ATF6 and pulmonary fibrosis: ER stress transducers, such as ATF6 and CHOP, are known to play a prominent role in apoptosis of alveolar type II epithelial cells in fibrotic lung diseases, such as Idiopathic Pulmonary Fibrosis (IPF) [19,20] and Hermansky Pudlak Syndrome (HPS) [21].