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The phenylalanine-and-glycine repeats of NUP98 oncofusion form condensates that selectively partition transcriptional coactivators

ABSTRACT: Cancer-associated genetic aberrations, such as the nucleoporin 98 (NUP98) gene rearrangement detected in human leukemias, often produce condensates, a type of membrane-less biomolecular assemblies. How exactly the cancer-related condensation contributes to oncogenesis remains far from clear. Here, we investigate NUP98-PHF23, a leukemia-causing chimeric protein that fuses NUP98’s sequence enriched in phenylalanine-and-glycine repeats (FG repeats, also known as intrinsically disordered region [IDR]) in-frame with PHF23’s PHD finger, a domain that specifically ‘reads’ and binds H3K4 trimethylation (H3K4me3). Our integrated analyses using protein module mutagenesis, cell imaging, genomic profiling and condensation reconstitution collectively demonstrate a multifaced role for NUP98’s FG repeats in driving fusion condensation while recruiting and co-mixing with a set of histone modifiers and chromatin remodelers, notably the MLL family of H3K4 methylation-‘writing’ enzymes. The H3K4me3-‘reading’ PHD finger and NUP98’s IDR are cooperative in mediating efficient targeting of NUP98-PHF23 and its coactivators onto leukemic genes, leading to active transcription. Together, we show that NUP98-PHF23 coordinates a set of homotypic and heterotypic interactions (IDR:IDR, IDR:coactivator and PHD:histone) to organize formation of the chromatin-bound multi-component condensates, wherein a feedforward loop involving the ‘reading’ and ‘writing’ of H3K4 methylation acts to enforce an open chromatin landscape at leukemogenic loci, thereby driving oncogenic transformation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE255508 | GEO | 2025/01/30

REPOSITORIES: GEO

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Project description:Development of cancer is intimately associated with genetic abnormalities that target proteins with intrinsically disordered regions (IDRs). In human hematological malignancies, recurrent chromosomal translocation of nucleoporin (NUP98 or NUP214) generates an aberrant chimera that invariably retains nucleoporin’s IDR, tandemly dispersed phenylalanine-andglycine (FG) repeats1-3. However, it remains largely elusive how unstructured IDRs contribute to oncogenesis. We here show that IDR or FG repeats harbored within NUP98-HOXA9, a homeodomain-containing transcription factor (TF) chimera recurrently detected in acute leukemia patients1,4,5, is essential for establishing nuclear liquid-liquid phase separation (LLPS) puncta and for inducing leukemic transformation of primary hematopoietic cells in vitro and in vivo. Strikingly, LLPS of NUP98-HOXA9 not only promotes chromatin occupancy of chimera TF oncoproteins but is also required for formation of a broad, ‘super-enhancer’-like binding pattern, typically seen at a battery of leukemia-related loci exemplified by HOX, MEIS and PBX genes, potentiating their transcriptional activation. An artificial HOX chimera, created by replacing NUP98’s FG repeats with an unrelated LLPSforming IDR of FUS6,7, had similar enhancement effects on chimera’s chromatin binding and target gene activation. Via Hi-C mapping, we further demonstrated that the phase-separated NUP98-HOXA9 protein assembly is able to induce formation of CTCF-independent chromatin looping enriched at leukemic oncogenes. Together, this report describes a proof-of-principle example wherein cancer acquires mutation to establish condensates of oncogenic TFs via a phase separation mechanism, which simultaneously enhances their chromatin targeting and induces organization of aberrant three-dimensional chromatin structure during tumorous transformation. As a range of LLPS-competent molecules are implicated in various human cancers, this mechanism can potentially be generalized to many malignant and diseased settings.

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The phenylalanine-and-glycine repeats of NUP98 oncofusion form condensates that selectively partition transcriptional coactivators

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