Oncogene-induced matrix reorganization controls CD8+ T cell function in the soft-tissue sarcoma microenvironment

CD8+ T cell dysfunction impedes anti-tumor immunity in solid cancers but the underlying mechanisms are diverse and poorly understood. Extracellular matrix (ECM) composition has been linked to impaired T cell migration and enhanced tumor progression; however, impacts of individual ECM molecules on T cell function in the tumor microenvironment (TME) are only beginning to be elucidated. Upstream regulators of aberrant ECM deposition and organization in solid tumors are equally ill-defined. Therefore, we investigated how ECM composition modulates CD8+ T cell function in undifferentiated pleomorphic sarcoma (UPS), an immunologically active desmoplastic tumor. Using an autochthonous murine model of UPS and data from multiple human patient cohorts, we discovered a multifaceted mechanism wherein the transcriptional co-activator YAP1 promotes collagen VI (COLVI) deposition in the UPS TME. In turn, COLVI induces CD8+ T cell dysfunction and immune evasion by remodeling fibrillar collagen and inhibiting T cell autophagic flux. Unexpectedly, collagen I (COLI) opposed COLVI in this setting, promoting CD8+ T cell function and acting as a tumor suppressor. Thus, CD8+ T cell responses in sarcoma depend upon oncogene-mediated ECM composition and remodeling.

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.

Comparative oncology reveals DNMT3B as a molecular vulnerability in undifferentiated pleomorphic sarcoma

PURPOSE

Undifferentiated pleomorphic sarcoma (UPS), an aggressive subtype of soft-tissue sarcoma (STS), is exceedingly rare in humans and lacks effective, well-tolerated therapies. In contrast, STS are relatively common in canine companion animals. Thus, incorporation of veterinary patients into studies of UPS offers an exciting opportunity to develop novel therapeutic strategies for this rare human disease. Genome-wide studies have demonstrated that UPS is characterized by aberrant patterns of DNA methylation. However, the mechanisms and impact of this epigenetic modification on UPS biology and clinical behavior are poorly understood.

METHODS

DNA methylation in mammalian cells is catalyzed by the canonical DNA methyltransferases DNMT1, DNMT3A and DNMT3B. Therefore, we leveraged cell lines and tissue specimens from human and canine patients, together with an orthotopic murine model, to probe the functional and clinical significance of DNMTs in UPS.

RESULTS

We found that the DNA methyltransferase DNMT3B is overexpressed in UPS relative to normal mesenchymal tissues and is associated with a poor prognosis. Consistent with these findings, genetic DNMT3B depletion strongly inhibited UPS cell proliferation and tumor progression. However, existing hypomethylating agents, including the clinically approved drug 5-aza-2'-deoxycytidine (DAC) and the DNMT3B-inhibiting tool compound nanaomycin A, were ineffective in UPS due to cellular uptake and toxicity issues.

CONCLUSIONS

DNMT3B represents a promising molecular susceptibility in UPS, but further development of DNMT3B-targeting strategies for these patients is required.

Abstract B017: Tumor-secreted collagen VI weakens endothelium and promotes metastasis

Metastasis is the leading cause of cancer-related deaths. However, the mechanisms behind the metastatic cascade remain poorly understood. Tumor’s metastatic potential is strongly influenced by microenvironmental cues such as low oxygen (hypoxia). Our published work reported that lung metastases in sarcoma are associated with increased primary tumor expression of the hypoxia-inducible collagen-modifying lysyl hydroxylase, Plod2; in multiple subtypes of sarcoma, excessive collagen lysyl hydroxylation results in secretion of immature collagen aggregates able to physically associate with tumor cells and promote both intravasation and extravasation. In the current study, we observed that Plod2 is colocalized with collagen VI and is important for its extracellular network structure, suggesting that collagen VI is a putative substrate of Plod2. Using an impedance sensing assay and a zebrafish intravital microinjection model, we demonstrated that tumoral Plod2 and collagen VI weaken the endothelial barrier and promote extravasation. With a tail vein injection mouse model, we determined that collagen VI is essential for lung metastasis. Clinically, we detected high levels of collagen VI in metastatic sarcoma in surgically resected patient lungs. Furthermore, by analyzing patient data in The Cancer Genome Atlas (TCGA), we found a strong correlation between the expression of both PLOD2 and collagen VI with disease outcomes. Together, our study identifies a novel mechanism of sarcoma lung metastasis, opening up opportunities for therapeutic intervention.

Citation Format: Ying Liu, Ashley M. Fuller, Ileana Murazzi, Ann Devine, Nicolas Skuli. Tumor-secreted collagen VI weakens endothelium and promotes metastasis [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr B017.

