Cancer cells frequently co-opt molecular programs that are normally activated in specific contexts, such as embryonic development and the response to injury. Determining the impact of cancer-associated mutations on cellular phenotypes within these discrete contexts can provide new insight into how such mutations lead to dysregulated cell behaviors and subsequent cancer onset. Here we assess the impact of heritable BRCA2 mutation on embryonic development and the injury response using a zebrafish model (Danio rerio). Unlike most mouse models for BRCA2 mutation, brca2-mutant zebrafish are fully viable and thus provide a unique tool for assessing both embryonic and adult phenotypes. We find that maternally provided brca2 is critical for normal oocyte development and embryonic survival in zebrafish, suggesting that embryonic lethality associated with BRCA2 mutation is likely to reflect defects in both meiotic and embryonic developmental programs. On the other hand, we find that adult brca2-mutant zebrafish exhibit aberrant proliferation of several cell types under basal conditions and in response to injury in tissues at high risk for cancer development. These divergent effects exemplify the often-paradoxical outcomes that occur in embryos (embryonic lethality) versus adult animals (cancer predisposition) with mutations in cancer susceptibility genes such as BRCA2. The altered cell behaviors identified in brca2-mutant embryonic and adult tissues, particularly in adult tissues at high risk for cancer, indicate that the effects of BRCA2 mutation on cellular phenotypes are both context- and tissue-dependent.

Contributions of the microenvironment to soft tissue sarcoma progression are relatively undefined, representing a major impediment to identifying essential regulatory networks in sarcomagenesis. Furthermore, genetic and molecular characteristics that distinguish precancerous versus cancerous microenvironments are not well known across human cancer types. While animal models have the potential to reveal these complex processes, significant impediments to such inquiries include (1) the difficulty in distinguishing microenvironmental cells from precancerous or cancer cells in tissue specimens; and (2) the challenge in defining a discrete tissue with known cancer predilection that represents a precancerous microenvironment. We developed a unique zebrafish model that allows segregation of microenvironmental, precancerous, and cancerous cell populations by fluorescence-activated cell sorting. This model exhibits high predilection for malignant peripheral nerve sheath tumor (MPNST), a type of soft tissue sarcoma with a particularly poor prognosis due to aggressive growth, limited response to conventional treatment, and ineffective targeted therapy options. Using RNA-seq, we profiled the transcriptomes of microenvironmental cells from our zebrafish MPNST model and determined that the precancerous and cancerous microenvironments exhibit broad activation of inflammatory and immune-associated signaling networks. Markers for both M1 and M2 macrophage polarization were upregulated in precancerous and cancerous microenvironments, suggesting the presence of a mixed macrophage population during sarcomagenesis. Patterns of ligand and receptor expression based on a previously defined human ligand-receptor network identified significant upregulation of multiple tumor-promoting ligands in both precancerous and cancerous microenvironments. We also identified specific ligand-receptor pairs that may mediate key signaling events during sarcoma initiation and progression. Together this work provide new insight into distinguishing characteristics of the cancer-prone cellular microenvironment that may promote MPNST initiation and progression in vertebrates. Citation Format: Heather R. Shive, John S. House, Jordan L. Ferguson, Dereje D. Jima, Aubrie A. Selmek, Dillon T. Lloyd. Characterization of the precancerous and cancer microenvironment in a zebrafish sarcoma model [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 PR011.

Cancer cells frequently co-opt molecular programs that are normally activated in specific contexts, such as embryonic development and the response to injury. Determining the impact of cancer-associated mutations on cellular phenotypes within these discrete contexts can provide new insight into how such mutations lead to dysregulated cell behaviors and subsequent cancer onset. Here we assess the impact of heritable BRCA2 mutation on embryonic development and the injury response using a zebrafish model (Danio rerio). Unlike most mouse models for BRCA2 mutation, brca2-mutant zebrafish are fully viable and thus provide a unique tool for assessing both embryonic and adult phenotypes. We find that maternally provided brca2 is critical for normal oocyte development and embryonic survival in zebrafish, suggesting that embryonic lethality associated with BRCA2 mutation is likely to reflect defects in both meiotic and embryonic developmental programs. On the other hand, we find that adult brca2-mutant zebrafish exhibit aberrant proliferation of several cell types under basal conditions and in response to injury in tissues at high risk for cancer development. These divergent effects exemplify the often-paradoxical outcomes that occur in embryos (embryonic lethality) versus adult animals (cancer predisposition) with mutations in cancer susceptibility genes such as BRCA2. The altered cell behaviors identified in brca2-mutant embryonic and adult tissues, particularly in adult tissues at high risk for cancer, indicate that the effects of BRCA2 mutation on cellular phenotypes are both context- and tissue-dependent.