Small Extracellular Vesicles Promote Stiffness-mediated Metastasis

Tissue stiffness is a critical prognostic factor in breast cancer and is associated with metastatic progression. Here we show an alternative and complementary hypothesis of tumor progression whereby physiologic matrix stiffness affects the quantity and protein cargo of small extracellular vesicles (EV) produced by cancer cells, which in turn aid cancer cell dissemination. Primary patient breast tissue released by cancer cells on matrices that model human breast tumors (25 kPa; stiff EVs) feature increased adhesion molecule presentation (ITGα2β1, ITGα6β4, ITGα6β1, CD44) compared with EVs from softer normal tissue (0.5 kPa; soft EVs), which facilitates their binding to extracellular matrix proteins including collagen IV, and a 3-fold increase in homing ability to distant organs in mice. In a zebrafish xenograft model, stiff EVs aid cancer cell dissemination. Moreover, normal, resident lung fibroblasts treated with stiff and soft EVs change their gene expression profiles to adopt a cancer-associated fibroblast phenotype. These findings show that EV quantity, cargo, and function depend heavily on the mechanical properties of the extracellular microenvironment.

SIGNIFICANCE

Here we show that the quantity, cargo, and function of breast cancer-derived EVs vary with mechanical properties of the extracellular microenvironment.

Sarcoma Cells Secrete Hypoxia-Modified Collagen VI to Weaken the Lung Endothelial Barrier and Promote Metastasis

Intratumoral hypoxia correlates with metastasis and poor survival in patients with sarcoma. Using an impedance sensing assay and a zebrafish intravital microinjection model, we demonstrated here that the hypoxia-inducible collagen-modifying enzyme lysyl hydroxylase PLOD2 and its substrate collagen type VI (COLVI) weaken the lung endothelial barrier and promote transendothelial migration. Mechanistically, hypoxia-induced PLOD2 in sarcoma cells modified COLVI, which was then secreted into the vasculature. Upon reaching the apical surface of lung endothelial cells, modified COLVI from tumor cells activated integrin β1 (ITGβ1). Furthermore, activated ITGβ1 colocalized with Kindlin2, initiating their interaction with F-actin and prompting its polymerization. Polymerized F-actin disrupted endothelial adherens junctions and induced barrier dysfunction. Consistently, modified and secreted COLVI was required for the late stages of lung metastasis in vivo. Analysis of patient gene expression and survival data from The Cancer Genome Atlas (TCGA) revealed an association between the expression of both PLOD2 and COLVI and patient survival. Furthermore, high levels of COLVI were detected in surgically resected sarcoma metastases from patient lungs and in the blood of tumor-bearing mice. Together, these data identify a mechanism of sarcoma lung metastasis, revealing opportunities for therapeutic intervention.

SIGNIFICANCE

Collagen type VI modified by hypoxia-induced PLOD2 is secreted by sarcoma cells and binds to integrin β1 on endothelial cells to induce barrier dysfunction, which promotes sarcoma vascular dissemination and metastasis.

Oncofusion-driven de novo enhancer assembly promotes malignancy in Ewing sarcoma via aberrant expression of the stereociliary protein LOXHD1

Ewing sarcoma (EwS) is a highly aggressive tumor of bone and soft tissues that mostly affects children and adolescents. The pathognomonic oncofusion EWSR1::FLI1 transcription factor drives EwS by orchestrating an oncogenic transcription program through de novo enhancers. By integrative analysis of thousands of transcriptomes representing pan-cancer cell lines, primary cancers, metastasis, and normal tissues, we identify a 32-gene signature (ESS32 [Ewing Sarcoma Specific 32]) that stratifies EwS from pan-cancer. Among the ESS32, LOXHD1, encoding a stereociliary protein, is the most highly expressed gene through an alternative transcription start site. Deletion or silencing of EWSR1::FLI1 bound upstream de novo enhancer results in loss of the LOXHD1 short isoform, altering EWSR1::FLI1 and HIF1α pathway genes and resulting in decreased proliferation/invasion of EwS cells. These observations implicate LOXHD1 as a biomarker and a determinant of EwS metastasis and suggest new avenues for developing LOXHD1-targeted drugs or cellular therapies for this deadly disease.

