MAPK1 and fibrosarcoma: Thus, determining the function and the regulatory mechanism of ERK in osteoblast differentiation and bone formation is clinically significant as the ERK pathway is the most frequently mutated pathway in cancer and, accordingly, ERK pathway components, including rat sarcoma (RAS), rapidly accelerated fibrosarcoma, and MEK isoforms, are all well-established targets to treat a wide variety of ERK pathway-activated cancers (Hong et al., 2020; Hyman et al., 2015; Robert et al., 2015; Tiacci et al., 2021).