Abstract 5898: Bone morphogenic protein receptor 2 (BMPR2) as a potential germline driver in Juvenile Polyposis Syndrome (JPS)

Abstract

Abstract Summary: Juvenile Polyposis Syndrome is a pediatric cancer predisposition syndrome for which approximately half of patients do not have a known germline driver; we propose BMPR2 as a possible germline driver of disease in mutation-negative JPS. Background: Juvenile Polyposis Syndrome (JPS) is a cancer predisposition syndrome characterized in some cases by inactivating germline mutations in BMPR1A or SMAD4. However, in 40-60% of patients the germline driver is unknown. Methods: Through whole exome sequencing, an individual with high polyp burden and negative genetic testing for variants in SMAD4 and BMPR1A was found to have a potentially inactivating germline variant in BMPR2. Under an IRB-approved protocol, patient-derived, three-dimensional organoids were established from adjacent colon and polyp tissue of this individual, as well as an individual with a BMPR1A deletion and age- and sex-matched controls. Proliferation, metabolic activity, and protein expression of each line were measured by Western blot, Ki67 staining, EdU labelling, cell titer glo (CTG) assay. Results: Distinct phenotypic differences are evident between colonoids from an individual with a BMPR1A deletion and both the colon and polyp BMPR2 variant colonoids, such as increased crypt budding and Ki67 staining. CTG assay data indicate higher metabolic activity in BMPR2 variant colonoids in comparison to normal controls (p= 0.0104.) Through Western blot analysis, both BMPR2 colon and polyp colonoids showed decreased SMAD4 expression and phosphorylation. Conclusions: These data demonstrate that clear phenotypic differences exist between colonoid lines established from normal controls, individuals with known JPS predisposition genes, and a novel candidate driver of disease, BMPR2. Proliferation and protein expression data suggest that both known and candidate genotypes are consistent with a hyperproliferative phenotype. In vitro data support BMPR2 as a candidate germline driver of the JPS phenotype, and additional study is ongoing regarding downstream pathway regulation in colonoids with a BMPR2 variant. Citation Format: Suzanne P. MacFarland, Bridgid Greed, Michael H. Xie, Garrett M. Brodeur, Zvi Cramer, Maiah H. Dent, Melani M. Duvall, Kathryn E. Hamilton, James Howe, Tatiana Karakasheva, Petar Mamula, Christopher Lengner. Bone morphogenic protein receptor 2 (BMPR2) as a potential germline driver in Juvenile Polyposis Syndrome (JPS) [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 5898.