Ajaya Kumar Reka

Peroxisome proliferator-activated receptor-gamma activation inhibits tumor metastasis by antagonizing Smad3-mediated epithelial-mesenchymal transition.

Epithelial-mesenchymal transition (EMT) was shown to confer tumor cells with abilities essential for metastasis, including migratory phenotype, invasiveness, resistance to apoptosis, evading immune surveillance, and tumor stem cell traits. Therefore, inhibition of EMT can be an important therapeutic strategy to inhibit tumor metastasis. Here, we show that activation of peroxisome proliferator-activated receptor γ (PPAR-γ) inhibits transforming growth factor β (TGF-β)-induced EMT in lung cancer cells and prevents metastasis by antagonizing Smad3 function. Activation of PPAR-γ by synthetic ligands (troglitazone and rosiglitazone) or by a constitutively active form of PPAR-γ prevents TGF-β–induced loss of E-cadherin expression and inhibits the induction of mesenchymal markers (vimentin, N-cadherin, fibronectin) and matrix metalloproteases. Consistently, activation of PPAR-γ also inhibited EMT-induced migration and invasion of lung cancer cells. Furthermore, effects of PPAR-γ ligands were attenuated by siRNA-mediated knockdown of PPAR-γ, indicating that the ligand-induced responses are PPAR-γ dependent. Selective knockdown of Smad2 and Smad3 by siRNA showed that TGF-β–induced EMT is Smad3 dependent in lung cancer cells. Activation of PPAR-γ inhibits TGF-β–induced Smad transcriptional activity but had no effect on the phosphorylation or nuclear translocation of Smads. Consistently, PPAR-γ activation prevented TGF-β–induced transcriptional repression of E-cadherin promoter and inhibited transcriptional activation of N-cadherin promoter. Finally, treatment of mice with troglitazone or knockdown of Smad3 in tumor cells significantly inhibited TGF-β–induced experimental metastasis in SCID-Beige mice. Together, with the low toxicity profile of PPAR-γ ligands, our data show that these ligands may serve as potential therapeutic agents to inhibit metastasis. Mol Cancer Ther; 9(12); 3221–32. ©2010 AACR.

Temporal quantitative proteomics by iTRAQ 2D-LC-MS/MS and corresponding mRNA expression analysis identify post-transcriptional modulation of actin-cytoskeleton regulators during TGF-β-Lnduced epithelial-mesenchymal transition

To gain insights into how TGF-beta regulates epithelial-mesenchymal transition (EMT), we assessed the time course of proteins and mRNAs during EMT by multiplex iTRAQ labeling and 2D-LC-MS/MS, and by hybridization, respectively. Temporal iTRAQ analysis identified 66 proteins as differentially expressed during EMT, including newly associated proteins calpain, fascin and macrophage-migration inhibitory factor (MIF). Comparing protein and mRNA expression overtime showed that all the 14 up-regulated proteins involved in the actin-cytoskeleton remodeling were accompanied by increases in corresponding mRNA expression. Interestingly, siRNA mediated knockdown of cofilin1 potentiated TGF-beta-induced EMT. Further analysis of cofilin1 and beta-actin revealed an increase in their mRNA stability in response to TGF-beta, contributing to the observed increase in mRNA and protein expression. These results are the first demonstration of post-transcriptional regulation of cytoskeletal remodelling and a key role for cofilin1 during TGF-beta-induced EMT.

Molecular cross-regulation between PPAR-γ and other signaling pathways: Implications for lung cancer therapy

Peroxisome proliferator-activated receptors (PPAR)-γ belongs to the nuclear hormone receptor superfamily of ligand-dependent transcription factors. It is a mediator of adipocyte differentiation, regulates lipid metabolism and macrophage function. The ligands of PPAR-γ have long been in the clinic for the treatment of type II diabetes and have a very low toxicity profile. Activation of PPAR-γ was shown to modulate various hallmarks of cancer through its pleiotropic affects on multiple different cell types in the tumor microenvironment. An overwhelming number of preclinical-studies demonstrate the efficacy of PPAR-γ ligands in the control of tumor progression through their affects on various cellular processes, including cell proliferation, apoptosis, angiogenesis, inflammation and metastasis. A variety of signaling pathways have been implicated as potential mechanisms of action. This review will focus on the molecular basis of these mechanisms; primarily PPAR-γ cross-regulation with other signaling pathways and its relevance to lung cancer therapy will be discussed.

