Table_1_An FGFR/AKT/SOX2 Signaling Axis Controls Pancreatic Cancer Stemness.DOCX

Cancer stemness is associated with high malignancy and low differentiation, as well as therapeutic resistance of tumors including pancreatic ductal adenocarcinoma (PDAC). Fibroblast growth factors (FGFs) exert pleiotropic effects on a variety of cellular processes and functions including embryonic stem cell pluripotency and cancer cell stemness via the activation of four tyrosine kinase FGF receptors (FGFRs). FGF ligands have been a major component of the cocktail of growth factors contained in the cancer stemness-inducing (CSI) and organoid culture medium. Although FGF/FGFR signaling has been hypothesized to maintain cancer stemness, its function in this process is still unclear. We report that inhibition of FGF/FGFR signaling impairs sphere-forming ability of PDAC in vitro, and knocking down FGFR1 and FGFR2 decreased their tumorigenesis abilities in vivo. Mechanistically, we demonstrated that SOX2 is down-regulated upon loss of FGFR signaling. The overexpression of SOX2 in SOX2-negative cells, which normally do not display stemness capabilities, is sufficient to induce spheroid formation. Additionally, we found that AKT phosphorylation was reduced upon FGFR signaling inhibition. The inhibition of AKT using specific pharmacological inhibitors in the context of CSI medium leads to the loss of spheroid formation associated with loss of SOX2 nuclear expression and increased degradation. We demonstrate that an FGFR/AKT/SOX2 axis controls cancer stemness in PDAC and therefore may represent an important therapeutic target in the fight against this very aggressive form of cancer.

癌症干细胞性（cancer stemness）与高恶性度、低分化以及包括胰腺导管腺癌（pancreatic ductal adenocarcinoma, PDAC）在内的多种肿瘤的治疗抵抗密切相关。成纤维细胞生长因子（fibroblast growth factors, FGFs）可通过激活4种酪氨酸激酶型成纤维细胞生长因子受体（tyrosine kinase FGF receptors, FGFRs），对包括胚胎干细胞多能性与癌细胞干细胞性在内的多种细胞过程与功能发挥多效性调控作用。FGF配体一直是癌症干细胞性诱导（cancer stemness-inducing, CSI）培养基与类器官培养基中所含生长因子混合物的核心组分。尽管已有假说提出FGF/FGFR信号通路可维持癌症干细胞性，但该通路在此过程中的具体功能仍不明确。本研究发现，抑制FGF/FGFR信号通路会在体外削弱胰腺导管腺癌的成球能力；而敲低FGFR1与FGFR2，则会在体内降低其成瘤能力。机制层面上，我们证实当FGFR信号通路缺失时，SOX2会发生下调。在原本不具备干细胞特性的SOX2阴性细胞中过表达SOX2，足以诱导其成球。此外，我们还发现FGFR信号通路受抑制时，AKT磷酸化水平会降低。在CSI培养基环境中，使用特异性药理学抑制剂抑制AKT，会导致成球能力丧失，同时伴随SOX2核表达缺失与降解增加。本研究证实，FGFR/AKT/SOX2轴调控胰腺导管腺癌中的癌症干细胞性，因此可作为对抗这种极具侵袭性癌症的重要治疗靶点。