Smoking Cessation after Cancer Diagnosis and Enhanced Therapy Response: Mechanisms and Significance

The adverse effects of smoking on human health have been recognized for several decades, especially in the context of cancer. The ability of tobacco smoke components, including tobacco-specific carcinogens and additive compounds such as nicotine, to initiate or promote tumor growth have been described in hundreds of studies. These investigations have revealed the tumor-promoting activities of nicotine and other tobacco smoke components and have also recognized the ability of these agents to suppress the efficacy of cancer therapy; it is now clear that smoking can reduce the efficacy of most of the widely used therapeutic modalities, including immunotherapy, radiation therapy, and chemotherapy. Several studies examined if continued smoking after cancer diagnosis affected therapy response; it was found that while never smokers or non-smokers had the best response to therapy, those who quit smoking at the time of diagnosis had higher overall survival and reduced side-effects than those who continued to smoke. These studies also revealed the multiple mechanisms via which smoking enhances the growth and survival of tumors while suppressing therapy-induced cell death. In conclusion, smoking cessation during the course of cancer therapy markedly increases the chances of survival and the quality of life.

HDAC11 activity contributes to MEK inhibitor escape in uveal melanoma

We previously demonstrated that pan-HDAC inhibitors could limit escape from MEK inhibitor (MEKi) therapy in uveal melanoma (UM) through suppression of AKT and YAP/TAZ signaling. Here, we focused on the role of specific HDACs in therapy adaptation. Class 2 UM displayed higher expression of HDACs 1, 2, and 3 than Class 1, whereas HDACs 6, 8, and 11 were uniformly expressed. Treatment of UM cells with MEKi led to modulation of multiple HDACs, with the strongest increases observed in HDAC11. RNA-seq analysis showed MEKi to decrease the expression of multiple HDAC11 target genes. Silencing of HDAC11 significantly reduced protein deacetylation, enhanced the apoptotic response to MEKi and reduced growth in long-term colony formation assays across multiple UM cell lines. Knockdown of HDAC11 led to decreased expression of TAZ in some UM cell lines, accompanied by decreased YAP/TAZ transcriptional activity and reduced expression of multiple YAP/TAZ target genes. Further studies showed this decrease in TAZ expression to be associated with increased LKB1 activation and modulation of glycolysis. In an in vivo model of uveal melanoma, silencing of HDAC11 limited the escape to MEKi therapy, an effect associated with reduced levels of Ki67 staining and increased cleaved caspase-3. We have demonstrated a novel role for adaptive HDAC11 activity in UM cells, that in some cases modulates YAP/TAZ signaling leading to MEKi escape.

A Novel PHD2/VHL-mediated Regulation of YAP1 Contributes to VEGF Expression and Angiogenesis

The transcriptional co-activator YAP1 is the major oncogenic component of the Hippo signaling pathway and contributes to the genesis and progression of various tumors, including non-small cell lung cancer (NSCLC). YAP1 levels are regulated by the canonical Hippo kinases, MST1/2 and LATS1/2, which modulate its cytoplasmic retention and proteasomal degradation. While non-canonical regulation of YAP1 has been reported, its role in hypoxic response is not fully elucidated. The studies presented here show that YAP1 levels and function are modulated by VHL and PHD2. YAP1 could regulate multiple genes involved in angiogenesis through E2F1; it also associates with HIF1α in cancer cells under hypoxic conditions, inducing the VEGF-A promoter. Under normoxic conditions, PHD2 associates with and hydroxylates specific proline residues on YAP1, facilitating its interaction with VHL and promoting ubiquitination and subsequent proteasomal degradation. Exposure to hypoxia dissociates YAP1 from PHD2 and VHL, elevating YAP1 levels and enhancing its association with HIF1α. YAP1-HIF1α interaction was higher in NSCLC and RCC samples, indicating a role for this interaction in the genesis of these cancers. Our results thus reveal a novel mode of regulation of YAP1 by PHD2 and VHL in normoxic cells, suggesting that YAP1-mediated induction of VEGF and other genes contributes to hypoxic response in tumors.

Lifetime ovulatory years and ovarian cancer gene expression profiles

BACKGROUND

Greater ovulatory years is associated with increased ovarian cancer risk. Although ovulation leads to an acute pro-inflammatory local environment, how long-term exposure to ovulation impacts ovarian carcinogenesis is not fully understood. Thus, we examined the association between gene expression profiles of ovarian tumors and lifetime ovulatory years to enhance understanding of associated biological pathways.

METHODS

RNA sequencing data was generated on 234 invasive ovarian cancer tumors that were high-grade serous, poorly differentiated, or high-grade endometrioid from the Nurses' Health Study (NHS), NHSII, and the New England Case Control Study. We used linear regression to identify differentially expressed genes by estimated ovulatory years, adjusted for birth decade and cohort, overall and stratified by menopausal status at diagnosis. We used false discovery rates (FDR) to account for multiple testing. Gene set enrichment analysis (GSEA) with Cancer Hallmarks, KEGG, and Reactome databases was used to identify biological pathways associated with ovulatory years.

RESULTS

No individual genes were significantly differentially expressed by ovulatory years (FDR > 0.19). However, GSEA identified several pathways that were significantly associated with ovulatory years, including downregulation of pathways related to inflammation and proliferation (FDR < 1.0 × 10-5). Greater ovulatory years were more strongly associated with downregulation of genes related to proliferation (e.g., E2F targets, FDR = 1.53 × 10-24; G2M checkpoints, FDR = 3.50 × 10-22) among premenopausal versus postmenopausal women at diagnosis. The association of greater ovulatory years with downregulation of genes involved in inflammatory response such as interferon gamma response pathways (FDR = 7.81 × 10-17) was stronger in postmenopausal women.

CONCLUSIONS

Our results provide novel insight into the biological pathways that link ovulatory years to ovarian carcinogenesis, which may lead to development of targeted prevention strategies for ovarian cancer.