Abstract A02: YAP1 opposes differentiation in mesenchymal tumors

Soft tissue sarcomas are aggressive mesenchymal malignancies diagnosed in ~15,000 Americans annually. Unlike in epithelial cancers, where novel targeted therapies have improved patient survival, the treatment approach for sarcomas has not changed significantly in 25 years. Our work revealed that deregulation of the Hippo pathway enhances sarcomagenesis in an aggressive muscle tumor called undifferentiated pleomorphic sarcoma (UPS). UPS is a commonly diagnosed and metastatic sarcoma subtype found most frequently in adult muscle tissues. We have observed that expression of Angiomotin (AMOT), a crucial mediator of Hippo-associated growth restriction, is commonly silenced in UPS. Among human tissues AMOT is most highly expressed in differentiated human muscle tissue. Ectopic re-expression of the p130 isoform of AMOT in muscle-derived UPS cells significantly inhibits proliferation in vitro. This finding is consistent with the central function of AMOT in cancer cells, which is to sequester the Hippo pathway effector YAP1 and facilitate its degradation, thereby inhibiting growth. YAP1 is a proproliferation transcriptional regulator whose deletion in an autochthonous genetically engineered mouse model (GEMM) of UPS significantly decreased tumorigenesis. Together these data suggest that AMOT loss promotes YAP1-mediated sarcomagenesis in muscle-derived UPS. We investigated the downstream effects of YAP1 signaling in UPS by gene expression analysis of control and Yap1-deficient murine tumors. Mechanistically, we found that Yap1 controls NF-κB transcriptional activity in UPS by inhibiting expression of Usp31, a negative regulator of NF-κB activity. Furthermore, using ChIP-seq of patient samples, we found that both YAP1 and NF-κB activity are substantially upregulated in human UPS. Consistent with these findings, UPS cell proliferation is highly sensitive to YAP1 and NF-κB inhibition. Importantly, loss of NF-κB completely prevents the formation in our murine UPS GEMM. In our effort to identify key transcriptional outputs of YAP1/NF-κB and determine how this signaling pathway controls sarcomagenesis, we found that it represses circadian clock gene expression (PER1, CRY2, ARNTL) and activity. Intriguingly, clock function is activated during muscle differentiation, whereas YAP1 and NF-κB inhibit differentiation is known to enhance proliferation of muscle precursor cells. These observations highlight a role for the YAP1/NF-κB axis in circadian regulation of muscle differentiation. Further studies revealed that YAP1/NF-κB-mediated suppression of the clock leads to downregulation of the unfolded protein response (UPR), a critical component of muscle cell differentiation. UPR transcriptional targets including ATF6 and CHOP are necessary for pruning of myoblasts and apoptosis of differentiation-incompetent muscle precursor cells. Together, our findings suggest a mechanism underlying YAP1-mediated sarcomagenesis via suppression of normal muscle differentiation pathways.

Citation Format: Ying Liu, Gabrielle Ciotti, T.S. Karin Eisinger-Mathason. YAP1 opposes differentiation in mesenchymal tumors [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A02.

Abstract B07: Regaining epigenetic control of the Hippo pathway to inhibit sarcomagenesis

