) with or without N-acetyl-l-cysteine (NAC) feeding for 5 days before irradiation. At 2-24 h postirradiation, the integrity of colonic epithelial tight junctions (TJ), adherens junctions (AJ), and the actin cytoskeleton was assessed by immunofluorescence microscopy and immunoblot analysis of detergent-insoluble fractions for TJ and AJ proteins. The barrier function was evaluated by measuring vascular-to-luminal flux of fluorescein isothiocyanate (FITC)-inulin in vivo and luminal-to-mucosal flux in vitro. Oxidative stress was evaluated by measuring protein thiol oxidation. Confocal microscopy showed that radiation caused redistribution of occludin, zona occludens-1, claudin-3, E-cadherin, and β-catenin, as well as the actin cytoskeleton as early as 2 h postirradiation, and this effect was sustained for at least 24 h. Feeding NAC before irradiation blocked radiation-induced disruption of TJ, AJ, and the actin cytoskeleton. Radiation increased mucosal permeability to inulin in colon, which was blocked by NAC feeding. The level of reduced-protein thiols in colon was depleted by radiation with a concomitant increase in the level of oxidized-protein thiol. NAC feeding blocked the radiation-induced protein thiol oxidation. These data demonstrate that radiation rapidly disrupts TJ, AJ, and the actin cytoskeleton by an oxidative stress-dependent mechanism that can be prevented by NAC feeding.

Lysophosphatidic acid inhibits CD8 T cell activation and control of tumor progression

CD8 T lymphocytes are able to eliminate nascent tumor cells through a process referred to as immune surveillance. However, multiple inhibitory mechanisms within the tumor microenvironment have been described that impede tumor rejection by CD8 T cells, including increased signaling by inhibitory receptors. Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that has been shown repeatedly to promote diverse cellular processes benefiting tumorigenesis. Accordingly, the increased expression of LPA and LPA receptors is a common feature of diverse tumor cell lineages and can result in elevated systemic LPA levels. LPA is recognized by at least 6 distinct G-protein-coupled receptors and several of which are expressed by T cells, although the precise role of LPA signaling in CD8 T cell activation and function has not been defined. Here, we demonstrate that LPA signaling via the LPA5 receptor expressed by CD8 T cells suppresses antigen receptor signaling, cell activation and proliferation in vitro and in vivo. Importantly, in a mouse melanoma model tumor-specific CD8 T cells that are LPA5-deficient are able to control tumor growth significantly better than wild-type tumor-specific CD8 T cells. Together, these data suggest that the production of LPA by tumors serves not only in an autocrine manner to promote tumorigenesis but also as a mechanism to suppress adaptive immunity and highlights a potential novel target for cancer treatment.

Abstract 5209: Non-tumoral autotaxin stored into platelet α-granules promotes breast cancer cell metastasis

Autotaxin (ATX) through its lysophospholipase D activity controls physiological levels of lysophosphatidic acid (LPA) in blood. ATX is overexpressed in multiple types of cancers and we have shown previously that together with LPA generated during platelet activation promotes skeletal metastasis of breast cancer. However, the mechanisms that regulate the pathophysiological significances of the interactions between circulating LPA, ATX, and platelets remain undefined in cancer. Here we show that ATX is stored in α-granules of resting human platelets and released upon tumor cell-induced platelet aggregation, leading to the production of LPA. For this study, we used two human breast cancer cell lines (MDA-MB-231, MDA-B02) that do not express ATX. Our in vitro and in vivo experiments demonstrate that non-tumoral ATX controls the early stage of bone colonization by tumor cells and to a less extent osteolytic bone metastasis progression. Moreover, expression of a dominant negative integrin αvβ3-Δ744 or treatment with the anti human αvβ&;3 monoclonal antibody LM609 completely abolished binding of ATX to tumor cells, demonstrating the requirement of a fully active integrin αvβ3 in this process. The present results establish a new mechanism for platelet contribution to LPA-dependent metastasis of breast cancer cells and demonstrate the therapeutic potential of disrupting the binding of non-tumor-derived ATX with the tumor cells for the prevention of metastasis.

Citation Format: Raphael Leblanc, Sue-Chin Lee, Dereck Norman, Johnny Ribeiro, Gabor Tigyi, Olivier Peyruchaud. Non-tumoral autotaxin stored into platelet α-granules promotes breast cancer cell metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5209. doi:10.1158/1538-7445.AM2015-5209

The autotaxin-LPA2 GPCR axis is modulated by γ-irradiation and facilitates DNA damage repair

In this study we characterized the effects of radiation injury on the expression and function of the autotaxin (ATX)-LPA2 GPCR axis. In IEC-6 crypt cells and jejunum enteroids quantitative RT-PCR showed a time- and dose-dependent upregulation of lpa2 in response to γ-irradiation that was abolished by mutation of the NF-κB site in the lpa2 promoter or by inhibition of ATM/ATR kinases with CGK-733, suggesting that lpa2 is a DNA damage response gene upregulated by ATM via NF-κB. The resolution kinetics of the DNA damage marker γ-H2AX in LPA-treated IEC-6 cells exposed to γ-irradiation was accelerated compared to vehicle, whereas pharmacological inhibition of LPA2 delayed the resolution of γ-H2AX. In LPA2-reconstituted MEF cells lacking LPA1&3 the levels of γ-H2AX decreased rapidly, whereas in Vector MEF were high and remained sustained. Inhibition of ERK1&2 or PI3K/AKT signaling axis by pertussis toxin or the C311A/C314A/L351A mutation in the C-terminus of LPA2 abrogated the effect of LPA on DNA repair. LPA2 transcripts in Lin(-)Sca-1(+)c-Kit(+) enriched for bone marrow stem cells were 27- and 5-fold higher than in common myeloid or lymphoid progenitors, respectively. Furthermore, after irradiation higher residual γ-H2AX levels were detected in the bone marrow or jejunum of irradiated LPA2-KO mice compared to WT mice. We found that γ-irradiation increases plasma ATX activity and LPA level that is in part due to the previously established radiation-induced upregulation of TNFα. These findings identify ATX and LPA2 as radiation-regulated genes that appear to play a physiological role in DNA repair.

