Elongation factor 1A1 regulates metabolic substrate preference in mammalian cells

Eukaryotic elongation factor 1A1 (EEF1A1) is canonically involved in protein synthesis but also has noncanonical functions in diverse cellular processes. Previously, we identified EEF1A1 as a mediator of lipotoxicity and demonstrated that chemical inhibition of EEF1A1 activity reduced mouse liver lipid accumulation. These findings suggested a link between EEF1A1 and metabolism. Therefore, we investigated its role in regulating metabolic substrate preference. EEF1A1-deficient Chinese hamster ovary (2E2) cells displayed reduced media lactate accumulation. These effects were also observed with EEF1A1 knockdown in human hepatocyte-like HepG2 cells and in WT Chinese hamster ovary and HepG2 cells treated with selective EEF1A inhibitors, didemnin B, or plitidepsin. Extracellular flux analyses revealed decreased glycolytic ATP production and increased mitochondrial-to-glycolytic ATP production ratio in 2E2 cells, suggesting a more oxidative metabolic phenotype. Correspondingly, fatty acid oxidation was increased in 2E2 cells. Both 2E2 cells and HepG2 cells treated with didemnin B exhibited increased neutral lipid content, which may be required to support elevated oxidative metabolism. RNA-seq revealed a >90-fold downregulation of a rate-limiting glycolytic enzyme, hexokinase 2, which we confirmed through immunoblotting and enzyme activity assays. Pathway enrichment analysis identified downregulations in TNFA signaling via NFKB and MYC targets. Correspondingly, nuclear abundances of RELB and MYC were reduced in 2E2 cells. Thus, EEF1A1 deficiency may perturb glycolysis by limiting NFKB- and MYC-mediated gene expression, leading to decreased hexokinase expression and activity. This is the first evidence of a role for a translation elongation factor, EEF1A1, in regulating metabolic substrate utilization in mammalian cells.

Mutant p53 murine oviductal epithelial cells induce progression of high-grade serous carcinoma and are most sensitive to simvastatin therapy in vitro and in vivo

High-grade serous carcinoma (HGSC) is the most common and aggressive subtype of epithelial ovarian cancer, characterized by gain-of-function TP53 mutations originating in the fallopian tube epithelium. Therapeutic intervention occurs at advanced metastatic disease, due to challenges in early-stage diagnosis, with common disease recurrence and therapy resistance despite initial therapy success. The mevalonate pathway is exploited by many cancers and is potently inhibited by statin drugs. Statins have shown anti-cancer activity in many, but not all cancers. Here, we investigated the role of p53 status in relation to mevalonate pathway signaling in murine oviductal epithelial (OVE) cells and identified OVE cell sensitivity to statin inhibition. We found that p53R175H mutant and Trp53 knockout OVE cells have increased mevalonate pathway signaling compared to p53 wild-type OVE cells. Through orthotopic implantation to replicate the fallopian tube origin of HGSC, p53R175H mutant cells upregulated the mevalonate pathway to drive progression to advanced-stage ovarian cancer, and simvastatin treatment abrogated this effect. Additionally, simvastatin was more efficacious at inhibiting cell metabolic activity in OVE cells than atorvastatin, rosuvastatin and pravastatin. In vitro, simvastatin demonstrated potent effects on cell proliferation, apoptosis, invasion and migration in OVE cells regardless of p53 status. In vivo, simvastatin induced ovarian cancer disease regression through decreased primary ovarian tumor weight and increased apoptosis. Simvastatin also significantly increased cytoplasmic localization of HMG-CoA reductase in ovarian tumors. Downstream of the mevalonate pathway, simvastatin had no effect on YAP or small GTPase activity. This study suggests that simvastatin can induce anti-tumor effects and could be an important inhibitor of ovarian cancer progression.

Comparative analysis of syngeneic mouse models of high-grade serous ovarian cancer

Ovarian cancers exhibit high rates of recurrence and poor treatment response. Preclinical models that recapitulate human disease are critical to develop new therapeutic approaches. Syngeneic mouse models allow for the generation of tumours comprising the full repertoire of non-malignant cell types but have expanded in number, varying in the cell type of origin, method for transformation, and ultimately, the properties of the tumours they produce. Here we have performed a comparative analysis of high-grade serous ovarian cancer models based on transcriptomic profiling of 22 cell line models, and intrabursal and intraperitoneal tumours from 12. Among cell lines, we identify distinct signalling activity, such as elevated inflammatory signalling in STOSE and OVE16 models, and MAPK/ERK signalling in ID8 and OVE4 models; metabolic differences, such as reduced glycolysis-associated expression in several engineered ID8 subclones; and relevant functional properties, including differences in EMT activation, PD-L1 and MHC class I expression, and predicted chemosensitivity. Among tumour samples, we observe increased variability and stromal content among intrabursal tumours. Finally, we predict differences in the microenvironment of ID8 models engineered with clinically relevant mutations. We anticipate that this work will serve as a valuable resource, providing new insight to help select models for specific experimental objectives.

Proteomic and Phosphoproteomic Reprogramming in Epithelial Ovarian Cancer Metastasis

Epithelial ovarian cancer (EOC) is a high-risk cancer presenting with heterogeneous tumors. The high incidence of EOC metastasis from primary tumors to nearby tissues and organs is a major driver of EOC lethality. We used cellular models of spheroid formation and readherence to investigate cellular signaling dynamics in each step toward EOC metastasis. In our system, adherent cells model primary tumors, spheroid formation represents the initiation of metastatic spread, and readherent spheroid cells represent secondary tumors. Proteomic and phosphoproteomic analyses show that spheroid cells are hypoxic and show markers for cell cycle arrest. Aurora kinase B abundance and downstream substrate phosphorylation are significantly reduced in spheroids and readherent cells, explaining their cell cycle arrest phenotype. The proteome of readherent cells is most similar to spheroids, yet greater changes in the phosphoproteome show that spheroid cells stimulate Rho-associated kinase 1 (ROCK1)-mediated signaling, which controls cytoskeletal organization. In spheroids, we found significant phosphorylation of ROCK1 substrates that were reduced in both adherent and readherent cells. Application of the ROCK1-specific inhibitor Y-27632 to spheroids increased the rate of readherence and altered spheroid density. The data suggest ROCK1 inhibition increases EOC metastatic potential. We identified novel pathways controlled by Aurora kinase B and ROCK1 as major drivers of metastatic behavior in EOC cells. Our data show that phosphoproteomic reprogramming precedes proteomic changes that characterize spheroid readherence in EOC metastasis.

Gain-of-function p53R175H blocks apoptosis in a precursor model of ovarian high-grade serous carcinoma

Ovarian high-grade serous carcinoma (HGSC) is a highly lethal malignancy for which early detection is a challenge and treatment of late-stage disease is ineffective. HGSC initiation involves exfoliation of fallopian tube epithelial (FTE) cells which form multicellular clusters called spheroids that colonize and invade the ovary. HGSC contains universal mutation of the tumour suppressor gene TP53. However, not all TP53 mutations are the same, as specific p53 missense mutants contain gain-of-function (GOF) properties that drive tumour formation. Additionally, the role of GOF p53 in spheroid-mediated spread is poorly understood. In this study, we developed and characterized an in vitro model of HGSC based on mutation of TP53 in mouse oviductal epithelial cells (OVE). We discovered increased bulk spheroid survival and increased anchorage-independent growth in OVE cells expressing the missense mutant p53R175H compared to OVE parental and Trp53ko cells. Transcriptomic analysis on spheroids identified decreased apoptosis signaling due to p53R175H. Further assessment of the apoptosis pathway demonstrated decreased expression of intrinsic and extrinsic apoptosis signaling molecules due to Trp53 deletion and p53R175H, but Caspase-3 activation was only decreased in spheroids with p53R175H. These results highlight this model as a useful tool for discovering early HGSC transformation mechanisms and uncover a potential anti-apoptosis GOF mechanism of p53R175H.

Insights into high-grade serous carcinoma pathobiology using three-dimensional culture model systems

Epithelial ovarian cancer (EOC) research has become more complex as researchers try to fully understand the metastatic process. Especially as we delve into the concept of tumour dormancy, where cells transition between proliferative and dormant states to survive during disease progression. Thus, the in vitro models used to conduct this research need to reflect this vast biological complexity. The innovation behind the many three-dimensional (3D) spheroid models has been refined to easily generate reproducible spheroids so that we may understand the various molecular signaling changes of cells during metastasis and determine therapeutic efficacy of treatments. This ingenuity was then used to develop the 3D ex vivo patient-derived organoid model, as well as multiple co-culture model systems for EOC research. Although, researchers need to continue to push the boundaries of these current models for in vitro and even in vivo work in the future. In this review, we describe the 3D models already in use, where these models can be developed further and how we can use these models to gain the most knowledge on EOC pathogenesis and discover new targeted therapies.

Abstract 2332: Repurposing simvastatin to inhibit the mevalonate pathway as a therapeutic strategy to treat high-grade serous ovarian cancer

Introduction: Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer, and its five-year survival rate has not changed appreciably in decades. As such, there is an imperative need for new and innovative therapies. Our lab has previously discovered that metastatic ascites-derived tumor cells have acquired a gain-of-function p53 mutation following interaction with the ovarian microenvironment in our orthotopic murine model of EOC. This p53 mutation is associated with an upregulation of the mevalonate pathway, which is known for its vital role in producing cholesterol. Tumor cells upregulate metabolic pathways as a survival advantage to fuel their rapid growth and metastasis. Simvastatin, a statin therapy, specifically targets HMG-CoA reductase, the rate-limiting enzyme of this pathway, and inhibits its activity. As such, simvastatin may serve as a potential therapeutic opportunity for EOC. Gain-of-function p53 mutations in the epithelial cells of the distal fallopian tube is now widely accepted as the origin of high-grade serous ovarian cancer. Thus, the purpose of our study was to investigate the relationship between p53 status and the mevalonate pathway in oviductal epithelial (OVE) cells as well as evaluate the effect of simvastatin treatment on OVE cell viability.

