Probable molecular chaperone assisting protein biosynthesis and transport in the endoplasmic reticulum (PubMed:26252542). Required for the proper biosynthesis and transport of pulmonary surfactant-associated protein A/SP-A, pulmonary surfactant-associated protein D/SP-D and the lipid transporter ABCA3 (PubMed:26252542). By regulating both the proper expression and the degradation through the endoplasmic reticulum-associated protein degradation pathway of these proteins plays a crucial role in pulmonary surfactant homeostasis (PubMed:26252542). Has an anti-fibrotic activity by negatively regulating the secretion of type I and type III collagens (By similarity). This calcium-binding protein also transiently associates with immature PCSK6 and regulates its secretion (By similarity). Interacts with PCSK6 (immature form including the propeptide); probably involved in the maturation and the secretion of PCSK6. Highly expressed in lung and heart. Also detected in liver, spleen, kidney, skeletal muscle, intestine, stomach, and brain. During lung development the expression is detected from 15.5 dpc to P1 with a maximum at 17.5 dpc which corresponds to the stage of development of alveolar saccules. Degraded by PCSK6 and other endoproteases including FURIN and PCSK5. N-glycosylated. Homozygous knockout mice show neonatal lethality (PubMed:26252542). Normally delivered newborn mice exhibit normal gross morphology, early motor activity, and response to painful stimuli (PubMed:26252542). They quickly develop severe respiratory distress with gasping and cyanosis, and die within 20 to 60 minutes after birth (PubMed:26252542). Normally developed trachea and diaphragm structure as well as no obvious gross morphological or histological abnormalities in the heart, brain, or liver suggest that abnormal lung development is the primary cause for the neonatal lethality (PubMed:26252542). Mutant mice exhibit morphological abnormalities of the lungs, including atelectasis with collapse of the alveolar space and unexpanded intra-alveolar septae (PubMed:26252542). This is associated with an impaired maturation of type 2 alveolar epithelial cells which is probably due to their failure to properly produce pulmonary surfactant (PubMed:26252542). Belongs to the CREC family.