ABSTRACT
FAT1, which encodes a protocadherin, is one of the most frequently mutated genes in human cancers1-5. However, the role and the molecular mechanisms by which FAT1 mutations control tumour initiation and progression are poorly understood. Here, using mouse models of skin squamous cell carcinoma and lung tumours, we found that deletion of Fat1 accelerates tumour initiation and malignant progression and promotes a hybrid epithelial-to-mesenchymal transition (EMT) phenotype. We also found this hybrid EMT state in FAT1-mutated human squamous cell carcinomas. Skin squamous cell carcinomas in which Fat1 was deleted presented increased tumour stemness and spontaneous metastasis. We performed transcriptional and chromatin profiling combined with proteomic analyses and mechanistic studies, which revealed that loss of function of FAT1 activates a CAMK2-CD44-SRC axis that promotes YAP1 nuclear translocation and ZEB1 expression that stimulates the mesenchymal state. This loss of function also inactivates EZH2, promoting SOX2 expression, which sustains the epithelial state. Our comprehensive analysis identified drug resistance and vulnerabilities in FAT1-deficient tumours, which have important implications for cancer therapy. Our studies reveal that, in mouse and human squamous cell carcinoma, loss of function of FAT1 promotes tumour initiation, progression, invasiveness, stemness and metastasis through the induction of a hybrid EMT state.
Subject(s)
Cadherins/deficiency , Epithelial-Mesenchymal Transition/genetics , Gene Deletion , Neoplasm Metastasis/genetics , Neoplasms/genetics , Neoplasms/pathology , Adaptor Proteins, Signal Transducing/metabolism , Animals , Cadherins/genetics , Cadherins/metabolism , Carcinoma, Squamous Cell/genetics , Carcinoma, Squamous Cell/pathology , Disease Progression , Enhancer of Zeste Homolog 2 Protein/metabolism , Epithelial Cells/metabolism , Epithelial Cells/pathology , Epithelial-Mesenchymal Transition/drug effects , Gene Expression Regulation, Neoplastic , Humans , Hyaluronan Receptors/metabolism , Lung Neoplasms/genetics , Lung Neoplasms/pathology , Mesoderm/metabolism , Mesoderm/pathology , Mice , Neoplasm Metastasis/drug therapy , Neoplasms/drug therapy , Neoplastic Stem Cells/metabolism , Neoplastic Stem Cells/pathology , Phenotype , Phosphoproteins/analysis , Phosphoproteins/metabolism , Proteomics , SOXB1 Transcription Factors/metabolism , Signal Transduction , Skin Neoplasms/genetics , Skin Neoplasms/pathology , Transcription Factors/metabolism , YAP-Signaling Proteins , Zinc Finger E-box-Binding Homeobox 1/metabolism , src-Family Kinases/metabolismABSTRACT
In cancer, the epithelial-to-mesenchymal transition (EMT) is associated with tumour stemness, metastasis and resistance to therapy. It has recently been proposed that, rather than being a binary process, EMT occurs through distinct intermediate states. However, there is no direct in vivo evidence for this idea. Here we screen a large panel of cell surface markers in skin and mammary primary tumours, and identify the existence of multiple tumour subpopulations associated with different EMT stages: from epithelial to completely mesenchymal states, passing through intermediate hybrid states. Although all EMT subpopulations presented similar tumour-propagating cell capacity, they displayed differences in cellular plasticity, invasiveness and metastatic potential. Their transcriptional and epigenetic landscapes identify the underlying gene regulatory networks, transcription factors and signalling pathways that control these different EMT transition states. Finally, these tumour subpopulations are localized in different niches that differentially regulate EMT transition states.
