Elucidating novel functions of ATRX in-frame fusion proteins in neuroblastoma

About This Grant

SUMMARY Neuroblastoma (NB) originates from immature nerve cells of the sympathetic nervous system and is the most common extra-cranial pediatric solid tumor. NB is remarkable in its diversity, displaying distinct genetic alterations, varied clinical manifestations, and heterogeneous responses to therapy. High-risk neuroblastoma can be rapidly progressive (e.g., in children whose tumors harbor MYCN amplification), while other patients present an indolent clinical course with months or even years of mild symptomatology prior to diagnosis. In such cases, ATRX in-frame fusions (IFFs) are among the most frequent and are significantly associated with indolent disease and chemotherapy resistance. The ATRX protein is a SWI/SNF-like chromatin remodeling factor that contains multiple domains essential for heterochromatin binding and the deposition of the histone variant H3.3 via its interaction with the histone chaperone DAXX. Therefore, its structural integrity is critical for maintaining chromatin organization and genome stability. Notably, ATRX IFF protein products lack these key chromatin- and protein-interaction domains, and the precise contribution of altered DAXX function and H3.3 deposition to the indolent NB phenotype remains unclear. We hypothesize that ATRX IFFs contribute to NB pathogenesis by disrupting the ATRX–DAXX– H3.3 regulatory axis, leading to accumulation of DAXX in the cytoplasm, altered H3.3 genomic distribution, and the aberrant activation of transposable elements (TEs) and other repetitive sequences. To address these questions, we will conduct a series of studies utilizing state-of-the- art genetic, epigenomic, and proteomic tools coupled to patient-derived NB cell lines, genetically engineered NB cellular models, and patient samples. In Aim 1, we will dissect the cytoplasmic role of DAXX and its potential as a biomarker in ATRX-altered NB, and in Aim 2 we will investigate the impact of ATRX IFFs on DAXX and H3.3 genomic distribution and the potential role of TE activation. With these proposed studies, we aim to reveal novel opportunities for therapeutic targeting and biomarker discovery in ATRX-altered NB with important implications for other ATRX- mutant cancers.