Essential roles of grp94 in gut homeostasis via chaperoning canonical Wnt pathway.

Increasing evidence points to a role for the protein quality control in the endoplasmic reticulum (ER) in maintaining intestinal homeostasis. However, the specific role for general ER chaperones in this process remains unknown. Herein, we report that a major ER heat shock protein grp94 interacts with MesD, a critical chaperone for the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6). Without grp94, LRP6 fails to export from the ER to the cell surface, resulting in a profound loss of canonical Wnt signaling. The significance of this finding is demonstrated in vivo in that grp94 loss causes a rapid and profound compromise in intestinal homeostasis with gut-intrinsic defect in the proliferation of intestinal crypts, compromise of nuclear β-catenin translocation, loss of crypt-villus structure, and impaired barrier function. Taken together, our work has uncovered the role of grp94 in chaperoning LRP6-MesD in coordinating intestinal homeostasis, placing canonical Wnt-signaling pathway under the direct regulation of the general protein quality control machinery in the ER.