Abstract 1523: Novel role of TBK1 in breast cancer EMT

TANK Binding Kinase 1 (TBK1) regulates interferon signaling and NFκB function by acting as a non-canonical IκB kinase. TBK1 also participates in RalB-mediated inflammatory responses and is essential for the survival of non-small cell lung cancers (NSCLC) driven by oncogenic KRAS. Recent evidence suggests a role for TBK1 as a driver of cancer progression and it is overexpressed in breast, colon, lung and pancreatic cancers. Our published results demonstrate that TBK1 is essential for proper microtubule dynamics and regulation of mitosis. Here we show that knockdown of TBK1 results in a decreased expression of mesenchymal genes involved in EMT and a re-distribution of β-catenin in breast cancer cells. Similarly, expression of matrix metalloproteinases 2 and 9 was altered. This led us to hypothesize that TBK1 acts as an EMT driver in cancer. Inhibition of TBK1 resulted in decreased adherence dependent as well as independent colony formation and stem cell self-renewal, while inducing senescence like phenotypes. We propose that TBK1 mediated EMT is mediated through its interaction with the transcription factor E2F1; the interaction was detected in breast cancer cell lines as well as breast cancer Tissue Micro Arrays. To get a holistic view of the changes that take place in the cell after TBK1 knockdown, we performed a global metabolomics and RNAseq analysis of breast cancer cell lines. An integrated analysis of this data suggested significant alterations in glucose, galactose and nucleotide metabolism upon TBK1 knockdown. Two of the genes that were markedly altered were aldoketoreductase1 B10 (AKR1B10) and thymidine phosphorylase (TP); attention was focused on these genes, as both have been reported to be cancer drivers and their over-expression results in poor prognosis. We observed a downregulation of AKR1B10 and TP in response to the TBK1 knockdown. Experiments are under way to investigate whether the pro-cancer role of TBK1 is dependent on AKR1B10 and TP, especially in breast cancer cells. These results suggest that TBK1 mediated EMT might be a function of the altered expression of mesenchymal proteins and the metabolic profile of the cell brought about by TBK1.

Citation Format: Meenu Maan, Mainak Dutta, Neha Jaiswal, Harold Saavedra, Srikumar Chellappan. Novel role of TBK1 in breast cancer EMT [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1523.

Novel HDAC11 inhibitors suppress lung adenocarcinoma stem cell self-renewal and overcome drug resistance by suppressing Sox2

Non-small cell lung cancer (NSCLC) is known to have poor patient outcomes due to development of resistance to chemotherapy agents and the EGFR inhibitors, which results in recurrence of highly aggressive lung tumors. Even with recent success in immunotherapy using the checkpoint inhibitors, additional investigations are essential to identify novel therapeutic strategies for efficacious treatment for NSCLC. Our finding that high levels of histone deacetylase 11 (HDAC11) in human lung tumor tissues correlate with poor patient outcome and that depletion or inhibition of HDAC11 not only significantly reduces self-renewal of cancer stem cells (CSCs) from NSCLC but also decreases Sox2 expression that is essential for maintenance of CSCs, indicates that HDAC11 is a potential target to combat NSCLC. We find that HDAC11 suppresses Sox2 expression through the mediation of Gli1, the Hedgehog pathway transcription factor. In addition, we have used highly selective HDAC11 inhibitors that not only target stemness and adherence independent growth of lung cancer cells but these inhibitors could also efficiently ablate the growth of drug-insensitive stem-like cells as well as therapy resistant lung cancer cells. These inhibitors were found to be efficacious even in presence of cancer associated fibroblasts which have been shown to contribute in therapy resistance. Our study presents a novel role of HDAC11 in lung adenocarcinoma progression and the potential use of highly selective inhibitors of HDAC11 in combating lung cancers.

Chromatin protein PC4 is downregulated in breast cancer to promote disease progression: Implications of miR-29a

The human transcriptional coactivator PC4 has numerous roles to play in the cell. Other than its transcriptional coactivation function, it facilitates chromatin organization, DNA damage repair, viral DNA replication, etc. Although it was found to be an essential protein in vivo, the importance of this multifunctional protein in the regulation of different cellular pathways has not been investigated in details, particularly in oncogenesis. In this study, PC4 downregulation was observed in a significant proportion of mammary tissues obtained from Breast cancer patient samples as well as in a subset of highly invasive and metastatic Breast cancer patient-derived cell lines. We have identified a miRNA, miR-29a which potentially reduce the expression of PC4 both in RNA and protein level. This miR-29a was found to be indeed overexpressed in a substantial number of Breast cancer patient samples and cell lines as well, suggesting one of the key mechanisms of PC4 downregulation. Stable Knockdown of PC4 in MCF7 cells induced its migratory as well as invasive properties. Furthermore, in an orthotopic breast cancer mice model system; we have shown that reduced expression of PC4 enhances the tumorigenic potential substantially. Absence of PC4 led to the upregulation of several genes involved in Epithelial to Mesenchymal Transition (EMT), indicating the possible mechanism of uniform tumour progression in the orthotropic mice. Collectively these data establish the role of PC4 in tumour suppression.

Abstract 378: HDAC inhibition enhances MEK antagonist therapy in uveal melanoma through combined blockade of YAP, AKT and RTK signaling

Around 85-90% of all uveal melanomas harbor driver mutations in GNAQ or GNA11 leading to constitutive activation of numerous signaling pathways, including the MAPK pathway. MEK inhibitors have been evaluated clinically for metastatic uveal melanoma, but the responses are short-lived and the mechanisms of adaptation are poorly understood. In the current study, we performed RNA-seq and activity-based protein profiling (ABPP) to define the adaptive response of uveal melanoma cells to MEK inhibition and to design more effective combination therapy strategies. These analyses showed that MEK inhibition caused cytoskeleton remodeling driven by cortactin/Rho-GTPases with an increase in YAP activity, which in turn allowed therapeutic escape. Cortactin knockdown decreased YAP activity in response to MEK inhibition, increased cell death in vitro and was associated with tumor shrinkage in vivo. The proteomic data showed that MEK inhibition increased HDAC activity and an increase in global protein deacetylation. Co-targeting of HDACs and MEK was associated with increased apoptosis, decreased survival in 2D and 3D cell culture assays and suppression of YAP signaling. As YAP was unlikely to be the only escape pathway, we performed kinome and RTK arrays and demonstrated MEK inhibition also increases ROR1/2 and IGF-1R phosphorylation, leading to downstream PI3K/AKT signaling. At a signal transduction level, the combination of a pan-HDAC inhibitor (panobinostat) with a MEK inhibitor (trametinib) blocked all of the adaptive signaling pathways we identified, including RTKs, AKT, YAP and cortactin. In vivo xenograft studies revealed the MEK/HDAC inhibitor combination to outperform either agent alone, leading to long-term decrease of tumor growth and the suppression of adaptive PI3K/AKT, cortactin and YAP signaling. These findings identify HDAC inhibitors as a promising combination partner for MEK inhibitors in advanced uveal melanoma that may lead to improved systemic responses.

Citation Format: Fernanda Faiao-Flores, Michael Emmons, Michael Durante, Biswarup Saha, Bin Fang, John Koomen, Srikumar Chellappan, Silvya Maria-Engler, Jonathan Licht, William Harbour, Keiran Smalley. HDAC inhibition enhances MEK antagonist therapy in uveal melanoma through combined blockade of YAP, AKT and RTK signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 378.