Nearly 11,000 individuals in the United States and 200,000 individuals worldwide are diagnosed with a form of soft-tissue sarcoma (STS) every year. STS is a rare heterogeneous and complex family of disease associated with no uniform underlying genetic abnormality. However, sarcoma treatment has not changed significantly in 25 years. Patients are limited to surgery, radiotherapy, and chemotherapy. Therefore, the discovery of novel targets and mechanisms is critical. The Hippo pathway functions as a signaling hub facilitating cellular responses to multiple stimuli during tumorigenesis. The most important downstream effector of the Hippo pathway is Yes-activated protein (YAP), a transcriptional coactivator that promotes pro-proliferation and suppresses apoptosis. Inactivation of the Hippo pathway promotes nuclear localization of YAP. Whereas many studies have defined YAP1's transcriptional targets in epithelial tumors and normal tissues, its role in mesenchymal tumors is unclear. Here, we confirm that increased YAP1 mRNA expression correlates with worse overall survival in undifferentiated pleomorphic sarcoma (UPS) patients and that YAP1 protein levels are frequently elevated in human sarcomas. Furthermore, immunohistochemical (IHC) analysis of human sarcoma tissue microarray (TMA) showed that YAP levels are dramatically increased in the nuclei of high-grade UPS tumor cells, compared with normal skeletal, adipose, and arterial tissue. UPS is one of the more commonly diagnosed and aggressive subtypes of sarcomas found in adults. To define mechanisms of YAP1-mediated sarcomagenesis, we developed a novel genetic mouse model in which YAP1 is conditionally deleted from KrasG12D+; Trp53fl/fl (KP) UPS tumors (KPY). Microarray analysis of both tumors revealed that YAP1 loss inhibits expression of NF-κB signaling components and transcriptional targets. Consistent with these findings, ChIP-seq and super-enhancer analysis of human UPS tumors (n=3) revealed that many of the 900 identified UPS super enhancers regulate expression of NF-κB targets dependent on YAP1 in our system. This finding is particularly relevant as NF-κB is a key regulator of muscle cell proliferation and suppresses differentiation by inhibiting expression of the myogenic transcription factor, MYOD1. Together, these data suggest that upregulation of YAP1 activity promotes NF-κB-mediated proliferation and inhibits differentiation. Importantly, we have discovered that a combination of JQ1, a BET family inhibitor, and vorinostat (SAHA), a histone deacetylase (HDAC) inhibitor, decreases YAP1 expression, YAP1 protein stability, and sarcoma cell proliferation. Mechanistically, SAHA/JQ1 treatment significantly increases expression of the tumor suppressor angiomotin (AMOT), which binds YAP1, sequesters it in the cytoplasm, and facilitates its degradation. We have also found that AMOT expression is lost in sarcomas compared with normal muscle tissue, likely due to epigenetic suppression. SAHA/JQ1 treatment also decreased gene expression of YAP1 targets and caused reexpression of the muscle differentiation markers p57, MEF2C, and MYOD1. Based on these data we will investigate the efficacy of SAHA/JQ1 against UPS and other sarcomas in vivo using subcutaneous and autochthonous mouse models. We will probe the ability of SAHA/JQ1 treatment to inhibit YAP1 in vivo, to suppress NF-κB dependent mechanisms of cell proliferation and tumorigenesis, and to promote terminal differentiation of sarcoma cells. Ultimately, we will determine whether this approach represents a novel course of targeted treatment for sarcoma patients.

Citation Format: Shuai Ye, Koreana Pak, Jennifer Shah, Susan Chor, Shaun Egolf, Gloria Marino, T.S. Karin Eisinger-Mathason. Regaining epigenetic control of the Hippo pathway to inhibit sarcomagenesis [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr B07.