Methods/Results: OVE cells were isolated from the distal oviducts of FVB/N mice with a p53 wildtype status, and we either deleted the Trp53 gene or introduced a gain-of-function R175H p53 mutation using CRISPR/Cas9. Cell viability was measured following treatment with varying doses of simvastatin and p53 mutant cells showed the greatest sensitivity (IC50: 5.48 uM) compared to p53 wildtype (IC50: 14.80 uM) and p53 knockout (IC50:9.78 uM) cells. For subsequent experiments, OVE cells were treated with 10 uM simvastatin or DMSO and subjected to Resazurin, Transwell migration, CyQUANT proliferative and Caspase-Glo 3/7 assays. Simvastatin significantly decreased resazurin reduction to resorufin in a time-dependent manner over 48 hours, regardless of p53 status, demonstrating reduced metabolic activity. Additionally, OVE cell invasion was significantly reduced in simvastatin treated p53 mutant cells, compared to p53 wildtype or p53 knockout cells. Simvastatin treatment diminished cell proliferation and enhanced apoptotic activity in all simvastatin treated OVE cells.

Conclusion: Overall, simvastatin appears to inhibit tumorigenic processes in vitro. The next steps of this project are to test simvastatin’s effect on disease regression in a novel murine oviductal cell injection model of EOC recently developed by our lab. In light of these results, repurposing simvastatin as a therapy for ovarian cancer may significantly improve the way we treat this vicious disease.

Citation Format: Madison Pereira, Kathy Matuszewska, Jacob Haagsma, Alice Glogova, Trevor G. Shepherd, Jim Petrik. Repurposing simvastatin to inhibit the mevalonate pathway as a therapeutic strategy to treat high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2332.

Principles of dormancy evident in high-grade serous ovarian cancer

In cancer, dormancy refers to a clinical state in which microscopic residual disease becomes non-proliferative and is largely refractory to chemotherapy. Dormancy was first described in breast cancer where disease can remain undetected for decades, ultimately leading to relapse and clinical presentation of the original malignancy. A long latency period can be explained by withdrawal from cell proliferation (cellular dormancy), or a balance between proliferation and cell death that retains low levels of residual disease (tumor mass dormancy). Research into cellular dormancy has revealed features that define this state. They include arrest of cell proliferation, altered cellular metabolism, and unique cell dependencies and interactions with the microenvironment. These characteristics can be shared by dormant cells derived from disparate primary disease sites, suggesting common features exist between them.

High-grade serous ovarian cancer (HGSOC) disseminates to locations throughout the abdominal cavity by means of cellular aggregates called spheroids. These growth-arrested and therapy-resistant cells are a strong contributor to disease relapse. In this review, we discuss the similarities and differences between ovarian cancer cells in spheroids and dormant properties reported for other cancer disease sites. This reveals that elements of dormancy, such as cell cycle control mechanisms and changes to metabolism, may be similar across most forms of cellular dormancy. However, HGSOC-specific aspects of spheroid biology, including the extracellular matrix organization and microenvironment, are obligatorily disease site specific. Collectively, our critical review of current literature highlights places where HGSOC cell dormancy may offer a more tractable experimental approach to understand broad principles of cellular dormancy in cancer.

MAIT cells accumulate in ovarian cancer-elicited ascites where they retain their capacity to respond to MR1 ligands and cytokine cues

The low mutational burden of epithelial ovarian cancer (EOC) is an impediment to immunotherapies that rely on conventional MHC-restricted, neoantigen-reactive T lymphocytes. Mucosa-associated invariant T (MAIT) cells are MR1-restricted T cells with remarkable immunomodulatory properties. We sought to characterize intratumoral and ascitic MAIT cells in EOC. Single-cell RNA sequencing of six primary human tumor specimens demonstrated that MAIT cells were present at low frequencies within several tumors. When detectable, these cells highly expressed CD69 and VSIR, but otherwise exhibited a transcriptomic signature inconsistent with overt cellular activation and/or exhaustion. Unlike mainstream CD8⁺ T cells, CD8⁺ MAIT cells harbored high transcript levels of TNF, PRF1, GZMM and GNLY, suggesting their arming and cytotoxic potentials. In a congenic, MAIT cell-sufficient mouse model of EOC, MAIT and invariant natural killer T cells amassed in the peritoneal cavity where they showed robust IL-17A and IFN-γ production capacities, respectively. However, they gradually lost these functions with tumor progression. In a cohort of 23 EOC patients, MAIT cells were readily detectable in all ascitic fluids examined. In a sub-cohort in which we interrogated ascitic MAIT cells for functional impairments, several exhaustion markers, most notably VISTA, were present on the surface. However, ascitic MAIT cells were capable of producing IFN-γ, TNF-α and granzyme B, but neither IL-17A nor IL-10, in response to an MR1 ligand, bacterial lysates containing MR1 ligands, or a combination of IL-12 and IL-18. In conclusion, ascitic MAIT cells in EOC possess inducible effector functions that may be modified in future immunotherapeutic strategies.

Molecular and cellular mechanisms controlling integrin-mediated cell adhesion and tumor progression in ovarian cancer metastasis: a review

Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy in the developed world. EOC metastasis is unique since malignant cells detach directly from the primary tumor site into the abdominal fluid and form multicellular aggregates, called spheroids, that possess enhanced survival mechanisms while in suspension. As such, altered cell adhesion properties are paramount to EOC metastasis with cell detachment from the primary tumor, dissemination as spheroids, and reattachment to peritoneal surfaces for secondary tumor formation. The ability for EOC cells to establish and maintain cell–cell contacts in spheroids is critical for cell survival in suspension. Integrins are a family of cell adhesion receptors that play a crucial role in cell–cell and cell-extracellular matrix interactions. These glycoprotein receptors regulate diverse functions in tumor cells and are implicated in multiple steps of cancer progression. Altered integrin expression is detected in numerous carcinomas, where they play a role in cell migration, invasion, and anchorage-independent survival. Like that observed for other carcinomas, epithelial-mesenchymal transition (EMT) occurs during metastasis and integrins can function in this process as well. Herein, we provide a review of the evidence for integrin-mediated cell adhesion mechanisms impacting steps of EOC metastasis. Taken together, targeting integrin function may represent a potential therapeutic strategy to inhibit progression of advanced EOC.

Maternal obesity reduces placental autophagy marker expression in uncomplicated pregnancies

AIM

Obesity has been associated with changes in autophagy and its increasing prevalence among pregnant women is implicated in higher rates of placental-mediated complications of pregnancy such as pre-eclampsia and intrauterine growth restriction. Autophagy is involved in normal placentation, thus changes in autophagy may lead to impaired placental function and development. The aim of this study was to investigate the connection between obesity and autophagy in the placenta in otherwise uncomplicated pregnancies.

METHODS

Immunohistochemistry and western blot analysis were done on placental and omental samples from obese (body mass index [BMI] ≥30 kg/m² ) and normal weight (BMI <25 kg/m² ) pregnant women with singleton pregnancies undergoing planned Caesarean delivery without labor at term. Samples were analyzed for autophagic markers LC3B and p62 in the peripheral, middle and central regions of the placenta and in omental adipocytes, milky spots and vasculature.

RESULTS

As pre-pregnancy BMI increased, there was an increase in both placental and fetal weight as well as decreased levels of LC3B in the central region of the placenta (P = 0.0046). Within the obese patient group, LC3B levels were significantly decreased in the placentas of male fetuses compared to females (P < 0.0001). Adipocytes, compared to milky spots and vasculature, had lower levels of p62 (P = 0.0127) and LC3B (P = 0.003) in obese omenta and lower levels of LC3B in control omenta (P = 0.0071).

CONCLUSION

Obesity leads to reduced placental autophagy in uncomplicated pregnancies; thus, changes in autophagy may be involved in the underlying mechanisms of obesity-related placental diseases of pregnancy.

A novel role for NUAK1 in promoting ovarian cancer metastasis through regulation of fibronectin production in spheroids

Epithelial ovarian cancer (EOC) has a unique mode of metastasis, where cells shed from the primary tumour, form aggregates called spheroids to evade anoikis, spread through the peritoneal cavity, and adhere to secondary sites. We previously showed that the master kinase Liver kinase B1 (LKB1) is required for EOC spheroid viability and metastasis. We have identified novel (nua) kinase 1 (NUAK1) as a top candidate LKB1 substrate in EOC cells and spheroids using a multiplex inhibitor beads-mass spectrometry approach. We confirmed that LKB1 maintains NUAK1 phosphorylation and promotes its stabilization. We next investigated NUAK1 function in EOC cells. Ectopic NUAK1-overexpressing EOC cell lines had increased adhesion, whereas the reverse was seen in OVCAR8-NUAK1KO cells. In fact, cells with NUAK1 loss generate spheroids with reduced integrity, leading to increased cell death after long-term culture. Following transcriptome analysis, we identified reduced enrichment for cell interaction gene expression pathways in OVCAR8-NUAK1KO spheroids. In fact, the FN1 gene, encoding fibronectin, exhibited a 745-fold decreased expression in NUAK1KO spheroids. Fibronectin expression was induced during native spheroid formation, yet this was completely lost in NUAK1KO spheroids. Co-incubation with soluble fibronectin restored the compact spheroid phenotype to OVCAR8-NUAK1KO cells. In a xenograft model of intraperitoneal metastasis, NUAK1 loss extended survival and reduced fibronectin expression in tumours. Thus, we have identified a new mechanism controlling EOC metastasis, through which LKB1-NUAK1 activity promotes spheroid formation and secondary tumours via fibronectin production.

Activated CAMKKβ-AMPK signaling promotes autophagy in a spheroid model of ovarian tumour metastasis

Background

A hallmark of epithelial ovarian cancer (EOC) metastasis is the process of spheroid formation, whereby tumour cells aggregate into 3D structures while in suspension in the peritoneal cavity. EOC spheroids are subjected to bioenergetic stress, thereby activating AMP-activated protein kinase (AMPK) signaling to enter a metabolically quiescent state, which can facilitate cell survival under nutrient-limiting conditions. Independently, we have also demonstrated that EOC spheroids induce autophagy, a process that degrades and recycles intracellular components to restore energy and metabolites. Herein, we sought to examine whether AMPK controls autophagy induction as a cell survival mechanism in EOC spheroids.