Sphingosine 1-phosphate is a ligand for peroxisome proliferator-activated receptor-γ that regulates neoangiogenesis

Sphingosine 1-phosphate (S1P) is a bioactive lipid that can function both extracellularly and intracellularly to mediate a variety of cellular processes. Using lipid affinity matrices and a radiolabeled lipid binding assay, we reveal that S1P directly interacts with the transcription factor peroxisome proliferator-activated receptor (PPAR)γ. Herein, we show that S1P treatment of human endothelial cells (ECs) activated a luciferase-tagged PPARγ-specific gene reporter by ∼12-fold, independent of the S1P receptors. More specifically, in silico docking, gene reporter, and binding assays revealed that His323 of the PPARγ ligand binding domain is important for binding to S1P. PPARγ functions when associated with coregulatory proteins, and herein we identify that peroxisome proliferator-activated receptor-γ coactivator 1 (PGC1)β binds to PPARγ in ECs and their progenitors (nonadherent endothelial forming cells) and that the formation of this PPARγ:PGC1β complex is increased in response to S1P. ECs treated with S1P selectively regulated known PPARγ target genes with PGC1β and plasminogen-activated inhibitor-1 being increased, no change to adipocyte fatty acid binding protein 2 and suppression of CD36. S1P-induced in vitro tube formation was significantly attenuated in the presence of the PPARγ antagonist GW9662, and in vivo application of GW9662 also reduced vascular development in Matrigel plugs. Interestingly, activation of PPARγ by the synthetic ligand troglitazone also reduced tube formation in vitro and in vivo. To support this, Sphk1(-/-)Sphk2(+/-) mice, with low circulating S1P levels, demonstrated a similar reduction in vascular development. Taken together, our data reveal that the transcription factor, PPARγ, is a bona fide intracellular target for S1P and thus suggest that the S1P:PPARγ:PGC1β complex may be a useful target to manipulate neovascularization.

miR-203 Functions as a Tumor Suppressor by Inhibiting Epithelial to Mesenchymal Transition in Ovarian Cancer

OBJECTIVE

Ovarian cancer is a gynecological malignancy that has a high mortality rate in women due to metastatic progression and recurrence. miRNAs are small, endogenous, noncoding RNAs that function as tumor suppressors or oncogenes in various human cancers by selectively suppressing the expression of target genes. The objective of this study is to investigate the role of miR-203 in ovarian cancer.

METHODS

miR-203 was expressed in ovarian cancer SKOV3 and OVCAR3 cells using lentiviral vector and cell proliferation, migration, invasion were examined using MTT, transwell and Matrigel assays, respectively. Tumor growth was examined using Xenograft mouse model.

RESULTS

miR-203 expression was downregulated, whereas expression of its target gene Snai2 was upregulated in human ovarian serous carcinoma tissue as compared to normal ovaries. In addition, high miR-203 expression was associated with long-term survival rate of ovarian cancer patients. miR-203 overexpression inhibited cell proliferation, migration, and invasion of SKOV3 and OVCAR3 ovarian cancer cells. Furthermore, miR-203 overexpression inhibited the epithelial to mesenchymal transition (EMT) in ovarian cancer cells. Silencing Snai2 with lentiviral short hairpin (sh) RNA mimics miR-203-mediated inhibition of EMT and tumor cell invasion. Xenografts of miR-203-overexpressing ovarian cancer cells in immunodeficient mice exhibited a significantly reduced tumor growth.

CONCLUSION

miR-203 functions as a tumor suppressor by down regulating Snai2 in ovarian cancer.

Opposing regulation of megakaryopoiesis by LPA receptors 2 and 3 in K562 human erythroleukemia cells

Erythrocytes and megakaryocytes (MK) are derived from a common progenitor that undergoes lineage specification. Lysophosphatidic acid (LPA), a lipid growth factor was previously shown to be a regulator for erythropoietic process through activating LPA receptor 3 (LPA3). However, whether LPA affects megakaryopoiesis remains unclear. In this study, we used K562 leukemia cell line as a model to investigate the roles of LPA in MK differentiation. We demonstrated that K562 cells express both LPA2 and LPA3, and the expression levels of LPA2 are higher than LPA3. Treatment with phorbol 12-myristate 13-acetate, a commonly used inducer of megakaryopoiesis, reciprocally regulates the expressions of LPA2 and LPA3. By pharmacological blockers and knockdown experiments, we showed that activation of LPA2 suppresses whereas, LPA3 promotes megakaryocytic differentiation in K562. The LPA2-mediated inhibition is dependent on β-catenin translocation, whereas reactive oxygen species (ROS) generation is a downstream signal for activation of LPA3. Furthermore, the hematopoietic transcriptional factors GATA-1 and FLI-1, appear to be involved in these regulatory mechanisms. Taken together, our results suggested that LPA2 and LPA3 may function as a molecular switch and play opposing roles during megakaryopoiesis of K562 cells.

Asymmetrical macromolecular complex formation of lysophosphatidic acid receptor 2 (LPA2) mediates gradient sensing in fibroblasts

Chemotactic migration of fibroblasts toward growth factors relies on their capacity to sense minute extracellular gradients and respond to spatially confined receptor-mediated signals. Currently, mechanisms underlying the gradient sensing of fibroblasts remain poorly understood. Using single-particle tracking methodology, we determined that a lysophosphatidic acid (LPA) gradient induces a spatiotemporally restricted decrease in the mobility of LPA receptor 2 (LPA2) on chemotactic fibroblasts. The onset of decreased LPA2 mobility correlates to the spatial recruitment and coupling to LPA2-interacting proteins that anchor the complex to the cytoskeleton. These localized PDZ motif-mediated macromolecular complexes of LPA2 trigger a Ca(2+) puff gradient that governs gradient sensing and directional migration in response to LPA. Disruption of the PDZ motif-mediated assembly of the macromolecular complex of LPA2 disorganizes the gradient of Ca(2+) puffs, disrupts gradient sensing, and reduces the directional migration of fibroblasts toward LPA. Our findings illustrate that the asymmetric macromolecular complex formation of chemoattractant receptors mediates gradient sensing and provides a new mechanistic basis for models to describe gradient sensing of fibroblasts.

