Mechanisms of BAP1 activity in human cancer development

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PROJECT SUMMARY This application investigates mechanisms of gene and environment interaction in carcinogenesis. Malignant mesothelioma (MM) is frequent in individuals continuously exposed to carcinogenic mineral fibers such as asbestos and erionite, but it is very rare in those with limited or no exposure. Genetics influences susceptibility to MM. We have recently demonstrated that carriers of germline BAP1 mutations have increased incidence of multiple cancer types, including MM (we named this condition the “BAP1 cancer syndrome”). In some BAP1-mutation carrying families, MM accounts for more than 50% of deaths, and we found that this may be due to increased susceptibility to MM from exposure to modest amounts of asbestos that would normally not cause MM in the general population. We also found that heterozygous BAP1 germline mutations in addition to asbestos, also increase susceptibility to malignant transformation following exposure to Ionizing Irradiation and ultraviolet (UV) light –which may account for the high prevalence of melanomas and skin carcinomas in carriers of BAP1 mutations. BAP1 is the first and so far the only gene shown to regulate environmental carcinogenesis. The mechanism(s) by which mutated BAP1 causes MM pathogenesis are being elucidated. Inositol 1,4,5-trisphosphate (IP3) binds and activates the IP3 receptors (IP3Rs). We demonstrated that BAP1 is present in the endoplasmic reticulum (ER) where it regulates the activity of the IP3-Receptor-3 (IP3R3), the main ER channel that controls Ca2+ release from the ER to the cytoplasm to the mitochondria, regulating apoptosis. We discovered that reduced levels of BAP1 in carriers of heterozygous BAP1 mutations impair apoptosis and favor cellular transformation of cells that accumulated DNA damage following exposure to asbestos, IR and UV-light. We also discovered that “normal” primary cells of carriers of heterozygous germline BAP1 mutations derive energy from aerobic glycolysis, known as Warburg effect, which so far had been considered a hallmark of cancer cells. We identified a specific metabolic signature associated with the Warburg effect by studying the metabolites present in the plasma of carriers of heterozygous germline BAP1 mutations. Our central hypothesis is that changes in Ca2+ concentration lead to increased resistance of cells containing BAP1 mutations to apoptosis and to changes in metabolic pathways that in turn are responsible for the very high cancer penetrance observed in BAP1 mutation carriers. To address this hypothesis we will examine the following specific Aims: AIM 1: To study the mechanisms by which BAP1 mutations induce a “Warburg effect”. AIM 2: To study the hypothesis that the Warburg effect is HIF-1α-independent in BAP1+/- cells. AIM 3: To study the contributions of calcium signaling and metabolic alterations due to germline BAP1 mutations to MM development. To elucidate the activity of BAP1 on the I P 3 R 3 and the related effects on cancer penetrance, we have assembled a unique cohort of families carrying germline BAP1 mutations and have access to unique reagents derived from volunteers from these families. These unique reagents include: primary cell cultures derived from family members that inherited germline BAP1 mutations as well as from sex- and age- matched controls from the same families, sera and plasma from germline BAP1 mutation carriers and matched controls, and a heterozygous BAP1 mouse model and derived cell cultures. In addition, we assembled a unique sets of heterozygous BAP1 and IP3R3 mice that recapitulate the human condition and that allow us to study the effects of BAP1 mutations in vivo upon exposure to carcinogens. Collaborations with some of the leading experts in the field, Drs. Pinton and Giorgi, experts in Ca2+ signaling and mitochondrial metabolism; and Dr. Mikoshiba, expert in IP3R3 activities, complement and synergize with the expertise of the two MPIs. These studies will be relevant to the multiple malignancies associated with the BAP1 cancer syndrome, in both carriers of BAP1 mutations and those who develop somatic mutations of BAP1 during tumor development.