Bone morphogenetic protein-4 (BMP4) acts downstream of HIF-1 and mediates hypoxia-induced up-regulation of transient receptor potential canonical (TRPC), leading to increased basal [Ca2+]i in pulmonary arterial smooth muscle cells (PASMCs), promoting chronic hypoxia-induced pulmonary hypertension pathogenesis (Wang et al., 2015). Here, BMP4 is linked to pulmonary hypertension.