Results

We observed a co-ordinate increase in phosphorylated AMPK and the autophagy marker LC3-II during EOC spheroid formation. Reduced AMPK expression by siRNA-mediated knockdown of PRKAA1 and PRKAA2 blocked autophagic flux in EOC spheroids as visualized by fluorescence microscopy using the mCherry-eGFP-LC3B reporter. A complementary approach using pharmacologic agents Compound C and CAMKKβ inhibitor STO-609 to inhibit AMPK activity both yielded a potent blockade of autophagic flux as well. However, direct activation of AMPK in EOC cells using oligomycin and metformin was insufficient to induce autophagy. STO-609 treatment of EOC spheroids resulted in reduced viability in 7 out of 9 cell lines, but with no observed effect in non-malignant FT190 cell spheroids.

Conclusions

Our results support the premise that CAMKKβ-mediated AMPK activity is required, at least in part, to regulate autophagy induction in EOC spheroids and support cell viability in this in vitro model of EOC metastasis.

Inhibiting ULK1 kinase decreases autophagy and cell viability in high-grade serous ovarian cancer spheroids

Metastasis in high-grade serous ovarian cancer (HGSOC) occurs through an unconventional route that involves exfoliation of cancer cells from primary tumors and peritoneal dissemination via multicellular clusters or spheroids. Previously, we demonstrated autophagy induction in HGSOC spheroids grown in vitro and in spheroids collected from ovarian cancer patient ascites; thus, we speculate that autophagy may contribute to spheroid cell survival and overall disease progression. Hence, in this study we sought to evaluate whether ULK1 (unc-51-like kinase-1), a serine-threonine kinase critical for stress-induced autophagy, is important for autophagy regulation in HGSOC spheroids. We demonstrate that HGSOC spheroids have increased ULK1 protein expression that parallels autophagy activation. ULK1 knockdown increased p62 accumulation and decreased LC3-II/I ratio in HGSOC spheroids. In addition, knocking down ATG13, a protein that regulates ULK1 activity via complex formation, phenocopied our ULK1 knockdown results. HGSOC spheroids were blocked in autophagic flux due to ULK1 and ATG13 knockdown as determined by an mCherry-eGFP-LC3B fluorescence reporter. These observations were recapitulated when HGSOC spheroids were treated with an ULK1 kinase inhibitor, MRT68921. Autophagy regulation in normal human fallopian tube epithelial FT190 cells, however, may bypass ULK1, since MRT68921 reduced viability in HGSOC spheroids but not in FT190 cells. Interestingly, ULK1 mRNA expression is negatively correlated with patient survival among stage III and stage IV serous ovarian cancer patients. As we observed using established HGSOC cell lines, cultured spheroids using our new, patient-derived HGSOC cells were also sensitive to ULK1 inhibition and demonstrated reduced cell viability to MRT68921 treatment. These results demonstrate the importance of ULK1 for autophagy induction in HGSOC spheroids and therefore justifies further evaluation of MRT68921, and other novel ULK1 inhibitors, as potential therapeutics against metastatic HGSOC.

Context-dependent activation of SIRT3 is necessary for anchorage-independent survival and metastasis of ovarian cancer cells

Tumor cells must alter their antioxidant capacity for maximal metastatic potential. Yet the antioxidant adaptations required for ovarian cancer transcoelomic metastasis, which is the passive dissemination of cells in the peritoneal cavity, remain largely unexplored. Somewhat contradicting the need for oxidant scavenging are previous observations that expression of SIRT3, a nutrient stress sensor and regulator of mitochondrial antioxidant defenses, is often suppressed in many primary tumors. We have discovered that this mitochondrial deacetylase is specifically upregulated in a context-dependent manner in cancer cells. SIRT3 activity and expression transiently increased following ovarian cancer cell detachment and in tumor cells derived from malignant ascites of high-grade serous adenocarcinoma patients. Mechanistically, SIRT3 prevents mitochondrial superoxide surges in detached cells by regulating the manganese superoxide dismutase (SOD2). This mitochondrial stress response is under dual regulation by SIRT3. SIRT3 rapidly increases SOD2 activity as an early adaptation to cellular detachment, which is followed by SIRT3-dependent increases in SOD2 mRNA during sustained anchorage-independence. In addition, SIRT3 inhibits glycolytic capacity in anchorage-independent cells thereby contributing to metabolic changes in response to detachment. While manipulation of SIRT3 expression has few deleterious effects on cancer cells in attached conditions, SIRT3 upregulation and SIRT3-mediated oxidant scavenging are required for anoikis resistance in vitro following matrix detachment, and both SIRT3 and SOD2 are necessary for colonization of the peritoneal cavity in vivo. Our results highlight the novel context-specific, pro-metastatic role of SIRT3 in ovarian cancer.

AMPK-Independent LKB1 Activity Is Required for Efficient Epithelial Ovarian Cancer Metastasis

Epithelial ovarian cancer (EOC) spreads by direct dissemination of malignant cells and multicellular clusters, known as spheroids, into the peritoneum followed by implantation and growth on abdominal surfaces. Using a spheroid model system of EOC metastasis, we discovered that Liver kinase B1 (LKB1), encoded by the STK11 gene, and its canonical substrate AMP-activated protein kinase (AMPK) are activated in EOC spheroids, yet only LKB1 is required for cell survival. We have now generated STK11-knockout cell lines using normal human FT190 cells and three EOC cell lines, OVCAR8, HeyA8, and iOvCa147. STK11KO did not affect growth and viability in adherent culture, but it decreased anchorage-independent growth of EOC cells. EOC spheroids lacking LKB1 had markedly impaired growth and viability, whereas there was no difference in normal FT190 spheroids. To test whether LKB1 loss affects EOC metastasis, we performed intraperitoneal injections of OVCAR8-, HeyA8-, and iOvCa147-STK11KO cells, and respective controls. LKB1 loss exhibited a dramatic reduction on tumor burden and metastatic potential; in particular, OVCAR8-STK11KO tumors had evidence of extensive necrosis, apoptosis, and hypoxia. Interestingly, LKB1 loss did not affect AMPKα phosphorylation in EOC spheroids and tumor xenografts, indicating that LKB1 signaling to support EOC cell survival in spheroids and metastatic tumor growth occurs via other downstream mediators. We identified the dual-specificity phosphatase DUSP4 as a commonly upregulated protein due to LKB1 loss; indeed, DUSP4 knockdown in HeyA8-STK11KO cells partially restored spheroid formation and viability. IMPLICATIONS: LKB1 possesses key tumor-promoting activity independent of downstream AMPK signaling during EOC metastasis.

Abstract A17: NUAK1 acts as a growth suppressor in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) cells form multicellular aggregates, or spheroids, and enter a dormant state during intraperitoneal metastasis. Dormant spheroids reduce anabolic metabolism and cell proliferation, which are linked to chemo-resistance. Liver kinase B1 (LKB1), encoded by the STK11 gene, is a critical regulator of stress metabolic signaling; LKB1 phosphorylates the downstream substrates AMP-activated protein kinase (AMPK) and AMPK-related kinases (ARKs) to mediate stress signaling. We have demonstrated that LKB1 expression and activity is required for EOC spheroid cell survival, yet knockdown of AMPKα1/α2 has no effect on viability. In addition, we have preliminary data demonstrating that phosphorylated AMPK is still maintained in EOC spheroids generated from CRISPR-mediated STK11-deleted cells, which completely lack LKB1 expression. Taken together, these results implicate the importance of other AMPK-independent effectors of LKB1 signaling in spheroid cell viability. Therefore, to identify critical downstream targets of LKB1-mediated signaling in EOC spheroids, we employed multiplex inhibitor beads/mass spectrometry (MIB/MS) using OVCAR8 STK11-knockout cells and OVCAR8 control cells grown in adherent and spheroid culture conditions. Using this proteomic approach, we identified NUAK1 as the sole ARK out of 12 different family members that is negatively affected by LKB1 loss. In fact, both phosphorylated and total NUAK1 protein expression are decreased in STK11-knockout cells and spheroids. NUAK1 can negatively control cell growth and proliferation by direct regulation of cell cycle checkpoint proteins in several cell systems; however, it has been relatively understudied in EOC. In analysis of the serous ovarian carcinoma data from TCGA, NUAK1 is infrequently altered (&lt;2% of tumors) and it has the highest mean mRNA expression level as compared with the other 11 ARK genes. However, using immunoblot analysis, we show that NUAK1 protein is largely underexpressed in many established (n=15) and new ascites-derived EOC cell lines (n=22). In fact, further NUAK1 knockdown increased spheroid cell viability, size, and reattachment capability, whereas knockdown of its closely-related family member NUAK2 had no effect compared with the non-targeting siRNA control. Likewise, treatment with the pharmacologic NUAK1/2 inhibitor WZ4003 increased EOC cell growth and clonogenicity. Conversely, ectopic overexpression of NUAK1 reduced EOC cell growth and clonogenicity. Collectively, our data indicate that NUAK1 acts as a newly identified growth suppressor downstream of LKB1 metabolic stress signaling in EOC. We are currently investigating mechanisms regulating NUAK1 protein stability and activity in EOC cells, and whether activated LKB1-NUAK1 signaling promotes stress metabolic signaling during tumor dormancy in the context of EOC metastasis.

Citation Format: Parima Saxena, Olga Collins, Yudith Ramos Valdes, Adrian Buensuceso, Kyle Francis, Kevin Brown, Karen Colwill, Anne-Claude Gingras, Robert Rottapel, Gabriel E. DiMattia, Trevor G. Shepherd. NUAK1 acts as a growth suppressor in epithelial ovarian cancer. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A17.

