RNA−binding protein FXR1 stabilizes receptor tyrosine kinase FGFR1 and enhances PI3K−Akt signaling to promote T−cell leukemogenesis

Abstract Introduction: T-cell acute lymphoblastic leukemia (T-ALL) is a highly aggressive hematologic malignancy with poor five-year survival rates, underscoring the need for better understanding of its molecular pathogenesis and new therapeutic strategies. RNA-binding proteins (RBPs) are key regulators of gene expression, influencing RNA splicing, transport, modification, and stability. Dysregulated RBPs such as MSI2 and HNRNPC have been implicated in leukemia development. Fragile X-related protein 1 (FXR1), an RBP encoded at chromosome 3q26.3, is overexpressed in several solid tumors, but its role in leukemia remains unclear. This study aims to investigate the functional significance and underlying mechanisms of FXR1 in T-ALL pathobiology. Methods: Public databases were queried to assess FXR1 expression, clinical relevance, and prognostic value in T-ALL. Western blotting confirmed FXR1 protein levels in primary T-ALL samples. FXR1 was knocked out (KO) in CCRF-CEM, Jurkat, and Molt-4 cells using CRISPR-Cas9, and FXR1 overexpression (OE) cell lines were also generated. Cell proliferation, apoptosis, and cell cycle progression were assessed. In vivo tumor growth was evaluated using T-ALL xenografts. To elucidate the mechanisms, RNA-seq and RIP-seq were applied in FXR1-KO Jurkat cells to identify direct FXR1 targets. Pulse-chase experiments were performed to measure protein stability, and RNA electromobility shift assays (REMSA) were used to determine FXR1–mRNA binding. Results: Bioinformatic analyses revealed frequent FXR1 amplification in acute leukemia, particularly T-ALL, and high FXR1 expression correlated with poor overall survival in patients with T-ALL. FXR1 protein levels were elevated in T-ALL cell lines and patient samples compared to healthy controls. FXR1-KO significantly impaired cell proliferation, induced apoptosis, and caused G2/M cell cycle arrest, whereas FXR1-OE enhanced cell viability and progression. In xenograft models, FXR1-KO markedly suppressed T-ALL leukemia growth. Using RNA-seq and RIP-seq, we identified FGFR1 as a direct FXR1 target. FXR1 depletion reduced FGFR1 at both mRNA and protein levels, shortened FGFR1 half-life, and decreased activation of PI3K/AKT/GSK3β signaling. Expression of cell cycle regulators (Cyclin B1, CDK1, CDK2) was also downregulated in FXR1-KO cells. Restoration of FGFR1 partially rescued the proliferation defect in FXR1-deficient cells. Preliminary REMSA data suggest FXR1 may directly bind FGFR1 mRNA. Conclusions: FXR1 promotes T-ALL leukemogenesis by binding to and stabilizing FGFR1 mRNA, thereby enhancing FGFR1 expression and activating the PI3K-AKT pathway. Targeting the FXR1–FGFR1 axis may represent a novel therapeutic strategy for T-ALL. Keywords: FXR1, T cell acute lymphoblastic leukemia, FGFR1, PI3K-AKT