Doxycycline inducible Krüppel-like factor 4 lentiviral vector mediates mesenchymal to epithelial transition in ovarian cancer cells

Ovarian cancer presents therapeutic challenges due to its typically late detection, aggressive metastasis, and therapeutic resistance. The transcription factor Krüppel-like factor 4 (KLF4) has been implicated in human cancers as a tumor suppressor or oncogene, although its role depends greatly on the cellular context. The role of KLF4 in ovarian cancer has not been elucidated in mechanistic detail. In this study, we investigated the role of KLF4 in ovarian cancer cells by transducing the ovarian cancer cell lines SKOV3 and OVCAR3 with a doxycycline-inducible KLF4 lentiviral vector. Overexpression of KLF4 reduced cell proliferation, migration, and invasion. The epithelial cell marker gene E-cadherin was significantly upregulated, whereas the mesenchymal cell marker genes vimentin, twist1and snail2 (slug) were downregulated in both KLF4-expressing SKOV3 and OVCAR3 cells. KLF4 inhibited the transforming growth factor β (TGFβ)-induced epithelial to mesenchymal transition (EMT) in ovarian cancer cells. Taken together, our data demonstrate that KLF4 functions as a tumor suppressor gene in ovarian cancer cells by inhibiting TGFβ-induced EMT.

Structural determinants of the transient receptor potential 1 (TRPV1) channel activation by phospholipid analogs

The transient receptor potential vanilloid 1 (TRPV1) ion channel is a polymodal protein that responds to various stimuli, including capsaicin (the pungent compound found in chili peppers), extracellular acid, and basic intracellular pH, temperatures close to 42 °C, and several lipids. Lysophosphatidic acid (LPA), an endogenous lipid widely associated with neuropathic pain, is an agonist of the TRPV1 channel found in primary afferent nociceptors and is activated by other noxious stimuli. Agonists or antagonists of lipid and other chemical natures are known to possess specific structural requirements for producing functional effects on their targets. To better understand how LPA and other lipid analogs might interact and affect the function of TRPV1, we set out to determine the structural features of these lipids that result in the activation of TRPV1. By changing the acyl chain length, saturation, and headgroup of these LPA analogs, we established strict requirements for activation of TRPV1. Among the natural LPA analogs, we found that only LPA 18:1, alkylglycerophosphate 18:1, and cyclic phosphatidic acid 18:1, all with a monounsaturated C18 hydrocarbon chain activate TRPV1, whereas polyunsaturated and saturated analogs do not. Thus, TRPV1 shows a more restricted ligand specificity compared with LPA G-protein-coupled receptors. We synthesized fatty alcohol phosphates and thiophosphates and found that many of them with a single double bond in position Δ9, 10, or 11 and Δ9 cyclopropyl group can activate TRPV1 with efficacy similar to capsaicin. Finally, we developed a pharmacophore and proposed a mechanistic model for how these lipids could induce a conformational change that activates TRPV1.

Lysophosphatidic acid receptor 5 inhibits B cell antigen receptor signaling and antibody response

Lysophospholipids have emerged as biologically important chemoattractants capable of directing lymphocyte development, trafficking, and localization. Lysophosphatidic acid (LPA) is a major lysophospholipid found systemically, and its levels are elevated in certain pathological settings, such as cancer and infections. In this study, we demonstrate that BCR signal transduction by mature murine B cells is inhibited upon LPA engagement of the LPA5 (GPR92) receptor via a Gα12/13-Arhgef1 pathway. The inhibition of BCR signaling by LPA5 manifests by impaired intracellular calcium store release and most likely by interfering with inositol 1,4,5-triphosphate receptor activity. We further show that LPA5 also limits Ag-specific induction of CD69 and CD86 expression and that LPA5-deficient B cells display enhanced Ab responses. Thus, these data show that LPA5 negatively regulates BCR signaling, B cell activation, and immune response. Our findings extend the influence of lysophospholipids on immune function and suggest that alterations in LPA levels likely influence adaptive humoral immunity.

Targeting the hydrophobic pocket of autotaxin with virtual screening of inhibitors identifies a common aromatic sulfonamide structural motif

Modulation of autotaxin (ATX), the lysophospholipase D enzyme that produces lysophosphatidic acid, with small-molecule inhibitors is a promising strategy for blocking the ATX-lysophosphatidic acid signaling axis. Although discovery campaigns have been successful in identifying ATX inhibitors, many of the reported inhibitors target the catalytic cleft of ATX. A recent study provided evidence for an additional inhibitory surface in the hydrophobic binding pocket of ATX, confirming prior studies that relied on enzyme kinetics and differential inhibition of substrates varying in size. Multiple hits from previous high-throughput screening for ATX inhibitors were obtained with aromatic sulfonamide derivatives interacting with the hydrophobic pocket. Here, we describe the development of a ligand-based strategy and its application in virtual screening, which yielded novel high-potency inhibitors that target the hydrophobic pocket of ATX. Characterization of the structure-activity relationship of these new inhibitors forms the foundation of a new pharmacophore model of the hydrophobic pocket of ATX.

