MAPK3 and systemic sclerosis: The implication of extracellular signal-regulated kinase (ERK)1/2 signaling in ROS production has been assessed in different cell types, including T lymphocytes [18], and in a previous work, we described an intracellular loop that involves Ha-Ras, ERK1/2, and ROS, leading to increased collagen gene expression in SSc fibroblasts [30].