Effect of Estrogen Receptor Alpha on Cardiopulmonary Adaptation to Chronic Developmental Hypoxia in a Rat Model

Humans living at high-altitude (HA) have adapted to this environment by increasing pulmonary vascular and alveolar growth. RNA sequencing data from a novel murine model that mimics this phenotypical response to HA suggested estrogen signaling via estrogen receptor alpha (ERα) may be involved in this adaptation. We hypothesized ERα was a key mediator in the cardiopulmonary adaption to chronic hypoxia and sought to delineate the mechanistic role ERα contributes to this process by exposing novel loss-of-function ERα mutant (ERαMut) rats to simulated HA. ERα mutant or wild type (wt) rats were exposed to normoxia or hypoxia starting at conception and continued postnatally until 6 weeks of age. Both wt and ERαMut animals born and raised in hypoxia exhibited lower body mass and higher hematocrits, total alveolar volumes (Va), diffusion capacities of carbon monoxide (DLCO), pulmonary arteriole (PA) wall thickness, and Fulton indices than normoxia animals. Right ventricle adaptation was maintained in the setting of hypoxia. While no major physiologic differences were seen between wt and ERαMut animals at either exposure, ERαMut animals exhibited smaller mean linear intercepts (MLI) and increased PA total and lumen areas. Hypoxia exposure or ERα loss-of-function did not affect lung mRNA abundance of vascular endothelial growth factor, angiopoietin 2 or apelin. Sexual dimorphisms were noted in PA wall thickness and lumen area in ERαMut rats. In summary, in room air-exposed rats and rats with peri- and postnatal hypoxia exposure, ERα loss-of-function was associated with decreased alveolar size (primarily driven by hypoxic animals) and increased PA remodeling.

17β-Estradiol and estrogen receptor α protect right ventricular function in pulmonary hypertension via BMPR2 and apelin

Women with pulmonary arterial hypertension (PAH) exhibit better right ventricular (RV) function and survival than men; however, the underlying mechanisms are unknown. We hypothesized that 17β-estradiol (E2), through estrogen receptor α (ER-α), attenuates PAH-induced RV failure (RVF) by upregulating the procontractile and prosurvival peptide apelin via a BMPR2-dependent mechanism. We found that ER-α and apelin expression were decreased in RV homogenates from patients with RVF and from rats with maladaptive (but not adaptive) RV remodeling. RV cardiomyocyte apelin abundance increased in vivo or in vitro after treatment with E2 or ER-α agonist. Studies employing ER-α-null or ER-β-null mice, ER-α loss-of-function mutant rats, or siRNA demonstrated that ER-α is necessary for E2 to upregulate RV apelin. E2 and ER-α increased BMPR2 in pulmonary hypertension RVs and in isolated RV cardiomyocytes, associated with ER-α binding to the Bmpr2 promoter. BMPR2 is required for E2-mediated increases in apelin abundance, and both BMPR2 and apelin are necessary for E2 to exert RV-protective effects. E2 or ER-α agonist rescued monocrotaline pulmonary hypertension and restored RV apelin and BMPR2. We identified what we believe to be a novel cardioprotective E2/ER-α/BMPR2/apelin axis in the RV. Harnessing this axis may lead to novel RV-targeted therapies for PAH patients of either sex.

Estrogen receptor-α prevents right ventricular diastolic dysfunction and fibrosis in female rats

Although women are more susceptible to pulmonary arterial hypertension (PAH) than men, their right ventricular (RV) function is better preserved. Estrogen receptor-α (ERα) has been identified as a likely mediator for estrogen protection in the RV. However, the role of ERα in preserving RV function and remodeling during pressure overload remains poorly understood. We hypothesized that loss of functional ERα removes female protection from adverse remodeling and is permissive for the development of a maladapted RV phenotype. Male and female rats with a loss-of-function mutation in ERα (ERαMut) and wild-type (WT) littermates underwent RV pressure overload by pulmonary artery banding (PAB). At 10 wk post-PAB, WT and ERαMut demonstrated RV hypertrophy. Analysis of RV pressure waveforms demonstrated RV-pulmonary vascular uncoupling and diastolic dysfunction in female, but not male, ERαMut PAB rats. Similarly, female, but not male, ERαMut exhibited increased RV fibrosis, comprised primarily of thick collagen fibers. There was an increased protein expression ratio of TIMP metallopeptidase inhibitor 1 (Timp1) to matrix metalloproteinase 9 (Mmp9) in female ERαMut compared with WT PAB rats, suggesting less collagen degradation. RNA-sequencing in female WT and ERαMut RV revealed kallikrein-related peptidase 10 (Klk10) and Jun Proto-Oncogene (Jun) as possible mediators of female RV protection during PAB. In summary, ERα in females is protective against RV-pulmonary vascular uncoupling, diastolic dysfunction, and fibrosis in response to pressure overload. ERα appears to be dispensable for RV adaptation in males. ERα may be a mediator of superior RV adaptation in female patients with PAH.NEW & NOTEWORTHY Using a novel loss-of-function mutation in estrogen receptor-α (ERα), we demonstrate that female, but not male, ERα mutant rats display right ventricular (RV)-vascular uncoupling, diastolic dysfunction, and fibrosis following pressure overload, indicating a sex-dependent role of ERα in protecting against adverse RV remodeling. TIMP metallopeptidase inhibitor 1 (Timp1), matrix metalloproteinase 9 (Mmp9), kallikrein-related peptidase 10 (Klk10), and Jun Proto-Oncogene (Jun) were identified as potential mediators in ERα-regulated pathways in RV pressure overload.