Identifying Inhibitors of Epithelial-Mesenchymal Transition by Connectivity Map–Based Systems Approach

Background: Acquisition of mesenchymal phenotype by epithelial cells by means of epithelial-mesenchymal transition (EMT) is considered as an early event in the multistep process of tumor metastasis. Therefore, inhibition of EMT might be a rational strategy to prevent metastasis. Methods: Using the global gene expression profile from a cell culture model of transforming growth factor-&bgr; (TGF-&bgr;)-induced EMT, we identified potential EMT inhibitors. We used a publicly available database (www.broad.mit.edu/cmap) comprising gene expression profiles obtained from multiple different cell lines in response to various drugs to derive negative correlations to EMT gene expression profile using Connectivity Map, a pattern matching tool. Results: Experimental validation of the identified compounds showed rapamycin as a novel inhibitor of TGF-&bgr; signaling along with 17-AAG, a known modulator of TGF-&bgr; pathway. Both of these compounds completely blocked EMT and the associated migratory and invasive phenotype. The other identified compound, LY294002, demonstrated a selective inhibition of mesenchymal markers, cell migration and invasion, without affecting the loss of E-cadherin expression or Smad phosphorylation. Conclusions: Our data reveal that rapamycin is a novel modulator of TGF-&bgr; signaling, and along with 17-AAG and LY294002, could be used as therapeutic agent for inhibiting EMT. This study demonstrates the potential of a systems approach in identifying novel modulators of a complex biological process.

TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia.

Toll-like receptors (TLRs) are required for protective host defense against bacterial pathogens. However, the role of TLRs in regulating lung injury during Gram-negative bacterial pneumonia has not been thoroughly investigated. In this study, experiments were performed to evaluate the role of TLR4 in pulmonary responses against Klebsiella pneumoniae (Kp). Compared with wild-type (WT) (Balb/c) mice, mice with defective TLR4 signaling (TLR4(lps-d) mice) had substantially higher lung bacterial colony-forming units after intratracheal challenge with Kp, which was associated with considerably greater lung permeability and lung cell death. Reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein was noted in lungs and bronchoalveolar lavage fluid of TLR4 mutant mice postintratracheal Kp compared with WT mice, and primary alveolar epithelial cells (AEC) harvested from TLR4(lps-d) mice produced significantly less GM-CSF in vitro in response to heat-killed Kp compared with WT AEC. TLR4(lps-d) AEC underwent significantly more apoptosis in response to heat-killed Kp in vitro, and treatment with GM-CSF protected these cells from apoptosis in response to Kp. Finally, intratracheal administration of GM-CSF in TLR4(lps-d) mice significantly decreased albumin leak, lung cell apoptosis, and bacteremia in Kp-infected mice. Based on these observations, we conclude that TLR4 plays a protective role on lung epithelium during Gram-negative bacterial pneumonia, an effect that is partially mediated by GM-CSF.

Regulation of complement-dependent cytotoxicity by TGF-β-induced epithelial–mesenchymal transition

The process of epithelial–mesenchymal transition (EMT), in addition to being an initiating event for tumor metastasis, is implicated in conferring several clinically relevant properties to disseminating cancer cells. These include stem cell-like properties, resistance to targeted therapies and ability to evade immune surveillance. Enrichment analysis of gene expression changes during transforming growth factor-β (TGF-β)-induced EMT in lung cancer cells identified complement cascade as one of the significantly enriched pathway. Further analysis of the genes in the complement pathway revealed an increase in the expression of complement inhibitors and a decrease in the expression of proteins essential for complement activity. In this study, we tested whether EMT confers resistance to complement-dependent cytotoxicity (CDC) in lung cancer cells and promotes tumor progression. CD59 is a potent inhibitor of membrane attack complex that mediates complement-dependent cell lysis. We observed a significant increase in the CD59 expression on the surface of cells after TGF-β-induced EMT. Furthermore, CD59 knockdown restored susceptibility of cells undergoing EMT to cetuximab-mediated CDC. TGF-β-induced CD59 expression during EMT is dependent on Smad3 but not on Smad2. Chromatin immunoprecipitation analysis confirmed that Smad3 directly binds to the CD59 promoter. Stable knockdown of CD59 in A549 cells inhibited experimental metastasis. These results demonstrate that TGF-β-induced EMT and CD59 expression confers an immune-evasive mechanism to disseminating tumor cells facilitating tumor progression. Together, our data demonstrates that CD59 inhibition may serve as an adjuvant to enhance the efficacy of antibody-mediated therapies, as well as to inhibit metastasis in lung cancer.

