Early-Onset Parkinson Mutation Remodels Monomer-Fibril Interactions to Allosterically Amplify Synuclein's Amyloid Cascade

Alpha synuclein (αS) aggregates are the main component of Lewy bodies (LBs) associated with Parkinson's disease (PD). A longstanding question about αS and PD pertains to the autosomal dominant E46K αS mutant, which leads to the early onset of PD and LB dementias. The E46K mutation not only promotes αS aggregation but also stabilizes αS monomers in "closed" conformers, which are compact and aggregation-incompetent. Hence, the mechanism of action of the E46K mutation is currently unclear. Here, we show that αS monomers harboring the E46K mutation exhibit more extensive interactions with fibrils compared to those of WT. Such monomer-fibril interactions are sufficient to allosterically drive transitions of αS monomers from closed to open conformations, enabling αS aggregation. We also show that E46K promotes head-to-tail monomer-monomer interactions in early self-association events. This multipronged mechanism provides a new framework to explain how the E46K mutation and possibly other αS variants trigger early-onset PD.

Inherited mutations affecting the SRCAP complex are central in moderate-penetrance predisposition to uterine leiomyomas

Uterine leiomyomas (ULs) are benign smooth muscle tumors that are common in premenopausal women. Somatic alterations in MED12, HMGA2, FH, genes encoding subunits of the SRCAP complex, and genes involved in Cullin 3-RING E3 ligase neddylation are mutually exclusive UL drivers. Established predisposition genes explain only partially the estimated heritability of leiomyomas. Here, we examined loss-of-function variants across 18,899 genes in a cohort of 233,614 White European women, revealing variants in four genes encoding SRCAP complex subunits (YEATS4, ZNHIT1, DMAP1, and ACTL6A) with a significant association to ULs, and YEATS4 and ZNHIT1 strikingly rank first and second, respectively. Positive mutation status was also associated with younger age at diagnosis and hysterectomy. Moderate-penetrance UL risk was largely attributed to rare non-synonymous mutations affecting the SRCAP complex. To examine this disease phenotype more closely, we set out to identify inherited mutations affecting the SRCAP complex in our in-house sample collection of Finnish individuals with ULs (n = 860). We detected one individual with an ACTL6A splice-site mutation, two individuals with a YEATS4 missense mutation, and four individuals with DMAP1 mutations: one splice-site, one nonsense, and two missense variants. These individuals had large and/or multiple ULs, were often diagnosed at an early age, and many had family history of ULs. When a somatic second hit was found, ACTL6A and DMAP1 were silenced in tumors by somatic mutation and YEATS4 by promoter hypermethylation. Decreased H2A.Z staining was observed in the tumors, providing further evidence for the pathogenic nature of the germline mutations. Our results establish inactivation of genes encoding SRCAP complex subunits as a central contributor to moderate-penetrance UL predisposition.

A rare germline CDKN2A variant (47T>G; p16-L16R) predisposes carriers to pancreatic cancer by reducing cell cycle inhibition

Germline mutations in CDKN2A, encoding the tumor suppressor p16, are responsible for a large proportion of familial melanoma cases and also increase risk of pancreatic cancer. We identified four families through pancreatic cancer probands that were affected by both cancers. These families bore a germline missense variant of CDKN2A (47T>G), encoding a p16-L16R mutant protein associated with high cancer occurrence. Here, we investigated the biological significance of this variant. When transfected into p16-null pancreatic cancer cells, p16-L16R was expressed at lower levels than wild-type (WT) p16. In addition, p16-L16R was unable to bind CDK4 or CDK6 compared with WT p16, as shown by coimmunoprecipitation assays and also was impaired in its ability to inhibit the cell cycle, as demonstrated by flow cytometry analyses. In silico molecular modeling predicted that the L16R mutation prevents normal protein folding, consistent with the observed reduction in expression/stability and diminished function of this mutant protein. We isolated normal dermal fibroblasts from members of the families expressing WT or L16R proteins to investigate the impact of endogenous p16-L16R mutant protein on cell growth. In culture, p16-L16R fibroblasts grew at a faster rate, and most survived until later passages than p16-WT fibroblasts. Further, western blotting demonstrated that p16 protein was detected at lower levels in p16-L16R than in p16-WT fibroblasts. Together, these results suggest that the presence of a CDKN2A (47T>G) mutant allele contributes to an increased risk of pancreatic cancer as a result of reduced p16 protein levels and diminished p16 tumor suppressor function.

Clinical Assessment and Diagnosis of Germline Predisposition to Hematopoietic Malignancies: The University of Chicago Experience

With the increasing use of clinical genomics to guide cancer treatment and management, there is a rise in the identification of germline cancer predisposition syndromes and a critical need for patients with germline findings to be referred for surveillance and care. The University of Chicago Hematopoietic Malignancies Cancer Risk Team has established a unique approach to patient care for individuals with hereditary hematologic malignancies through close communication and coordination between our pediatric and adult programs. Dedicated program members, including physicians, nurses, genetic counselors, and clinical research assistants, screen individuals for cancer predisposition at initial diagnosis through survivorship, in addition to testing individuals with an established family history of a cancer predisposition syndrome. Sample procurement, such as a skin biopsy at the time of bone marrow aspirate/biopsy in individuals with a positive screen, has facilitated timely identification of clinical germline findings or has served as a pipeline for translational research. Our integrated translational research program has led to the identification of novel syndromes in collaboration with other investigators, which have been incorporated iteratively into our clinical pipeline. Individuals are referred for clinical assessment based on personal and family history, identification of variants in susceptibility genes via molecular tumor testing, and during evaluation for matched related allogeneic stem cell transplantation. Upon referral, genetic counseling incorporates education with mindfulness of the psychosocial issues surrounding germline testing at different ages. The training and role of genetic counselors continues to grow, with the discovery of new predisposition syndromes, in the age of improved molecular diagnostics and new models for service delivery, such as telemedicine. With the identification of new syndromes that may predispose individuals to hematologic malignancies, surveillance guidelines will continue to evolve and may differ between children and adults. Thus, utilizing a collaborative approach between the pediatric and adult oncology programs facilitates care within families and optimizes the diagnosis and care of individuals with cancer predisposition syndromes.