MST1 (macrophage stimulating 1) is a serine/threonine kinase and core component of the Hippo signaling pathway, a conserved cascade regulating cell proliferation, survival, and organ size control 1. MST1 functions as part of a kinase cascade with MST2 and LATS1/2 to phosphorylate and inhibit the transcriptional coactivators YAP and TAZ, thereby suppressing cell growth programs 1. MST1 mechanistically responds to diverse signals including mechanical forces and cellular stress; for example, oscillatory shear stress inhibits MST1 phosphorylation, reducing its ability to phosphorylate connexin 43 and leading to endothelial dysfunction and atherosclerosis 2. MST1 also phosphorylates Nur77 at threonine 366 to enhance endometrial receptivity by promoting β3-integrin expression, facilitating embryo implantation 3. In liver, accumulated glycogen sequesters MST1/2 in liquid droplets, blocking Hippo signaling and promoting YAP-dependent tumorigenesis 4. MST1 inhibition by IL-17A in keratinocytes reduces MST1-LATS1 interaction, activating YAP-AREG signaling in psoriasis 5. Pharmacological MST1/2 inhibition augments tissue repair and regeneration 6. Genetically predicted MST1 levels show inverse association with inflammatory bowel disease risk 7, suggesting therapeutic potential in IBD management.