The role of yes activated protein (YAP) in melanoma metastasis.

Hippo was first identified in a genetic screen as a protein that suppressed proliferation and cell growth. Subsequently, it was shown that hippo acted in a so-called canonical cascade to suppress Yorkie, the Drosophila equivalent of Yes-activated protein (YAP), a mechanosensitive transcriptional cofactor that enhances the activity of the TEAD family of transcription factors. YAP promotes fibrosis, activation of cancer-associated fibroblasts, angiogenesis and cancer cell invasion. YAP activates the expression of the matricellular proteins CCN1 (cyr61) and CCN2 (ctgf), themselves mediators of fibrogenesis and oncogenesis, and coordination of matrix deposition and angiogenesis. This review discusses how therapeutically targeting YAP through YAP inhibitors verteporfin and celastrol and its downstream mediators CCN1 and CCN2 might be useful in treating melanoma.

The role of positional information in determining dermal fibroblast diversity.

The largest mammalian organ, skin, consisting of a dermal connective tissue layer that underlies and supports the epidermis, acts as a protective barrier that excludes external pathogens and disseminates sensory signals emanating from the local microenvironment. Dermal connective tissue is comprised of a collagen-rich extracellular matrix (ECM) that is produced by connective tissue fibroblasts resident within the dermis. When wounded, a tissue repair program is induced whereby fibroblasts, in response to alterations in the microenvironment, produce new ECM components, resulting in the formation of a scar. Failure to terminate the normal tissue repair program causes fibrotic conditions including: hypertrophic scars, keloids, and the systemic autoimmune connective tissue disease scleroderma (systemic sclerosis, SSc). Histological and single-cell RNA sequencing (scRNAseq) studies have revealed that fibroblasts are heterogeneous and highly plastic. Understanding how this diversity contributes to dermal homeostasis, wounding, fibrosis, and cancer may ultimately result in novel anti-fibrotic therapies and personalized medicine. This review summarizes studies supporting this concept.

The yes-associated protein-1 (YAP1) inhibitor celastrol suppresses the ability of transforming growth factor ß to activate human gingival fibroblasts.

OBJECTIVE: To determine whether celastrol, an inhibitor of the mechanosensitive transcriptional cofactor yes-associated protein-1 (YAP1), impairs the ability of TGFß1 to stimulate fibrogenic activity in human gingival fibroblast cell line. DESIGN: Human gingival fibroblasts were pre-treated with celastrol or DMSO followed by stimulation with or without TGFß1 (4 ng/ml). We then utilized bulk RNA sequencing (RNAseq), real-time polymerase chain reaction (RT-PCR), Western blot, immunofluorescence, cell proliferation assays to determine if celastrol impaired TGFß1-induced responses in a human gingival fibroblast cell line. RESULTS: Celastrol impaired the ability of TGFß1 to induce expression of the profibrotic marker and mediator CCN2. Bulk RNAseq analysis of gingival fibroblasts treated with TGFß1, in the presence or absence of celastrol, revealed that celastrol impaired the ability of TGFß1 to induce mRNA expression of genes within extracellular matrix, wound healing, focal adhesion and cytokine/Wnt signaling clusters. RT-PCR analysis of extracted RNAs confirmed that celastrol antagonized the ability of TGFß1 to induce expression of genes anticipated to contribute to fibrotic responses. Celastrol also reduced gingival fibroblast proliferation, and YAP1 nuclear localization in response to TGFß1. CONCLUSION: YAP1 inhibitors such as celastrol could be used to impair pro-fibrotic responses to TGFß1 in human gingival fibroblasts.

Tripterygium wilfordii derivative celastrol, a YAP inhibitor, has antifibrotic effects in systemic sclerosis.

OBJECTIVES: Systemic sclerosis (SSc) is characterised by extensive tissue fibrosis maintained by mechanotranductive/proadhesive signalling. Drugs targeting this pathway are therefore of likely therapeutic benefit. The mechanosensitive transcriptional co-activator, yes activated protein-1 (YAP1), is activated in SSc fibroblasts. The terpenoid celastrol is a YAP1 inhibitor; however, if celastrol can alleviate SSc fibrosis is unknown. Moreover, the cell niches required for skin fibrosis are unknown. METHODS: Human dermal fibroblasts from healthy individuals and patients with diffuse cutaneous SSc were treated with or without transforming growth factor ß1 (TGFß1), with or without celastrol. Mice were subjected to the bleomycin-induced model of skin SSc, in the presence or absence of celastrol. Fibrosis was assessed using RNA Sequencing, real-time PCR, spatial transcriptomic analyses, Western blot, ELISA and histological analyses. RESULTS: In dermal fibroblasts, celastrol impaired the ability of TGFß1 to induce an SSc-like pattern of gene expression, including that of cellular communication network factor 2, collagen I and TGFß1. Celastrol alleviated the persistent fibrotic phenotype of dermal fibroblasts cultured from lesions of SSc patients. In the bleomycin-induced model of skin SSc, increased expression of genes associated with reticular fibroblast and hippo/YAP clusters was observed; conversely, celastrol inhibited these bleomycin-induced changes and blocked nuclear localisation of YAP. CONCLUSIONS: Our data clarify niches within the skin activated in fibrosis and suggest that compounds, such as celastrol, that antagonise the YAP pathway may be potential treatments for SSc skin fibrosis.

Using the Bleomycin-Induced Model of Fibrosis to Study the Contribution of CCN Proteins to Scleroderma Fibrosis.

Approximately 45% of the deaths in the developed world result from conditions with a fibrotic component. Although no specific, focused anti-fibrotic therapies have been approved for clinical use, a long-standing concept is that targeting CCN proteins may be useful to treat fibrosis. Herein, we summarize current data supporting the concept that targeting CCN2 may be a viable anti-fibrotic approach to treat scleroderma. Testing this hypothesis has been made possible by using a mouse model of inflammation-driven skin and lung fibrosis.