Fibroblast-specific ERK5 deficiency changes tumor vasculature and exacerbates tumor progression in a mouse model

The roles of cancer-associated fibroblasts (CAFs) have been studied in the tumor progression, and CAFs are expected to become the new targets for cancer pharmacotherapies. CAFs contribute to tumor cell survival and proliferation, tumor angiogenesis, immune suppression, tumor inflammation, tumor cell invasion and metastasis, and extracellular matrix remodeling. However, detailed mechanisms of how CAFs function in the living system remain unclear. CAFs include alpha-smooth muscle actin, expressing activated fibroblasts similar to myofibroblasts, and are highly capable of producing collagen. Several reports have demonstrated the contributions of extracellular-signal-regulated kinase 5 (ERK5) in fibroblasts to the fibrotic processes; however, the roles of CAF-derived ERK5 remain unclear. To investigate the roles of CAF-derived ERK5 in the tumor progression, we created mice lacking the ERK5 gene specifically in fibroblasts. Colon-26 mouse colon cancer cells were implanted into the mice subcutaneously, and the histological analyses of the tumor tissue were performed after 2 weeks. Immunofluorescence analyses showed that recipient-derived fibroblasts existed within the tumor tissue. The present study demonstrated that fibroblast-specific ERK5 deficiency exacerbated tumor progression and it was accompanied with thicker tumor vessel formation and the increase in the number of activated fibroblasts. We combined the results of The Cancer Genome Atlas (TCGA) database analysis with our animal studies, and indicated that regulating ERK5 activity in CAFs or CAF invasion into the tumor tissue can be important strategies for the development of new targets in cancer pharmacotherapies.