Moloy T. Goswami

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.

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.

MicroRNA-101 regulated transcriptional modulator SUB1 plays a role in prostate cancer

MicroRNA-101, a tumor suppressor microRNA (miR), is often downregulated in cancer and is known to target multiple oncogenes. Some of the genes that are negatively regulated by miR-101 expression include histone methyltransferase EZH2 (enhancer of zeste homolog 2), COX2 (cyclooxygenase-2), POMP (proteasome maturation protein), CERS6, STMN1, MCL-1 and ROCK2, among others. In the present study, we show that miR-101 targets transcriptional coactivator SUB1 homolog (Saccharomyces cerevisiae)/PC4 (positive cofactor 4) and regulates its expression. SUB1 is known to have diverse role in vital cell processes such as DNA replication, repair and heterochromatinization. SUB1 is known to modulate transcription and acts as a mediator between the upstream activators and general transcription machinery. Expression profiling in several cancers revealed SUB1 overexpression, suggesting a potential role in tumorigenesis. However, detailed regulation and function of SUB1 has not been elucidated. In this study, we show elevated expression of SUB1 in aggressive prostate cancer. Knockdown of SUB1 in prostate cancer cells resulted in reduced cell proliferation, invasion and migration in vitro, and tumor growth and metastasis in vivo. Gene expression analyses coupled with chromatin immunoprecipitation revealed that SUB1 binds to the promoter regions of several oncogenes such as PLK1 (Polo-like kinase 1), C-MYC, serine-threonine kinase BUB1B and regulates their expression. Additionally, we observed SUB1 downregulated CDKN1B expression. PLK1 knockdown or use of PLK1 inhibitor can mitigate oncogenic function of SUB1 in benign prostate cancer cells. Thus, our study suggests that miR-101 loss results in increased SUB1 expression and subsequent activation of known oncogenes driving prostate cancer progression and metastasis. This study therefore demonstrates functional role of SUB1 in prostate cancer, and identifies its regulation and potential downstream therapeutic targets of SUB1 in prostate cancer.

TLR9-Dependent IL-23/IL-17 Is Required for the Generation of Stachybotrys chartarum–Induced Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease that develops after repeated exposure to inhaled particulate Ag. Stachybotrys chartarum is a dimorphic fungus that has been implicated in a number of respiratory illnesses, including HP. In this study, we have developed a murine model of S. chartarum–induced HP that reproduces pathology observed in human HP, and we have hypothesized that TLR9-mediated IL-23 and IL-17 responses are required for the generation of granulomatous inflammation induced by inhaled S. chartarum. Mice that undergo i.p. sensitization and intratracheal challenge with 106 S. chartarum spores developed granulomatous inflammation with multinucleate giant cells, accompanied by increased accumulation of T cells. S. chartarum sensitization and challenge resulted in robust pulmonary expression of IL-17 and IL-23. S. chartarum–mediated granulomatous inflammation required intact IL-23 or IL-17 responses and required TLR9, because TLR9−/− mice displayed reduced IL-17 and IL-23 expression in whole lung associated with decreased accumulation of IL-17 expressing CD4+ and γδ T cells. Compared with S. chartarum–sensitized dendritic cells (DC) isolated from WT mice, DCs isolated from TLR9−/− mice had a reduced ability to produce IL-23 in responses to S. chartarum. Moreover, shRNA knockdown of IL-23 in DCs abolished IL-17 production from splenocytes in response to Ag challenge. Finally, the intratracheal reconstitution of IL-23 in TLR9−/− mice recapitulated the immunopathology observed in WT mice. In conclusion, our studies suggest that TLR9 is critical for the development of Th17-mediated granulomatous inflammation in the lung in response to S. chartarum.

Expression and Role of PAICS, a De Novo Purine Biosynthetic Gene in Prostate Cancer.

Our goal was to investigate de novo purine biosynthetic gene PAICS expression and evaluate its role in prostate cancer progression.

miR-34a Regulates Expression of the Stathmin-1 Oncoprotein and Prostate Cancer Progression

In aggressive prostate cancers, the oncoprotein STMN1 (also known as stathmin 1 and oncoprotein 18) is often overexpressed. STMN1 is involved in various cellular processes, including cell proliferation, motility, and tumor metastasis. Here, it was found that the expression of STMN1 RNA and protein is elevated in metastatic prostate cancers. Knockdown of STMN1 resulted in reduced proliferation and invasion of cells and tumor growth and metastasis in vivo. Furthermore, miR-34a downregulated STMN1 by directly binding to its 3′-UTR. Overexpression of miR-34a in prostate cancer cells reduced proliferation and colony formation, suggesting that it is a tumor suppressor. The transcriptional corepressor C-terminal binding protein 1 (CtBP1) negatively regulated expression of miR-34a. Furthermore, gene expression profiling of STMN1-modulated prostate cancer cells revealed molecular alterations, including elevated expression of growth differentiation factor 15 (GDF15), which is involved in cancer progression and potentially in STMN1-mediated oncogenesis. Thus, in prostate cancer, CtBP1-regulated miR-34a modulates STMN1 expression and is involved in cancer progression through the CtBP1\miR-34a\STMN1\GDF15 axis. Implications: The CtBP1\miR-34a\STMN1\GDF15 axis is a potential therapeutic target for treatment of aggressive prostate cancer. Mol Cancer Res; 16(7); 1125–37. ©2017 AACR.

