Abrogation of myofibroblast activities in metastasis and fibrosis by methyltransferase inhibition.

Myofibroblasts are a population of highly contractile fibroblasts that express and require the activity of the transcription factor Snail1. Cancer‐associated fibroblasts (CAFs) correlate with low survival of cancer patients when present in the stroma of primary tumors. Remarkably, the presence of myofibroblastic CAFs (which express Snail1) creates mechanical properties in the tumor microenvironment that support metastasis. However, therapeutic blockage of fibroblast activity in patients with cancer is a double‐edged sword, as normal fibroblast activities often restrict tumor cell invasion. We used fibroblasts depleted of Snail1 or protein arginine methyltransferases 1 and 4 (PRMT1/‐4) to identify specific epigenetic modifications induced by TGFβ/Snail1. Furthermore, we analyzed the in vivo efficiency of methyltransferase inhibitors using mouse models of wound healing and metastasis, as well as fibroblasts isolated from patients with idiopathic pulmonary fibrosis (IPF). Mechanistically, TGFβ‐induced Snail1 promotes the epigenetic mark of asymmetrically dimethylated arginine. Critically, we found that inhibitors of methyltransferases prevent myofibroblast activity (but not regular fibroblast activity) in the extracellular matrix, both in cell culture and in vivo. In a mouse breast cancer model, the inhibitor sinefungin reduces both the myofibroblast activity in the tumor stroma and the metastatic burden in the lung. Two distinct inhibitors effectively blocked the exacerbated myofibroblast activity of patient‐derived IPF fibroblasts. Our data reveal epigenetic regulation of myofibroblast transdifferentiation in both wound healing and in disease (fibrosis and breast cancer). Thus, methyltransferase inhibitors are good candidates as therapeutic reagents for these diseases. What's new? Cancer‐associated fibroblasts (CAFs) facilitate solid tumor progression, in part by generating tension force for extracellular matrix (ECM) remodeling. Of particular significance for ECM remodeling are myoblastic CAFs expressing cytoskeletal factors, namely smooth muscle actin (αSMA). Here, in fibrosis and breast cancer, fibroblast activation was found to be dependent on methylation induced by the transcription factor Snail1, which is required for organization of the contractile αSMA cytoskeleton. Methyltransferase inhibitors, including AMI1 and sinefungin, prevented fibrotic ECM generation by CAFs, wound‐healing myofibroblasts, and idiopathic pulmonary fibrosis fibroblasts, warranting further investigation of this strategy as a means of treating cancer progression and fibrosis. [ABSTRACT FROM AUTHOR]