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Loss-of-function of the nucleoside transporter SLC29A3 drives ERK activation, establishing an alternative pathway for histiocytosis development

ABSTRACT: Histiocytoses are inflammatory myeloid neoplasms, driven by somatic activating mutations in mitogen-activated protein kinase (MAPK) genes. H syndrome is a genetic disorder caused by germline loss-of-function mutations in SLC29A3, encoding the lysosomal equilibrative nucleoside transporter 3 (ENT3). Patients with H syndrome are predisposed to develop histiocytosis, yet the mechanism is unclear. Here, we demonstrate that loss-of-function of ENT3 leads to MAPK signaling activation, via the nucleoside sensor Toll-like receptor (TLR). We show that H syndrome monocytes exhibit an inflammatory expression pattern, display elevated levels of phospho-ERK, and secrete enhanced amounts of inflammatory cytokines in a TLR8/MEK-dependent manner. Finally, MEK inhibitor therapy successfully eliminated a histiocytic tumor of a patient with H syndrome. These results demonstrate a yet-unrecognized link between a defect in a lysosomal transporter and pathological activation of MAPK signaling, a novel alternative pathway to histiocytosis development, and establish MEK inhibition as a promising new treatment for H syndrome.

ORGANISM(S): Homo sapiens

PROVIDER: GSE221581 | GEO | 2023/09/27

REPOSITORIES: GEO

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Project description:Langerhans-cell histiocytosis (LCH) is characterized by heterogeneous lesions containing CD207+ Langerhans cells (LCs) and lymphocytes. In this study, we isolated CD207+ cells and CD3+ T cells from LCH lesions to determine cell-specific gene expression. Compared to control epidermal CD207+ cells, the LCH CD207+ cells yielded 2113 differentially-expressed genes (FDR<0.01). Surprisingly, expression of many genes previously associated with LCH, including cell-cycle regulators, pro-inflammatory cytokines and chemokines were not significantly different from control LCs in our study. However, several novel genes whose products activate and recruit T cells to sites of inflammation, including SPP1 (osteopontin), were highly over-expressed in LCH CD207+ cells. Furthermore, several genes associated with immature myeloid dendritic cells were over-expressed in LCH CD207+ cells. Compared to the peripheral CD3+ cells from LCH patients, the LCH lesion CD3+ cells yielded only 162 differentially-regulated genes (FDR<0.01), and the expression profile of the LCH lesion CD3+ cells was consistent with an activated regulatory T cell phenotype with increased expression of FOXP3, CTLA4 as well as SPP1. Based on these results, we propose a new model of LCH pathogenesis in which lesions do not arise from epidermal Langerhans cells, but from accumulation of bone-marrow derived immature myeloid dendritic cells that recruit activated lymphocytes. Cell-specific gene expression from LCH biopsy specimens was evaluated by comparing hybridization signal from amplified cDNA on Affymetrix gene chips (U133A Plus 2.0) (Table1). Three sets of comparisons were performed: 1) Thirteen LCH CD207+ samples were compared to 12 control skin LCH CD207+ samples. 2) Seven LCH lesion CD3+ samples were compared to 7 peripheral blood CD3+ samples from the same patients. 3) Twelve LCH lesion CD3+ samples were compared to 4 pooled control tonsil CD3+ samples (5 individual tonsil CD3+ samples/pool).

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Loss-of-function of the nucleoside transporter SLC29A3 drives ERK activation, establishing an alternative pathway for histiocytosis development

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