UBE2I and pulmonary fibrosis: Upregulation of SUMO1 and Ubc9 has been observed in human bronchial epithelial cells after exposure to cigarette smoke extract in chronic obstructive pulmonary disease (Zhou et al., 2020a), and upregulation of SUMO1, SUMO2, and Ubc9 has been noted in the lung tissues of patients with idiopathic pulmonary fibrosis (Yu et al., 2022b).