Oncofetal protein IGF2BP1 regulates IQGAP3 expression to maintain stem cell potential in cancer [RIP-Seq]

We reported earlier that IQGAP3 is an important stem cell factor in rapidly proliferating isthmus stem cells in the stomach. Furthermore, we observed robust induction of IQGAP3 expression in terminally differentiated chief cells and de-differentiated cells following tissue damage. The elevated expression of IQGAP3 in cancer and its association with metastasis suggest a fundamental role for IQGAP3 in proliferating cancer stem cells. What causes the upregulation of IQGAP3 in cancer is unclear. Here, we show that IGF2BP1 and IQGAP3 expression levels are highest in the blastocyst, with both showing decreases during adulthood. This suggests that IQGAP3, like IGF2BP1, is an early developmental gene that is aberrantly upregulated upon reexpression of IGF2BP1 during carcinogenesis. We found that IGF2BP1 binds and stabilizes m 6 A-modified IQGAP3 transcripts. Furthermore, downstream targets of IGF2BP1, namely SRF and FOXM1, also upregulate IQGAP3 expression. These multiple layers of IQGAP3 regulation, which may safeguard against inappropriate stem cell proliferation, present additional drug targets to inhibit IQGAP3-driven malignant growth. RIP-seq in NTERA2 cells with Flag-tagged IGF2BP1 overexpression.

此前我们曾报道，IQGAP3是胃内快速增殖的峡部干细胞中重要的干细胞因子。此外，我们观察到，在组织损伤后，终末分化的主细胞与去分化细胞中IQGAP3的表达会被显著诱导上调。IQGAP3在癌症中表达升高，且与肿瘤转移相关，这提示IQGAP3在增殖性癌症干细胞中发挥基础性作用。目前尚不清楚癌症中IQGAP3表达上调的具体机制。本研究证实，胰岛素样生长因子2 mRNA结合蛋白1（IGF2BP1）与IQGAP3在囊胚中的表达水平最高，且二者在成年个体中表达均呈下降趋势。这表明，与IGF2BP1类似，IQGAP3属于早期发育基因，在癌变过程中因IGF2BP1的重新表达而发生异常上调。我们发现，IGF2BP1可结合并稳定经N6-甲基腺嘌呤（m⁶A）修饰的IQGAP3转录本。此外，IGF2BP1的下游靶基因——即血清反应因子（SRF）与叉头框蛋白M1（FOXM1）——同样可上调IQGAP3的表达。这种多层面的IQGAP3调控机制，或可防止异常的干细胞增殖，同时也为抑制IQGAP3介导的恶性生长提供了额外的药物靶点。本研究在过表达Flag标签的IGF2BP1的NTERA2细胞中开展了RNA免疫沉淀测序（RIP-seq）实验。