Defining the role of germline Daam2 variant R414W in familial glioma

ABSTRACT Malignant glioma, the most common subtype of primary brain tumor in adults, causes high patient morbidity and mortality due to its aggressive nature and limited efficacious treatment options. To improve this prognosis, increasing studies have investigated a growing list of genetic factors that may contribute to glioma pathophysiology. These brain tumors are heterogeneous and generally arise sporadically; however, in 5-10% of cases, glioma stems from inherited genetic variations and are classified as familial glioma. Although there are many studies exploring mechanisms behind somatic mutations in glioma, less is known about hereditary variants that promote glioma susceptibility. Recently, germline mutations in Daam2 (Dishevelled associated activator of morphogenesis 2) were discovered in familial glioma patients. Daam2 is a formin protein known for its role in potentiating intracellular signaling during early development, regulating myelin structure, and influencing glial cell differentiation and morphology. Our research established the role of Daam2 in glioma in which its overexpression increases tumorigenesis by promoting the degradation of hypoxia-related tumor suppressor von Hippel-Lindau (VHL). While a handful of studies have linked Daam2 mutations to diseases such as lung cancer and renal disorder, the relationship between Daam2 mutations and glioma remains undefined. Moreover, whether and how Daam2 variants contribute to gliomagenesis, glioma growth, and progression remains unknown. To address this knowledge gap, I overexpressed these newly discovered Daam2 variants in patient-derived glioma stem-like cells and assessed their proliferation in vivo. In a patient-derived orthotopic xenograft immunodeficient mouse model, mice bearing tumors with Daam2 R414W overexpression showed a significant increase in tumor size and proliferation. These preliminary findings suggest that the Daam2 R414W germline variant promotes glioma growth. To study this variant in an immunocompetent model, I generated a Daam2 R414W knock-in mouse and discovered an expansion of proliferating glial progenitors in these Daam2 R414W mutant mice. Moreover, in search of a potential mechanism for this phenomenon, I found significant changes in cytoskeletal remodeling signatures in Daam2 R414W overexpression tumors from proteomic profiling gene ontology analysis. In this proposal, I propose to further define this mutation’s impact on glioma with three aims: (1) evaluate the capacity for this variant to promote glioma susceptibility and growth, (2) define the role of this variant in malignant progression, and (3) delineate a potential underlying mechanism of cytoskeletal dysregulation in glioma pathogenesis. When completed, this work will represent a significant advancement in our fundamental understanding of familial mutations and their role in glioma development. Moreover, the functional characterization and identification of familial mutations in Daam2 as potential early markers for glioma predisposition will have a far-reaching impact on patient survival.