Lysophosphatidic acid induces vasodilation mediated by LPA1 receptors, phospholipase C, and endothelial nitric oxide synthase

Lysophosphatidic acid (LPA) has been implicated as a mediator of several cardiovascular functions, but its potential involvement in the control of vascular tone is obscure. Here, we show that both LPA (18:1) and VPC31143 (a synthetic agonist of LPA1-3 receptors) relax intact mouse thoracic aorta with similar Emax values (53.9 and 51.9% of phenylephrine-induced precontraction), although the EC50 of LPA- and VPC31143-induced vasorelaxations were different (400 vs. 15 nM, respectively). Mechanical removal of the endothelium or genetic deletion of endothelial nitric oxide synthase (eNOS) not only diminished vasorelaxation by LPA or VPC31143 but converted it to vasoconstriction. Freshly isolated mouse aortic endothelial cells expressed LPA1, LPA2, LPA4 and LPA5 transcripts. The LPA1,3 antagonist Ki16425, the LPA1 antagonist AM095, and the genetic deletion of LPA1, but not that of LPA2, abolished LPA-induced vasorelaxation. Inhibition of the phosphoinositide 3 kinase-protein kinase B/Akt pathway by wortmannin or MK-2206 failed to influence the effect of LPA. However, pharmacological inhibition of phospholipase C (PLC) by U73122 or edelfosine, but not genetic deletion of PLCε, abolished LPA-induced vasorelaxation and indicated that a PLC enzyme, other than PLCε, mediates the response. In summary, the present study identifies LPA as an endothelium-dependent vasodilator substance acting via LPA1, PLC, and eNOS.

Hits of a high-throughput screen identify the hydrophobic pocket of autotaxin/lysophospholipase D as an inhibitory surface

Autotaxin (ATX), a lysophospholipase D, plays an important role in cancer invasion, metastasis, tumor progression, tumorigenesis, neuropathic pain, fibrotic diseases, cholestatic pruritus, lymphocyte homing, and thrombotic diseases by producing the lipid mediator lysophosphatidic acid (LPA). A high-throughput screen of ATX inhibition using the lysophosphatidylcholine-like substrate fluorogenic substrate 3 (FS-3) and ∼10,000 compounds from the University of Cincinnati Drug Discovery Center identified several small-molecule inhibitors with IC₅₀ vales ranging from nanomolar to low micromolar. The pharmacology of the three most potent compounds: 918013 (1; 2,4-dichloro-N-(3-fluorophenyl)-5-(4-morpholinylsulfonyl) benzamide), 931126 (2; 4-oxo-4-{2-[(5-phenoxy-1H-indol-2-yl)carbonyl]hydrazino}-N-(4-phenylbutan-2-yl)butanamide), and 966791 (3; N-(2,6-dimethylphenyl)-2-[N-(2-furylmethyl)(4-(1,2,3,4-tetraazolyl)phenyl)carbonylamino]-2-(4-hydroxy-3-methoxyphenyl) acetamide), were further characterized in enzyme, cellular, and whole animal models. Compounds 1 and 2 were competitive inhibitors of ATX-mediated hydrolysis of the lysophospholipase substrate FS-3. In contrast, compound 3 was a competitive inhibitor of both FS-3 and the phosphodiesterase substrate p-nitrophenyl thymidine 5'-monophosphate. Computational docking and mutagenesis suggested that compounds 1 and 2 target the hydrophobic pocket, thereby blocking access to the active site of ATX. The potencies of compounds 1-3 were comparable to each other in each of the assays. All of these compounds significantly reduced invasion of A2058 human melanoma cells in vitro and the colonization of lung metastases by B16-F10 murine melanoma cells in C57BL/6 mice. The compounds had no agonist or antagonist effects on select LPA or sphingosine 1-phosphate receptors, nor did they inhibit nucleotide pyrophosphatase/phosphodiesterase (NPP) enzymes NPP6 and NPP7. These results identify the molecular surface of the hydrophobic pocket of ATX as a target-binding site for inhibitors of enzymatic activity.

Abstract 5680: Identification and characterization of a novel class of ATX inhibitors

The lysophospholipase D (autotaxin, ATX) plays an important role in cancer invasion and metastasis. A High-throughput screen of over 10,000 compounds from the University of Cincinnati Drug Discovery Center, identified several small-molecule inhibitors with IC50 values ranging from nanomolar to low micromolar. The pharmacology of the two most potent compounds, 966791(1) and 918103(2), were further characterized in enzyme, cellular, and whole animal systems. Both of these compounds, significantly reduced cell invasion in melanoma cancer cell lines without any apparent cytotoxicity. Compound (1) was shown to be a competitive inhibitor of ATX for both FS-3 and Pnp-TMP substrates, while compound (2) was competitive only for FS-3. This suggest that compound (2) targets the hydrophobic pocket not the active site of ATX, which was supported by docking of compounds 1 and 2, along with mutagenesis data. The potency of the compounds was comparable to each other in each of the assays. Current ATX inhibitors reported in literature target the active site in the catalytic domain. In our search for ATX inhibitors we identified compounds able to inhibit both the active site and hydrophobic pocket. We conclude that these data suggest compounds solely inhibiting the hydrophobic pocket are sufficient to disrupt the ATX-LPA signaling axis can serve as specific small-molecule modulators for mechanistic studies of ATX as well as a potential leads for the development of anti-cancer drugs.

