Alternatively spliced colony stimulating factor 3 receptor (CSF3R) isoforms Class III and Class IV are observed in myelodysplastic syndromes (MDS), but their roles in disease remain unclear. We report that the MDS-associated splicing factor SRSF2 affects the expression of Class III and Class IV isoforms and perturbs granulopoiesis. Add-back of the Class IV isoform in Csf3r-null mouse progenitor cells increased granulocyte progenitors with impaired neutrophil differentiation, while add-back of the Class III produced dysmorphic neutrophils in fewer numbers. These CSF3R isoforms were elevated in patients with myeloid neoplasms harboring SRSF2 mutations. Using in vitro splicing assays, we confirmed increased Class III and Class IV transcripts when SRSF2 P95 mutations were co-expressed with the CSF3R minigene in K562 cells. Since SRSF2 regulates splicing partly by recognizing exonic splicing enhancer (ESE) sequences on pre-mRNA, deletion of either ESE motifs within CSF3R exon 17 decreased Class IV transcript levels without affecting Class III. CD34+ cells expressing SRSF2 P95H showed impaired neutrophil differentiation in response to G-CSF and was accompanied by increased levels of Class IV. Our findings suggest that SRSF2 P95H promotes Class IV splicing by binding to key ESE sequences in CSF3R exon 17, and that SRSF2, when mutated, contributes to dysgranulopoiesis.

在骨髓增生异常综合征 (MDS) 中观察到选择性剪接的集落刺激因子 3 受体 ( CSF3R ) 亚型 III 和 IV，但它们在疾病中的作用仍不清楚。我们报告 MDS 相关剪接因子 SRSF2 影响 III 类和 IV 类亚型的表达并扰乱粒细胞生成。在Csf3r- null 小鼠祖细胞中添加 IV 类亚型会增加中性粒细胞分化受损的粒细胞祖细胞，而添加 III 类会产生数量较少的畸形中性粒细胞。这些CSF3R亚型在携带SRSF2的髓系肿瘤患者中升高突变。使用体外剪接试验，我们证实当 SRSF2 P95 突变与K562 细胞中的CSF3R 小基因共表达时，III 类和 IV 类转录物增加。由于 SRSF2 部分通过识别前 mRNA 上的外显子剪接增强子 (ESE) 序列来调节剪接，因此删除CSF3R外显子 17 中的任一 ESE 基序会降低 IV 类转录物水平，而不会影响 III 类。表达 SRSF2 P95H 的 CD34+ 细胞显示出对 G-CSF 的中性粒细胞分化受损，并伴有 IV 类水平升高。我们的研究结果表明，SRSF2 P95H 通过与CSF3R外显子 17 中的关键 ESE 序列结合来促进 IV 类剪接，并且 SRSF2 在发生突变时会导致粒细胞生成障碍。