Investigational new drug enabling angiotensin oral-delivery studies to attenuate pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a deadly and uncurable disease characterized by remodeling of the pulmonary vasculature and increased pulmonary artery pressure. Angiotensin Converting Enzyme 2 (ACE2) and its product, angiotensin-(1-7) [ANG-(1-7)] were expressed in lettuce chloroplasts to facilitate affordable oral drug delivery. Lyophilized lettuce cells were stable up to 28 months at ambient temperature with proper folding, assembly of CTB-ACE2/ANG-(1-7) and functionality. When the antibiotic resistance gene was removed, Ang1-7 expression was stable in subsequent generations in marker-free transplastomic lines. Oral gavage of monocrotaline-induced PAH rats resulted in dose-dependent delivery of ANG-(1-7) and ACE2 in plasma/tissues and PAH development was attenuated with decreases in right ventricular (RV) hypertrophy, RV systolic pressure, total pulmonary resistance and pulmonary artery remodeling. Such attenuation correlated well with alterations in the transcription of Ang-(1-7) receptor MAS and angiotensin II receptor AGTRI as well as IL-1β and TGF-β1. Toxicology studies showed that both male and female rats tolerated ~10-fold ACE2/ANG-(1-7) higher than efficacy dose. Plant cell wall degrading enzymes enhanced plasma levels of orally delivered protein drug bioencapsulated within plant cells. Efficient attenuation of PAH with no toxicity augurs well for clinical advancement of the first oral protein therapy to prevent/treat underlying pathology for this disease.

Small Molecules Target the Interaction between Tissue Transglutaminase and Fibronectin

Tissue transglutaminase (TG2) is a multifunctional protein with enzymatic, GTP-ase, and scaffold properties. TG2 interacts with fibronectin (FN) through its N-terminus domain, stabilizing integrin complexes, which regulate cell adhesion to the matrix. Through this mechanism, TG2 participates in key steps involved in metastasis in ovarian and other cancers. High-throughput screening identified several small molecule inhibitors (SMI) for the TG2/FN complex. Rational medicinal chemistry optimization of the hit compound (TG53) led to second-generation analogues (MT1-6). ELISA demonstrated that these analogues blocked TG2/FN interaction, and bio-layer interferometry (BLI) showed that the SMIs bound to TG2. The compounds also potently inhibited cancer cell adhesion to FN and decreased outside-in signaling mediated through the focal adhesion kinase. Blockade of TG2/FN interaction by the small molecules caused membrane ruffling, delaying the formation of stable focal contacts and mature adhesions points and disrupted organization of the actin cytoskeleton. In an in vivo model measuring intraperitoneal dissemination, MT4 and MT6 inhibited the adhesion of ovarian cancer cells to the peritoneum. Pretreatment with MT4 also sensitized ovarian cancer cells to paclitaxel. The data support continued optimization of the new class of SMIs that block the TG2/FN complex at the interface between cancer cells and the tumor niche.

