MAP2K7 and pulmonary arterial hypertension: As previously mentioned, even transient exposure of picomolar concentrations of S1 protein alone is sufficient to trigger cell growth signalling via the MEK/ERK pathway in human pulmonary vascular smooth muscle and endothelial cells and (Suzuki et al., 2021)this can promote hyperplasia and/or hypertrophy of the pulmonary vasculature as MEK phosphorylation has been associated with de-differentiation, nuclear activation and proliferation of pulmonary vascular smooth muscle cells in pulmonary hypertension (Xing et al., 2019; Suzuki et al., 2021).