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.

A modest proposal: targeting αv integrin-mediated activation of latent TGFbeta as a novel therapeutic approach to treat scleroderma fibrosis.

INTRODUCTION: The potent profibrotic cytokine transforming growth factor-ß (TGF-ß) has been associated with the onset and progression of the fibrosis seen in the autoimmune connective tissue disease scleroderma (systemic sclerosis, SSc). AREA COVERED: This review explores the data supporting the notion that TGF-ß contributes to SSc fibrosis and examines why initiating clinical trials in SSc aimed at targeting integrin-mediated latent TGF-ß activation is timely. EXPERT OPINION: Targeting TGF-ß directly has not been proven to be clinically effective in this disease. Conversely, targeting matrix stiffness, which perpetuates fibrosis, may have more promise. Intriguingly, targeting integrin-mediated activation of latent TGF-ß, which bridges these concepts, may have therapeutic value.

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.

Back to the future: targeting the extracellular matrix to treat systemic sclerosis.

Fibrosis is the excessive deposition of a stable extracellular matrix (ECM); fibrotic tissue is composed principally of highly crosslinked type I collagen and highly contractile myofibroblasts. Systemic sclerosis (SSc) is a multisystem autoimmune connective tissue disease characterized by skin and organ fibrosis. The fibrotic process has been recognized in SSc for >40 years, but drugs with demonstrable efficacy against SSc fibrosis in ameliorating the lung involvement have only recently been identified. Unfortunately, these treatments are ineffective at improving the skin score in patients with SSc. Previous clinical trials in SSc have largely focused on the cross-purposing of anti-inflammatory drugs and the use of immunosuppressive drugs from the transplantation field, which address inflammatory and/or autoimmune processes. Limited examination has taken place of specific anti-fibrotic agents developed through their ability to directly target the ECM in SSc by, for example, alleviating the persistent matrix stiffness and mechanotransduction that might be required for both the initiation and maintenance of fibrosis, including in SSc. However, because of the importance of the ECM in the SSc phenotype, attempts have now been made to identify drugs that specifically target the ECM, including some drugs that are currently under consideration for the treatment of cancer.

Tumor-associated fibrosis impairs the response to immunotherapy.

Previously, impaired responses to immunotherapy in cancer had been attributed mainly to inherent tumor characteristics (tumor cell intrinsic factors) such as low immunogenicity, (low) mutational burden, weak host immune system, etc. However, mapping the responses of immunotherapeutic regimes in clinical trials for different types of cancer has pointed towards an obvious commonality - that tumors with a rich fibrotic stroma respond poorly or not at all. This has prompted a harder look on tumor cell extrinsic factors such as the surrounding tumor microenvironment (TME), and specifically, the fibrotic stroma as a potential enabler of immunotherapy failure. Indeed, the role of cancer-associated fibrosis in impeding efficacy of immunotherapy is now well-established. In fact, recent studies reveal a complex interconnection between fibrosis and treatment efficacy. Accordingly, in this review we provide a general overview of what a tumor associated fibrotic reaction is and how it interacts with the members of immune system that are frequently seen to be modulated in a failed immunotherapeutic regime.