HSPA5 and idiopathic pulmonary fibrosis: Interestingly, a recent in vitro study showed that the weak pan-HDAC inhibitor 4-phenyl-butyrate (4-PBA) alleviated the aggregation and improved the secretion of IPF-associated mutant SP-A2 proteins in A549 cells through the upregulation of glucose-regulated protein (GRP)78 [255].