Citation Format: James Fells, Sue Chin Lee, Derek Norman, Yuko Fujiwara, Ryoko Tsukahara, Jianxiong Liu, Jason Kirby, Sandra Nelson, Gabor Tigyi. Identification and characterization of a novel class of ATX inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5680. doi:10.1158/1538-7445.AM2013-5680

Abstract 3884: Targeting ATX and LPA receptors melanoma invasion and metastasis

ATX, a lysophospholipase D that generates LPA, is highly up-regulated in metastatic and chemotherapy-resistant carcinomas. Many cancers secrete ATX, and it contributes to their invasive properties. LPA produced by ATX activates LPA1-8 G protein-coupled receptors on the cell surface. Many cancers over-express multiple subtypes of LPAR and the overexpression of LPAR leads to malignant transformation, metastasis, and resistance to therapy. Therefore, ATX-LPA signaling axis is an emerging target for cancer therapy. We have previously shown that knockdown of ATX expression in B16F10 melanoma cells decreased tumor invasion in vitro and metastasis in vivo. In this study, we sought to understand the roles of the LPA GPCRs both in the tumor cells and tissues targeted by metastatic cancer cells. Using the in vivo B16 melanoma metastasis model syngeneic to the C57BL/6 mouse strain, we found that the incidence of lung metastasis was greatly reduced in the LPA5KO mice compared to WT, LPA1KO, and LPA2KO mice, respectively. In addition, we found that the selective inhibitor of LPA1&3, Ki16425 also reduced lung metastasis, suggesting that inhibition of LPA5 and LPA1 receptors in the target tissues may prevent cancer metastasis. B16 melanoma cells predominantly express LPA5 receptor. These cells do not invade across a matrigel layer in response to LPA. We found that siRNA knockdown of LPA5 receptors in B16 melanoma cells relieves this inhibition and resulted in an increase in invasion. These results suggest that the LPAR, in particular LPA5 receptors in tumor and stromal cells may play different roles in invasion and metastasis.

Citation Format: Gabor Tigyi, Yuko Fujiwara, SueChin Lee, Jianxiong Liu, Renukadevi Patil, Renuka Gupte, Duane D. Miller, Tamas Oravecz, Louisa Balazs. Targeting ATX and LPA receptors melanoma invasion and metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3884. doi:10.1158/1538-7445.AM2013-3884

Regulation of interleukin-6 secretion by the two-pore-domain potassium channel Trek-1 in alveolar epithelial cells

We recently proposed a role for the two-pore-domain K(+) (K2P) channel Trek-1 in the regulation of cytokine release from mouse alveolar epithelial cells (AECs) by demonstrating decreased interleukin-6 (IL-6) secretion from Trek-1-deficient cells, but the underlying mechanisms remained unknown. This study was designed to investigate the mechanisms by which Trek-1 decreases IL-6 secretion. We hypothesized that Trek-1 regulates tumor necrosis factor-α (TNF-α)-induced IL-6 release via NF-κB-, p38-, and PKC-dependent pathways. We found that Trek-1 deficiency decreased IL-6 secretion from mouse and human AECs at both transcriptional and translational levels. While NF-κB/p65 phosphorylation was unchanged, p38 phosphorylation was decreased in Trek-1-deficient cells, and pharmacological inhibition of p38 decreased IL-6 secretion in control but not Trek-1-deficient cells. Similarly, pharmacological inhibition of PKC also decreased IL-6 release, and we found decreased phosphorylation of the isoforms PKC/PKDμ (Ser(744/748)), PKCθ, PKCδ, PKCα/βII, and PKCζ/λ, but not PKC/PKDμ (Ser(916)) in Trek-1-deficient AECs. Phosphorylation of PKCθ, a Ca(2+)-independent isoform, was intact in control cells but impaired in Trek-1-deficient cells. Furthermore, TNF-α did not elevate the intracellular Ca(2+) concentration in control or Trek-1-deficient cells, and removal of extracellular Ca(2+) did not impair IL-6 release. In summary, we report the expression of Trek-1 in human AECs and propose that Trek-1 deficiency may alter both IL-6 translation and transcription in AECs without affecting Ca(2+) signaling. The results of this study identify Trek-1 as a new potential target for the development of novel treatment strategies against acute lung injury.

Virtual screening for LPA2-specific agonists identifies a nonlipid compound with antiapoptotic actions

Lysophosphatidic acid (LPA) is a highly potent endogenous lipid mediator that protects and rescues cells from programmed cell death. Earlier work identified the LPA₂ G protein-coupled receptor subtype as an important molecular target of LPA mediating antiapoptotic signaling. Here we describe the results of a virtual screen using single-reference similarity searching that yielded compounds 2-((9-oxo-9H-fluoren-2-yl)carbamoyl)benzoic acid (NSC12404), 2-((3-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)propyl)thio)benzoic acid (GRI977143), 4,5-dichloro-2-((9-oxo-9H-fluoren-2-yl)carbamoyl)benzoic acid (H2L5547924), and 2-((9,10-dioxo-9,10-dihydroanthracen-2-yl)carbamoyl) benzoic acid (H2L5828102), novel nonlipid and drug-like compounds that are specific for the LPA₂ receptor subtype. We characterized the antiapoptotic action of one of these compounds, GRI977143, which was effective in reducing activation of caspases 3, 7, 8, and 9 and inhibited poly(ADP-ribose)polymerase 1 cleavage and DNA fragmentation in different extrinsic and intrinsic models of apoptosis in vitro. Furthermore, GRI977143 promoted carcinoma cell invasion of human umbilical vein endothelial cell monolayers and fibroblast proliferation. The antiapoptotic cellular signaling responses were present selectively in mouse embryonic fibroblast cells derived from LPA(1&2) double-knockout mice reconstituted with the LPA₂ receptor and were absent in vector-transduced control cells. GRI977143 was an effective stimulator of extracellular signal-regulated kinase 1/2 activation and promoted the assembly of a macromolecular signaling complex consisting of LPA₂, Na⁺ - H⁺ exchange regulatory factor 2, and thyroid receptor interacting protein 6, which has been shown previously to be a required step in LPA-induced antiapoptotic signaling. The present findings indicate that nonlipid LPA₂-specific agonists represent an excellent starting point for development of lead compounds with potential therapeutic utility for preventing the programmed cell death involved in many types of degenerative and inflammatory diseases.