Abstract A12: The metabolic stress mediator LKB1 is required for ovarian cancer metastasis

Most epithelial ovarian cancer (EOC) patients with metastatic disease initially respond to cytotoxic chemotherapy, yet almost all will relapse with resistant disease. Thus, improving patient outcomes will require novel approaches to limit metastasis and overcome chemo-resistance. Liver Kinase B1 (LKB1), encoded by the STK11 gene, is a key intracellular regulator of metabolic stress and is considered a putative tumor suppressor in some cancers. However, we have demonstrated that LKB1 is intact and required for EOC cell viability and growth in an in vitro spheroid model of ovarian cancer metastasis.

We propose that LKB1 signaling enables malignant EOC cells to maintain viability and survive in metabolically challenging environments like that encountered during intraperitoneal metastasis. To further investigate the therapeutic potential of targeting LKB1 activity in metastatic EOC, we generated STK11-knockout cell lines—normal FT190 cells, and EOC cell lines OVCAR8, HeyA8, and iOvCa147—using CRISPR technology. STK11KO resulted in decreased malignant properties of EOC cells in vitro, including clonogenicity and anchorage-independent growth; however, loss of LKB1 in FT190 cells had no effect on cell proliferation, clonogenicity, or anchorage-independent growth, indicating LKB1 does not likely act as a tumor suppressor in EOC.

Loss of LKB1 sensitized EOC cells to the growth-inhibiting effects of specific metabolic stresses. OVCAR8-STK11KO cells were more sensitive to nutrient deprivation in adherent culture, and to carboplatin and paclitaxel treatment in spheroid culture, as compared with OVCAR8 cells. Among the three EOC cell lines, STK11KO yielded variable sensitivity to inhibition of mitochondrial ATP production via oligomycin treatment. Interestingly, STK11KO did not affect induction of AMP-activated protein kinase (AMPK) phosphorylation in EOC spheroids, indicating that metabolic stress signaling to support EOC cell survival in spheroids during metastasis may occur via alternative pathways.

In support of our previous knockdown results, EOC spheroids completely lacking LKB1 had markedly impaired growth in suspension culture compared to parental cell controls. In contrast, FT190 spheroids exhibited rapid cell attrition in spheroid culture regardless of LKB1 status. These results indicate that LKB1 may be specifically required in EOC cells to evade anoikis during metastatic spread. Finally, to test directly whether loss of LKB1 activity affects the metastatic potential of EOC cells, we performed intraperitoneal injections of OVCAR8-STK11KO and HeyA8-STK11KO cells with their respective parental cell controls. Loss of LKB1 in both aggressive EOC cell lines exhibited a dramatic reduction on tumor burden. STK11KO significantly decreased the establishment of large, solid tumor masses, reduced adhesion of OVCAR8 tumor nodules, and even changed the metastatic trajectory of HeyA8 cells with evidence of tumor cell growth only as a thin layer on peritoneal walls. Histologic analysis revealed evidence of extensive necrosis in STK11KO tumors, which was likely the major contributor to reduced tumor burden.

These results strongly indicate that loss of LKB1 activity abrogates the metabolic stress response necessary during EOC metastasis both in spheroids and establishment of intraperitoneal tumors. Overall, LKB1 or its AMPK-independent signaling mediators represent unique yet very potent therapeutic vulnerabilities in metastatic EOC.

Citation Format: Adrian Buensuceso, Yudith R. Valdes, Rene Figueredo, Gabriel E. DiMattia, Trevor G. Shepherd. The metabolic stress mediator LKB1 is required for ovarian cancer metastasis. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A12.

Spatial and temporal epithelial ovarian cancer cell heterogeneity impacts Maraba virus oncolytic potential

Background

Epithelial ovarian cancer exhibits extensive interpatient and intratumoral heterogeneity, which can hinder successful treatment strategies. Herein, we investigated the efficacy of an emerging oncolytic, Maraba virus (MRBV), in an in vitro model of ovarian tumour heterogeneity.

Methods

Four ovarian high-grade serous cancer (HGSC) cell lines were isolated and established from a single patient at four points during disease progression. Limiting-dilution subcloning generated seven additional subclone lines to assess intratumoral heterogeneity. MRBV entry and oncolytic efficacy were assessed among all 11 cell lines. Low-density receptor (LDLR) expression, conditioned media treatments and co-cultures were performed to determine factors impacting MRBV oncolysis.

Results

Temporal and intratumoral heterogeneity identified two subpopulations of cells: one that was highly sensitive to MRBV, and another set which exhibited 1000-fold reduced susceptibility to MRBV-mediated oncolysis. We explored both intracellular and extracellular mechanisms influencing sensitivity to MRBV and identified that LDLR can partially mediate MRBV infection. LDLR expression, however, was not the singular determinant of sensitivity to MRBV among the HGSC cell lines and subclones. We verified that there were no apparent extracellular factors, such as type I interferon responses, contributing to MRBV resistance. However, direct cell-cell contact by co-culture of MRBV-resistant subclones with sensitive cells restored virus infection and oncolytic killing of mixed population.

Conclusions

Our data is the first to demonstrate differential efficacy of an oncolytic virus in the context of both spatial and temporal heterogeneity of HGSC cells and to evaluate whether it will constitute a barrier to effective viral oncolytic therapy.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3600-2) contains supplementary material, which is available to authorized users.

Differences in MEK inhibitor efficacy in molecularly characterized low-grade serous ovarian cancer cell lines

Advanced or recurrent low-grade serous ovarian cancers (LGSC) are resistant to conventional systemic treatments. LGSC carry mutations in RAS or RAF, leading to several clinical trials evaluating MEK inhibitors (MEKi). As LGSC cell lines and xenografts have been difficult to establish, little is known about the efficacy and on-target activity of MEKi treatment in this disease. We compared four different MEKi (trametinib, selumetinib, binimetinib and refametinib) in novel LGSC patient-derived cell lines. Molecular characterization of these cells included copy-number variation and hotspot mutational analysis. Proliferation, apoptosis and cell viability assays were used to study drug efficacy. MEKi on-target efficacy was measured using western blotting and isoelectric point focusing for ERK1/2 phosphorylation. Ten LGSC cell lines were derived from 7 patients with advanced/recurrent disease. Copy number variation showed significant heterogeneity among cell lines, however all samples showed deletions in chromosome 9p21.3, and frequent copy number gains in chromosomes 12 and 20. Mutations in KRAS/NRAS were identified in 4 patients (57%) and RAS mutation status was not associated with higher baseline levels of ERK phosphorylation. Different degrees of MEKi sensitivity were observed in the LGSC cell lines. Two cell lines, both with KRAS mutations, were highly sensitive to MEKi. Drug anti-proliferative efficacy correlated with the degree of inhibition of ERK phosphorylation, with trametinib being the most potent agent. Differences in MEKi efficacy were observed in LGSC cell lines. Trametinib showed the greatest anti-proliferative effects. This study serves as a basis for much needed future research on MEKi drug efficacy in LGSC.

Intact LKB1 activity is required for survival of dormant ovarian cancer spheroids

Metastatic epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in suspension and disperse directly throughout the peritoneum to seed secondary lesions. There is growing evidence that EOC spheroids are key mediators of metastasis, and they use specific intracellular signalling pathways to control cancer cell growth and metabolism for increased survival. Our laboratory discovered that AKT signalling is reduced during spheroid formation leading to cellular quiescence and autophagy, and these may be defining features of tumour cell dormancy. To further define the phenotype of EOC spheroids, we have initiated studies of the Liver kinase B1 (LKB1)-5′-AMP-activated protein kinase (AMPK) pathway as a master controller of the metabolic stress response. We demonstrate that activity of AMPK and its upstream kinase LKB1 are increased in quiescent EOC spheroids as compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient ascites. Functional studies reveal that treatment with the AMP mimetic AICAR or allosteric AMPK activator A-769662 led to a cytostatic response in proliferative adherent ovarian cancer cells, but they fail to elicit an effect in spheroids. Targeted knockdown of STK11 by RNAi to reduce LKB1 expression led to reduced viability and increased sensitivity to carboplatin treatment in spheroids only, a phenomenon which was AMPK-independent. Thus, our results demonstrate a direct impact of altered LKB1-AMPK signalling function in EOC. In addition, this is the first evidence in cancer cells demonstrating a pro-survival function for LKB1, a kinase traditionally thought to act as a tumour suppressor.

TGFβ signaling regulates epithelial-mesenchymal plasticity in ovarian cancer ascites-derived spheroids

Epithelial-mesenchymal transition (EMT) serves as a key mechanism driving tumor cell migration, invasion, and metastasis in many carcinomas. Transforming growth factor-beta (TGFβ) signaling is implicated in several steps during cancer pathogenesis and acts as a classical inducer of EMT. Since epithelial ovarian cancer (EOC) cells have the potential to switch between epithelial and mesenchymal states during metastasis, we predicted that modulation of TGFβ signaling would significantly impact EMT and the malignant potential of EOC spheroid cells. Ovarian cancer patient ascites-derived cells naturally underwent an EMT response when aggregating into spheroids, and this was reversed upon spheroid re-attachment to a substratum. CDH1/E-cadherin expression was markedly reduced in spheroids compared with adherent cells, in concert with an up-regulation of several transcriptional repressors, i.e., SNAI1/Snail, TWIST1/2, and ZEB2. Treatment of EOC spheroids with the TGFβ type I receptor inhibitor, SB-431542, potently blocked the endogenous activation of EMT in spheroids. Furthermore, treatment of spheroids with SB-431542 upon re-attachment enhanced the epithelial phenotype of dispersing cells and significantly decreased cell motility and Transwell migration. Spheroid formation was significantly compromised by exposure to SB-431542 that correlated with a reduction in cell viability particularly in combination with carboplatin treatment. Thus, our findings are the first to demonstrate that intact TGFβ signaling is required to control EMT in EOC ascites-derived cell spheroids, and it promotes the malignant characteristics of these structures. As such, we show the therapeutic potential for targeted inhibition of this pathway in ovarian cancer patients with late-stage disease.

