STAT1-IFITM3 promotes autophagy in epithelial cells to control Cryptosporidium parvum infection.

Cryptosporidium parvum infects intestinal epithelial cells, causing cryptosporidiosis in humans and neonatal livestock. Autophagy is an important component of the defense against C. parvum infection. IFITM3 is an IFN-stimulated gene that regulates viral infection through autophagy; however, its role in C. parvum infection is unknown. Herein, IFITM3 levels increased significantly after C. parvum infection and promoted autophagy. IFITM3 overexpression up-regulated LC3B II/LC3B I, Beclin-1, ATG7, and ATG5, but down-regulated p62 during infection. In C. parvum-infected HCT-8 cells, IFITM3 interacted with LC3B, Beclin-1, and ATG5. IFITM3 knockdown or autophagy-inhibitor treatment decreased the ratio of LC3B II/LC3B I, Beclin-1, ATG7, and ATG5, but increased p62 expression. Furthermore, IFITM3-regulated autophagy was associated with the inflammatory response, cell survival, and C. parvum clearance. IFITM3 overexpression inhibited apoptosis, increased inflammatory cytokine IL-8 production, and decreased the cellular C. parvum burden. IFITM3 silencing had the opposite effects. IFITM3 expression was positively regulated by STAT1 during infection, whereas IFITM3 knockdown increased STAT1's compensatory effect. Thus, intestinal epithelial cells resist C. parvum infection via autophagy through the STAT1-IFITM3 axis.