Hypoxia Upregulates Estrogen Receptor β in Pulmonary Artery Endothelial Cells in a HIF-1α-Dependent Manner

17β-Estradiol (E2) attenuates hypoxia-induced pulmonary hypertension (HPH) through estrogen receptor (ER)-dependent effects, including inhibition of hypoxia-induced endothelial cell proliferation; however, the mechanisms responsible for this remain unknown. We hypothesized that the protective effects of E2 in HPH are mediated through hypoxia-inducible factor 1α (HIF-1α)-dependent increases in ERβ expression. Sprague-Dawley rats and ERα or ERβ knockout mice were exposed to hypobaric hypoxia for 2-3 weeks. The effects of hypoxia were also studied in primary rat or human pulmonary artery endothelial cells (PAECs). Hypoxia increased expression of ERβ, but not ERα, in lungs from HPH rats as well as in rat and human PAECs. ERβ mRNA time dependently increased in PAECs exposed to hypoxia. Normoxic HIF-1α/HIF-2α stabilization increased PAEC ERβ, whereas HIF-1α knockdown decreased ERβ abundance in hypoxic PAECs. In turn, ERβ knockdown in hypoxic PAECs increased HIF-2α expression, suggesting a hypoxia-sensitive feedback mechanism. ERβ knockdown in hypoxic PAECs also decreased expression of the HIF inhibitor prolyl hydroxylase 2 (PHD2), whereas ERβ activation increased PHD2 and decreased both HIF-1α and HIF-2α, suggesting that ERβ regulates the PHD2/HIF-1α/HIF-2α axis during hypoxia. Whereas hypoxic wild-type or ERα knockout mice treated with E2 demonstrated less pulmonary vascular remodeling and decreased HIF-1α after hypoxia compared with untreated hypoxic mice, ERβ knockout mice exhibited increased HIF-2α and an attenuated response to E2 during hypoxia. Taken together, our results demonstrate a novel and potentially therapeutically targetable mechanism whereby hypoxia, via HIF-1α, increases ERβ expression and the E2-ERβ axis targets PHD2, HIF-1α, and HIF-2α to attenuate HPH development.

Abstract A66: The tissue transglutaminase 2–fibronectin protein complex: A new target in ovarian cancer

Here we describe a small-molecule inhibitor (SMI) that disrupts the tissue transglutaminase 2 (TG2)-fibronectin (FN) interaction. TG2 is a multifunctional protein, with enzymatic (transglutaminase, isopeptidase, protein disulfide isomerase), GTPase, and extracellular matrix (ECM) scaffold activities. TG2 directly interacts with FN through its N-terminus domain, playing an important role in stabilizing ternary TG2/FN/integrin complexes, which regulate cell adhesion to the matrix. Our group has previously shown that TG2 overexpressed in ovarian cancer (OC) promotes epithelial-to-mesenchymal transition (EMT) contributing to OC cell invasiveness and metastatic behavior. We showed that the interaction with FN is critical to these functions. Proximity ligation assay was used to measure TG2/integrin beta 1 interaction in OC tumors and identified TG2/integrin beta 1 complex in >50% of ovarian tumors, irrespective of histologic type. Based on those findings, we conducted the high-throughput screening and identified TG53 as the lead TG2/FN inhibitory compound. Structure-activity relationship-based approach was used to optimize the physicochemical properties of TG53, leading to design and chemical synthesis of 6 analogues (MT1-6). All analogues blocked TG2/FN interaction, as measured by an ELISA assay, and OC cell adhesion to FN, as measured by a solid phase assay, MT4 being the most potent inhibitor. MT4 downregulates integrin-initiated signaling in OC cells, leading to downstream inhibition of FAK and ERK. Immunofluorescence staining demonstrated that the actin cytoskeleton adopts a cortical localization pattern in MT4-treated cells. MT4 caused membrane ruffling delaying the formation of stable focal contacts and mature adhesions points. Pretreatment with MT4 sensitized OC cells to paclitaxel, as measured by colony-forming assay. In an intraperitoneal OC mouse model, MT4 caused decreased OC cell adhesion to the peritoneum, inhibiting peritoneal dissemination. Hence, MT4 is a potential candidate to be developed and used in combination with current chemotherapeutics to target OC tumor progression. Further studies will continue to optimize this new class of TG2/FN SMIs for potential clinical use in OC.

Citation Format: Livia Elena Sima, Bakhtiyor Yakubov, Salvatore Condello, Horacio Cardenas, Zhong Yin Zhang, Lan Chen, Daniela Elena Matei. The tissue transglutaminase 2–fibronectin protein complex: A new target in ovarian cancer. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A66.

