Interference in xbp1 gene expression induces defective cell differentiation and sensory organ development in Drosophila

Integration of UPRER and oxidative stress signaling in the control of intestinal stem cell proliferation

The Unfolded Protein Response of the endoplasmic reticulum (UPR^ER) controls proteostasis by adjusting the protein folding capacity of the ER to environmental and cell-intrinsic conditions. In metazoans, loss of proteostasis results in degenerative and proliferative diseases and cancers. The cellular and molecular mechanisms causing these phenotypes remain poorly understood. Here we show that the UPR^ER is a critical regulator of intestinal stem cell (ISC) quiescence in Drosophilamelanogaster. We find that ISCs require activation of the UPR^ER for regenerative responses, but that a tissue-wide increase in ER stress triggers ISC hyperproliferation and epithelial dysplasia in aging animals. These effects are mediated by ISC-specific redox signaling through Jun-N-terminal Kinase (JNK) and the transcription factor CncC. Our results identify a signaling network of proteostatic and oxidative stress responses that regulates ISC function and regenerative homeostasis in the intestinal epithelium.

Loss of proper protein homeostasis (proteostasis) as well as increased production of reactive oxygen species (ROS) is a hallmark of aging. In complex metazoans, these processes can result in proliferative diseases and cancers. The protein folding capacity of the endoplasmic reticulum (ER) is monitored and maintained by the unfolded protein response of the ER (UPR^ER). In this study, we identify a coordinated role of UPR^ER and oxidative stress signaling in regulating the proliferation of intestinal stem cells (ISCs). We find that the ER-stress responsive transcription factor Xbp1 and the ER-associated degradation pathway component Hrd1 are sufficient and required cell autonomously in ISCs to limit their proliferative activity. This function is dependent on the activities of the stress sensor JNK and the redox-responsive transcription factor CncC, which we have previously identified as regulators of ISC proliferation. We further show here that promoting ER homeostasis in aging ISCs is sufficient to limit age-associated epithelial dysplasia. Our results establish the integration of UPR^ER and oxidative stress signaling as a central mechanism promoting regenerative homeostasis in the intestinal epithelium.