Gruszczynska, A. | Search bioRxiv

bioRxiv2023

Missense mutations in Myc Box I influence MYC cellular localization, mRNA partitioning and turnover to promote leukemogenesis

Somatic missense mutations in the phosphodegron domain of the MYC gene (MYC Box I) are detected in the dominant clones of a subset of acute myeloid leukemia (AML) patients, but the mechanisms by which they contribute to AML are unknown. To unveil unique proprieties of MBI MYC mutant proteins, we systematically compared the cellular and molecular consequences of expressing similar oncogenic levels of wild type and MBI mutant MYC. We found that MBI MYC mutants can accelerate leukemia by driving unique transcriptional signatures in highly selected, myeloid progenitor subpopulations. Although these mutations increase MYC stability, they overall dampen MYC chromatin localization and lead to a cytoplasmic accumulation of the mutant proteins. This phenotype is coupled with increased translation of RNA binding proteins and nuclear export machinery, which results in altered RNA partitioning and accelerated decay of select transcripts encoding proapoptotic and proinflammatory genes. Heterozygous knockin mice harboring the germline MBI mutation Myc p.T73N exhibit cytoplasmic MYC localization, myeloid progenitors expansion with similar transcriptional signatures to the overexpression model, and eventually develop hematological malignancies. This study uncovers that MBI MYC mutations alter MYC localization and disrupt mRNA subcellular distribution and turnover of select transcripts to accelerate tumor initiation and growth.

cancer biology↗

bioRxiv2023

Costimulatory domains direct distinct fates of CAR-driven T cell dysfunction

Chimeric antigen receptor (CAR) engineered T cells often fail to enact effector functions after infusion into patients. Understanding the biological pathways that lead CAR T cells to failure is of critical importance in the design of more effective therapies. We developed and validated an in vitro model that drives T cell dysfunction through chronic CAR activation and interrogated how CAR costimulatory domains contribute to T cell failure. We found that dysfunctional CD28-based CARs targeting CD19 bear hallmarks of classical T cell exhaustion while dysfunctional 41BB-based CARs are phenotypically, transcriptionally and epigenetically distinct. We confirmed activation of this unique transcriptional program in CAR T cells that failed to control clinical disease. Further, we demonstrate that 41BB-dependent activation of the transcription factor FOXO3 is a significant contributor to this dysfunction and disruption of FOXO3 improves CAR T cell function. These findings identify that chronic activation of 41BB leads to novel state of T cell dysfunction that can be alleviated by genetic modification of FOXO3. SummaryChronic stimulation of CARs containing the 41BB costimulatory domain leads to a novel state of T cell dysfunction that is distinct from T cell exhaustion.

immunology↗