FOXF2调控乳腺癌微环境中成纤维细胞活化的作用和机制

Cancer-associated fibroblasts (CAFs) play a critical role in the metastasis and drug resistance of cancer cells. The activation and functional mechanisms of CAFs in breast cancer microenvironment remains to be clarified. Forkhead box F2 (FOXF2) is a member of the FOX transcription factor family and is specifically expressed in the mesenchyme adjacent to the epithelium in the organs derived from the splanchnic mesoderm. FOXF2 maintains the tissue homeostasis through controlling the differentiation of mesenchymal and inhibiting the epithelial to mesenchymal transition. In previous study, we demonstrated that CAFs induce epithelial-mesenchymal transition (EMT) and metastatic potential of breast cancer cells through paracrine TGF-β signaling. In addition, we found that FOXF2 was under-expressed in CAFs compared with the normal fibroblasts (NFs). Furthermore, we screened a set of candidate transcriptional target genes of FOXF2 which coding proteins involved in the activation of fibroblasts and CAFs characteristic. Our finding suggesting that FOXF2 deficiency transcriptionally upregulates the expression of these targets in fibroblasts, thereby drives the activation of fibroblasts via autocrine signaling, as well as the metastatic potential and drug sensitivity of breast cancer cells via paracrine signaling. The current study aims to clearfy the function and mechanism of FOXF2-regulated activation of fibroblasts in breast cancer microenvironment, and explore the effect of FOXF2-regulated CAFs on the metastastic potential and drug sensitivity of breast cancer cells. The findings under the investigation of this project will improve the theoretical understanding regarding the mechanism of the activation of fibroblasts and the interaction between fibroblast and cancer cells, and will provide a novel therapeutic strategy for targeting breast cancer mircoenvironment.

癌相关成纤维细胞（CAFs）在肿瘤转移和耐药中起重要作用，乳腺癌微环境中CAFs的形成和作用机制尚待阐明。转录因子FOXF2特异性表达于邻近上皮细胞的间质细胞，通过促进间质细胞分化和抑制上皮细胞间质转化维持组织稳态。前期研究发现，乳腺癌微环境中CAFs促进乳腺癌细胞EMT和转移潜能；FOXF2在CAFs中的表达低于正常成纤维细胞；CAFs标志分子以及活化诱导信号分子的编码基因启动子区含FOXF2的转录结合域，推测FOXF2可多效性转录调控成纤维细胞活化状态进而影响乳腺癌细胞转移潜能和药物敏感性。本研究拟通过体内外实验阐明FOXF2调控乳腺癌微环境中成纤维细胞活化并影响乳腺癌转移的作用和机制；探讨FOXF2调控的成纤维细胞活化状态对乳腺癌细胞药物敏感性的影响。研究结果将丰富对乳腺癌微环境中成纤维细胞活化及其与肿瘤细胞相互作用机制的理论认识，并为基于靶向肿瘤微环境的抗肿瘤治疗提供新的策略。

肿瘤微环境在肿瘤恶性进展中起重要作用，成纤维细胞是肿瘤微环境中最丰富的机制细胞且可被活化为均有促进肿瘤进展的癌相关成纤维细胞（Cancer-associated fibroblasts，CAFs），但CAF的活化机制有待阐明。此外，肿瘤细胞可通过上皮-间质转化（epithelial-mesenchymal transition，EMT）并在微环境的诱导下处于不同的分化状态，且肌原性分化可在EMT进程中激活，使肿瘤细胞获得肌成纤维细胞/CAF样表型，但癌细胞转分化为CAF样细胞的机制有待研究。本项目通过临床病例研究证实，FOXF2在浸润性乳腺癌组织中CAFs的表达显著高于其在配对癌旁正常组织中的正常成纤维细胞的表达；体外细胞学实验证实，FOXF2表达缺乏增强NFs/CAFs的CAF活化特征及其对乳腺癌细胞EMT、恶性表型和转移潜能的促进作用；动物实验证实FOXF2表达缺乏增强NFs/CAFs促进乳腺癌细胞内脏转移能力；分子机制研究证实，FOXF2多效性直接转录抑制CAFs标志分子以及活化诱导信号分子ACTA2、FGF1、PDGFD、PDGFRL、TGF-β2、TGF-β3和CXCR4表达，还间接调节FAP、TGF-β1和CXCL12表达；FOXF2通过直接转录抑制α-SMA表达抑制成纤维细胞的CAFs 特性；FOXF2负调节成纤维细胞活化诱导生长因子和受体表达，从而维持组织微环境的稳态；FOXF2表达缺乏的CAFs通过增加TGF-β分泌促进乳腺癌细胞恶性进展和转移；多受体酪氨酸激酶Dasatinib可抑制FOXF2表达缺乏导致的成纤维细胞活化。另外，研究证实FOXF2通过直接抑制基底样乳腺癌（basal-like breast cancer，BLBC）中TGF-β2和TGF-β3表达控制TGF-β/SMAD信号通路活化；FOXF2缺陷的BLBC细胞可转分化为肌成纤维细胞/CAF样表型，且通过增加自分泌TGF-β信号促进内脏转移，通过增加旁分泌TGF-β信号促进邻近细胞恶性进展。本项目研究结果丰富了对乳腺癌微环境中成纤维细胞活化及其与肿瘤细胞相互作用和转分化机制的理论认识，并为靶向治疗高恶性乳腺癌提供了新的策略。