Grundy, M. | Search bioRxiv

bioRxiv2024

Nucleophosmin mutations lead to abnormal, but reversible, nucleoli architecture and aggregate formation - implications for NPM1-targeting therapies in AML

Mutations in the NPM1 gene represent the most common (>30% of patients) genetic alteration in Acute Myeloid Leukaemia (AML) and results in the mis-localisation of the mutated NPM1 protein from a predominantly nucleolar localisation to a predominantly cytoplasmic distribution. Numerous studies of NPM1 mutated AML have focussed on the aberrant cytoplasmic localisation of the mutated protein but efforts to reverse this mis-localisation therapeutically have so far resulted in limited clinical benefit. More recently, attention has shifted towards the nucleus with studies showing that mutant NPM1 binds to specific chromatin regions, where it directly regulates oncogenic gene expression. Here, we use high resolution imaging to demonstrate that Nucleophosmin (NPM1) is critical for maintaining normal nucleoli architecture and specifically the integrity of the nucleoli rim. We report for the first time that NPM1 mutated cell lines and primary samples have aberrant nucleoli architecture and demonstrate that the abnormal nucleoli phenotype is reversible. We also report the novel finding that NPM1 mutated protein forms distinct aggregates in NPM1 mutated cells and characterise these for the first time. This work reveals how nucleolar organisation contributes to the molecular mechanisms underpinning NPM1 driven AML and reveals unexpected novel vulnerabilities to be exploited for therapeutic intervention.

cancer biology↗

bioRxiv2021

ANALYSIS OF CHD-7 DEFECTIVE DAUER NEMATODES IMPLICATES COLLAGEN MISREGULATION IN CHARGE SYNDROME FEATURES.

CHARGE syndrome is a complex developmental disorder caused by mutations in the chromodomain helicase DNA-binding protein7 (CHD7) and characterized by retarded growth and malformations in the heart and nervous system. Despite the public health relevance of this disorder, relevant targets of CHD7 that relate to disease pathology are still poorly understood. Here we report that chd-7, the nematode ortholog of Chd7, is required for dauer morphogenesis, lifespan determination, and stress response. Consistent with our discoveries, we found chd-7 to be allelic to scd-3, a previously identified dauer suppressor from the TGF-{beta} pathway. Notably, DAF-12 promoted chd-7 expression, which is necessary to repress daf-9 for execution of the dauer program. Transcriptomic analysis comparing chd-7-defective and normal dauers showed enrichment of collagen genes, consistent with a conserved role for the TGF-{beta} pathway in formation of the extracellular matrix. To validate a conserved function for chd-7 in vertebrates, we used Xenopus laevis embryos, an established model to study craniofacial development. Morpholino mediated knockdown of Chd7 led to a reduction in col2a1 mRNA levels. Both embryonic lethality and craniofacial defects in Chd7-depleted tadpoles were partially rescued by over-expression of col2a1 mRNA. We suggest that pathogenic features of CHARGE syndrome caused by Chd7 mutations, such as craniofacial malformations, result from the reduction of collagen levels, implying that the extracellular matrix might represent a critical target of Chd7 in CHARGE development. SIGNIFICANCE STATEMENTCHARGE Syndrome is a complex developmental disorder caused by mutations in the chromodomain helicase DNA-binding protein-7 (CHD7). Unfortunately, the cellular events that lead to CHARGE syndrome are still poorly understood. In C. elegans, we identified chd-7 in a screen for suppressors of dauer formation, an alternative larval stage that develops in response to sensory signals of a harsh environment. We found that chd-7 regulates expression of collagens, which constitute the worms cuticle, a specialized extracellular matrix. In frogs embryos, we show that Chd7 inhibition leads to poor Col2a1, which is necessary and sufficient to exhibit CHARGE features. These studies establish C. elegans as an amenable animal model to study the etiology of the developmental defects associated with pathogenic Chd7.

genetics↗