Abstract 4394: Molecular interplay between Tank-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality in the United States. Lung adenocarcinomas are highly correlated with smoking and are characterized by mutations in KRAS, EGFR, BRAF and other oncogenes. KRAS mutations are widespread in adenocarcinomas among smokers and known to be a key player in various downstream signaling pathways contributing to the tumorigenesis. Recently, a non-canonical IκB kinase, Tank Binding Kinase 1 (TBK1), has been found to contribute in KRAS mutant cancers. TBK1 has well documented functions in immune response, cell survival and in mitosis. While it has been suggested that TBK1-mediated regulation of Akt signaling might facilitate oncogenesis, the molecular mechanisms underlying TBK1 function downstream of KRAS is not fully elucidated.

Yes associated protein 1 (YAP1) is an oncogenic component of the Hippo signaling cascade which could promote KRAS mediated oncogenesis and could substitute for the loss of Kras in mouse models of pancreatic cancer. In our present study, we demonstrate a unique and novel interplay between TBK1 and the oncogenic Hippo effector molecule, YAP1. YAP1 and its paralog, TAZ are known transcriptional co-activators that function to maintain organ size during development and is often activated in cancers.

We find that TBK1 could physically interact with YAP1 and phosphorylate it at T110, T114, S128 and S131 residues in vitro. Knocking down (KD) or knock out (KO) of TBK1 resulted in a significant elevation of YAP1 expression at the protein level; surprisingly, without any effect at the mRNA level. Interestingly, the upregulation of YAP1 upon depletion of TBK1 was restricted to KRAS mutant NSCLC cell-lines and not in EGFR mutant cell lines. This elevation of YAP1 upon TBK1 KD was mainly observed in the nucleus; notably, there were only minimal changes in the levels of MST and LATS, raising the possibility that these changes occur independent of the classic hippo signaling pathway. Treatment with cycloheximide, an inhibitor of protein-translation, could not diminish the elevated level of YAP1 protein in the TBK1 depleted cells, indicating that the increased YAP1 level is due to enhanced protein stability, probably as a result of post-translational modification(s). Depletion of TBK1 also resulted in the induction of EMT-like features, promoting cell-migration in scratch assays and elevated the proportion of stem-like side-population cells, probably in a YAP1-dependent manner. An unbiased RNA-Seq analysis in A549 and H460 cells indicated that MAP kinase (MAPK) pathway is activated upon TBK1 KD, which might also be involved in the YAP1 protein regulation. Our recent experiments further support this argument. The in-depth molecular mechanism(s) by which TBK1 regulates YAP1 in KRAS mutant cells are under investigation, and we hypothesize that this regulatory event contributes to KRAS mediated oncogenesis in NSCLC.

Citation Format: Biswarup Saha, Neha Jaiswal, Namrata Bora-Singhal, Srikumar Chellappan. Molecular interplay between Tank-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4394.

Abstract 2052: A novel PHD2/VHL- mediated regulation of YAP1 and its role in vascular mimicry and tumor angiogenesis

Non-small cell lung cancer (NSCLC) is the leading cause of cancer related death worldwide. In this study, we show that transcriptional co-activator YAP1, the oncogenic component of the Hippo pathway, may contribute to the progression of NSCLC by supporting tumor angiogenesis and vascular mimicry of cancer stem-like cells (CSCs). NSCLC CSCs were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2); depletion of YAP1 inhibited the promoter activity as well as the mRNA expression of VEGF, KDR and AngPT-2, with a corresponding reduction in vascular mimicry as well as tumor growth in a mouse xenograft studies. These results suggest a possible mechanism by which YAP1 regulates tumor angiogenesis.

A role for YAP1 in tumor angiogenesis was further supported by the finding that NSCLC cells grown in hypoxic conditions showed higher levels of YAP1. There was little to no changes in the canonical Hippo pathway proteins like LATS1/2, MST1/2, SAV and MOB as well as in the expression of TAZ, an orthologue of YAP1. Elevated YAP1 was found to associate with HIF1α under hypoxic conditions and enhance its transcriptional activity; YAP1 could increase HIF1α-mediated induction of the VEGF promoter confirmed by chromatin immunoprecipitations and transient transfection assays. Elevated levels of YAP1 and HIF1α interaction was detected in lung tumor tissues compared to normal lung tissue, as detected by proximity ligation assay (PLA), suggesting that the higher association of YAP1 with HIF1α and resulting transcriptional activity might have contributed to tumor growth.

An examination of the underlying mechanism by which YAP1 levels are elevated under hypoxic conditions revealed a novel regulation of YAP1 protein by prolyl hydroxylase PHD2 and E3 ubiquitin ligase VHL, which are mainly known to regulate HIF1α under normoxia. PHD2 was found to hydroxylate proline residue(s) of YAP1 between aa 284 to aa 289 as seen by mutational studies. YAP1 was found to directly associate with PHD2 as well as with VHL. Depletion of PHD2 or treatment with DMOG, an inhibitor of prolyl hydroxylases, reduced YAP1 association with VHL ligase. This further elevated YAP1 levels in the nucleus. Interestingly, disruption of the YAP1-PHD2 interaction using a domain specific peptide enhanced the angiogenic tubule formation by endothelial cells. Our data therefore identifies a novel non-canonical pathway of regulation of YAP1 that supports angiogenesis and tumor growth.

Citation Format: Namrata Bora Singhal, Biswarup Saha, Srikumar Chellappan. A novel PHD2/VHL- mediated regulation of YAP1 and its role in vascular mimicry and tumor angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2052.

Abstract 1998: Novel interplay between TANK-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality in the United States. Lung adenocarcinomas are highly correlated with smoking and are characterized by mutations in KRAS, EGFR, BRAF and other oncogenes. Among them, KRAS mutations are widespread in adenocarcinomas in smokers and known to be a key player in various downstream signaling pathways contributing to genesis and progression of these tumors. More recently, the non-canonical IκB kinase, Tank Binding Kinase 1 (TBK1), has been found to facilitate tumorigenesis in KRAS mutant cancers. TBK1 has well documented functions in immune response, cell survival as well as in mitosis. While it has been suggested that TBK1-mediated regulation of Akt signaling might facilitate oncogenesis, the molecular mechanisms underlying TBK1 function downstream of KRAS is not fully elucidated. In a similar vein, Yes associated protein 1 (YAP1), the oncogenic component of the Hippo signaling cascade has been found to promote KRAS mediated oncogenesis and could substitute for the loss of Kras in mouse models of pancreatic cancer. In the present study, we have demonstrated a unique and novel molecular interplay between TBK1 and the oncogenic components of Hippo effector molecules, YAP1/TAZ. YAP1 and its ortholog, TAZ are known to be transcriptional co-activators, function to maintain organ size but often get activated in various types of cancer.

