FAT1, which encodes a protocadherin, is one of the most frequently mutated genes in human cancers [1][2][3][4][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.

Skin ageing is characterized by small and fine wrinkles, roughness, laxity, and pigmentation as a result of epidermal thinning, collagen degradation, dermal atrophy, and fewer fibroblasts. Plasma rich in growth factors (PRGF) is an autologous plasma preparation enriched in proteins obtained from patient's own blood aimed at accelerating tissue repair and regeneration. To evaluate the benefits of PRGF in skin photodamage, 10 healthy volunteers were treated with three consecutive intradermal injections of PRGF in the facial area. Clinical outcomes and histological analysis were performed. A statistically significant increase in the epidermis and papillary dermis thickness was seen after PRGF treatment (p < 0.001). Skin thickening was observed in all patients studied, being more intense in the group of patients with photodamage (p < 0.001). After PRGF treatment, a reduction of the average area fraction of solar elastosis was observed in patients with clinical and histological signs of skin photodamage (p < 0.05).No changeswere observed in the number of CD31, XIIIa factor, cKit, CD10, nor p53-positive cells. The improvement score after PRGF use was 0.75 (9/12) for the group of patients with signs of skin photodamage. Intradermal PRGF infiltration appears to be an effective treatment for the photodamaged skin.

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