Introduction
Gastric chief cells can re-enter the cell cycle after injury through paligenosis, a conserved regenerative program regulated by mTORC1. This process involves (1) cellular degradation, (2) induction of progenitor genes (spasmolytic polypeptide-expressing metaplasia, SPEM), and (3) cell cycle re-entry. Dysregulated paligenosis contributes to gastric cancer, but mechanisms governing this reprogramming remain incompletely understood. Here, we investigated the role and regulation of YAP1, a key effector of the Hippo pathway, during paligenosis.
Aims & Methods
Our objectives were to determine whether YAP1 is activated during paligenosis, define its role, and identify upstream regulators. Using a mouse model of injury-induced paligenosis (via high-dose tamoxifen, HDTAM, intraperitoneal injection), we analyzed YAP1 activation and Hippo pathway dynamics via proteomics, single-cell RNA sequencing, western blot, immunohistochemistry, and immunofluorescence. To dissect upstream signaling, we employed a series of genetically engineered mouse models targeting Hippo pathway components.
Results
YAP1 is rapidly activated (via dephosphorylation) during the early stage of paligenosis. Functional assays revealed that YAP1 (and its paralog, TAZ) are necessary and sufficient to drive chief cell reprogramming. Among upstream kinases, only STK38 activity mirrored YAP1 activation patterns. STK38 is essential for YAP1 activation and is degraded via autophagy during transition to stage 2. Notably, STK38 harbors a UFM1/LC3-interacting region (LIR) domain and is targeted to autophagosomes. We found that MIST1 induces UFM1, which protects STK38 from autophagic degradation. In Mist1−/− mice, reduced UFM1 correlates with heightened basal autophagy, STK38 loss, and constitutive YAP1 activation. Furthermore, STK38 interacts with NF2, similar to canonical Hippo kinases, modulating YAP1 regulation.
Conclusion
We identify a novel MIST1–UFM1–STK38 axis that regulates YAP1 activity in an autophagy-dependent manner during paligenosis. STK38 acts as a non-canonical Hippo kinase whose stability dictates YAP1 activation. These findings uncover new layers of Hippo pathway regulation and highlight the dynamic control of YAP1 during gastric epithelial regeneration.