Contribution of reactive oxygen species to ovarian cancer cell growth arrest and killing by the anti-malarial drug artesunate

Ovarian cancer is a leading cause of cancer-related death in women and the most lethal gynecological malignancy in the developed world. The morbidity and mortality of ovarian cancer underscore the need for novel treatment options. Artesunate (ART) is a well-tolerated anti-malarial drug that also has anti-cancer activity. In this study, we show that ART inhibited the in vitro growth of a panel of ovarian cancer cell lines, as well as the growth of ovarian cancer cells isolated from patients. Moreover, ART decreased tumor growth in vivo in a mouse model of ovarian cancer. ART-treated ovarian cancer cells showed a strong induction of reactive oxygen species (ROS) and reduced proliferation. ROS-dependent cell cycle arrest occurred in the G2/M phase whereas ROS-independent cell cycle arrest occurred in the G1 phase, depending on the concentration of ART to which ovarian cancer cells were exposed. The anti-proliferative effect of ART was associated with altered expression of several key cell cycle regulatory proteins, including cyclin D3, E2F-1, and p21, as well as inhibition of mechanistic target of rapamycin signaling. Exposure of ovarian cancer cells to higher concentrations of ART resulted in ROS-dependent DNA damage and cell death. Pretreatment of ovarian cancer cells with a pan-caspase inhibitor or ferroptosis inhibitor decreased but did not completely eliminate ART-mediated cytotoxicity, suggesting the involvement of both caspase-dependent and caspase-independent pathways of killing. These data show that ART has potent anti-proliferative and cytotoxic effects on ovarian cancer cells, and may therefore be useful in the treatment of ovarian cancer. © 2016 Wiley Periodicals, Inc.

Abstract B51: Stress management: LKB1 controls growth and survival of dormant epithelial ovarian cancer spheroid cells

Aberrant cell metabolism is rapidly establishing itself as a critical hallmark of human malignancies. Cancer cells are faced with huge metabolic demands to support rapid tumor growth, yet are commonly starved for nutrients. In response, cancer cells hijack alternative signaling pathways during these times of energy and metabolic stress to sustain viability. Metastatic epithelial ovarian cancer (EOC) cells are faced with additional stressors during transcoelomic spread, such as detachment from a matrix substratum and inhospitable conditions in peritoneal fluid. However, EOC cells have a natural ability to aggregate when in suspension to form multicellular aggregates, or spheroids, which supports a survival advantage for cells when transiting the peritoneal space during metastatic progression. Therefore, we utilize an in vitro spheroid culture model system to investigate signaling pathways altered in EOC cells that may be implicated in ovarian cancer pathobiology and promote metastasis. For example, we have shown that spheroid formation induces cellular quiescence and autophagy, two disparate processes which promote EOC cell survival and resistance to platinum-based chemotherapeutics. In addition, we discovered that EOC spheroids have significantly reduced mitochondrial activity and ATP levels compared with matched proliferating adherent cells. Liver kinase B1 (LKB1) acts as a chief responder to intracellular stress due to reduced energy and nutrients by eliciting general growth suppression during these starvation-like conditions. Thus, we hypothesized that LKB1 activity is increased in EOC spheroids to promote tumor cell dormancy and cell survival. Although the STK11 gene encoding LKB1 is heterozygously deleted in 84% of serous ovarian tumors, we demonstrate that almost all ovarian tumor cells and established EOC cell lines retain intact LKB1 expression. In fact, LKB1 protein expression increases when EOC cells form spheroids and this coincides with induced serine-428 phosphorylation, a modification that is required for LKB1 growth suppressive activity. To address the potential functional requirement of LKB1 in EOC spheroids, we first performed transient knockdown of STK11 to block LKB1 expression. Indeed, reduced LKB1 renders spheroids susceptible to cell death and increases sensitivity to carboplatin. Next, we utilized Cas9-mediated genome editing of the STK11 locus to completely ablate LKB1 expression in HEYA8 and OVCAR8 cells. STK11-knockout HEYA8 and OVCAR8 cells yielded significantly decreased spheroid number and viability compared with parental cell lines. In a reciprocal fashion, forced re-expression of LKB1 in CaOV3 and TOV21G cells—two EOC cell lines which harbor inactivating STK11 mutations—reduces cell growth and colony formation in proliferating adherent culture. Proliferation and dispersion of CaOV3-LKB1 and TOV21G-LKB1 cells from re-attached spheroids are also reduced. Taken together, LKB1 has growth suppressive effects in EOC cells, yet it serves the additional purpose to promote cell survival in spheroids. The canonical target of LKB1 is AMP-activated protein kinase (AMPK), which is thought to elicit the majority of LKB1 growth suppressive effects during stress metabolism signaling. As expected, AMPK phosphorylation at threonine-172 is also induced upon spheroid formation. Using STK11-knockout EOC cells, however, we demonstrate that LKB1 is not required to phosphorylate AMPK in spheroids; more importantly, knockdown of PRKAA1 encoding the catalytic alpha-subunit of AMPK has no effect on spheroid cell viability. Thus, our results suggest that LKB1 utilizes alternative mechanisms to regulate the dormancy phenotype in EOC spheroids. Future work will entail direct experiments testing whether LKB1-mediated stress metabolism signaling has the potential to promote EOC metastasis and recurrence of chemo-resistant disease.

Citation Format: Trevor G. Shepherd, Yudith Ramos Valdes, Teresa Peart, Meera Shah, Gabriel E. DiMattia. Stress management: LKB1 controls growth and survival of dormant epithelial ovarian cancer spheroid cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B51.

Evidence for differential viral oncolytic efficacy in an in vitro model of epithelial ovarian cancer metastasis

Epithelial ovarian cancer is unique among most carcinomas in that metastasis occurs by direct dissemination of malignant cells traversing throughout the intraperitoneal fluid. Accordingly, we test new therapeutic strategies using an in vitro three-dimensional spheroid suspension culture model that mimics key steps of this metastatic process. In the present study, we sought to uncover the differential oncolytic efficacy among three different viruses—Myxoma virus, double-deleted vaccinia virus, and Maraba virus—using three ovarian cancer cell lines in our metastasis model system. Herein, we demonstrate that Maraba virus effectively infects, replicates, and kills epithelial ovarian cancer (EOC) cells in proliferating adherent cells and with slightly slower kinetics in tumor spheroids. Myxoma virus and vaccinia viruses infect and kill adherent cells to a much lesser extent than Maraba virus, and their oncolytic potential is almost completely attenuated in spheroids. Myxoma virus and vaccinia are able to infect and spread throughout spheroids, but are blocked in the final stages of the lytic cycle, and oncolytic-mediated cell killing is reactivated upon spheroid reattachment. Alternatively, Maraba virus has a remarkably reduced ability to initially enter spheroid cells, yet rapidly infects and spreads throughout spheroids generating significant cell killing effects. We show that low-density lipoprotein receptor expression in ovarian cancer spheroids is reduced and this controls efficient Maraba virus binding and entry into infected cells. Taken together, these results are the first to implicate the potential impact of differential viral oncolytic properties at key steps of ovarian cancer metastasis.

Beclin-1 expression is retained in high-grade serous ovarian cancer yet is not essential for autophagy induction in vitro

Background

Autophagy is a conserved cellular self-digestion mechanism that can either suppress or promote cancer in a context-dependent manner. In ovarian cancer, prevalent mono-allelic deletion of BECN1 (a canonical autophagy-inducer) suggests that autophagy is impaired to promote carcinogenesis and that Beclin-1 is a haploinsufficient tumor suppressor. Nonetheless, autophagy is known to be readily inducible in ovarian cancer cells. We sought to clarify whether Beclin-1 expression is in fact disrupted in ovarian cancer and whether this impacts autophagy regulation.

Methods

BECN1 expression levels were assessed using The Cancer Genome Atlas (TCGA) datasets from 398 ovarian high-grade serous cystadenocarcinomas (HGSC) and protein immunoblot data from HGSC samples obtained at our institution. Knockdown of BECN1 and other autophagy-related gene expression was achieved using siRNA in established human ovarian cancer cell lines (CaOV3, OVCAR8, SKOV3, and HeyA8) and a novel early-passage, ascites-derived cell line (iOvCa147-E2). LC3 immunoblot, autophagic flux assays, transmission electron microscopy and fluorescence microscopy were used to assess autophagy.

Results

We observed prevalent mono-allelic BECN1 gene deletion (76 %) in TCGA tumors, yet demonstrate for the first time that Beclin-1 protein expression remains relatively unaltered in these and additional samples generated at our institution. Surprisingly, efficient siRNA-mediated Beclin-1 knockdown did not attenuate autophagy induction, whereas knockdown of other autophagy-related genes blocked the process. Beclin-1 knockdown instead decreased cell viability without inducing apoptosis.

Conclusions

Taken together, these data demonstrate that despite its sustained expression, Beclin-1 is dispensable for autophagy induction in ovarian tumor cells in vitro, yet may be retained to promote cell viability by a mechanism independent of autophagy or apoptosis regulation. Overall, this work makes novel observations about tumor expression of Beclin-1 and challenges the accepted understanding of its role in regulating autophagy in ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-015-0182-y) contains supplementary material, which is available to authorized users.

Vertical structure of stratospheric water vapour trends derived from merged satellite data

Stratospheric water vapour is a powerful greenhouse gas. The longest available record from balloon observations over Boulder, Colorado, USA shows increases in stratospheric water vapour concentrations that cannot be fully explained by observed changes in the main drivers, tropical tropopause temperatures and methane. Satellite observations could help resolve the issue, but constructing a reliable long-term data record from individual short satellite records is challenging. Here we present an approach to merge satellite data sets with the help of a chemistry-climate model nudged to observed meteorology. We use the models' water vapour as a transfer function between data sets that overcomes issues arising from instrument drift and short overlap periods. In the lower stratosphere, our water vapour record extends back to 1988 and water vapour concentrations largely follow tropical tropopause temperatures. Lower and mid-stratospheric long-term trends are negative, and the trends from Boulder are shown not to be globally representative. In the upper stratosphere, our record extends back to 1986 and shows positive long-term trends. The altitudinal differences in the trends are explained by methane oxidation together with a strengthened lower-stratospheric and a weakened upper-stratospheric circulation inferred by this analysis. Our results call into question previous estimates of surface radiative forcing based on presumed global long-term increases in water vapour concentrations in the lower stratosphere.