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 LB-115: TPRKB dependency in p53-deficient cancers

TP53 (p53) is an extensively studied tumor suppressor mutated in approximately 50% of all cancers. Identification of vulnerabilities imposed by p53 alterations may enable effective targeted therapy development. Thus, this study aimed to identify and characterize novel vulnerabilities in this context. Through analyzing shRNA screening data from the Broad Institute’s Project Achilles, we identified TPRKB, a poorly characterized member of the tRNA-modifying EKC/KEOPS complex, as the most significant vulnerability in p53 mutated cancer cell lines. In vitro, across multiple benign-immortalized and cancer cell lines, we confirmed that TPRKB knockdown in p53-deficient cells significantly inhibited proliferation, while there was little to no effect in p53 wild-type cells. Furthermore, p53 reintroduction into TPRKB-sensitive p53-null cells resulted in loss of TPRKB sensitivity, confirming the importance of p53 status in this context. To determine whether this response was unique to TPRKB or a result of impairment of the EKC/KEOPS complex, we knocked down other members of the complex: PRPK, OSGEP, and LAGE3. PRPK loss showed minor changes between p53 wild type versus deficient cells; while OSGEP and LAGE3 loss resulted in a significant decrease regardless of p53 status. For the first time, we have demonstrated a potential role for TPRKB in cancer, and our results suggest that effects of TPRKB knockdown in p53-deficient cancer cells may be independent of its role in the EKC/KEOPS complex. Citation Format: Kelly VanDenBerg, Moloy Goswami, Lei Lucy Wang, Bhavneet Singh, Travis Weiss, Sumin Han, Dan Rhodes, Felix Feng, Scott Tomlins. TPRKB dependency in p53-deficient cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-115. doi:10.1158/1538-7445.AM2017-LB-115

Abstract 1447: Identification of an oncogenic germline KRAS truncating mutation in hereditary cancers

Somatic strongly activating KRAS mutations play an oncogenic role across numerous human cancers, while less activating germline KRAS mutations are associated with developmental disorders. KRAS encodes two splice variant products—KRAS-4A and KRAS-4B—differing in their C-terminus through alternative fourth coding exons. Though KRAS-4A is homologous to the original transforming transcript identified in Kirsten rat sarcoma virus, its role in human cancer is less characterized compared to KRAS-4B. Here, through genetic analyses of three cohorts of patients with hereditary and/or aggressive cancers, we identified a rare KRAS-4A specific C-terminal truncating germline mutation (KRAS-4A C180X; rs373169526) in affected men of three families with hereditary prostate cancer and a patient with hereditary melanoma (minor allele frequency [MAF] of 0.0014 in these combined cancer cohorts assessed vs. 0.000056 in the ExAC population database, odds ratio 24.6 [95% confidence interval 5.1-103.5], two sided Fisher’s exact test p = 9.0E-5). The KRAS-4A C180X mutation truncates the C-terminus, removing the polybasic region and -CAAX motifs previously demonstrated to be necessary for Ras family member membrane association, MAP kinase signaling activation and transformation, suggesting a loss of function phenotype. However, in silico assessment of reported human variation demonstrates truncating germline variants only in KRAS-4A and not KRAS-4B, consistent with tolerance. Expression of KRAS-4A protein in NIH3T3 and MDCK leads to loss of exclusive membrane association and inhibits GTP loading, as expected, but paradoxically resulted in modest but significantly increased proliferation and soft agar colony growth compared to control or wildtype KRAS expressing cells. Pro-oncogenic phenotypes were not dependent on MAPK signaling, but showed sensitivity to AKT inhibition. In summary, we identified a germline truncating KRAS-4A mutation over-represented in hereditary cancers that defines a novel mechanism of KRAS activation not dependent on the C-terminal polybasic and -CAAX motifs. Citation Format: Moloy T. Goswami, Daniel H. Hovelson, Anna Johnson, Scott A. Tomlins, Lucy Wang, Kimberly Zhulke, Bhavneet Singh, Sharath Kumar Anand, Andi Cani, Albert Liu, Steven Kamberov, Yi-Mi Wu, Dan Robinson, Arul Chinnaiyan, Kathleen A. Cooney. Identification of an oncogenic germline KRAS truncating mutation in hereditary cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1447. doi:10.1158/1538-7445.AM2017-1447

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