Abstract 3531: YAP1-mediated circadian oscillation in sarcoma

Soft tissue sarcomas have presented a unique challenge to researchers due to their heterogeneity. One common mechanism underlying more than 25% of diagnosed sarcomas is the deregulation of the Hippo pathway, a critical signaling cascade that responds to cell contact inhibition, among other factors, and negatively regulates cell proliferation. In quiescent cells the pathway remains “on,” which maintains activation of a kinase cascade that phosphorylates and degrades YAP1. However, inactivation of the pathway stabilizes YAP1 allowing it to translocate to the nucleus and activate transcription of pro-proliferative gene targets. Microarray analysis of muscle tissue from the LSL-KrasG12D/+;Trp53fl/fl (KP) mouse model of undifferentiated pleomorphic sarcoma (UPS) revealed that YAP1 deletion (KPY) reduces cell proliferation and increases expression of circadian rhythm genes including PER1. UPS is a commonly diagnosed and aggressive type of muscle-derived sarcoma. The KP model recapitulates human UPS morphologically and histologically, as well as by gene expression profiling. Although PER1 has primarily been characterized as a negative regulator of the circadian clock, upregulation of PER1 is known to modulate the G2/M cell cycle checkpoint at both the protein and mRNA level independent of p53. However, our findings represent a novel link between the circadian clock and the hippo pathway. Notably, deletion of YAP1 in KP tumors leads to a statistically significant 2.5 fold increase in expression of PER1. The study has two specific aims: 1) to identify the YAP1-dependent function of PER1 in sarcoma and 2) determine whether YAP1 directly or indirectly regulates PER1. We have validated the microarray results in KP tumor derived cell lines as well as in KP and KPY tumor tissue. I have also confirmed PER1 suppression in KP cells under YAP1 short hairpin RNA conditions. Our lab has previously observed that treatment with epigenetic modulating drugs JQ1, a BET inhibitor, and SAHA, an HDAC inhibitor, significantly decreased sarcoma growth in vivo and in vitro when administered alone and had an additive effect when combined. These effects can be explained in part by the finding that treatment with these inhibitors significantly reduces YAP1 expression. Under these conditions, as well as YAP1 knockdown conditions, I demonstrated via qRT-PCR and western blot that PER1 is significantly increased at both the protein and transcriptional levels in KP cells. Additionally, preliminary evidence from an MTT proliferation assay showed loss of PER1 increased sarcoma cell proliferation. Further supporting the hypothesis that PER1 modulation impacts sarcoma proliferation, it has been reported that MyoD, the master regulator of muscle cell differentiation, is itself a clock-controlled gene. Together, these results suggest that YAP1 represses PER1 expression in sarcoma, and that epigenetic treatments can cause re-expression of PER1 which functions to inhibit cell proliferation and may promote differentiation.

Citation Format: Gloria Marino, Shuai Ye, Koreana Pak, Jennifer Shah, Jason Godfrey, Susan Chor, Shaun Egolf, T.S. Karin Eisinger-Mathason. YAP1-mediated circadian oscillation in sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3531. doi:10.1158/1538-7445.AM2017-3531

Abstract 3342: Hippo signaling promotes sarcomagenesis through the NF-kB pathway

Nearly 200,000 individuals worldwide are diagnosed with a form of soft-tissue sarcoma (STS) every year. Due to a lack of novel targeted therapeutics sarcoma for these malignancies treatment has not changed significantly in 25 years. Therefore, the discovery of novel targets and mechanisms is critical. One promising avenue the Hippo pathway, which we have identified as a key regulator of sarcomagenesis in undifferentiated pleomorphic sarcoma (UPS), a commonly diagnosed and aggressive subtype of sarcomas. Inactivation of the pathway, promotes nuclear localization of YAP1, a transcriptional co-activator that promotes proliferation. Whereas, many studies have defined YAP1’s transcriptional targets in epithelial tumors and normal tissues, its role in mesenchymal tumors is unclear. Here, we confirm that increased YAP1 mRNA expression correlates with worse overall survival in UPS patients. To define mechanisms of YAP1-mediated sarcomagenesis, we developed a novel genetic mouse model in which YAP1 is conditionally deleted in UPS tumors. Microarray analysis of these tumors revealed that YAP1 loss inhibits expression of NF-κB targets. We have performed ChIP-seq and super-enhancer analysis of human UPS tumors and found that many of the 900 identified super enhancers regulate expression of NF-κB targets that are dependent on YAP1 in our system. This finding is particularly relevant as NF-κB is a key regulator of muscle cell proliferation and suppresses myoblast differentiation. Together, these data suggest that upregulation of YAP1 activity promotes NF-κB-mediated proliferation and inhibits differentiation, resulting in sarcomagenesis. Importantly, we have discovered that a combination of JQ1, a BET family inhibitor, and SAHA, a histone deacetylase inhibitor, decreases YAP1 expression, YAP1 protein stability, and sarcoma cell proliferation. SAHA/JQ1 treatment significantly increased expression of Angiomotin (AMOT), which binds YAP1, sequesters it in the cytoplasm, and facilitates it degradation. We have also found that AMOT expression is lost in sarcomas, likely due to epigenetic suppression. Consistent with these observations, SAHA/JQ1 treatment also decreased gene expression of YAP1 targets and caused re-expression of the muscle differentiation markers p57, MEF2C, and MYOD1. We have investigated the effect of of SAHA/JQ1 in vivo and found dramatic inhibition of tumor growth, as well as reduced YAP1 expression, and increased AMOT expression. Importantly SAHA/JQ1 treatment also inhibited NF-κB activity. Our studies have revealed for the first time that YAP1 expression is epigenetically modulated through AMOT de-regulation in sarcomas, resulting in elevated NF-κB activity and sarcomagenesis. SAHA/JQ1 treatment re-establishes epigenetic control of the Hippo pathway reducing proliferation and enhancing differentiation. Ultimately, we will determine whether this approach represents a novel course of targeted treatment for sarcoma patients.

