Phosphorylation of serine/arginine-rich splicing factor 1 at tyrosine 19 promotes cell proliferation in pediatric acute lymphoblastic leukemia.

Serine/arginine-rich splicing factor 1 (SRSF1) has been linked to various human cancers including pediatric acute lymphoblastic leukemia (ALL). Our previous study has shown that SRSF1 potentially contributes to leukemogenesis; however, its underlying mechanism remains unclear. In this study, leukemic cells were isolated from pediatric ALL bone marrow samples, followed by immunoprecipitation assays and mass spectrometry analysis specific to SRSF1. Subcellular localization of the SRSF1 protein and its mutants were analyzed by immunofluorescence staining. Cell growth, colony formation, cell apoptosis, and the cell cycle were investigated using stable leukemic cell lines generated with lentivirus-mediated overexpressed WT or mutant plasmids. Cytotoxicity of the Tie2 kinase inhibitor was also evaluated. Our results showed the phosphorylation of SRSF1 at tyrosine 19 (Tyr-19) was identified in newly diagnosed ALL samples, but not in complete remission or normal control samples. Compared to the SRSF1 WT cells, the missense mutants of the Tyr-19 phosphorylation affected the subcellular localization of SRSF1. In addition, the Tyr-19 phosphorylation of SRSF1 also led to increased cell proliferation and enhanced colony-forming properties by promoting the cell cycle. Remarkably, we further identified the kinase Tie2 as a potential therapeutic target in leukemia cells. In conclusion, we identify for the first time that the phosphorylation state of SRSF1 is linked to different phases in pediatric ALL. The Tyr-19 phosphorylation of SRSF1 disrupts its subcellular localization and promotes proliferation in leukemia cells by driving cell-cycle progression. Inhibitors targeting Tie2 kinase that could catalyze Tyr-19 phosphorylation of SRSF1 offer a promising therapeutic target for treatment of pediatric ALL.