We find that TBK1 physically interacts with YAP1, and knock-down (KD) or knocking-out (KO) of TBK1 resulted in a significant elevation of YAP1/TAZ expressions at protein level. We have tested four different KRAS and EGFR mutant NSCLC cell-lines; interestingly, the upregulation of YAP1 upon depletion of TBK1 was only restricted to the KRAS mutant cell-lines. Further, depletion of TBK1 led to the enrichment of YAP1 in the nucleus; notably, there were only minimal changes in the levels of MST1/2 and LATS, raising the possibility that these changes occur independent of the classic hippo signaling pathway. Depletion of TBK1 also resulted in the induction of EMT-like features in these cells, and increased the proportion of stem-like side-population. Mechanistically, TBK1 physically interacts with YAP1 in the cultured cells, and could phosphorylate it in vitro, on T110, T114, S128 and S131 residues. The underlying molecular mechanism(s) by which TBK1 regulates YAP1 expression are under investigation, and we hypothesize that this regulatory event is exclusive to KRAS mediated oncogenesis, especially in the context of NSCLC.

Citation Format: Biswarup Saha, Neha Jaiswal, Namrata Bora-Singhal, Srikumar Chellappan. Novel interplay between TANK-binding kinase (TBK1) and Yes-associated protein (YAP1) in KRAS mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1998.

Abstract 2310: Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons

Glioblastoma multiforme (GBM) is the most prevalent and malignant brain tumor in adults. Currently there are no effective therapies to manage the disease efficiently. Medulloblastoma is the most common type of pediatric tumor and accounts for approximately 15% of all pediatric brain tumors. We aimed to determine if targeting the transcription-associated cyclin-dependent kinases, cdk7 and cdk9, using specific inhibitors, could interfere with the growth and metastatic properties of glioblastoma and medulloblastoma cell lines. We tested the effectiveness of Flavopiridol, a known inhibitor of cdk4, cdk6, pTEFb and cdk9; THZ1, a cdk7 inhibitor; and SNS032, which is known to inhibit cdk2, cdk7 and cdk9, on U87 and SNB19 glioblastoma, H4 neuroglioma and Daoy medullobastoma cells. Treatment with these pharmacological agents showed very strong cytotoxic effects on these cancer cells as measured by MTT (3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide) assay. Among these agents the cdk7 inhibitor was most effective and showed efficacy at nanomolar concentrations. Additionally, the inhibitors interfered with the cancer cell migration, as measured by wound healing assay, and anchorage independent growth, as measured by soft agar colony formation. In stark contrast, the inhibitors had no cytotoxic effects on primary neurons. Mechanistically, western blot analysis showed that the tumor cells treated with the inhibitors had reduced levels of Pol II C-terminal domain phosphorylation, indicative of its inhibition and suppression of transcription. Furthermore, inhibitor treatment resulted in a significant reduction in p70S6 kinase phosphorylation, suggesting that in addition to the transcriptional machinery, the translational machinery is also affected upon treatment with the aforementioned cdk inhibitors. Immunostaining analysis of the cells showed a marked reduction in the levels of P-Pol II and P-p70S6 kinase upon inhibitor treatment, confirming that the cdk inhibitors indeed interfere with both transcription and translation. These inhibitors appear to be working in a p53-dependent fashion. These novel findings shed light on potential mechanisms that can be targeted to combat both glioblastoma and medulloblastoma effectively. More specifically, our studies imply that cdk7 and cdk9 inhibitors may serve as potential therapies for effective management of brain tumor.

Citation Format: Isha Bhutada, Srikumar Chellappan, Jaya Padmanabhan. Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2310.

Abstract 5063: Beta-arrestin-1 function in CAFs is necessary for enhancement of self-renewal of NSCLC stem-like cells

Cigarette smoking is a major risk factor in the genesis of non-small cell lung cancer (NSCLC), which accounts for 85% of all lung cancer. Nicotine, the addictive component of tobacco smoke, has been shown to induce proliferation, invasion and epithelial-mesenchymal transition (EMT) in NSCLC cells in vitro and promote growth and metastasis of NSCLCs in vivo. These nicotine-induced pro-tumorigenic functions are facilitated through activation of nicotinic acetylcholine receptors (nAChRs). The scaffolding protein β-arrestin-1 (ARRB1), which is involved in the desensitization of signals from activated G-protein-coupled receptors (GPCRs), plays a vital role in mediating the proliferative effects of nicotine through nAChR signaling. Nicotine induces the nuclear translocation of ARRB1 and increases the expression of E2F-regulated proliferative and survival genes to promote the growth and progression of NSCLCs. β-arrestin-1 is also necessary for nicotine-mediated induction of EMT; nicotine could induce a variety of mesenchymal genes including fibronectin, vimentin, ZEB1 and ZEB2 in a β-arrestin-1 dependent manner. Further, nicotine promotes stemness of NSCLCs by inducing SCF (Stem cell factor) in a β-arrestin-1 dependent manner. While all these studies from NSCLC derived cell lines and tumor tissues highlight the significance of β-arrestin-1 in cell-autonomous pro-tumorigenic functions, the role of β-arrestin-1 in NSCLC microenvironment is largely unknown. Cancer associated fibroblasts (CAFs) are shown to promote the self-renewal and proliferation of cancer stem cells in vitro and in vivo. In the present study we address whether β-arrestin-1 is necessary for CAFs to promote self-renewal of stem like cells from NSCLCs.

We generated a GFP expressing KRAS mutant NSCLC cell line A549 (A549-GFP). The side population (SP) cells from A549-GFP was isolated and used in 3D co-culture with lung CAFs in a stem cell selective medium. Our results show that CAFs can promote the self-renewal of SP cells, as measured by a sphere formation assay. Interestingly, depletion of β-arrestin-1 in CAFs significantly impaired the ability of CAFs to promote self-renewal and enhance sphere formation. Experiments are under way to assess the downstream mediators of β-arrestin-1 in CAFs that bring about the impairment in self renewal, which includes signaling molecules like TBK1 and a variety of cytokines. These studies are expected to shed new light on the mechanisms by which CAFs promote self-renewal and tumor growth, enabling identification of actionable pathways downstream of β-arrestin-1 that can potentially be targeted for NSCLC therapy.

Citation Format: Mohan Kumar Durai Raj, Namrata Bora-Singhal, Srikumar Chellappan. Beta-arrestin-1 function in CAFs is necessary for enhancement of self-renewal of NSCLC stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5063.

Abstract 4701: Verteporfin inhibits surface PD-L1 expression in triple-negative breast cancer (TNBC) cells

Background: Programmed death ligand 1 (PDL1) is commonly expressed on the surface of many tumor cells, including breast cancer. The activity of tumor-infiltrating lymphocytes (TIL) is inhibited by PDL1. High PD-L1 basal cells (particularly basal B) overexpress genes involved in invasion, motility, and chemoresistance (Soliman et al., 2014). Targeting and blocking PD-L1 may enhance eradication of aggressive breast cancer cells by the immune system. Verteporfin (VP), a photosensitizer used to treat macular degeneration, was found to inhibit PD-L1 expression in a high-throughput screen. Studies demonstrated VP inhibits YAP activation by disrupting YAP-TEAD interactions and preventing YAP induced oncogenic growth (Zhang et al., 2016). Here we demonstrate the inhibitory effect of VP on PD-L1 expression in TNBC cell lines.

