Table4_Assessing the epithelial-to-mesenchymal plasticity in a small cell lung carcinoma (SCLC) and lung fibroblasts co-culture model.XLSX

The tumor microenvironment (TME) is the source of important cues that govern epithelial-to-mesenchymal transition (EMT) and facilitate the acquisition of aggressive traits by cancer cells. It is now recognized that EMT is not a binary program, and cancer cells rarely switch to a fully mesenchymal phenotype. Rather, cancer cells exist in multiple hybrid epithelial/mesenchymal (E/M) states responsible for cell population heterogeneity, which is advantageous for the ever-changing environment during tumor development and metastasis. How are these intermediate states generated and maintained is not fully understood. Here, we show that direct interaction between small cell lung carcinoma cells and lung fibroblasts induces a hybrid EMT phenotype in cancer cells in which several mesenchymal genes involved in receptor interaction with the extracellular matrix (ECM) and ECM remodeling are upregulated while epithelial genes such as E-cadherin remain unchanged or slightly increase. We also demonstrate that several core EMT-regulating transcription factors (EMT-TFs) are upregulated in cancer cells during direct contact with fibroblasts, as is Yes-associated protein (YAP1), a major regulator of the Hippo pathway. Further, we show that these changes are transient and reverse to the initial state once the interaction is disrupted. Altogether, our results provide evidence that tumor cells’ direct contact with the fibroblasts in the TME initiates a signaling cascade responsible for hybrid E/M states of cancer cells. These hybrid states are maintained during the interaction and possibly contribute to therapy resistance and immune evasion, while interference with direct contact will result in slow recovery and switch to the initial states.

肿瘤微环境（tumor microenvironment, TME）是调控上皮间质转化（epithelial-to-mesenchymal transition, EMT）并促进癌细胞获得侵袭性表型的重要信号来源。目前学界已明确，EMT并非二元调控程序，癌细胞极少完全转化为间质表型。反之，癌细胞可处于多种混合上皮/间质（hybrid epithelial/mesenchymal, E/M）状态，这一状态是细胞群体异质性的重要来源，有助于癌细胞适应肿瘤发生与转移过程中不断变化的微环境。目前学界尚未完全阐明这些中间状态的产生与维持机制。本研究证实，小细胞肺癌细胞与肺成纤维细胞的直接相互作用可诱导癌细胞产生混合EMT表型：在此表型下，癌细胞中参与细胞外基质（extracellular matrix, ECM）受体互作与ECM重塑的多项间质基因表达上调，而E-钙粘蛋白（E-cadherin）等上皮基因的表达则保持不变或仅轻度升高。研究同时发现，在与成纤维细胞直接接触的过程中，癌细胞内多项核心EMT调控转录因子（EMT-TFs）的表达显著上调，作为Hippo通路主要调控因子的Yes相关蛋白（Yes-associated protein, YAP1）亦是如此。进一步实验表明，上述基因表达变化具有瞬时性：一旦细胞间的直接相互作用被阻断，癌细胞的基因表达模式将恢复至初始状态。综上，本研究结果证实，肿瘤细胞与TME内成纤维细胞的直接接触可启动信号级联反应，进而诱导癌细胞形成混合E/M表型。这类混合表型在细胞相互作用过程中得以维持，或可参与癌细胞的治疗抵抗与免疫逃逸；而阻断直接细胞接触则会使癌细胞的基因表达缓慢恢复，并重新转变为初始状态。