Combination of AKT inhibition with autophagy blockade effectively reduces ascites-derived ovarian cancer cell viability

Recent genomics analysis of the high-grade serous subtype of epithelial ovarian cancer (EOC) show aberrations in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway that result in upregulated signaling activity. Thus, the PI3K/AKT pathway represents a potential therapeutic target for aggressive high-grade EOC. We previously demonstrated that treatment of malignant ascites-derived primary human EOC cells and ovarian cancer cell lines with the allosteric AKT inhibitor Akti-1/2 induces a dormancy-like cytostatic response but does not reduce cell viability. In this report, we show that allosteric AKT inhibition in these cells induces cytoprotective autophagy. Inhibition of autophagy using chloroquine (CQ) alone or in combination with Akti-1/2 leads to a significant decrease in viable cell number. In fact, Akti-1/2 sensitizes EOC cells to CQ-induced cell death by exhibiting markedly reduced EC50 values in combination-treated cells compared with CQ alone. In addition, we evaluated the effects of the novel specific and potent autophagy inhibitor-1 (Spautin-1) and demonstrate that Spautin-1 inhibits autophagy in a Beclin-1-independent manner in primary EOC cells and cell lines. Multicellular EOC spheroids are highly sensitive to Akti-1/2 and CQ/Spautin-1 cotreatments, but resistant to each agent alone. Indeed, combination index analysis revealed strong synergy between Akti-1/2 and Spautin-1 when both agents were used to affect cell viability; Akti-1/2 and CQ cotreatment also displayed synergy in most samples. Taken together, we propose that combination AKT inhibition and autophagy blockade would prove efficacious to reduce residual EOC cells for supplying ovarian cancer recurrence.

Abstract A45: Beclin1-independent autophagy promotes the survival of metastatic ovarian cancer cells

Epithelial ovarian cancer (EOC) metastasis proceeds by an intra-peritoneal route, involving detachment of cells from the primary tumor and dissemination throughout the peritoneal cavity as multicellular aggregates, or spheroids. Herein, we demonstrate that ascites-derived cells upregulate the process of macroautophagy (autophagy), a highly-conserved self-digestion mechanism that functions to mitigate cellular stresses. Both non-adherent culture of these cells to form in vitro spheroids as well as exposure to an allosteric AKT inhibitor stimulated this process, as evidenced by Western blot and immunofluorescence staining for the autophagy marker MAP1LC3B (LC3). Likewise, expression of an eGFP-labeled LC3 protein revealed a shift from diffuse to ‘punctate’ cytoplasmic localization, demonstrating the formation of intracellular autophagic vesicles (autophagosomes). Additionally, we performed transmission electron microscopy and autophagy flux assays, confirming that autophagic degradation proceeded to completion. To determine the role of autophagy upregulation, we attempted to block this process using siRNAs targeting critical autophagy-related (ATG) genes. Interestingly, we found that depletion of Beclin1/ATG6 had no effect on autophagy, despite its role as a canonical inducer of the process. Conversely, depletion of the autophagy regulators ATG5 & ATG7 efficiently blocked LC3 processing and autophagosome formation. Likewise, autophagy was also blocked pharmacologically using the classical inhibitor Chloroquine and the novel agent Spautin-1 (the first targeted autophagy inhibitor to be published). Autophagy blockade by any of these mechanisms reduced EOC cell viability in both adherent and spheroid cultures, suggesting that the upregulation of this process serves to promote cell survival. Moreover, when autophagy blockade was combined with AKT inhibition, a synergistic reduction in cell survival was observed based on combination index analysis. Taken together, this work describes spheroid formation as a stimulus for a non-canonical, Beclin1-independent autophagy program, but also reveals autophagy to be a promoter of tumor cell survival during ovarian cancer metastasis, particularly in cells subjected to AKT/mTOR inhibition. In light of these findings, we propose that clinical autophagy inhibition could enhance the effectiveness of current or investigational ovarian cancer therapies.

Citation Format: Rohann Correa, Yudith Ramos-Valdes, Teresa Peart, Elena Fazio, Monique Bertrand, Jacob McGee, Michel Préfontaine, Akira Sugimoto, Trevor G. Shepherd, Gabriel E. DiMattia. Beclin1-independent autophagy promotes the survival of metastatic ovarian cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A45.

Abstract A47: The LKB1-AMPK pathway mediates the metabolic stress response of dormant ovarian cancer spheroids

Metastatic epithelial ovarian cancer (EOC) cells can form multicellular spheroids while in suspension and disperse throughout the peritoneum via ascites to seed secondary lesions. We hypothesize that EOC spheroids are key mediators of metastasis, which use specific signaling pathways to alter cell metabolism for increased survival. Our lab discovered that AKT signaling is reduced during spheroid formation leading to cellular quiescence and autophagy. Given the induction of quiescence and autophagy in EOC spheroids, we are studying the 5′-AMP-activated protein kinase (AMPK) pathway as a master controller of the metabolic stress response and dormant phenotype of EOC spheroids. We demonstrate AMPK activity and its upstream kinase LKB1 are increased in quiescent EOC spheroids compared with proliferating adherent EOC cells. We also show elevated AMPK activity in spheroids isolated directly from patient ascites. Targeted knockdown of STK11, encoding LKB1, reduces cell viability in ovarian cancer cell line spheroids; PRKAA1 (AMPKα1) knockdown has little to no effect on EOC cell or spheroid viability. Combination of STK11 knockdown with carboplatin treatment leads to a synergistic enhancement in EOC spheroid cell death. In contrast, AICAR treatment of proliferating adherent ovarian cancer cell lines and primary EOC cells induces AMPK activity and causes either cytostasis or cell death. In addition, AICAR treatment of spheroids during reattachment decreases the dispersion capacity of migrating EOC cells. These results offer a glimpse of the potential important contributions of LKB1-AMPK pathway in stress signaling related to EOC cell survival during metastasis. In addition, downstream effectors of upregulated LKB1-AMPK signalling may provide additional mechanisms by which EOC evades chemotherapy. It is foreseeable that these findings will allow us to identify new therapeutic targets within this pathway critical to EOC progression for ultimate translation to the clinic.

Citation Format: Teresa Peart, Elena Fazio, Yudith Ramos-Valdes, Monique Bertrand, Jacob McGee, Michel Prefontaine, Akira Sugimoto, Gabriel E. DiMattia, Trevor G. Shepherd. The LKB1-AMPK pathway mediates the metabolic stress response of dormant ovarian cancer spheroids. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A47.

Expression of Ski can act as a negative feedback mechanism on retinoic acid signaling

BACKGROUND

Retinoic acid signaling is essential for many aspects of early development in vertebrates. To control the levels of signaling, several retinoic acid target genes have been identified that act to suppress retinoic acid signaling in a negative feedback loop. The nuclear protein Ski has been extensively studied for its ability to suppress transforming growth factor-beta (TGF-β) signaling but has also been implicated in the repression of retinoic acid signaling.

RESULTS

We demonstrate that ski expression is up-regulated in response to retinoic acid in both early Xenopus embryos and in human cell lines. Blocking retinoic acid signaling using a retinoic acid antagonist results in a corresponding decrease in the levels of ski mRNA. Finally, overexpression of SKI in human cells results in reduced levels of CYP26A1 mRNA, a known target of retinoic acid signaling.

CONCLUSIONS

Our results, coupled with the known ability of Ski to repress retinoic acid signaling, demonstrate that Ski expression is a novel negative feedback mechanism acting on retinoic acid signaling.

Oncolytic virotherapy for ovarian cancer

In the past two decades, more than 20 viruses with selective tropism for tumor cells have been developed as oncolytic viruses (OVs) for treatments of a variety of malignancies. Of these viruses, eleven have been tested in human ovarian cancer models in preclinical studies. So far, nine phase I or II clinical trials have been conducted or initiated using four different types of OVs in patients with recurrent ovarian cancers. In this article, we summarize the different OVs that are being assessed as therapeutics for ovarian cancer. We also present an overview of recent advances in identification of key genetic or immune-response pathways involved in tumorigenesis of ovarian cancer, which provides a better understanding of the tumor specificities and oncolytic properties of OVs. In addition, we discuss how next-generation OVs could be genetically modified or integrated into multimodality regimens to improve clinical outcomes based on recent advances in ovarian cancer biology.

BMP signalling controls the malignant potential of ascites-derived human epithelial ovarian cancer spheroids via AKT kinase activation

Epithelial ovarian cancer (EOC) cells have the ability to form multi-cellular aggregates in malignant ascites which dramatically alters cell signalling, survival, and metastatic potential. Herein, we demonstrate that patient ascites-derived EOC cells down-regulate endogenous bone morphogenetic protein (BMP) signalling by decreasing BMP ligand expression when grown in suspension culture to form spheroids. Enforced BMP signalling in these cells via constitutively-active BMP type I ALK3(QD) receptor expression causes the formation of smaller, more loosely-aggregated spheroids. Additionally, ALK3(QD)-expressing spheroids have an increased rate of adhesion and dispersion upon reattachment to substratum. Inhibition of endogenous BMP signalling using recombinant Noggin or small molecule inhibitor LDN-193189, on the other hand, opposed these phenotypic changes. To identify potential targets that impact the phenotype of EOC spheroids due to activated BMP signalling, we performed genome-wide expression analyses using Affymetrix arrays. Using the online Connectivity Map resource, the BMP signalling gene expression signature revealed that the AKT pathway is induced by activated BMP signalling in EOC cells; this finding was further validated by phospho-AKT immuno-blotting. In fact, treatment of EOC spheroids with an AKT inhibitor, Akti-1/2, reduced BMP-stimulated cell dispersion during reattachment as compared to controls. Thus, we have identified AKT as being one important downstream component of activated BMP signalling on EOC spheroid pathobiology, which may have important implications on the metastatic potential of this malignancy.