A new potential target for enhancing the anti-tumor T cell response: Lysophosphatidic acid signaling inhibits CD8+ T cell activation (127.29)

Lysophosphatidic acid (LPA) is a lysophospholipid that is present at low nanomolar concentrations in the plasma of healthy individuals. It has been well documented that many cancers aberrantly produce LPA and the increased level of LPA has been shown to be beneficial to the tumor, promoting tumorigenesis, invasion, metastases, and vascularization. However the effects of elevated levels of LPA on the adaptive immune response to the tumor have not been addressed. The immune system, and T cells in particular, are important for their ability to recognize and eliminate nascent tumors in cancer immunosurveillance and tumor rejection. However multiple inhibitory mechanisms within the tumor microenvironment have been described that protect the tumor from T cells. Work in our laboratory has found that LPA inhibits CD8+ T cell activation in vitro and in vivo. Specifically, we have demonstrated that CD8+ T cells express an LPA receptor that, in the presence of LPA, is able to inhibit T cell receptor (TCR) signaling and subsequent cell activation, proliferation and function. These data document that LPA is able to negatively regulate T cell activation and function. We have preliminary data that increased LPA production by tumors functions to protect the tumor from CD8+ T cell-mediated eradication. If true, these findings would represent the first report of lysophospholipid-mediated protection of tumor from adaptive immunity and highlight a potential target for cancer treatment.

DiGeorge syndrome critical region 8 (DGCR8) protein-mediated microRNA biogenesis is essential for vascular smooth muscle cell development in mice

DiGeorge Critical Region 8 (DGCR8) is a double-stranded RNA-binding protein that interacts with Drosha and facilitates microRNA (miRNA) maturation. However, the role of DGCR8 in vascular smooth muscle cells (VSMCs) is not well understood. To investigate whether DGCR8 contributes to miRNA maturation in VSMCs, we generated DGCR8 conditional knockout (cKO) mice by crossing VSMC-specific Cre mice (SM22-Cre) with DGCR8(loxp/loxp) mice. We found that loss of DGCR8 in VSMCs resulted in extensive liver hemorrhage and embryonic mortality between embryonic days (E) 12.5 and E13.5. DGCR8 cKO embryos displayed dilated blood vessels and disarrayed vascular architecture. Blood vessels were absent in the yolk sac of DGCR8 KOs after E12.5. Disruption of DGCR8 in VSMCs reduced VSMC proliferation and promoted apoptosis in vitro and in vivo. In DGCR8 cKO embryos and knockout VSMCs, differentiation marker genes, including αSMA, SM22, and CNN1, were significantly down-regulated, and the survival pathways of ERK1/2 mitogen-activated protein kinase and the phosphatidylinositol 3-kinase/AKT were attenuated. Knockout of DGCR8 in VSMCs has led to down-regulation of the miR-17/92 and miR-143/145 clusters. We further demonstrated that the miR-17/92 cluster promotes VSMC proliferation and enhances VSMC marker gene expression, which may contribute to the defects of DGCR8 cKO mutants. Our results indicate that the DGCR8 gene is required for vascular development through the regulation of VSMC proliferation, apoptosis, and differentiation.

High-throughput assays to measure intracellular Ca²⁺ mobilization in cells that express recombinant S1P receptor subtypes

Intracellular Ca(2+) mobilization is a useful readout to screen for agonists or antagonists of G-protein -coupled receptors (GPCRs). Here, we describe methods to conduct high-throughput screening of stably or transiently transfected HTC4 cells expressing the individual S1P1-5 receptor subtypes. The cells are grown in 96-well plates and loaded with the cell permeable fluorescent Ca(2+) indicator dye Fura-2-AM. Changes in intracellular Ca(2+) levels in response to S1P or test compounds are detected using a FlexStation II scanning fluorometer with integrated fluidics transfer capabilities.

FTY720 (Gilenya) phosphate selectivity of sphingosine 1-phosphate receptor subtype 1 (S1P1) G protein-coupled receptor requires motifs in intracellular loop 1 and transmembrane domain 2

FTY720 phosphate (FTY720P) is a high potency agonist for all the endothelial differentiation gene family sphingosine 1-phosphate (S1P) receptors except S1P receptor subtype 2 (S1P(2)). To map the distinguishing features of S1P(2) ligand recognition, we applied a computational modeling-guided mutagenesis strategy that was based on the high degree of sequence homology between S1P(1) and S1P(2). S1P(2) point mutants of the ligand-binding pocket were characterized. The head group-interacting residues Arg3.28, Glu3.29, and Lys7.34 were essential for activation. Mutation of residues Ala3.32, Leu3.36, Val5.41, Phe6.44, Trp6.48, Ser7.42, and Ser7.46, predicted to interact with the S1P hydrophobic tail, impaired activation by S1P. Replacing individual or multiple residues in the ligand-binding pocket of S1P(2) with S1P(1) sequence did not impart activation by FTY720P. Chimeric S1P(1)/S1P(2) receptors were generated and characterized for activation by S1P or FTY720P. The S1P(2) chimera with S1P(1) sequence from the N terminus to transmembrane domain 2 (TM2) was activated by FTY720P, and the S1P(2)(IC1-TM2)(S1P1) domain insertion chimera showed S1P(1)-like activation. Twelve residues in this domain, distributed in four motifs a-d, differ between S1P(1) and S1P(2). Insertion of (78)RPMYY in motif b alone or simultaneous swapping of five other residues in motifs c and d from S1P(1) into S1P(2) introduced FTY720P responsiveness. Molecular dynamics calculations indicate that FTY720P binding selectivity is a function of the entropic contribution to the binding free energy rather than enthalpic contributions and that preferred agonists retain substantial flexibility when bound. After exposure to FTY720P, the S1P(2)(IC1-TM2)(S1P1) receptor recycled to the plasma membrane, indicating that additional structural elements are required for the selective degradative trafficking of S1P(1).

