Abstract 2631: HMGA1 chromatin regulators drive immune evasion in myeloproliferative neoplasms by repressing gene networks involved in antigen presentation

Abstract Myeloproliferative neoplasms (MPN) are clonal hematopoietic stem cell disorders caused by hyperactive JAK/STAT signaling and increased risk of transformation to acute myeloid leukemia (AML). However, targetable mechanisms driving progression remain elusive and therapies are ineffective after leukemia develops. We discovered that HMGA1 chromatin regulators are required for leukemogenesis in JAK2V617F models of MPN AML by dysregulating transcriptional networks involved in proliferation and cell fate (Li et al, Blood 2022). Multi-omics analyses also showed that HMGA1 represses gene networks involved in interferon γ signaling in JAK2V617F AML cells, a pathway that drives immune escape in solid tumors. We therefore sought to test whether HMGA1 drives immune evasion during leukemic transformation in MPN. Integrating RNA/ChIP/ATACseq in JAK2V617F AML cells revealed that HMGA1 represses transcriptional networks involved in antigen presentation, including genes encoding major histocompatibility complex (MHC) class I and II proteins. Silencing HMGA1 via CRISPR or shRNA results in up-regulation of MHC genes, with greatest induction of MHC class II (MHC II) genes (HLA-DRA, DRB1, DPA1, DPB1). Further, HMGA1 depletion increases protein levels of MHC II. To determine how HMGA1 represses MHCII genes, we examined genome architecture at the MHC II loci. We found that HMGA1 recruits repressive histone marks to regulatory regions for MHC II genes which preclude binding by CTCF, a chromatin regulator involved in genome organization, and CIITA, a transcription factor that activates MHC II genes. HMGA1 depletion enhances chromatin accessibility at critical enhancers (super enhancers) involved in MHC II expression, which allows CIITA and CTCF to activate MHC II genes. Because the histone acetylase inhibitor, entinostat, induces MHC II genes in solid tumors, we assessed MHC II with entinostat and HMGA1 depletion. HMGA1 silencing enhances up-regulation of MHC II by entinostat. To test the functional significance of HMGA1 in immune evasion, we performed co-culture experiments with T cells and JAK2V617F AML cells which showed that HMGA1 silencing in AML cells activates T cells, resulting in cytotoxic T cell killing of JAK2V617F AML cells. To examine the relevance of this pathway in patients, we interrogated RNAseq from peripheral blood mononuclear cells and found that HMGA1 overexpression is associated with repression in MHC II genes in about 30% of MPN patients after progression to AML. Together, these data define a new mechanism of gene repression by HMGA1 through chromatin compaction and repressive histone marks that preclude CIITA and CTCF binding to the MHC II loci. Both HMGA1 depletion and entinostat up-regulate MHCII genes, thus illuminating HMGA1 as a potential therapeutic target to stimulate an immune attack and prevent MPN progression. Citation Format: Linda M. S. Resar, Joseph Kim, Audrey-Ann Supreme, Bailey West, Mariah Antopia, Hyungsung Woo, Karen Reddy, Jung-Hyun Kim, Leslie Cope, Jerry Spivak, Alison Moliterno. HMGA1 chromatin regulators drive immune evasion in myeloproliferative neoplasms by repressing gene networks involved in antigen presentation abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2631.