Methods: MDA-MB-231 cells co-cultured with human PBMCs were treated with VP (Sigma) in presence of concanavalin A (ConA) and analyzed using flow cytometry to study levels of CD8+IFNg+ cells. TNBC cell lines (MDA-MB-231, BT-20, HCC-1143, Hs-578T) were treated with VP at doses ranging from 1µM-10µM for 24 hrs. The cells were processed for flow cytometry, Western blot and RT-PCR to check PD-L1 in mechanistic studies looking at manipulation of YAP pathway genes.

Results: When MDA-MB-231 cells were co-cultured with normal human PBMCs in the presence of ConA, the CD8+IFNg+ stained cells were reduced compared to PBMC + ConA alone. Interestingly, in the group treated with VP, rescue of CD8+IFNg+ cells was observed. Moreover, MDA-MB-231, BT-20, HCC-1143 and Hs-578T TNBC cells treated with VP showed a significant dose-dependent inhibition of PD-L1 expression by flow cytometry. Western blot analysis also showed complete clearance of PD-L1 protein band with the lowest dose (1µM) used. However, RT-PCR analysis did not show a significant fold change in mRNA levels of PD-L1 in MDA-MB-231 treated cells. Surprisingly, mechanistic studies performed by silencing YAP1, E2F1, and TBK1 in MDA-MB-231, BT-20 and HS-578 T showed a decline in PD-L1 in E2F1 silenced cells, highlighting a plausible role of E2F1-PDL1 signaling axis. However, no change in PD-L1 expression was seen in cells silenced with YAP1 and TBK1. Further, chromatin-immunoprecipitation assay demonstrated E2F1 binding to PD-L1 promoter.

Conclusion: Our data so far demonstrate that verteporfin treatment leads to inhibition of PD-L1 in TNBC cell lines and improvement in CD8+IFNg+ cells, indicating that VP might have potential for treatment approaches. Our study warrants further attention towards understanding the mechanism of action of VP in inhibiting PD-L1 and the role of E2F1 in the process.

Citation Format: Fatema Khambati, Neha Jaiswal, Srikumar Chellappan, Hatem Soliman. Verteporfin inhibits surface PD-L1 expression in triple-negative breast cancer (TNBC) cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4701.

Abstract 3460: TBK1 regulates mitotic progression by modulating spindle assembly checkpoint in cancer cells

TANK Binding Kinase 1 (TBK1) is a non-canonical IkB kinase that contributes to KRAS-driven lung cancer. It is activated by phosphorylation of Serine-172 by TLR and RIG1 signaling, and this circuit triggers phosphorylation of IRF3 and IRF7, activation of NFκB and the expression of proinflammatory genes and interferons. In addition to its role role in regulating innate immunity, TBK1 also promotes oncogenesis by phosphorylating Akt and enhancing cell survival and by promoting autophagy and mitophagy. TBK1 is also induced under hypoxic conditions and expressed at significant levels in many solid tumors. TBK1 also contributes to prostate cancer dormancy and drug resistance by inhibiting mTOR and to tamoxifen resistance of breast cancer cells by enhancing transcriptional activity of ERα.

Recent studies from our lab revealed a novel role for TBK1 in regulating mitosis. It was found that levels of phospho-TBK1 increases and localizes to centrosomes and the mitotic spindles during mitosis. Depletion of TBK1 was shown to trigger defects in spindle apparatus and prevents mitotic progression (Pillai et al., Nature Communications, 2015). TBK1 physically interacts and phosphorylates centrosomal protein CEP170 and mitotic apparatus protein NuMA. At the same time, it is not clear whether TBK1 regulates mitosis my modulating the Spindle Assembly Checkpoint (SAC).

Our results show that TBK1 colocalizes with Cdc20 on the centrosomes. Additionally, TBK1-inhibited cells showed an increase in the colocalization of BUBR1 and Cdc20, with enhanced recruitment of BUBR1 to kinetochores. To further study how TBK1 affects SAC, lung and breast cancer cells were depleted of TBK1 by CRISPR/Cas9 mediated genome editing. Cells depleted of TBK1 showed very few cells in the mitotic stage; those that entered mitosis had residual levels of TBK1 and showed multipolarity and unusually stable and bundled microtubules. TBK1 knockout cells not only showed aberrant mitotic structures and had elevated levels of SAC components including BUBR1 and Cdc20. Surprisingly, level of mitotic Cyclin B1 remained unchanged in spite of elevated levels of Cdc20 indicating a possible inactivation of Anaphase Promoting complex (APC/C). Also, percentage of Cyclin B1 positive cells was significantly high in mitotic cells enriched using double thymidine block in the presence of TBK1 inhibitor BX795 (R9+BX) and MRT67307 (R9+MRT) as compared to untreated mitotic cells (R9). Further, double thymidine blocked released cells displayed elevated levels of SAC components upon treatment with TBK1 inhibitors. All these findings suggest that TBK1 facilitates mitotic progression through satisfying SAC.

Citation Format: Neha Jaiswal, Smitha Pillai, Namrata BoraSinghal, Srikumar Chellappan. TBK1 regulates mitotic progression by modulating spindle assembly checkpoint in cancer cells [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 3460. doi:10.1158/1538-7445.AM2017-3460

Abstract 365: Cross-talk between BRAF and Hippo/YAP1 signaling in melanoma

Hippo/YAP1 signaling pathway is a tumor suppressive pathway that controls the organ size by modulating the cell growth, proliferation and apoptosis and is conserved from Drosophila to mammals. In mammals, the Hippo tumor suppressor pathway consists of cascade of kinases in which MST1/2 phosphorylates and activates LATS1/2. The latter phosphorylates the oncogenic transcriptional coactivators YAP1 and TAZ, leading to their cytoplasmic retention by 14-3-3 proteins and/or degradation. Inactivation of MST and LATS kinases allows YAP1 and/ or TAZ nuclear translocation and subsequent activation of their target genes.

Deregulation of Hippo pathway can induce tumors in model organisms and occurs in wide range of human cancers including melanoma. Merlin, a key component of this pathway which inhibits YAP1, is mutated/deleted in 8% of melanoma. Majority of uveal melanomas are driven by Gq/11 mutations that trigger YAP1 nuclear translocation, promoting tumor growth. High levels of YAP1 in BRAFV600E mutant tumors confer resistance to RAF- and MEK- targeted therapy in patients.

Our results show that YAP1 level is elevated in melanoma and the YAP1 inhibitor verteporfin alone or in combination with B-RAF inhibitor PLX4720 reduces the viability, invasion and anchorage-independent growth of B-RAF V600E mutant SK-MEL-28 and SK-MEL-5 cells. In addition, verteporfin treatment also reduced the viability of PLX4720 resistant 1205 cells. Western blot analysis of verteporfin and PLX4720 treated SK-MEL-28 and SK-MEL-5 cells displayed reduced levels of YAP1, B-RAF, pERK, MEK and pMEK.