Benzyl and naphthalene methylphosphonic acid inhibitors of autotaxin with anti-invasive and anti-metastatic activity

Autotaxin (ATX, NPP2) is a member of the nucleotide pyrophosphate phosphodiesterase enzyme family. ATX catalyzes the hydrolytic cleavage of lysophosphatidylcholine (LPC) by lysophospholipase D activity, which leads to generation of the growth-factor-like lipid mediator lysophosphatidic acid (LPA). ATX is highly upregulated in metastatic and chemotherapy-resistant carcinomas and represents a potential target to mediate cancer invasion and metastasis. Herein we report the synthesis and pharmacological characterization of ATX inhibitors based on the 4-tetradecanoylaminobenzylphosphonic acid scaffold, which was previously found to lack sufficient stability in cellular systems. The new 4-substituted benzylphosphonic acid and 6-substituted naphthalen-2-ylmethylphosphonic acid analogues block ATX activity with K(i) values in the low micromolar to nanomolar range against FS3, LPC, and nucleotide substrates through a mixed-mode inhibition mechanism. None of the compounds tested inhibit the activity of related enzymes (NPP6 and NPP7). In addition, the compounds were evaluated as agonists or antagonists of seven LPA receptor (LPAR) subtypes. Analogues 22 and 30 b, the two most potent ATX inhibitors, inhibit the invasion of MM1 hepatoma cells across murine mesothelial and human vascular endothelial monolayers in vitro in a dose-dependent manner. The average terminal half-life for compound 22 is 10±5.4 h and it causes a long-lasting decrease in plasma LPA levels. Compounds 22 and 30 b significantly decrease lung metastasis of B16-F10 syngeneic mouse melanoma in a post-inoculation treatment paradigm. The 4-substituted benzylphosphonic acids and 6-substituted naphthalen-2-ylmethylphosphonic acids described herein represent new lead compounds that effectively inhibit the ATX-LPA-LPAR axis both in vitro and in vivo.

The phospholipase A1 activity of lysophospholipase A-I links platelet activation to LPA production during blood coagulation

Platelet activation initiates an upsurge in polyunsaturated (18:2 and 20:4) lysophosphatidic acid (LPA) production. The biochemical pathway(s) responsible for LPA production during blood clotting are not yet fully understood. Here we describe the purification of a phospholipase A(1) (PLA(1)) from thrombin-activated human platelets using sequential chromatographic steps followed by fluorophosphonate (FP)-biotin affinity labeling and proteomics characterization that identified acyl-protein thioesterase 1 (APT1), also known as lysophospholipase A-I (LYPLA-I; accession code O75608) as a novel PLA(1). Addition of this recombinant PLA(1) significantly increased the production of sn-2-esterified polyunsaturated LPCs and the corresponding LPAs in plasma. We examined the regioisomeric preference of lysophospholipase D/autotaxin (ATX), which is the subsequent step in LPA production. To prevent acyl migration, ether-linked regioisomers of oleyl-sn-glycero-3-phosphocholine (lyso-PAF) were synthesized. ATX preferred the sn-1 to the sn-2 regioisomer of lyso-PAF. We propose the following LPA production pathway in blood: 1) Activated platelets release PLA(1); 2) PLA(1) generates a pool of sn-2 lysophospholipids; 3) These newly generated sn-2 lysophospholipids undergo acyl migration to yield sn-1 lysophospholipids, which are the preferred substrates of ATX; and 4) ATX cleaves the sn-1 lysophospholipids to generate sn-1 LPA species containing predominantly 18:2 and 20:4 fatty acids.

Location, location, location: a crystal-clear view of autotaxin saturating LPA receptors

The interaction of autotaxin with its substrates leads to the production of lysophosphatidic acids (LPA), bioactive lipids with an emerging prominent role in inflammation and cancer. Two papers in this issue tell the previously unknown story of autotaxin, from substrate discrimination to highly efficient local delivery of LPA to target receptors.

Synthesis and pharmacological evaluation of the stereoisomers of 3-carba cyclic-phosphatidic acid

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of lysophosphatidic acid (LPA) in which the sn-2 hydroxy group forms a five-membered ring with the sn-3 phosphate. Here, we describe the synthesis of R-3-CCPA and S-3-CCPA along with their pharmacological properties as inhibitors of lysophospholipase D/autotaxin, agonists of the LPA(5) GPCR, and blockers of lung metastasis of B16-F10 melanoma cells in a C57BL/6 mouse model. S-3CCPA was significantly more efficacious in the activation of LPA(5) compared to the R-stereoisomer. In contrast, no stereoselective differences were found between the two isomers toward the inhibition of autotaxin or lung metastasis of B16-F10 melanoma cells in vivo. These results extend the potential utility of these compounds as potential lead compounds warranting evaluation as cancer therapeutics.

FTY720 and (S)-FTY720 vinylphosphonate inhibit sphingosine kinase 1 and promote its proteasomal degradation in human pulmonary artery smooth muscle, breast cancer and androgen-independent prostate cancer cells

Sphingosine kinase 1 (SK1) is an enzyme that catalyses the phosphorylation of sphingosine to produce the bioactive lipid sphingosine 1-phosphate (S1P). We demonstrate here that FTY720 (Fingolimod) and (S)-FTY720 vinylphosphonate are novel inhibitors of SK1 catalytic activity and induce the proteasomal degradation of this enzyme in human pulmonary artery smooth muscle cells, MCF-7 breast cancer cells and androgen-independent LNCaP-AI prostate cancer cells. Proteasomal degradation of SK1 in response to FTY720 and (S)-FTY720 vinylphosphonate is associated with the down-regulation of the androgen receptor in LNCaP-AI cells. (S)-FTY720 vinylphosphonate also induces the apoptosis of these cells. These findings indicate that SK1 is involved in protecting LNCaP-AI from apoptosis. This protection might be mediated by so-called 'inside-out' signalling by S1P, as LNCaP-AI cells exhibit increased expression of S1P(2/3) receptors and reduced lipid phosphate phosphatase expression (compared with androgen-sensitive LNCaP cells) thereby potentially increasing the bioavailability of S1P at S1P(2/3) receptors.