Abstract 1541: Heterogeneous response to platinum in metastatic ovarian cancer detectable by biodynamic imaging

The mechanisms by which tumors develop multi-drug resistance are not well understood. Biodynamic imaging (BDI) is a label-free assay that detects phenotypic response of ex vivo tissue to chemotherapeutic drugs. In the current study, we used BDI to measure the response of primary and metastatic ovarian tumors to cisplatin. Xenografts from two human ovarian cancer cell lines, A2780 and SKOV3, were grown orthotopically in the ovaries of nude mice and allowed to metastasize in the peritoneal space. Primary and metastatic tumors were harvested and tested for response to 25 μM cisplatin by using BDI. Sensitivity was assessed through selected response biomarkers. Metastatic tumors of the platinum-sensitive A2780 cell line showed 20% decrease in sensitivity to cisplatin compared with the response of the primary tumors, while the less sensitive SKOV3 tumors exhibited a 6% decrease in response of metastatic vs. primary tumors. In parallel, RNA sequencing profiled primary ovarian and metastatic implants. Differential gene expression was detected in primary tumors vs. metastatic sites. Genes upregulated in metastases include TIMP3, WNT2, OSR1, elastin (SKOV3 tumor model) and MMP1, MMP3, MMP10, MET, EGFR, PDGF-C (A2780 tumor model). The study demonstrates the ability of BDI to detect differences in drug sensitivity between primary and metastatic tumors and provides support for the association of metastasis and chemoresistance in ovarian cancer. Supported by NIH R01 EB016582.

Citation Format: Daniel Merrill, Hao Sun, Daniela Matei, Bakhtiyor Yakubov, John Turek, David Nolte. Heterogeneous response to platinum in metastatic ovarian cancer detectable by biodynamic imaging. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1541.

17β-Estradiol mediates superior adaptation of right ventricular function to acute strenuous exercise in female rats with severe pulmonary hypertension

17β-Estradiol (E2) exerts protective effects on right ventricular (RV) function in pulmonary arterial hypertension (PAH). Since acute exercise-induced increases in afterload may lead to RV dysfunction in PAH, we sought to determine whether E2 allows for superior RV adaptation after an acute exercise challenge. We studied echocardiographic, hemodynamic, structural, and biochemical markers of RV function in male and female rats with sugen/hypoxia (SuHx)-induced pulmonary hypertension, as well as in ovariectomized (OVX) SuHx females, with or without concomitant E2 repletion (75 μg·kg(-1)·day(-1)) immediately after 45 min of treadmill running at 75% of individually determined maximal aerobic capacity (75% aerobic capacity reserve). Compared with males, intact female rats exhibited higher stroke volume and cardiac indexes, a strong trend for better RV compliance, and less pronounced increases in indexed total pulmonary resistance. OVX abrogated favorable RV adaptations, whereas E2 repletion after OVX markedly improved RV function. E2's effects on pulmonary vascular remodeling were complex and less robust than its RV effects. Postexercise hemodynamics in females with endogenous or exogenous E2 were similar to hemodynamics in nonexercised controls, whereas OVX rats exhibited more severely altered postexercise hemodynamics. E2 mediated inhibitory effects on RV fibrosis and attenuated increases in RV collagen I/III ratio. Proapoptotic signaling, endothelial nitric oxide synthase phosphorylation, and autophagic flux markers were affected by E2 depletion and/or repletion. Markers of impaired autophagic flux correlated with endpoints of RV structure and function. Endogenous and exogenous E2 exerts protective effects on RV function measured immediately after an acute exercise challenge. Harnessing E2's mechanisms may lead to novel RV-directed therapies.

Intracellular Doppler Signatures of Platinum Sensitivity Captured by Biodynamic Profiling in Ovarian Xenografts

Three-dimensional (3D) tissue cultures are replacing conventional two-dimensional (2D) cultures for applications in cancer drug development. However, direct comparisons of in vitro 3D models relative to in vivo models derived from the same cell lines have not been reported because of the lack of sensitive optical probes that can extract high-content information from deep inside living tissue. Here we report the use of biodynamic imaging (BDI) to measure response to platinum in 3D living tissue. BDI combines low-coherence digital holography with intracellular Doppler spectroscopy to study tumor drug response. Human ovarian cancer cell lines were grown either in vitro as 3D multicellular monoculture spheroids or as xenografts in nude mice. Fragments of xenografts grown in vivo in nude mice from a platinum-sensitive human ovarian cell line showed rapid and dramatic signatures of induced cell death when exposed to platinum ex vivo, while the corresponding 3D multicellular spheroids grown in vitro showed negligible response. The differences in drug response between in vivo and in vitro growth have important implications for predicting chemotherapeutic response using tumor biopsies from patients or patient-derived xenografts.

Abstract 208: Novel intracellular Doppler imaging predicts therapeutic efficacy for personalized medicine

This study reports first application of biodynamic imaging (BDI), a novel Doppler imaging technology, in studies of ovarian cancer xenografts and preclinical trials of canine multicentric lymphoma responding to doxorubicin.