We also report a novel physical interaction between YAP1 and B-RAF; this could be detected using double immunofluorescence and immunoprecipitation-western blotting techniques in both B-RAF V600E mutant and N-Ras mutant melanoma cells. Proximity ligation assays on tissue microarray showed that YAP1-B-RAF interaction is elevated in metastatic melanoma compared to normal skin. These novel findings highlight the crosstalk between B-RAF and Hippo/YAP1 signaling which might have a

potential role in melanoma development and progression. Further, experiments are in progress to elucidate the functional significance of YAP1-B-RAF interaction in melanoma.

Citation Format: Mohan Kumar Durai Raj, Jonathan Nguyen, Namrata Bora-singhal, Jane Messina, Geoffrey Gibney, Srikumar Chellappan. Cross-talk between BRAF and Hippo/YAP1 signaling in melanoma [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 365. doi:10.1158/1538-7445.AM2017-365

Abstract 2145: Regulation of YAP1 during hypoxia and its novel role in vascular mimicry and angiogenesis

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality. As in other solid tumors, angiogenesis is necessary for the growth and progression of NSCLC. Vascular mimicry is a phenomenon in which non-endothelial tumor cells form angiogenic vascular structures. We have shown in the past that NSCLC cancer stem-like cells (CSCs) have unique ability to undergo vascular mimicry. The present study shows that transcriptional co-activator YAP1, the oncogenic component of the Hippo pathway, enables the NSCLC CSCs to form angiogenic tubule-like structures in matrigel. Inhibition of YAP1 or depletion of YAP1 suppressed vascular mimicry of CSCs as well as angiogenic tubule formation by HUVECs in matrigel as well as in a fibrin gel bead assay (FIBA) assay. The NSCLC CSCs were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2) and depletion of YAP1 reduced the expression of VEGF, KDR and AngPT-2 mRNA; these promoters were induced by YAP1 in transient transfection assays, suggesting a possible molecular mechanism by which YAP1 regulates angiogenesis. Hypoxia is a strong inducer of tumor angiogenesis, cancer progression and metastasis. Our experiments showed that NSCLC cells grown in hypoxic conditions or treated with hypoxia mimetic DMOG have higher YAP1 mRNA and protein expression. However, such a change was not observed in the expression of YAP1 orthologue, TAZ, nor in the canonical Hippo pathway proteins like LATS1&2, Mst1&2, Sav or Mob. We identified a novel regulation of YAP1 by prolyl hydroxylase PHD2, which is mainly known to regulate HIF1α. PHD2 was found to hydroxylate proline residue(s) in YAP1 in a region between aa 284 to aa 289 as seen by mutational analysis. YAP1 was found to directly bind to PHD2 and depletion of PHD2 or treatment with DMOG which is an inhibitor of prolyl hydroxylases, elevated YAP1 protein levels in the nucleus. Further, YAP1 was found to associate with HIF1α as detected by co-immunoprecipitation experiments and could enhance HIF1α-mediated induction of the VEGF promoter. Proximity ligation assays performed on TMA showed enhanced YAP1 and HIF1α interaction in lung tumor tissues compared to normal cells. Our data suggest a novel regulation of YAP1 in hypoxic environment that supports angiogenesis and tumor growth.

Citation Format: Namrata Bora Singhal, Srikumar Chellappan. Regulation of YAP1 during hypoxia and its novel role in vascular mimicry and angiogenesis [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 2145. doi:10.1158/1538-7445.AM2017-2145

Abstract 2496: Novel role of YAP1 in tumor angiogenesis and vascular mimicry

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that cancer stem-like cells (CSCs) contribute to the genesis and progression of NSCLC. These cells have been shown to form differentiated tumor cells upon receiving appropriate micro-environmental cues and can give rise to multiple components of the tumor, including the vasculature. We isolated the CSCs from NSCLC cell lines and PDX tumors based on the side population (SP) phenotype. SP cells displayed high self-renewal capacity, were highly drug resistant, and could form metastatic tumors in immunocompromised mice. The present study shows that the transcriptional co-activator YAP1, which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and the ability to form angiogenic tubule-like structures in matrigel, a unique feature of cancer stem-like cells that is also called as vascular mimicry. Inhibition of YAP1 by a small molecule inhibitor Visudyne or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of SP cells. The stem -like SP cells from NSCLC were found to have higher mRNA expression of VEGF receptor II (KDR) and Angiopoietin-2 (AngPT-2) which are crucial genes during angiogenic tubule regression and growth in addition to YAP1. Further, depletion of YAP1 with siRNAs reduced the expression of VEGF, KDR and AngPT-2 mRNA levels. Overexpression of YAP1 resulted in increase in the promoter activity of both KDR and AngPT-2 in transient transfection experiments. This suggests that YAP1 might play a role in regulating VEGF, KDR and AngPT-2 mediated angiogenic functions in cancer cells.

In addition to vascular mimicry, YAP1 appears to play a unique role in regulating the expression of genes involved in angiogenesis. Hypoxia is known to contribute towards angiogenesis as well as cancer progression and metastasis. Preliminary experiments showed that cells grown in hypoxic conditions or treated with hypoxia mimetic compounds like DMOG resulted in increase in YAP1 mRNA and protein expression. However, such an increase was not observed in YAP1 orthologue, TAZ or other canonical Hippo pathway proteins. Hypoxia-inducible factor-1alpha (HIF-1α) is the key transcription factor that regulates the expression of various hypoxia response genes like VEGF. We find that YAP1 directly interacts with HIF-1α as detected by co-immunoprecipitation experiments and proximity ligation assays (PLA). YAP1 also associated with VEGF promoter as seen in ChIP RT-PCRs, and this interaction was elevated under hypoxic environment. Our data suggest a distinct role for YAP1 in regulating hypoxia response, promoting tumor angiogenesis and vascular mimicry.

Citation Format: Namrata Bora Singhal, Srikumar Chellappan. Novel role of YAP1 in tumor angiogenesis and vascular mimicry. [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 2496.

