Joseph Testa, Michele Carbone and colleagues report that germline mutations in BAP1 predispose to malignant mesothelioma and uveal melanoma. They further hypothesize that mesothelioma predominates in BAP1 mutation carriers following exposure to asbestos. Because only a small fraction of asbestos-exposed individuals develop malignant mesothelioma1, and because mesothelioma clustering is observed in some families, we searched for genetic predisposing factors. We discovered germline mutations in the gene encoding BRCA1 associated protein-1 (BAP1) in two families with a high incidence of mesothelioma, and we observed somatic alterations affecting BAP1 in familial mesotheliomas, indicating biallelic inactivation. In addition to mesothelioma, some BAP1 mutation carriers developed uveal melanoma. We also found germline BAP1 mutations in 2 of 26 sporadic mesotheliomas; both individuals with mutant BAP1 were previously diagnosed with uveal melanoma. We also observed somatic truncating BAP1 mutations and aberrant BAP1 expression in sporadic mesotheliomas without germline mutations. These results identify a BAP1-related cancer syndrome that is characterized by mesothelioma and uveal melanoma. We hypothesize that other cancers may also be involved and that mesothelioma predominates upon asbestos exposure. These findings will help to identify individuals at high risk of mesothelioma who could be targeted for early intervention.

Mesothelioma affects mostly older individuals who have been occupationally exposed to asbestos. The global mesothelioma incidence and mortality rates are unknown, because data are not available from developing countries that continue to use large amounts of asbestos. The incidence rate of mesothelioma has decreased in Australia, the United States, and Western Europe, where the use of asbestos was banned or strictly regulated in the 1970s and 1980s, demonstrating the value of these preventive measures. However, in these same countries, the overall number of deaths from mesothelioma has not decreased as the size of the population and the percentage of old people have increased. Moreover, hotspots of mesothelioma may occur when carcinogenic fibers that are present in the environment are disturbed as rural areas are being developed. Novel immunohistochemical and molecular markers have improved the accuracy of diagnosis; however, about 14% (high‐resource countries) to 50% (developing countries) of mesothelioma diagnoses are incorrect, resulting in inadequate treatment and complicating epidemiological studies. The discovery that germline BRCA1‐asssociated protein 1 ( BAP1 ) mutations cause mesothelioma and other cancers (BAP1 cancer syndrome) elucidated some of the key pathogenic mechanisms, and treatments targeting these molecular mechanisms and/or modulating the immune response are being tested. The role of surgery in pleural mesothelioma is controversial as it is difficult to predict who will benefit from aggressive management, even when local therapies are added to existing or novel systemic treatments. Treatment outcomes are improving, however, for peritoneal mesothelioma. Multidisciplinary international collaboration will be necessary to improve prevention, early detection, and treatment.

BRCA1-associated protein 1 (BAP1) regulates calcium flux in the endoplasmic reticulum to facilitate the execution of apoptosis, unveiling a new facet of the role of BAP1 as an environmental tumour suppressor. BAP1 is a tumour suppressor associated with germline mutations in several malignancies including uveal melanoma and mesothelioma. BAP1 tumour suppressor activity has previously been linked to its nuclear role in maintaining genome integrity. Here, the authors reveal a new role for BAP1 in the endoplasmic reticulum, where it regulates calcium flux to facilitate the execution of apoptosis. Loss of BAP1 function prevents apoptosis in transformed cells with accumulated DNA damage. The results unveil a new facet of the role of BAP1 as an environmental tumour suppressor. BRCA1-associated protein 1 (BAP1) is a potent tumour suppressor gene that modulates environmental carcinogenesis1,2,3. All carriers of inherited heterozygous germline BAP1-inactivating mutations (BAP1+/−) developed one and often several BAP1−/− malignancies in their lifetime4, mostly malignant mesothelioma, uveal melanoma2,5, and so on6,7,8,9,10. Moreover, BAP1-acquired biallelic mutations are frequent in human cancers8,11,12,13,14. BAP1 tumour suppressor activity has been attributed to its nuclear localization, where it helps to maintain genome integrity15,16,17. The possible activity of BAP1 in the cytoplasm is unknown. Cells with reduced levels of BAP1 exhibit chromosomal abnormalities and decreased DNA repair by homologous recombination18, indicating that BAP1 dosage is critical. Cells with extensive DNA damage should die and not grow into malignancies. Here we discover that BAP1 localizes at the endoplasmic reticulum. Here, it binds, deubiquitylates, and stabilizes type 3 inositol-1,4,5-trisphosphate receptor (IP3R3), modulating calcium (Ca2+) release from the endoplasmic reticulum into the cytosol and mitochondria, promoting apoptosis. Reduced levels of BAP1 in BAP1+/− carriers cause reduction both of IP3R3 levels and of Ca2+ flux, preventing BAP1+/− cells that accumulate DNA damage from executing apoptosis. A higher fraction of cells exposed to either ionizing or ultraviolet radiation, or to asbestos, survive genotoxic stress, resulting in a higher rate of cellular transformation. We propose that the high incidence of cancers in BAP1+/− carriers results from the combined reduced nuclear and cytoplasmic activities of BAP1. Our data provide a mechanistic rationale for the powerful ability of BAP1 to regulate gene–environment interaction in human carcinogenesis.

Background Breast cancer 1-associated protein 1 (BAP1) is a nuclear deubiquitinase that regulates gene expression, transcription, DNA repair, and more. Several findings underscore the apparent driver role of BAP1 in malignant mesothelioma (MM). However, the reported frequency of somatic BAP1 mutations in MM varies considerably, a discrepancy that appeared related to either methodological or ethnical differences across various studies. Methods To address this discrepancy, we carried out comprehensive genomic and immunohistochemical (IHC) analyses to detect somatic BAP1 gene alterations in 22 frozen MM biopsies from U.S. MM patients. Results By combining Sanger sequencing, multiplex ligation-dependent probe amplification, copy number analysis, and cDNA sequencing, we found alteration of BAP1 in 14 of 22 biopsies (63.6%). No changes in methylation were observed. IHC revealed normal nuclear BAP1 staining in the eight MM containing wild-type BAP1, whereas no nuclear staining was detected in the 14 MM biopsies containing tumor cells with mutated BAP1. Thus, IHC results were in agreement with those obtained by genomic analyses. We then extended IHC analysis to an independent cohort of 70 MM biopsies, of which there was insufficient material to perform molecular studies. IHC revealed loss of BAP1 nuclear staining in 47 of these 70 MM biopsies (67.1%). Conclusions Our findings conclusively establish BAP1 as the most commonly mutated gene in MM, regardless of ethnic background or other clinical characteristics. Our data point to IHC as the most accessible and reliable technique to detect BAP1 status in MM biopsies.

BRCA1–associated protein 1 (BAP1) is a tumor suppressor gene located on chromosome 3p21. Germline BAP1 mutations have been recently associated with an increased risk of malignant mesothelioma, atypical melanocytic tumors and other neoplasms. To answer the question if different germline BAP1 mutations may predispose to a single syndrome with a wide phenotypic range or to distinct syndromes, we investigated the presence of melanocytic tumors in two unrelated families (L and W) with germline BAP1 mutations and increased risk of malignant mesothelioma.