Mohamed H. Abdel-Rahman, Ph.D. - US grants

DESCRIPTION (provided by applicant): Uveal melanoma (UM) is a subtype of melanoma characterized by the strong contribution of genetic rather than environmental factors in the pathogenesis of the disease, making it an ideal model disease to study the genetic basis of cancer. The long-term goal of our laboratory is to determine the genes and mechanisms responsible for hereditary cancer predisposition associated with UM. To accomplish this, we have collected a large cohort of UM patients with high risk of hereditary cancer predisposition. Our work to date with this cohort supports that germline inactivation of BAP1 and other gene(s), account for the hereditary cancer syndromes in a subset of UM patients. This will be tested with two specific aims, one focused on BAP1 studies and one on other candidate genes: Aim 1: Identify mechanisms of germline BAP1 inactivation in UM patients with clinical phenotype suggestive of tumor predisposition syndrome (TPDS). Aim 2: Identification of novel candidate genes contributing to hereditary predisposition to UM. Scientific and Translational Impact: Outcomes will include identification of molecular mechanisms of heritable germline inactivation in BAP1 in patients with UM. This will provide much needed information for genetic counseling of patients at risk of TPDS, especially now that this gene is being added to clinical genetic testing panels. Identification of additional candidate genes associated with hereditary predisposition to UM will lead to further studies by us and others to further characterize the clinical phenotype and potential targets for therapy of these syndromes

ABSTRACT Hereditary mutations in the BRCA1-associated protein 1 (BAP1) gene, causes a diverse cancer phenotype with at least four cancers, uveal (eye) melanoma (UM), mesothelioma (MMe), skin melanoma (CM), kidney cancer (RCC) and benign skin lesions (AST). Variants associated with blue eye color at the HERC2/OCA2 gene locus have been associated with increased risk for melanoma and non-melanoma skin cancers. Historically this has been thought to be due to the loss of dark pigmentation protection from ultraviolet (UV) light. However, other molecular mechanisms have been suggested including impact of the melanin precursors on DNA damage, angiogenesis and formation of reactive oxygen species. The goal of this study is to address the National Cancer Institute?s Provocative Question ?What molecular mechanisms influence disease penetrance in individuals who inherit a cancer susceptibility gene? by determining whether variants in HERC2/OCA2 impact the clinical phenotype associated with BAP1 germline mutations. We hypothesize that variants impacting the function and/or expression of OCA2 lead to modification of the penetrance of clinical phenotypes such as risk of UM and CM, through both pigmentary and non-pigmentary mechanisms. The molecular mechanisms of reduced functional OCA2 levels on different cancers associated with BAP1 gene will be tested in cell lines representative of four major cancers namely UM, CM, RCC and MMe by the following two aims: Aim 1: To determine if increased melanin precursors as the result of HERC2/OCA2 variants impact angiogenesis, DNA damage and reactive oxygen species and if this is enhanced in a BAP1 deficient background. Aim 2: To determine the impact of host loss of OCA2 on the in-vivo tumorigenesis of BAP1 mutant melanocytes. Impact: BAP1 germline mutations increase the risk of UM, CM, RCC and MMe. Mechanistic studies of the effect of HERC2/OCA2 variant on the different cancers associated with BAP1 gene will provide crucial information on how these factors interact to augment or suppress tumor development in patients. Understanding these interactions will ultimately provide important information on the role of melanin precursors on cancer risk via photo-protective and non-photo protective mechanisms. This may lead to new preventive and/or treatment strategies in these patients.

ABSTRACT Germline mutation in the tumor suppressor gene BAP1 is associated with the hereditary tumor predisposition syndrome, BAP1-TPDS (OMIM 614327), that we and others identified in 2011. The syndrome is associated with predisposition to mainly four cancers: uveal melanoma, mesothelioma, cutaneous melanoma, and renal cell carcinoma in addition to a preneoplastic melanocytic skin lesions (BAP1-Inactivated Melanocytic Tumors). Other cancers have been also reported in patients with germline BAP1 mutation but it is not clear whether they are part of the BAP1-TPDS. Since its characterization, more than 200 distinct families have been reported with an increasing number of pathogenic/likely pathogenic variants being deposited in ClinVar. Our our analysis of variants in the Exome Aggregation Consortium (ExAC) database suggests that BAP1-TPDS is underreported in cancer patients. BAP1 is a deubiquitinating hydrolase that has four known functions: (i) cell cycle regulation and cell growth, (ii) DNA damage repair, (iii) chromatin remodelling and regulation of gene expression, and (iv) regulation of apoptosis. Which of these complex functional roles are responsible for its tumor suppressor function is unknown, and needs to be determined to enable identification of the best experimental model system(s) to predict the clinical significance of the variants of uncertain significance. Our goal is to characterize the clinical phenotypes associated with different germline variants of BAP1 in order to dissect its complex functions. We will address the following critical barriers: 1) the limited number of reported germline variants in BAP1 with known clinical phenotype; 2) the need for experimental model system(s) to assess the clinical impact of different coding variants in BAP1; and 3) the need to assess the contribution of non-coding variants in germline inactivation of BAP1. Specific Aim1: To expand the understanding of the clinical phenotypes of BAP1-TPDS and correlate with variants in the gene. Specific Aim2: Establish experimental model systems for evaluation of BAP1 germline missense variants of uncertain significance. Specific Aim3: To assess the contribution of non-coding variants in germline inactivation of BAP1. Scientific and Translational Impact: The outcomes of these studies have the potential to provide clinicians with crucial resources needed to address a major barrier for proper counseling and management of patients and families with germline mutations in BAP1. The results will also provide basic scientists with important resources for further studies of various tumor suppressor functions of BAP1, as well as crucial resources for the NCI ClinGen and ClinVar projects.