Modulation of AKT activity is associated with reversible dormancy in ascites-derived epithelial ovarian cancer spheroids

Epithelial ovarian cancer (EOC) metastasis is a direct contributor to high recurrence and low survival for patients with this disease. Metastasis in EOC occurs by cell exfoliation from the primary tumor into the fluid-filled peritoneal cavity, persistence of these cells as non-adherent multicellular aggregates or spheroids and reattachment of spheroids to form secondary lesions. We have recovered native spheroids from ascites fluid and demonstrated that EOC cells within these structures exhibit reduced proliferation, yet regain the capacity to attach and reinitiate cell division. To model this process in vitro for further investigation, primary EOC cells from patient peritoneal fluid were cultured under non-adherent conditions. Here we show that these cells naturally form spheroids resembling those observed in ascites. Spheroids exhibit reduced cell proliferation and a protein expression pattern consistent with cellular quiescence: specifically, decreased phospho-AKT and p45/SKP2 with a concomitant increase in p130/RBL2 and p27(Kip1). However, when spheroids are seeded to an adherent surface, reattachment occurs rapidly and is followed by reinitiation of AKT-dependent cell proliferation. These results were strikingly consistent among numerous clinical specimens and were corroborated in the EOC cell line OVCAR3. Therefore, our data reveal that EOC cells become quiescent when forming spheroids, but reactivate proliferative mechanisms upon attachment to a permissive substratum. Overall, this work utilizes a novel in vitro model of EOC metastasis that employs primary human EOC cells and introduces the important concept of reversible dormancy in EOC pathogenesis.

On the path to translation: Highlights from the 2010 Canadian Conference on Ovarian Cancer Research

Ovarian cancer continues to be the most lethal of the gynaecologic malignancies due to the lack of early detection, screening strategies and ineffective therapeutics for late-stage metastatic disease, particularly in the recurrent setting. The gathering of researchers investigating fundamental pathobiology of ovarian cancer and the clinicians who treat patients with this insidious disease is paramount to meeting the challenges we face. Since 2002, the Canadian Conference on Ovarian Cancer Research, held every two years, has served this essential purpose. The objectives of this conference have been to disseminate new information arising from the most recent ovarian cancer research and identify the most pressing challenges we still face as scientists and clinicians. This is best accomplished through direct encounters and exchanges of innovative ideas among colleagues and trainees from the realms of basic science and clinical disciplines. This meeting has and continues to successfully facilitate rapid networking and establish new collaborations from across Canada. This year, more guest speakers and participants from other countries have extended the breadth of the research on ovarian cancer that was discussed at the meeting. This report summarizes the key findings presented at the fifth biennial Canadian Conference on Ovarian Cancer Research held in Toronto, Ontario, and includes the important issues and challenges we still face in the years ahead to make a significant impact on this devastating disease.

Abstract 4309: Establishment of the chick chorioallantoic membrane (CAM) as an ex vivo model system to study mechanisms underlying epithelial ovarian tumour growth and metastasis

Epithelial ovarian cancer (EOC) accounts for approximately 90% of all human ovarian malignancies. Unfortunately, 75% of EOC cases are not diagnosed until advanced stages when the tumour has metastasized, after which standard therapy is less effective. Therefore, it remains vital to directly study the molecular and cellular mechanisms contributing to EOC metastasis in an experimentally-tractable system. The chick chorioallantoic membrane (CAM) is a highly-vascularized tissue responsible for gas and nutrient exchange in the avian embryo, and has been used extensively to study angiogenesis and tumour formation by highly-aggressive cancer cell lines. Herein, we report that ascites-derived primary human EOC cells and established EOC cell lines readily form well-vascularized tumours on the chick CAM. To investigate this property further, we have generated GFP-expressing clones from the mouse ovarian tumour cell lines MOSE-RM (oncogenic Ras & Myc overexpression, SV40 TAg), MASC-2 (SV40 TAg), and 4306 (oncogenic Kras & Pten-null) which will facilitate visualization of tumour growth on the CAM as well as complementary studies in syngeneic mouse models for future studies. Xenografts of MOSE-RM and 4306 cell lines onto the surface of the chick CAM establish tumours that are significantly larger in mass and size compared with MASC-2 cells. Importantly, EOC tumours grown on the chick CAM are histologically identical to those arising within the peritoneal cavity. MOSE-RM and 4306 cell lines promote angiogenesis using HUVEC cells and the chick CAM, whereas MASC-2 cells lack this ability. Overall, these results demonstrate that EOC tumour growth on the chick CAM can be exploited as a highly amenable model system for studying late-stage EOC metastasis. Our findings also indicate that neo-vascularization is an obligatory process for establishment of secondary tumours; thus, we are currently investigating signaling pathways that impact primary human EOC tumour growth and angiogenesis using the chick CAM.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4309. doi:10.1158/1538-7445.AM2011-4309

Constitutive activation of BMP signalling abrogates experimental metastasis of OVCA429 cells via reduced cell adhesion

Background

Activation of bone morphogenetic protein (BMP)4 signalling in human ovarian cancer cells induces a number of phenotypic changes in vitro, including altered cell morphology, adhesion, motility and invasion, relative to normal human ovarian surface epithelial cells. From these in vitro analyses, we had hypothesized that active BMP signalling promotes the metastatic potential of ovarian cancer.

Methods

To test this directly, we engineered OVCA429 human ovarian cancer cells possessing doxycycline-inducible expression of a constitutively-active mutant BMP receptor, ALK3^QD, and administered these cells to immunocompromised mice. Further characterization was performed in vitro to address the role of activated BMP signalling on the EOC phenotype, with particular emphasis on epithelial-mesenchymal transition (EMT) and cell adhesion.

Results

Unexpectedly, doxycycline-induced ALK3^QD expression in OVCA429 cells reduced tumour implantation on peritoneal surfaces and ascites formation when xenografted into immunocompromised mice by intraperitoneal injection. To determine the potential mechanisms controlling this in vivo observation, we followed with several cell culture experiments. Doxycycline-induced ALK3^QD expression enhanced the refractile, spindle-shaped morphology of cultured OVCA429 cells eliciting an EMT-like response. Using in vitro wound healing assays, we observed that ALK3^QD-expressing cells migrated with long, cytoplasmic projections extending into the wound space. The phenotypic alterations of ALK3^QD-expressing cells correlated with changes in specific gene expression patterns of EMT, including increased Snail and Slug and reduced E-cadherin mRNA expression. In addition, ALK3^QD signalling reduced β1- and β3-integrin expression, critical molecules involved in ovarian cancer cell adhesion. The combination of reduced E-cadherin and β-integrin expression correlates directly with the reduced EOC cell cohesion in spheroids and reduced cell adhesion to the extracellular matrix substrates fibronectin and vitronectin that was observed.

Conclusions

We propose that the key steps of ovarian cancer metastasis, specifically cell cohesion of multicellular aggregates in ascites and cell adhesion for reattachment to secondary sites, may be inhibited by overactive BMP signalling, thereby decreasing the ultimate malignant potential of ovarian cancer in this model system.

The Pea3 Ets transcription factor regulates differentiation of multipotent progenitor cells during mammary gland development

The Pea3 Ets transcription factor is overexpressed in breast tumors suggesting that it plays a role in mammary oncogenesis. However, the normal biological function of Pea3 in the mammary gland is not known. Here we report that Pea3 was expressed in the epithelium of the mouse mammary anlagen commensurate with their genesis, and at later times in the nipple and mammary ducts of female embryos. In adult mice Pea3 transcripts peaked at the onset of puberty and early pregnancy, times of active epithelial cell proliferation and differentiation. Pea3 was expressed in all progenitor cap cells and rare body cells of terminal end buds, and in the myoepithelial cells of ducts and alveoli. Analyses of the mammary glands of Pea3-null mice during puberty revealed an increased number of terminal end buds and an increased fraction of proliferating progenitor cells within these structures compared to their wild type littermates. Tissue transplant experiments demonstrated that these phenotypes were intrinsic to the Pea3-null mammary epithelium. During pregnancy, mammary glands isolated from Pea3-null females had impaired alveolar development as revealed by a decreased fraction of alveolar structures. We performed in vitro colony forming assays of mammary epithelial cells and discovered that loss of Pea3 altered the distribution of specific multipotent progenitor cells. Double-immunofluorescence confirmed that multipotential progenitors co-expressing markers of the myoepithelial and luminal epithelial lineage were amplified in the mammary glands of Pea3-null mice by comparison to their wild type counterparts. We propose that Pea3 functions in multipotential progenitors to regulate their lineage-specific differentiation potential.

The impact of stratospheric ozone recovery on the Southern Hemisphere westerly jet

In the past several decades, the tropospheric westerly winds in the Southern Hemisphere have been observed to accelerate on the poleward side of the surface wind maximum. This has been attributed to the combined anthropogenic effects of increasing greenhouse gases and decreasing stratospheric ozone and is predicted to continue by the Intergovernmental Panel on Climate Change/Fourth Assessment Report (IPCC/AR4) models. In this paper, the predictions of the Chemistry-Climate Model Validation (CCMVal) models are examined: Unlike the AR4 models, the CCMVal models have a fully interactive stratospheric chemistry. Owing to the expected disappearance of the ozone hole in the first half of the 21st century, the CCMVal models predict that the tropospheric westerlies in Southern Hemisphere summer will be decelerated, on the poleward side, in contrast with the prediction of most IPCC/AR4 models.

Autocrine BMP4 signalling regulates ID3 proto-oncogene expression in human ovarian cancer cells

Bone morphogenetic protein (BMP)-4 signalling leads to the direct upregulation of ID3 proto-oncogene expression in human ovarian cancer cells. An upstream BMP4-responsive enhancer element consisting of a palindromic BMP response element (BRE) site and CAGA box was identified ~3.0 kb upstream of the human ID3 gene, and a nearly-identical element exists in the second intron of the ID3 gene. BMP4 stimulation leads to the direct binding of Smads 1/5 and Smad4 to the upstream and intronic enhancers, and together both enhancers cooperate to yield heightened BMP4-mediated ID3 promoter activity. We further demonstrate that ID3 is overexpressed in human ovarian cancer cells when compared to normal ovarian surface epithelial cells, and treatment of ovarian cancer cells with the BMP4 antagonist Noggin abrogates endogenous ID3 gene expression. Our findings define the mechanism of BMP4-mediated ID3 gene expression, and support the notion that ovarian cancer cells possess autocrine BMP4 signalling required to sustain ID3 overexpression which may contribute to human ovarian cancer pathogenesis.