In a study of A2780 human ovarian cell lines implanted in mice, an unexpected and large difference was discovered between mouse tumor explants versus A2780 cells grown as 3D tumor spheroids. The biopsied explants from mice were three times more sensitive to platinum, applied in vitro, than were multicellular tumor spheroids. A preclinical trial has been completed for canine non-Hodgkins lymphoma using BDI to predict patient outcome under doxorubicin therapy. The 3D imaging capability of BDI enabled the measurement of tumor heterogeneity in response to the therapy. The biodynamic assay took only 24 hours to complete, while the clinical outcome was often unknown for one to several months. The therapeutic efficacy of doxorubicin was predicted by BDI with 90% accuracy. Based on this success, biodynamic imaging is entering human pilot trials in ovarian, pancreatic, and esophageal cancer.

Biodynamic imaging is a radically different approach to the prediction of therapeutic efficacy for personalized medicine with higher accuracy and more biological relevance than standard cell-based assays. Supported in part by NIH NIBIB 1R01EB016582-01.

Citation Format: John J. Turek, Dan Merrill, Michelle Custead, Michael Childress, David D. Nolte, Bakhtiyor Yakubov, Ran An, Daniela Matei. Novel intracellular Doppler imaging predicts therapeutic efficacy for personalized medicine. [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 208. doi:10.1158/1538-7445.AM2015-208

Tissue Transglutaminase Mediated Tumor-Stroma Interaction Promotes Pancreatic Cancer Progression

PURPOSE

Aggressive pancreatic cancer is commonly associated with a dense desmoplastic stroma, which forms a protective niche for cancer cells. The objective of the study was to determine the functions of tissue transglutaminase (TG2), a Ca(2+)-dependent enzyme that cross-links proteins through transamidation and is abundantly expressed by pancreatic cancer cells in the pancreatic stroma.

EXPERIMENTAL DESIGN

Orthotopic pancreatic xenografts and coculture systems tested the mechanisms by which the enzyme modulates tumor-stroma interactions.

RESULTS

We show that TG2 secreted by cancer cells effectively molds the stroma by cross-linking collagen, which, in turn, activates fibroblasts and stimulates their proliferation. The stiff fibrotic stromal reaction conveys mechanical cues to cancer cells, leading to activation of the YAP/TAZ transcription factors, promoting cell proliferation and tumor growth. Stable knockdown of TG2 in pancreatic cancer cells leads to decreased size of pancreatic xenografts.

CONCLUSIONS

Taken together, our results demonstrate that TG2 secreted in the tumor microenvironment orchestrates the cross-talk between cancer cells and stroma fundamentally affecting tumor growth. Our study supports TG2 inhibition in the pancreatic stroma as a novel strategy to block pancreatic cancer progression.

Small molecule inhibitors target the tissue transglutaminase and fibronectin interaction

Tissue transglutaminase (TG2) mediates protein crosslinking through generation of ε-(γ-glutamyl) lysine isopeptide bonds and promotes cell adhesion through interaction with fibronectin (FN) and integrins. Cell adhesion to the peritoneal matrix regulated by TG2 facilitates ovarian cancer dissemination. Therefore, disruption of the TG2-FN complex by small molecules may inhibit cell adhesion and metastasis. A novel high throughput screening (HTS) assay based on AlphaLISA™ technology was developed to measure the formation of a complex between His-TG2 and the biotinylated FN fragment that binds TG2 and to discover small molecules that inhibit this protein-protein interaction. Several hits were identified from 10,000 compounds screened. The top candidates selected based on >70% inhibition of the TG2/FN complex formation were confirmed by using ELISA and bioassays measuring cell adhesion, migration, invasion, and proliferation. In conclusion, the AlphaLISA bead format assay measuring the TG2-FN interaction is robust and suitable for HTS of small molecules. One compound identified from the screen (TG53) potently inhibited ovarian cancer cell adhesion to FN, cell migration, and invasion and could be further developed as a potential inhibitor for ovarian cancer dissemination.

Identification of paxillin domains interacting with β-catenin

Barrier-protective agonists induce association of focal adhesions (FA) and adherens junctions (AJ) in endothelial cells. Here we identified specific domains of FA protein paxillin interacting with AJ protein and examined regulation of paxillin domain interactions with β-catenin by Rac GTPase. Co-expression of paxillin LD-1,2; LD-3,4; LIM-1,2; and LIM-3,4 domains with β-catenin showed exclusive interaction of LIM-1,2 and LIM-3,4 with β-catenin, which was enhanced by agonist-induced Rac activation or expression of activated Rac mutant. These results demonstrate a novel function of paxillin LIM domains in targeting β-catenin in a Rac-dependent manner, which may play a role in Rac-dependent control of FA-AJ interactions and monolayer integrity.