Epithelial-mesenchymal transition-associated secretory phenotype predicts survival in lung cancer patients.

In cancer cells, the process of epithelial-mesenchymal transition (EMT) confers migratory and invasive capacity, resistance to apoptosis, drug resistance, evasion of host immune surveillance and tumor stem cell traits. Cells undergoing EMT may represent tumor cells with metastatic potential. Characterizing the EMT secretome may identify biomarkers to monitor EMT in tumor progression and provide a prognostic signature to predict patient survival. Utilizing a transforming growth factor-β-induced cell culture model of EMT, we quantitatively profiled differentially secreted proteins, by GeLC-tandem mass spectrometry. Integrating with the corresponding transcriptome, we derived an EMT-associated secretory phenotype (EASP) comprising of proteins that were differentially upregulated both at protein and mRNA levels. Four independent primary tumor-derived gene expression data sets of lung cancers were used for survival analysis by the random survival forests (RSF) method. Analysis of 97-gene EASP expression in human lung adenocarcinoma tumors revealed strong positive correlations with lymph node metastasis, advanced tumor stage and histological grade. RSF analysis built on a training set (n = 442), including age, sex and stage as variables, stratified three independent lung cancer data sets into low-, medium- and high-risk groups with significant differences in overall survival. We further refined EASP to a 20 gene signature (rEASP) based on variable importance scores from RSF analysis. Similar to EASP, rEASP predicted survival of both adenocarcinoma and squamous carcinoma patients. More importantly, it predicted survival in the early-stage cancers. These results demonstrate that integrative analysis of the critical biological process of EMT provides mechanism-based and clinically relevant biomarkers with significant prognostic value.

Nanoroughened adhesion-based capture of circulating tumor cells with heterogeneous expression and metastatic characteristics

BackgroundCirculating tumor cells (CTCs) have shown prognostic relevance in many cancer types. However, the majority of current CTC capture methods rely on positive selection techniques that require a priori knowledge about the surface protein expression of disseminated CTCs, which are known to be a dynamic population.MethodsWe developed a microfluidic CTC capture chip that incorporated a nanoroughened glass substrate for capturing CTCs from blood samples. Our CTC capture chip utilized the differential adhesion preference of cancer cells to nanoroughened etched glass surfaces as compared to normal blood cells and thus did not depend on the physical size or surface protein expression of CTCs.ResultsThe microfluidic CTC capture chip was able to achieve a superior capture yield for both epithelial cell adhesion molecule positive (EpCAM+) and EpCAM- cancer cells in blood samples. Additionally, the microfluidic CTC chip captured CTCs undergoing transforming growth factor beta-induced epithelial-to-mesenchymal transition (TGF-β-induced EMT) with dynamically down-regulated EpCAM expression. In a mouse model of human breast cancer using EpCAM positive and negative cell lines, the number of CTCs captured correlated positively with the size of the primary tumor and was independent of their EpCAM expression. Furthermore, in a syngeneic mouse model of lung cancer using cell lines with differential metastasis capability, CTCs were captured from all mice with detectable primary tumors independent of the cell lines’ metastatic ability.ConclusionsThe microfluidic CTC capture chip using a novel nanoroughened glass substrate is broadly applicable to capturing heterogeneous CTC populations of clinical interest independent of their surface marker expression and metastatic propensity. We were able to capture CTCs from a non-metastatic lung cancer model, demonstrating the potential of the chip to collect the entirety of CTC populations including subgroups of distinct biological and phenotypical properties. Further exploration of the biological potential of metastatic and presumably non-metastatic CTCs captured using the microfluidic chip will yield insights into their relevant differences and their effects on tumor progression and cancer outcomes.