Abstract IA024: Identification of a “hypoxic secretome” and its role in metastasis

Only a small percentage of disseminating tumor cells are capable of forming lethal metastatic foci. Though advances in sequencing and genomics have dramatically enhanced our understanding of primary tumor biology and novel target identification, these techniques alone have not proven sufficient to identify the factors that permit metastasis of this small cellular fraction. For example, we observed that in some tumors the major molecular predictor of metastatic potential is HIF1α protein stabilization in response to low intratumoral O2 tension (hypoxia). These observations clearly show that in-depth understanding of environmental signals and subsequent cellular responses is necessary to fully characterize metastatic potential. Consistent with our earlier observations, we discovered that the collagen-modifying enzyme PLOD2, a direct transcriptional target of HIF1α, dramatically enhances both early (cell migration/invasion) and late (extravasation/lung colonization) steps of the metastatic cascade. We previously reported the role of PLOD2 in modulating the primary tumor microenvironment to facilitate cell migration and intravasation. However, the mechanisms by which PLOD2 and tumor associated collagen impact later metastatic stages (i.e., endothelial adherence, extravasation) are unknown- in part because these processes are particularly difficult to simulate in vitro and to visualize in vivo. Therefore, we have developed new models and tools including a zebrafish embryo xenograft system to image migrating and extravasating tumor cells in vivo. This approach allows us to investigate the late metastatic cascade and define the microenvironmental cues that promote tumor cell dissemination. We also observed that PLOD2-modified collagen is secreted into the extracellular milieu during dissemination and weakens endothelial barrier function. We are investigating the role of tumor collagen and PLOD2 in endothelial adherence and extravasation for the purpose of therapeutically targeting the molecular underpinnings of metastases. Our work focuses on soft tissue sarcomas. However, recent studies by other groups have linked PLOD2 and modified collagen to carcinoma metastasis as well, suggesting a broader applicability for our work. Ultimately, we believe these studies will transform our ability to treat and even prevent metastasis, a unique possibility in sarcoma patients due to the relatively long interval between primary tumor diagnosis and metastatic outgrowth in some patients (5-10 years). The tools we have developed and the mechanisms we are pursuing will open new avenues of research that were once inaccessible and lead to novel therapeutic opportunities for the treatment of metastatic disease in multiple cancer contexts.

Citation Format: T.S. Karin Eisinger, Ying Liu, Ileana Murazzi. Identification of a “hypoxic secretome” and its role in metastasis [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA024.

Abstract PR001: Oncogene-induced matrix reorganization controls CD8+ T cell immunity in the UPS microenvironment

CD8+ T cell dysfunction, characterized by reduced effector function, impaired proliferation, and inhibitory receptor upregulation, is a fundamental barrier to anti-tumor immunity. However, molecular mechanisms underlying the regulation of CD8+ T cell dysfunction in the tumor microenvironment (TME) are incompletely understood. In solid cancers, the extracellular matrix (ECM) facilitates tumor progression in part by inhibiting T cell migration/infiltration, but the impact of individual tumor-associated ECM molecules on T cell function remains unclear. Therefore, we investigated the regulation and impact of ECM composition on CD8+ T cell function in muscle-derived undifferentiated pleomorphic sarcoma (UPS). UPS exhibits durable responses to checkpoint therapy in a subset of human patients, potentially offering valuable insights into strategies for ameliorating T cell function and improving patient responses to immunotherapy. Using the autochthonous Kras G12D/+; Trp53 fl/fl (KP) murine model of UPS, we previously showed that deletion of the central Hippo pathway effector Yap1 (Kras G12D/+; Trp53 fl/fl; Yap1 fl/fl; KPY) suppressed UPS cell proliferation and tumor progression. Given the well-established role of Yap1 in mechanotransduction, we leveraged this system to investigate the effects of Yap1 on the ECM and CD8+ T cell function in UPS. We discovered that loss of UPS-cell intrinsic Yap1 reduced the proportion of dysfunctional CD8+ T cells in the TME and enhanced T cell cytolytic capacity. Yap1 loss also downregulated expression of multiple collagen genes in UPS cells and bulk tumors, including those that encode collagen type VI (ColVI). ColVI is a beaded microfilament collagen that binds to fibril-forming collagens in the ECM, such as collagen type I (ColI), and has been implicated in the pathogenesis of skeletal muscle myopathies. These data suggest that proper ColVI structure and function are critical for normal skeletal muscle physiology, with important implications for muscle-derived tumors such as UPS. Accordingly, COL6A1 was upregulated in human UPS relative to normal skeletal muscle, and inversely associated with UPS patient survival. Moreover, loss of UPS cell-intrinsic Col6a1 suppressed tumor progression, enhanced T cell cytolytic function, and attenuated CD8+ T cell exhaustion, phenocopying the effects of Yap1 deletion. Mechanistically, Yap1-mediated ColVI deposition promoted CD8+ T cell dysfunction by remodeling ColI networks in the UPS TME, and inhibiting T cell autophagic flux. Furthermore, ColI depletion dramatically increased tumor growth in an immunocompetent setting. Our findings reveal a novel role for UPS cell-intrinsic Yap1 in immune activation, and demonstrate that ColVI and ColI have opposing functions downstream of Yap in this context. These results underscore the need to systematically evaluate the roles of individual ECM components in the regulation of immune cell function, and implicate YAP1 and/or COLVI targeting as potential strategies for improving the efficacy of immunotherapy in human patients.

Citation Format: Ashley M. Fuller, Hawley C. Pruitt, Hoogeun Song, Ying Liu, Ann Devine, Rohan S. Katti, Samir Devalaraja, Gabrielle E. Ciotti, Michael Gonzalez, Erik F. Williams, Ileana Murazzi, Nicolas Skuli, Hakon Hakonarson, Kristy Weber, Malay Haldar, Joseph A. Fraietta, Sharon Gerecht, T. S. Karin Eisinger-Mathason. Oncogene-induced matrix reorganization controls CD8+ T cell immunity in the UPS microenvironment [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr PR001.