Primary culture of ovarian surface epithelial cells and ascites-derived ovarian cancer cells from patients

Our laboratory has refined the technique for isolating primary cultures of normal human ovarian surface epithelial (OSE) cells by combining two different protocols involving the enzymatic and mechanical removal of OSE cells from ovarian biopsies. A simple protocol of obtaining primary epithelial ovarian cancer (EOC) cells from the ascites fluid removed from patients with high-grade ovarian cancer is also described. These methods allow for the direct application of many molecular and cellular analyses of normal versus cancer cells isolated freshly from patients, with the added potential for retrospective analyses of archived cells and tissues. Thus, we have included optional steps for the immediate preparation of ascites-derived EOC cells to be used for subsequent cytological analyses. Initial isolation of OSE or EOC cells can be completed in 1 h, and primary cells are further expanded in culture for several weeks.

BMP4 induces EMT and Rho GTPase activation in human ovarian cancer cells

We identified previously an autocrine bone morphogenetic protein-4 (BMP4) signalling pathway in primary human normal ovarian surface epithelial (OSE) and epithelial ovarian cancer (OvCa) cells. Herein we show that treatment of OvCa cells with BMP4 produced morphological alterations and increased cellular adhesion, motility and invasion. The BMP4 inhibitor noggin blocked the BMP4-induced phenotype, and decreased autocrine BMP4-mediated OvCa cell motility and adherence. In response to exogenous BMP4, the epithelial-mesenchymal transition (EMT) markers Snail and Slug mRNA and protein were up-regulated, E-cadherin mRNA and protein were down-regulated and the network of alpha smooth muscle actin changed to resemble a mesenchymal cell. We also observed changes in the level of activated Rho GTPases in OvCa cells treated with BMP4, strongly suggesting that the changes in morphology, adhesion, motility and invasion are probably mediated through the activation of these molecules. Strikingly, treatment of normal OSE cells with BMP4 or noggin failed to alter cell motility, providing evidence that OSE and OvCa cells possess a distinct capability to respond to BMP4. Overall, our studies suggest a link between autocrine BMP signalling mediated through the Rho GTPase family and Snail- and Slug-induced EMT that may collectively contribute to aggressive OvCa behaviour.

The p38 MAPK inhibitor, PD169316, inhibits transforming growth factor β-induced Smad signaling in human ovarian cancer cells

Transforming growth factor beta (TGFbeta) can signal through a variety of Smad-independent pathways, including the p38 MAPK pathway. Recent work has shown that inhibitors of p38 MAPK, such as SB203580 and SB202190, can inhibit signaling induced by TGFbeta. Here we show that another p38 MAPK inhibitor, PD169316, abrogates signaling initiated by both TGFbeta and Activin A, but not bone morphogenetic protein (BMP) 4. Inhibition of TGFbeta signaling is dose dependent and results in reduced Smad2 and Smad3 phosphorylation, nuclear translocation, and up-regulation of the TGFbeta target gene Smad7. Reduced TGFbeta signaling is not due to abrogation of p38 MAPK activity, since blocking p38 MAPK activity with a dominant negative form of p38 MAPK has no effect on TGFbeta/Smad signaling. Our results show that use of PD169316 at 5 MICROM or higher can block TGFbeta signaling activity and thus caution must be used when attributing cellular activities exclusively to p38 MAPK signaling when these inhibitors are used experimentally.

Identification of a putative autocrine bone morphogenetic protein-signaling pathway in human ovarian surface epithelium and ovarian cancer cells

Bone morphogenetic proteins (BMPs) are members of the TGFbeta superfamily of cytokines that are involved in development, differentiation, and disease. In an analysis of normal ovarian surface epithelium (OSE) and ovarian cancer (OC) cells, we observed BMP4 mRNA expression and found that primary OC cells produce mature BMP4. In addition, each member of the downstream signaling pathway was expressed in primary OSE and OC cells. Smad1 was phosphorylated and underwent nuclear translocation in normal OSE and OC cells upon treatment with BMP4. Interestingly, the BMP target genes ID1 and ID3 were up-regulated 10- to 15-fold in primary OC cells, compared with a 2- to 3-fold increase in normal OSE. The growth of several primary OC cells was relatively unaltered by BMP4 treatment; however, long-term BMP4 treatment of primary OC cells resulted in decreased cell density as well as increased cell spreading and adherence. These data demonstrate the existence and putative function of BMP signaling in normal OSE and OC cells, and thus the continued examination of BMP4 signaling in the regulation of these two processes will be critical to further our current understanding of the role of BMP biology in OC pathogenesis.

Epigenetic regulation of proprotein convertase PACE4 gene expression in human ovarian cancer cells

Proprotein convertases (PC) are a family of serine endoproteases that play important roles in regulating cell function by converting proproteins to biologically active molecules. Several lines of evidence suggest that overexpression of PCs contributes to tumor formation and progression in various types of cancer. In this study, we examined PC expression in six normal ovarian surface epithelium (OSE) cultures, nine primary ovarian cancer (OC) cultures, and three established OC cell lines (Hey, HeyC2, and OCC-1). Our results show that furin and PC7 expression in OC cells was comparable to that in normal OSE. However, PACE4 expression was greatly reduced in all OC samples studied. PACE4 promoter activity was measured in HeyC2 and OCC-1 cells using transiently transfected luciferase reporter plasmids. Both cell lines supported PACE4 promoter activity, showing that the transcription factors critical for PACE4 expression are present in OC cells. The observation that established OC cell lines have reduced PACE4 expression, but maintained the ability to support PACE4 promoter activity, led to the hypothesis that reduced expression may be due to epigenetic modification of the PACE4 gene, such as DNA methylation and histone deacetylation. Methylation analysis of 79 CpG dinucleotides within the PACE4 promoter and exon I (-196/+340) revealed that the percentage of methylated cytosine nucleotides was 8-9% in normal OSE, but 58-93% in OC cells. Treatment with the demethylating agent 5-aza-2'-deoxycytidine and/or the histone deacetylase inhibitor trichostatin A greatly increased PACE4 expression in OC cells. These data suggest that the reduction of PACE4 expression in OC cells is caused, in part, by DNA hypermethylation and histone deacetylation.

Function of PEA3 Ets transcription factors in mammary gland development and oncogenesis

The Ets gene families of mice and man currently comprise 27 genes that encode sequence-specific transcription factors. Ets proteins share an approximately 85 amino acid structurally conserved ETS DNA binding domain. Genetic analyses in model organisms suggest roles for Ets proteins in embryonic development and various adult physiological processes. Chromosomal translocations involving several ETS genes are associated with Ewing's sarcomas and leukemias, whereas the overexpression of some ETS genes is linked with numerous malignancies, including breast cancer. Indeed PEA3, ETS-1, PDEF, and ELF-3 transcripts have all been reported to be elevated in human breast tumors. Some of the ETS genes that are overexpressed in human breast tumors are also overexpressed in mouse models of this disease. Notably, pea3, as well as its close paralogs er81 and erm, which comprise the pea3 subfamily of ets genes, are coordinately overexpressed in mouse mammary tumors. Genetic analyses in mice reveal required roles for one or more of the PEA3 subfamily Ets proteins in the initiation and progression of mouse mammary tumors. The pea3 subfamily genes are normally expressed in the primitive epithelium of mouse mammary buds during embryogenesis, and these three genes are expressed in epithelial progenitor cells during postnatal mammary gland development. Loss-of-function mutations in the mouse pea3 gene results in increased numbers of terminal end buds and an increased fraction of proliferating cells in these structures, suggesting a role for PEA3 in progenitor cell renewal or terminal differentiation. Taken together these observations suggest that the PEA3 subfamily proteins play key regulatory roles in both mammary gland development and oncogenesis.

Primary culture and mRNA analysis of human ovarian cells

Established cell lines are invaluable for studying cell and molecular biological questions. A variety of human ovarian cancer (OC) cell lines exist, however, most have acquired significant genetic alterations from their cells of origin, including deletion of important cell cycle regulatory genes. In order to analyze signaling events related to cell cycle control in human OC, we have modified existing protocols for isolating and culturing OC cells from patient ascites fluid and normal ovarian surface epithelial (OSE) cells from benign ovarian tissue sections. These cells maintain an epithelial phenotype and can be manipulated experimentally for several passages before cellular senescence. An example using TGFb1 treatment of OC cells to examine signaling and target gene activation is presented.

The pea3 subfamily ets genes are required for HER2/Neu-mediated mammary oncogenesis

BACKGROUND

The PEA3 Ets transcription factor is overexpressed in the vast majority of human breast tumors and in nearly all of those of the HER2/Neu-positive subclass. PEA3 is also overexpressed in various transgenic mouse models of this disease. Whether PEA3 plays an essential role in HER2/Neu-mediated oncogenesis has heretofore not been addressed.

RESULTS

Here, we report that each of the three highly related ets genes of the pea3 subfamily (pea3, er81, and erm) were coordinately overexpressed in mammary tumors of MMTV-neu transgenic mice. Other ets genes normally expressed in the mammary gland were not upregulated in these tumors. Expression of a dominant-negative pea3 transgene under the control of the MMTV promoter in mammary epithelial cells of MMTV-neu transgenic mice dramatically delayed the onset of mammary tumors and reduced the number and size of such tumors in individual mice. Those tumors that arose in bitransgenic mice expressed the MMTV-neu transgene, but not the MMTV-dominant-negative pea3 transgene.

CONCLUSIONS

These findings imply that one or more of the PEA3 subfamily Ets proteins or other Ets proteins with related DNA binding specificity play an essential role in Neu-mediated mammary oncogenesis. Hence, agents that inhibit the expression or activity of the PEA3 subfamily proteins may prove efficacious in the treatment of breast cancer.