Abstract 331: Epithelial-mesenchymal transition confers resistance to complement-dependent cytotoxicity in lung cancer cells

Recent studies have implicated Epithelial-mesenchymal transition (EMT) in conferring several clinically relevant properties to cancer cells, in addition to initiating tumor metastasis. These include stem-cell like properties, resistance to targeted therapies and ability to evade immune surveillance. Pathway analysis of gene expression changes in TGF-β induced EMT identified the complement cascade as one of the significantly enriched pathway. Further analysis of the genes in the complement pathway revealed EMT-induced expression of complement inhibitors and decrease in expression of proteins essential for complement activity, suggesting resistance to complement dependent cytotoxicity (CDC) during EMT. We found lung cancer cells that undergo EMT showed marked decrease in C3 deposition and concomitant resistance to apoptosis by CDC as measured by 7-Aminoactinomycin D staining. Flow cytometric and RT-PCR analysis showed a significant increase in the CD59 expression on the surface of cells undergoing EMT, which is a potent inhibitor of formation of membrane attack complex that mediates complement dependent cell lysis. Furthermore, CD59 inhibition by siRNA mediated knock-down overcame the EMT-induced resistance to anti-EGFR antibody (Cetuximab) mediated CDC. The increase in CD59 was abrogated on disruption of TGF-β signaling as revealed by TGF- β Receptor kinase inhibitor and is dependent on Smad3 signaling. Chromatin immunoprecipitation analysis revealed increased occupancy of Smad3 on CD59 promoter, suggesting a direct regulation by Smad3. These results demonstrate that TGF-β-induced EMT confers another novel immune evasive mechanism to tumor cells that facilitates tumor progression and CD59 as a potential therapeutic target for enhancing the efficacy of anti-EGFR Antibody therapies and against tumor metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 331. doi:1538-7445.AM2012-331

Abstract 4677: Slug is a potential target to restore transforming growth factor-β mediated apoptosis in lung cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Transforming growth factor-β (TGFβ) inhibits carcinogenesis at early stages by inhibiting cell growth and inducing apoptosis. Cancer cells acquire resistance to TGFβ induced apoptosis and divert the TGF-β signaling to stimulate tumor promoting processes such as Epithelial-Mesenchymal-Transition (EMT), immunosuppression and angiogenesis. Hence, the identification of molecular targets/ pathways enabling cancer cells to overcome TGFβ-mediated apoptosis is critical for exploiting tumor suppressive functions of TGFβ for therapy. We have identified slug (snai2), a zinc-finger transcription factor, as a critical regulator of TGF-β mediated apoptosis in lung cancer cells. In EMT models of lung cancer slug is up-regulated by several fold upon TGFβ treatment. Knock down of Smad 3 or Smad 4, but not Smad 2, completely abrogated the TGF-β induced up-regulation of Slug. Chromatin immunoprecipitation analysis revealed increased occupancy of Smad 3 to the slug promoter on TGFβ treatment indicating slug might be a direct target gene of Smad 3. Slug is often described as a potent E-cadherin suppressor and an important regulator of EMT along with other E-box proteins. In contrast siRNA knock-down of slug (slug KD) in lung cancer cells did not prevent TGFβ induced E-cadherin suppression or acquisition of mesenchymal markers such as N-cadherin, vimentin and fibronectin; instead lead to increased cell death. Slug KD cells on TGFβ treatment underwent apoptosis through the typical apoptosis cascade characterized by increased annexin-v staining and caspase-3 activation. This apoptotic cell death is abrogated by inhibitors of caspase-3 and caspase-9. Inhibition of caspase-8, an initiator of extrinsic apoptotic pathway or siRNA knockdown of RIP1 that promotes necroptosis did not inhibit the death of TGFβ treated slug KD cells. Together these finding suggests slug KD results in cell death via intrinsic apoptosis pathway in response to TGFβ. This study indicates slug induction during EMT allows cancer cells to escape from apoptotic functions of TGFβ and might function as a critical regulatory switch to shift TGFβ role from tumor suppressor to tumor promoter. Thus slug inhibition might serve as a potential mechanism to reinstate the apoptotic functions of TGFβ in lung cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4677. doi:1538-7445.AM2012-4677