Gli1-Mediated Regulation of Sox2 Facilitates Self-Renewal of Stem-Like Cells and Confers Resistance to EGFR Inhibitors in Non-Small Cell Lung Cancer

Non–small cell lung cancer (NSCLC) patients have very low survival rates because the current therapeutic strategies are not fully effective. Although EGFR tyrosine kinase inhibitors are effective for NSCLC patients harboring EGFR mutations, patients invariably develop resistance to these agents. Alterations in multiple signaling cascades have been associated with the development of resistance to EGFR inhibitors. Sonic Hedgehog and associated Gli transcription factors play a major role in embryonic development and have recently been found to be reactivated in NSCLC, and elevated Gli1 levels correlate with poor prognosis. The Hedgehog pathway has been implicated in the functions of cancer stem cells, although the underlying molecular mechanisms are not clear. In this context, we demonstrate that Gli1 is a strong regulator of embryonic stem cell transcription factor Sox2. Depletion of Gli1 or inhibition of the Hedgehog signaling significantly abrogated the self-renewal of stem-like side-population cells from NSCLCs as well as vascular mimicry of such cells. Gli1 was found to transcriptionally regulate Sox2 through its promoter region, and Gli1 could be detected on the Sox2 promoter. Inhibition of Hedgehog signaling appeared to work cooperatively with EGFR inhibitors in markedly reducing the viability of NSCLC cells as well as the self-renewal of stem-like cells. Thus, our study demonstrates a cooperative functioning of the EGFR signaling and Hedgehog pathways in governing the stem-like functions of NSCLC cancer stem cells and presents a novel therapeutic strategy to combat NSCLC harboring EGFR mutations.

Nicotine-Mediated Regulation of Nicotinic Acetylcholine Receptors in Non-Small Cell Lung Adenocarcinoma by E2F1 and STAT1 Transcription Factors

Cigarette smoking is the major risk factor for non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, the addictive component of tobacco smoke, can induce proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), angiogenesis, and survival in NSCLC cell lines, as well as growth and metastasis of NSCLC in mice. This nicotine-mediated tumor progression is facilitated through activation of nicotinic acetylcholine receptors (nAChRs), specifically the α7 subunit; however, how the α7 nAChR gene is regulated in lung adenocarcinoma is not fully clear. Here we demonstrate that the α7 nAChR gene promoter is differentially regulated by E2F and STAT transcription factors through a competitive interplay; E2F1 induces the promoter, while STAT transcription factors repress it by binding to an overlapping site at a region -294 through -463bp upstream of the transcription start site. Treatment of cells with nicotine induced the mRNA and protein levels of α7 nAChR; this could be abrogated by treatment with inhibitors targeting Src, PI3K, MEK, α7 nAChR, CDK4/6 or a disruptor of the Rb-Raf-1 interaction. Further, nicotine–mediated induction of α7 nAChR was reduced when E2F1 was depleted and in contrast elevated when STAT1 was depleted by siRNAs. Interestingly, extracts from e-cigarettes, which have recently emerged as healthier alternatives to traditional cigarette smoking, can also induce α7 nAChR expression in a manner similar to nicotine. These results suggest an autoregulatory feed-forward loop that induces the levels of α7 nAChR upon exposure to nicotine, which enhances the strength of the signal. It can be imagined that such an induction of α7 nAChR contributes to the tumor-promoting functions of nicotine.

YAP1 Regulates OCT4 Activity and SOX2 Expression to Facilitate Self-Renewal and Vascular Mimicry of Stem-Like Cells

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that stem-like cells contribute to the genesis and progression of NSCLC. Our results show that the transcriptional coactivator yes-associated protein 1 (YAP1), which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and ability to form angiogenic tubules. Inhibition of YAP1 by a small molecule or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of stem-like cells. These effects of YAP1 were mediated through the embryonic stem cell transcription factor, Sox2. YAP1 could transcriptionally induce Sox2 through a physical interaction with Oct4; Sox2 induction occurred independent of TEAD2 transcription factor, which is the predominant mediator of YAP1 functions. The binding of Oct4 to YAP1 could be detected in cell lines as well as tumor tissues; the interaction was elevated in NSCLC samples compared to normal tissue as seen by proximity ligation assays. YAP1 bound to Oct4 through the WW domain, and a peptide corresponding to this region could disrupt the interaction. Delivery of the WW domain peptide to stem-like cells disrupted the interaction and abrogated Sox2 expression, self-renewal, and vascular mimicry. Depleting YAP1 reduced the expression of multiple epithelial-mesenchymal transition genes and prevented the growth and metastasis of tumor xenografts in mice; overexpression of Sox2 in YAP1 null cells rescued these functions. These results demonstrate a novel regulation of stem-like functions by YAP1, through the modulation of Sox2 expression.

Abstract 2085: Nicotine-mediated regulation of Sox2 and its implications in the biology of non-small cell lung adenocarcinoma stem-like cells

Nicotine, the addictive component of tobacco smoke, is known to promote proliferation, migration, and invasion of multiple cancer cells, including those of the lung and the pancreas. In addition, nicotine can promote the growth and metastasis of such cancers in mouse xenograft models. More recently, nicotine has also been implicated in promotion of cancer stem cell properties such as self-renewal. Our lab has shown that stimulation of lung cancer cells with nicotine results in activation of Src kinase in a β-arrestin-1 dependent manner, resulting in inactivation of the Rb tumor suppressor protein and subsequently the activation of E2F-mediated transcription of proliferative and survival genes. In addition to proliferative and survival genes, the E2F family of transcription factors has been shown to activate genes like matrix metalloproteinases that are involved in invasion and migration, indicating a role for E2F in the growth and metastasis of cancers downstream of nicotine. Our recent studies have shown that E2F1 can also induce genes which promote stemness, such as Stem Cell Factor (SCF/c-kit ligand), promoting nicotine-mediated enhancement of self-renewal of stem-like cells. In addition to these findings, here we demonstrate the ability of nicotine to induce the embryonic stem cell factor Sox2, which is indispensable for self-renewal and maintenance of stem cell properties, as well as the ability of E2F1 transcription factor to regulate Sox2 gene expression in non-small cell lung cancer cells. Western blot analysis revealed an induction of Sox2 protein at 18 and 24 hours post nicotine stimulation, which diminished by 48 hours. Similarly, quantitative real time PCR analysis showed an increase in Sox2 mRNA levels at 18 and24, hours post nicotine stimulation. Analysis of a 1500bp region of the human Sox2 gene promoter revealed multiple predicted E2F binding sites. Chromatin immunoprecipitation assays demonstrated E2F transcription factors to associate with the Sox2 promoter at multiple predicted binding sites. Transient transfection experiments further demonstrated the ability of E2F1 to induce the expression of a Sox2-luciferase reporter. These results suggest that nicotine may enhance lung cancer stem cell properties in part through the induction of Sox2, and this could potentially be mediated via E2F transcriptional activation. Further studies are underway to elucidate the impact of nicotine mediated induction of Sox2 on stemness, the underlying mechanism of activation, and the implications this has for non-small cell lung cancer. These studies can be expected to have a direct impact on our understanding of the molecular mechanism involved in the initiation, growth and metastasis of non-small cell lung cancer, especially in smokers.