Citation Format: Shuai Ye, Koreana Pak, Jennifer Shah, Susan Chor, Shaun Egolf, Gloria Marino, T.S. Karin Eisinger-Mathason. Hippo signaling promotes sarcomagenesis through the NF-kB pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3342. doi:10.1158/1538-7445.AM2017-3342

Abstract A41: Hypoxia-dependent modification of collagen networks promotes sarcoma metastasis

Intratumoral hypoxia and expression of Hypoxia Inducible Factor 1α (HIF1α) correlate with metastasis and poor survival in sarcoma patients. We demonstrate here that hypoxia controls sarcoma metastasis through a novel mechanism wherein HIF1α enhances expression of the intracellular enzyme procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2). We show that loss of HIF1α or PLOD2 expression disrupts collagen modification, cell migration and pulmonary metastasis (but not primary tumor growth) in allograft and autochthonous LSL-KrasG12D/+; Trp53fl/fl murine sarcoma models. Biochemical analyses revealed that overexpression of HIF1α and PLOD2 in sarcoma cells alters collagen structure and organization. The increase in lysyl hydroxylation and concomitant loss of prolyl hydroxylation, promotes adherence of tumor cells, collagen-associated migration and tumor cell dissemination. Furthermore, ectopic PLOD2 expression restores migration and metastatic potential in HIF1α-deficient tumors, and analysis of human sarcomas reveal elevated HIF1α and PLOD2 expression in metastatic primary lesions. Pharmacological inhibition of PLOD enzymatic activity suppresses metastases. Collectively, these data indicate that HIF1α controls sarcoma metastasis through PLOD2-dependent collagen modification and organization in primary tumors. We conclude that PLOD2 is a novel therapeutic target in sarcomas and successful inhibition of this enzyme may reduce tumor cell dissemination.

Citation Format: T.S. Karin Eisinger-Mathason, Minsi Zhang, Qiu Qiong, Nicolas Skuli, Michael S. Nakazawa, Tatiana Karakasheva, Vera Mucaj, Jessica E.S. Shay, Lars Stangenberg, Ellen Pure, Sam S. Yoon, David G. Kirsch, M. Celeste Simon. Hypoxia-dependent modification of collagen networks promotes sarcoma metastasis. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr A41. doi:10.1158/1538-7445.CHTME14-A41

HIF-1alpha partners with FoxA2, a neuroendocrine-specific transcription factor, to promote tumorigenesis

In this issue of Cancer Cell, Qi et al. report a novel mechanism by which HIF-1alpha synergizes with a tissue-specific transcription factor, FoxA2, to promote a transcriptional program that supports prostate tumor formation and progression.

RSK in tumorigenesis: connections to steroid signaling

The Ser/Thr kinase family, RSK, has been implicated in numerous types of hormone-dependent and -independent cancers. However, there has been little consideration of RSKs as downstream mediators of steroid hormone non-genomic effects or of their ability to facilitate steroid receptor-mediated gene expression. Steroid hormone signaling can directly stimulate the MEK/ERK/RSK pathway to regulate cellular proliferation and survival in transformed cells. To date, multiple mechanisms of RSK and steroid hormone receptor-mediated proliferation/survival have been elucidated. For example, RSK enhances proliferation of breast and prostate cancer cells via its ability to control the levels of the estrogen receptor co-activator, cyclin D1. While in lung and other tumors RSK may control apoptosis via estrogen-mediated regulation of mitochondrial integrity. Thus the RSKs could be important anti-cancer therapeutic targets in many different transformed tissues. The recent discovery of RSK-specific inhibitors will advance our current understanding of RSK in transformation and drive these studies into animal and clinical models. In this review we explore the mechanisms associated with RSK in tumorigenesis and their relationship to steroid hormone signaling.