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Bap1 Is a Bona Fide Tumor Suppressor: Genetic Evidence from Mouse Models Carrying Heterozygous Germline Bap1 Mutations.

ABSTRACT: Individuals harboring inherited heterozygous germline mutations in BAP1 are predisposed to a range of benign and malignant tumor types, including malignant mesothelioma, melanoma, and kidney carcinoma. However, evidence to support a tumor-suppressive role for BAP1 in cancer remains contradictory. To test experimentally whether BAP1 behaves as a tumor suppressor, we monitored spontaneous tumor development in three different mouse models with germline heterozygous mutations in Bap1, including two models in which the knock-in mutations are identical to those reported in human BAP1 cancer syndrome families. We observed spontaneous malignant tumors in 54 of 93 Bap1-mutant mice (58%) versus 4 of 43 (9%) wild-type littermates. All three Bap1-mutant models exhibited a high incidence and similar spectrum of neoplasms, including ovarian sex cord stromal tumors, lung and mammary carcinomas, and spindle cell tumors. Notably, we also observed malignant mesotheliomas in two Bap1-mutant mice, but not in any wild-type animals. We further confirmed that the remaining wild-type Bap1 allele was lost in both spontaneous ovarian tumors and mesotheliomas, resulting in the loss of Bap1 expression. Additional studies revealed that asbestos exposure induced a highly significant increase in the incidence of aggressive mesotheliomas in the two mouse models carrying clinically relevant Bap1 mutations compared with asbestos-exposed wild-type littermates. Collectively, these findings provide genetic evidence that Bap1 is a bona fide tumor suppressor gene and offer key insights into the contribution of carcinogen exposure to enhanced cancer susceptibility. Cancer Res; 76(9); 2836-44. ©2016 AACR.

SUBMITTER: Kadariya Y

PROVIDER: S-EPMC4873414 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Bap1 Is a Bona Fide Tumor Suppressor: Genetic Evidence from Mouse Models Carrying Heterozygous Germline Bap1 Mutations.

Kadariya Yuwaraj Y Cheung Mitchell M Xu Jinfei J Pei Jianming J Sementino Eleonora E Menges Craig W CW Cai Kathy Q KQ Rauscher Frank J FJ Klein-Szanto Andres J AJ Testa Joseph R JR

Cancer research 20160219 9

Individuals harboring inherited heterozygous germline mutations in BAP1 are predisposed to a range of benign and malignant tumor types, including malignant mesothelioma, melanoma, and kidney carcinoma. However, evidence to support a tumor-suppressive role for BAP1 in cancer remains contradictory. To test experimentally whether BAP1 behaves as a tumor suppressor, we monitored spontaneous tumor development in three different mouse models with germline heterozygous mutations in Bap1, including two ...[more]

PMID: 26896281

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Project description:UnlabelledMammalian prions are PrP proteins with altered structures causing transmissible fatal neurodegenerative diseases. They are self-perpetuating through formation of beta-sheet-rich assemblies that seed conformational change of cellular PrP. Pathological PrP usually forms an insoluble protease-resistant core exhibiting beta-sheet structures but no more alpha-helical content, loosing the three alpha-helices contained in the correctly folded PrP. The lack of a high-resolution prion structure makes it difficult to understand the dynamics of conversion and to identify elements of the protein involved in this process. To determine whether completeness of residues within the protease-resistant domain is required for prions, we performed serial deletions in the helix H2 C terminus of ovine PrP, since this region has previously shown some tolerance to sequence changes without preventing prion replication. Deletions of either four or five residues essentially preserved the overall PrP structure and mutant PrP expressed in RK13 cells were efficiently converted into bona fide prions upon challenge by three different prion strains. Remarkably, deletions in PrP facilitated the replication of two strains that otherwise do not replicate in this cellular context. Prions with internal deletion were self-propagating and de novo infectious for naive homologous and wild-type PrP-expressing cells. Moreover, they caused transmissible spongiform encephalopathies in mice, with similar biochemical signatures and neuropathologies other than the original strains. Prion convertibility and transfer of strain-specific information are thus preserved despite shortening of an alpha-helix in PrP and removal of residues within prions. These findings provide new insights into sequence/structure/infectivity relationship for prions.ImportancePrions are misfolded PrP proteins that convert the normal protein into a replicate of their own abnormal form. They are responsible for invariably fatal neurodegenerative disorders. Other aggregation-prone proteins appear to have a prion-like mode of expansion in brains, such as in Alzheimer's or Parkinson's diseases. To date, the resolution of prion structure remains elusive. Thus, to genetically define the landscape of regions critical for prion conversion, we tested the effect of short deletions. We found that, surprisingly, removal of a portion of PrP, the C terminus of alpha-helix H2, did not hamper prion formation but generated infectious agents with an internal deletion that showed characteristics essentially similar to those of original infecting strains. Thus, we demonstrate that completeness of the residues inside prions is not necessary for maintaining infectivity and the main strain-specific information, while reporting one of the few if not the only bona fide prions with an internal deletion.

Project description:BackgroundThe BRCA1-associated protein-1 (BAP1) tumor predisposition syndrome (BAP1-TPDS) is a hereditary tumor syndrome caused by germline pathogenic variants in BAP1 encoding a tumor suppressor associated with uveal melanoma, mesothelioma, cutaneous melanoma, renal cell carcinoma, and cutaneous BAP1-inactivated melanocytic tumors. However, the full spectrum of tumors associated with the syndrome is yet to be determined. Improved understanding of the BAP1-TPDS is crucial for appropriate clinical management of BAP1 germline variant carriers and their families, including genetic counseling and surveillance for new tumors.MethodsWe collated germline variant status, tumor diagnoses, and information on BAP1 immunohistochemistry or loss of somatic heterozygosity on 106 published and 75 unpublished BAP1 germline variant-positive families worldwide to better characterize the genotypes and phenotypes associated with the BAP1-TPDS. Tumor spectrum and ages of onset were compared between missense and null variants. All statistical tests were two-sided.ResultsThe 181 families carried 140 unique BAP1 germline variants. The collated data confirmed the core tumor spectrum associated with the BAP1-TPDS and showed that some families carrying missense variants can exhibit this phenotype. A variety of noncore BAP1-TPDS -associated tumors were found in families of variant carriers. Median ages of onset of core tumor types were lower in null than missense variant carriers for all tumors combined (P < .001), mesothelioma (P < .001), cutaneous melanoma (P < .001), and nonmelanoma skin cancer (P < .001).ConclusionsThis analysis substantially increases the number of pathogenic BAP1 germline variants and refines the phenotype. It highlights the need for a curated registry of germline variant carriers for proper assessment of the clinical phenotype of the BAP1-TPDS and pathogenicity of new variants, thus guiding management of patients and informing areas requiring further research.

Dataset Information

Bap1 Is a Bona Fide Tumor Suppressor: Genetic Evidence from Mouse Models Carrying Heterozygous Germline Bap1 Mutations.

Publications

Bap1 Is a Bona Fide Tumor Suppressor: Genetic Evidence from Mouse Models Carrying Heterozygous Germline Bap1 Mutations.

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