Opposite effects of ANP receptors in attenuation of LPS-induced endothelial permeability and lung injury

Atrial natriuretic peptide (ANP) has been recently identified as a modulator of acute lung injury (ALI) induced by pro-inflammatory agonists. While previous studies tested effects of exogenous ANP administration, the role of endogenous ANP in the course of ALI remains unexplored. This study examined regulation of ANP and its receptors NPR-A, NPR-B and NPR-C by LPS and involvement of ANP receptors in the modulation of LPS-induced lung injury. Primary cultures of human pulmonary endothelial cells (EC) were used in the in vitro tests. Expression of ANP and its receptors was determined by quantitative RT-PCR analysis. Agonist-induced cytoskeletal remodeling was evaluated by immunofluorescence staining, and EC barrier function was characterized by measurements of transendothelial electrical resistance. In the murine model of ALI, LPS-induced lung injury was assessed by measurements of protein concentration and cell count in bronchoalveolar lavage fluid (BAL). LPS stimulation significantly increased mRNA expression levels of ANP and NPR-A in pulmonary EC. Pharmacological inhibition of NPR-A augmented LPS-induced EC permeability and blocked barrier protective effects of exogenous ANP on LPS-induced intercellular gap formation. In contrast, pharmacological inhibition of ANP clearance receptor NPR-C significantly attenuated LPS-induced barrier disruptive effects. Administration of NPR-A inhibitor in vivo exacerbated LPS-induced lung injury, whereas inhibition of NPR-C suppressed LPS-induced increases in BAL cell count and protein content. These results demonstrate for the first time opposite effects of NPR-A and NPR-C in the modulation of ALI and suggest a compensatory protective mechanism of endogenous ANP in the maintenance of lung vascular permeability in ALI.

Abstract 1551: Soluble tissue transglutaminase modulates cellular adhesion to matrix and peritoneal metastasis in ovarian cancer

Background: Tissue transglutaminase (TG2) is a secreted protein that binds fibronectin (FN) and exerts protein transamidating activity in the presence of Ca2+. We previously reported that TG2 is upregulated in ovarian cancer (OC) cells and enhances intraperitoneal (ip) metastasis. TG2 is secreted abundantly in OC ascites, yet the function of soluble (s) TG2 remains unknown. We hypothesized that sTG2 acts as a permissive factor in the ECM by promoting cancer cell proliferation and adhesion to the matrix.

Materials and Methods: Recombinant his6-tagged full length human TG2 and its inactive enzymatic mutant C277S were purified by immobilized metal (Co2+) affinity and anion exchange chromatography. OV90 and A2780 OC cells that do not express endogenous TG2 were used. Solid phase adhesion assay measured adhesion to ECM proteins, MTT assay measured cell proliferation and an ip xenograft model quantified tumor formation and metastasis.

Results: S-TG2 enhanced cell adhesion to FN (p = 0.01) and vitronectin (VN, p = 0.01), but not to collagen and laminin. A neutralizing antibody to α5β1 and to αVβ3 blocked sTG2 induced cell adhesion to FN or to VN, respectively, suggesting that sTG2 modulates cell interaction with the matrix via integrins. Digestion of FN with matrix metallo-proteinase 2 blocked OC cell adhesion to digested fragments of FN, while addition of sTG2 restored OC cells’ binding to this protease-digested matrix (p = 0.02). This suggests that the soluble enzyme may facilitate the interaction of OC cells with a protease-remodeled matrix remodeled, similar to the tumor ECM. Enzymatically inactive soluble C277S TG2 enhanced OC cell adhesion to FN to the same extent as wild type TG2. In contrast, an antibody raised against the FN-binding domain of TG2 blocked sTG2 induced OC cell adhesion to FN (p =0.01). These data suggest that the interaction between TG2 and FN, but not the transamidating activity, is important to sTG2-mediated cell interaction with the ECM. When added to conditioned media, sTG2 (2.5ug/mL) increased OC cell proliferation by 20% (p = 0.01). Biweekly ip inoculation of 2.5ug sTG2 increased peritoneal dissemination of OV90 cells in nude mice (11.38 vs. 27.75, p = 0.02), but did not affect tumor volume (412.3 vs. 578.2 mm3, p = 0.34).