Citation Format: Courtney Schaal, Namrata Bora Singhal, Smitha Pillai, Jonathan Nguyen, Srikumar Chellappan. Nicotine-mediated regulation of Sox2 and its implications in the biology of non-small cell lung adenocarcinoma stem-like cells. [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 2085. doi:10.1158/1538-7445.AM2015-2085

Abstract 3771: Tank-binding kinase 1 associates with centrosomes and regulates microtubule dynamics and mitosis

TANK Binding Kinase 1 (TBK1) regulates interferon signaling and NFκB function by acting as a non-canonical IκB kinase. TBK1 also participates in RalB-mediated inflammatory responses and contributes to the survival of non-small cell lung cancers (NSCLC) driven by oncogenic KRAS. In addition, TBK1 could phosphorylate and activate Akt, modulate autophagy and alter the autocrine cytokine network in cancer cells indicating oncogenic roles in addition to its immune regulatory functions. Our studies reveal that TBK1 plays a novel and direct role in promoting mitotic progression of lung cancer cells by phosphorylating multiple substrates during mitosis as well as by modulating microtubule dynamics. Levels of active phospho-TBK1 are elevated in mitotic cells where it localized to centrosomes, mitotic spindles and midbody as seen by confocal microscopy. Inhibition of TBK1 by kinase inhibitors such as BX795, Amlexanox, MRT67037 or depletion of TBK1 by shRNA resulted in mitotic defects and decreased the number of mitotic cells. TBK1 could interact with the centrosomal protein CEP170 and the nuclear mitotic apparatus protein NuMA as seen by GST binding assays, immunoprecipitation-western blot assays and proximity ligation assays. In addition, TBK1 could phosphorylate CEP170 and NuMA in in vitro kinase assays; mass spectrometry analysis revealed that TBK1 phosphorylated 12 serine residues and a threonine residue of CEP170 and five serine residues of NuMA. Inhibition or depletion of TBK1 prevented the centrosomal localization of CEP170 and the association of NuMA with the spindle poles. TBK1 depletion in A549 and H1650 cells resulted in more stable microtubules; further, depletion of TBK1 inhibited the interaction of CEP170 with the microtubule depolymerase Kif2b and the binding of NuMA to Dynein, resulting in mitotic abnormalities or mitotic arrest. In addition, inhibition of specific interaction between TBK1 and CEP170 using a 13 amino acid peptide resulted in inhibition of mitosis, enhanced microtubule stability and mitotic defects. These results are paradigm shifting that suggest TBK1 plays a significant role in regulating microtubule dynamics and mitotic progression of cells and this might have significant relevance to cancer as well as innate immune response.

Citation Format: Smitha R. Pillai, Jonathan Nguyen, Joseph Johnson, Eric Haura, Domenico Coppola, Srikumar Chellappan. Tank-binding kinase 1 associates with centrosomes and regulates microtubule dynamics and mitosis. [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 3771. doi:10.1158/1538-7445.AM2015-3771

Abstract 1516: YAP1 regulates Oct4 activity and Sox2 expression, facilitating self-renewal and vascular mimicry of stem-like cells

Non-small cell lung cancer (NSCLC) is highly correlated with smoking and has very low survival rates. Multiple studies have shown that cancer stem-like cells (CSCs) contribute to the genesis and progression of NSCLC. These cells have been shown to form differentiated tumor cells upon receiving appropriate microenvironmental cues and can give rise to multiple components of the tumor, including the vasculature. Earlier work from our laboratory had shown that Hoechst 33342 dye excluding side-population (SP) cells are enriched in cells having stem-like properties. SP cells displayed high self-renewal capacity, were highly drug resistant, and could form metastatic tumors in immunocompromised mice. The present study shows that the transcriptional co-activator YAP1, which is the oncogenic component of the Hippo signaling pathway, is elevated in the stem-like cells from NSCLC and contributes to their self-renewal and ability to form angiogenic tubules in matrigel. Inhibition of YAP1 by a small molecule inhibitor Visudyne or depletion of YAP1 by siRNAs suppressed self-renewal and vascular mimicry of stem-like cells. These effects of YAP1 were mediated through the embryonic stem cell transcription factor Sox2. YAP1 could associate with the Sox2 promoter and could transcriptionally induce Sox2 as seen by qRT-PCRs, ChIP assays and promoter luciferase assays; this induction was through a physical interaction of YAP1 with Oct4 protein. The binding of Oct4 to YAP1 could be detected in cell lines as well as NSCLC tumor tissues as seen by immunofluorescence, proximity ligation assays (PLA), immunoprecipitation-western blot experiments and GST binding assays. Interestingly, the interaction was elevated in NSCLC samples compared to normal tissue as seen by PLA. A peptide that could disrupt the interaction between YAP1 and Oct4 abrogated Sox2 expression, self-renewal and vascular mimicry. Depleting YAP1 reduced the expression of EMT genes and prevented the growth and metastasis of tumor xenografts in mice, while overexpression of Sox2 in YAP1 depleted cells could rescue self-renewal of stem-like cells. In conclusion, our results demonstrate that YAP1 can modulate the stem-like functions of cancer stem cells by regulating Sox2, and this regulatory pathway can potentially be targeted for combating NSCLC.

Citation Format: Namrata Bora Singhal, Jonathan Nguyen, Courtney Schaal, Deepak Perumal, Sandeep Singh, Domenico Coppola, Srikumar Chellappan. YAP1 regulates Oct4 activity and Sox2 expression, facilitating self-renewal and vascular mimicry of stem-like cells. [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 1516. doi:10.1158/1538-7445.AM2015-1516

β-arrestin-1 mediates nicotine-induced metastasis through E2F1 target genes that modulate epithelial-mesenchymal transition

Cigarette smoking is a major risk factor in the development of non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, the major addictive component of tobacco smoke, can induce proliferation, invasion, and epithelial-to-mesenchymal transition (EMT) in NSCLC cell lines and promote metastasis of NSCLC in mice. Here, we demonstrate that the scaffolding protein β-arrestin-1 is necessary for nicotine-mediated induction of mesenchymal genes vimentin and fibronectin as well as EMT regulators ZEB1 and ZEB2. Nicotine induced changes in cell morphology and ablate tight junctions consistent with EMT; β-arrestin-1, but not β-arrestin-2, was required for these changes. β-Arrestin-1 promoted the expression of the mesenchymal genes, as well as ZEB1 and ZEB2, through the mediation of the E2F1 transcription factor; this required Src kinase activity. Stimulation of multiple NSCLC cell lines with nicotine led to enhanced recruitment of β-arrestin-1 and E2F1 on vimentin, fibronectin, and ZEB1 and ZEB2 promoters. Furthermore, there was significantly more β-arrestin-1 and E2F1 associated with these promoters in human NSCLC tumors, and β-arrestin-1 levels correlated with vimentin and fibronectin levels in human NSCLC samples. A549-luciferase cells lacking β-arrestin-1 showed a significantly reduced capacity for tumor growth and metastasis when orthotopically implanted into the lungs of SCID-beige mice. Taken together, these studies reveal a novel role for β-arrestin-1 in the growth and metastasis of NSCLC.