Sphingosine 1-phosphate receptor 4 uses HER2 (ERBB2) to regulate extracellular signal regulated kinase-1/2 in MDA-MB-453 breast cancer cells

We demonstrate here that the bioactive lipid sphingosine 1-phosphate (S1P) uses sphingosine 1-phosphate receptor 4 (S1P(4)) and human epidermal growth factor receptor 2 (HER2) to stimulate the extracellular signal regulated protein kinase 1/2 (ERK-1/2) pathway in MDA-MB-453 cells. This was based on several lines of evidence. First, the S1P stimulation of ERK-1/2 was abolished by JTE013, which we show here is an S1P(2/4) antagonist and reduced by siRNA knockdown of S1P(4). Second, the S1P-stimulated activation of ERK-1/2 was almost completely abolished by a HER2 inhibitor (ErbB2 inhibitor II) and reduced by siRNA knockdown of HER2 expression. Third, phyto-S1P, which is an S1P(4) agonist, stimulated ERK-1/2 activation in an S1P(4)- and HER2-dependent manner. Fourth, FTY720 phosphate, which is an agonist at S1P(1,3,4,5) but not S1P(2) stimulated activation of ERK-1/2. Fifth, S1P stimulated the tyrosine phosphorylation of HER2, which was reduced by JTE013. HER2 which is an orphan receptor tyrosine kinase is the preferred dimerization partner of the EGF receptor. However, EGF-stimulated activation of ERK-1/2 was not affected by siRNA knockdown of HER2 or by ErbB2 (epidermal growth factor receptor 2 (or HER2)) inhibitor II in MDA-MB-453 cells. Moreover, S1P-stimulated activation of ERK-1/2 does not require an EGF receptor. Thus, S1P and EGF function in a mutually exclusive manner. In conclusion, the magnitude of the signaling gain on the ERK-1/2 pathway produced in response to S1P can be increased by HER2 in MDA-MB-453 cells. The linkage of S1P with an oncogene suggests that S1P and specifically S1P(4) may have an important role in breast cancer progression.

Phospholipase D2-dependent inhibition of the nuclear hormone receptor PPARgamma by cyclic phosphatidic acid

Cyclic phosphatidic acid (1-acyl-2,3-cyclic-glycerophosphate, CPA), one of nature's simplest phospholipids, is found in cells from slime mold to humans and has a largely unknown function. We find here that CPA is generated in mammalian cells in a stimulus-coupled manner by phospholipase D2 (PLD2) and binds to and inhibits the nuclear hormone receptor PPARgamma with nanomolar affinity and high specificity through stabilizing its interaction with the corepressor SMRT. CPA production inhibits the PPARgamma target-gene transcription that normally drives adipocytic differentiation of 3T3-L1 cells, lipid accumulation in RAW264.7 cells and primary mouse macrophages, and arterial wall remodeling in a rat model in vivo. Inhibition of PLD2 by shRNA, a dominant-negative mutant, or a small molecule inhibitor blocks CPA production and relieves PPARgamma inhibition. We conclude that CPA is a second messenger and a physiological inhibitor of PPARgamma, revealing that PPARgamma is regulated by endogenous agonists as well as by antagonists.

Aiming drug discovery at lysophosphatidic acid targets

Lysophosphatidic acid (LPA, 1-radyl-2-hydroxy-sn-glycero-3-phosphate) is the prototype member of a family of lipid mediators and second messengers. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and a nuclear hormone receptor within the cell. In addition, there are several enzymes that utilize LPA as a substrate or generate it as a product and are under its regulatory control. LPA is present in biological fluids, and attempts have been made to link changes in its concentration and molecular composition to specific disease conditions. Through their many targets, members of the LPA family regulate cell survival, apoptosis, motility, shape, differentiation, gene transcription, malignant transformation and more. The present review depicts arbitrary aspects of the physiological and pathophysiological actions of LPA and attempts to link them with select targets. Many of us are now convinced that therapies targeting LPA biosynthesis and signalling are feasible for the treatment of devastating human diseases such as cancer, fibrosis and degenerative conditions. However, successful targeting of the pathways associated with this pleiotropic lipid will depend on the future development of as yet undeveloped pharmacons.

(S)-FTY720-vinylphosphonate, an analogue of the immunosuppressive agent FTY720, is a pan-antagonist of sphingosine 1-phosphate GPCR signaling and inhibits autotaxin activity

FTY720 (Fingolimod), a synthetic analogue of sphingosine 1-phosphate (S1P), activates four of the five EDG-family S1P receptors and is in a phase-III clinical study for the treatment of multiple sclerosis. (S)-FTY720-phosphate (FTY720-P) causes S1P(1) receptor internalization and targeting to the proteasomal degradative pathway, and thus functions as an antagonist of S1P(1) by depleting the functional S1P(1) receptor from the plasma membrane. Here we describe the pharmacological characterization of two unsaturated phosphonate enantiomers of FTY720, (R)- and (S)-FTY720-vinylphosphonate. (R)-FTY720-vinylphosphonate was a full agonist of S1P(1) (EC(50) 20+/-3 nM). In contrast, the (S) enantiomer failed to activate any of the five S1P GPCRs and was a full antagonist of S1P(1,3,4) (K(i) 384 nM, 39 nM, and 1190 nM, respectively) and a partial antagonist of S1P(2), and S1P(5). Both enantiomers dose-dependently inhibited lysophospholipase D (recombinant autotaxin) with K(i) values in the low micromolar range, although with different enzyme kinetic mechanisms. When injected into mice, both enantiomers caused transient peripheral lymphopenia. (R)- and (S)-FTY720-vinylphosphonates activated ERK1/2, AKT, and exerted an antiapoptotic effect in camptothecin-treated IEC-6 intestinal epithelial cells, which primarily express S1P(2) transcripts and traces of S1P(5). (S)-FTY720-vinylphosphonate is the first pan-antagonist of S1P receptors and offers utility in probing S1P responses in vitro and in vivo. The biological effects of the (R)- and (S)-FTY720-vinylphosphonate analogues underscore the complexity of FTY720 cellular targets.