Conclusions: These data demonstrate that sTG2 increases OC cell adhesion to the ECM and peritoneal metastasis. The key mechanism involved in this process is the interaction between sTG2, FN, and integrins.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1551. doi:10.1158/1538-7445.AM2011-1551

Atrial natriuretic peptide attenuates LPS-induced lung vascular leak: role of PAK1

Increased levels of atrial natriuretic peptide (ANP) in the models of sepsis, pulmonary edema, and acute respiratory distress syndrome (ARDS) suggest its potential role in the modulation of acute lung injury. We have recently described ANP-protective effects against thrombin-induced barrier dysfunction in pulmonary endothelial cells (EC). The current study examined involvement of the Rac effector p21-activated kinase (PAK1) in ANP-protective effects in the model of lung vascular permeability induced by bacterial wall LPS. C57BL/6J mice or ANP knockout mice (Nppa(-/-)) were treated with LPS (0.63 mg/kg intratracheal) with or without ANP (2 μg/kg iv). Lung injury was monitored by measurements of bronchoalveolar lavage protein content, cell count, Evans blue extravasation, and lung histology. Endothelial barrier properties were assessed by morphological analysis and measurements of transendothelial electrical resistance. ANP treatment stimulated Rac-dependent PAK1 phosphorylation, attenuated endothelial permeability caused by LPS, TNF-α, and IL-6, decreased LPS-induced cell and protein accumulation in bronchoalveolar lavage fluid, and suppressed Evans blue extravasation in the murine model of acute lung injury. More severe LPS-induced lung injury and vascular leak were observed in ANP knockout mice. In rescue experiments, ANP injection significantly reduced lung injury in Nppa(-/-) mice caused by LPS. Molecular inhibition of PAK1 suppressed the protective effects of ANP treatment against LPS-induced lung injury and endothelial barrier dysfunction. This study shows that the protective effects of ANP against LPS-induced vascular leak are mediated at least in part by PAK1-dependent signaling leading to EC barrier enhancement. Our data suggest a direct role for ANP in endothelial barrier regulation via modulation of small GTPase signaling.

Mechanotransduction by GEF-H1 as a novel mechanism of ventilator-induced vascular endothelial permeability

Pathological lung overdistention associated with mechanical ventilation at high tidal volumes (ventilator-induced lung injury; VILI) compromises endothelial cell (EC) barrier leading to development of pulmonary edema and increased morbidity and mortality. We have previously shown involvement of microtubule (MT)-associated Rho-specific guanine nucleotide exchange factor GEF-H1 in the agonist-induced regulation of EC permeability. Using an in vitro model of human pulmonary EC exposed to VILI-relevant magnitude of cyclic stretch (18% CS) we tested a hypothesis that CS-induced alterations in MT dynamics contribute to the activation of Rho-dependent signaling via GEF-H1 and mediate early EC response to pathological mechanical stretch. Acute CS (30 min) induced disassembly of MT network, cell reorientation, and activation of Rho pathway, which was prevented by MT stabilizer taxol. siRNA-based GEF-H1 knockdown suppressed CS-induced disassembly of MT network, abolished Rho signaling, and attenuated CS-induced stress fiber formation and EC realignment compared with nonspecific RNA controls. Depletion of GEF-H1 in the murine two-hit model of VILI attenuated vascular leak induced by lung ventilation at high tidal volume and thrombin-derived peptide TRAP6. These data show for the first time the critical involvement of microtubules and microtubule-associated GEF-H1 in lung vascular endothelial barrier dysfunction induced by pathological mechanical strain.

Transcriptional activation and localization of expression of Brassica juncea putative metal transport protein BjMTP1

BACKGROUND

Metal hyperaccumulators, including various Thlaspi species, constitutively express the putative metal transporter MTP1 to high levels in shoots. Here we present data on the transcriptional regulation and localization of expression of the homologous gene BjMTP1 in Brassica juncea. Though B. juncea lacks the ability to hyperaccumulate metals, its relatively high biomass, rapid growth and relatedness to true metal hyperaccumulating plants makes it a promising starting point for the development of plants for phytoremediation. Our goal in this study is to determine the transcriptional regulation of MTP1 in order to start to better understanding the physiological role of MTP1 in B. juncea.

RESULTS

Steady-state mRNA levels of BjMTP1 were found to be enhanced 8.8, 5.9, and 1.6-fold in five-day-old B. juncea seedlings after exposure to Ni2+, Cd2+ or Zn2+, respectively. This was also reflected in enhanced GUS activity in B. juncea seedlings transformed with BjMTP1 promoter::GUSPlus after exposure to these metals over a similar range of toxicities from mild to severe. However, no increase in GUS activity was observed after exposure of seedlings to cold or heat stress, NaCl or hydrogen peroxide. GUS expression in Ni2+ treated seedlings was localized in roots, particularly in the root-shoot transition zone. In four- week- old transgenic plants BjMTP1 promoter activity also primarily increased in roots in response to Ni2+ or Cd2+ in plants transformed with either GUS or mRFP1 as reporter genes, and expression was localized to the secondary xylem parenchyma. In leaves, BjMTP1 promoter activity in response to Ni2+ or Cd2+ spiked after 24 h then decreased. In shoots GUS expression was prominently present in the vasculature of leaves, and floral parts.

CONCLUSION

Our studies establish that a 983 bp DNA fragment upstream of the BjMTP1 translational start site is sufficient for the specific activation by Ni2+ and Cd2+ of BjMTP1 expression primarily in roots. Activation of expression by both metals in roots is primarily localized to the xylem parenchyma cells. This study is the first to identify specific Ni2+ and Cd2+ transcriptional regulation and tissue localization of BjMTP1.

Distinguishing adaptive from nonadaptive genetic differentiation: comparison of QST and FST at two spatial scales

Genetic differentiation in 20 hierarchically sampled populations of wild barley was analyzed with quantitative traits, allozymes and Random Amplified Polymorphic DNAs (RAPDs), and compared for three marker types at two hierarchical levels. Regional subdivision for both molecular markers was much lower than for quantitative traits. For both allozymes and RAPDs, most loci exhibited minor or no regional differentiation, and the relatively high overall estimates of the latter were due to several loci with exceptionally high regional differentiation. The allozyme- and RAPD-specific patterns of differentiation were concordant in general with one another, but not with quantitative trait differentiation. Divergent selection on quantitative traits inferred from very high regional Q(ST) was in full agreement with our previous results obtained from a test of local adaptation and multilevel selection analysis. In contrast, most variation in allozyme and RAPD variation was neutral, although several allozyme loci and RAPD markers were exceptional in their levels of regional differentiation. However, it is not possible to answer the question whether these exceptional loci are directly involved in the response to selection pressure or merely linked to the selected loci. The fact that Q(ST) and F(ST) did not differ at the population scale, that is, within regions, but differed at the regional scale, for which local adaptation has been previously shown, implies that comparison of the level of subdivision in quantitative traits, as compared with molecular markers, is indicative of adaptive population differentiation only when sampling is carried out at the appropriate scale.

A transmembrane hybrid-type histidine kinase in Arabidopsis functions as an osmosensor

Water deficit and the resulting osmotic stress affect plant growth. To understand how plant cells monitor and respond to osmotic change from water stress, we isolated a cDNA from dehydrated Arabidopsis plants. This cDNA encodes a novel hybrid-type histidine kinase, ATHK1. Restriction fragment length polymorphism mapping showed that the ATHK1 gene is on chromosome 2. The predicted ATHK1 protein has two putative transmembrane regions in the N-terminal half and has structural similarity to the yeast osmosensor synthetic lethal of N-end rule 1 (SLN1). The ATHK1 transcript was more abundant in roots than other tissues under normal growth conditions and accumulated under conditions of high or low osmolarity. Histochemical analysis of beta-glucuronidase activities driven by the ATHK1 promoter further indicates that the ATHK1 gene is transcriptionally upregulated in response to changes in external osmolarity. Overexpression of the ATHK1 cDNA suppressed the lethality of the temperature-sensitive osmosensing-defective yeast mutant sln1-ts. By contrast, ATHK1 cDNAs in which conserved His or Asp residues had been substituted failed to complement the sln1-ts mutant, indicating that ATHK1 functions as a histidine kinase. Introduction of the ATHK1 cDNA into the yeast double mutant sln1Delta sho1Delta, which lacks two osmosensors, suppressed lethality in high-salinity media and activated the high-osmolarity glycerol response 1 (HOG1) mitogen-activated protein kinase (MAPK). These results imply that ATHK1 functions as an osmosensor and transmits the stress signal to a downstream MAPK cascade.

Stress-responsive expression of genes for two-component response regulator-like proteins in Arabidopsis thaliana

Four cDNAs that encode two-component response regulator-like proteins were cloned from Arabidopsis thaliana. Putative proteins (ATRR1-4) contain a receiver domain with a conserved aspartate residue - a possible phosphorylation site - at the N-terminal half. ATRR2 lacks the C-terminal half; the others contain a C-terminal domain abundant in acidic amino acids or proline residues. ATRR1 and ATRR2 are expressed more in roots than in other tissues and are induced by low temperature, dehydration and high salinity. Levels of ATRR3 and ATRR4 were not affected by stress treatments. These results suggest that ATRRs play distinct physiological roles in Arabidopsis, and that some are involved in stress responses.