MOB1B (MOB kinase activator 1B) is a core regulatory protein in the Hippo signaling pathway that functions as a kinase activator and tumor suppressor. As a co-activator of LATS1/2 kinases, MOB1B phosphorylates and inactivates the oncoproteins YAP1 and TAZ, preventing their nuclear translocation and thereby restricting cell proliferation and promoting apoptosis 1. MOB1B is phosphorylated by MST1/MST2 kinases, and this phosphorylation enhances its ability to activate NDR kinases including LATS1 and LATS2 2. Beyond Hippo signaling, MOB1B regulates microtubule stability during cytokinesis; depletion causes abscission failure through microtubule hyper-stabilization in the midbody region 3. In disease contexts, MOB1B functions as a tumor suppressor—MOB1A/1B double-knockout mice develop spontaneous cancers with elevated YAP1 activity 4. MOB1B is frequently suppressed in cancer progression: miR-548ag promotes obesity-related endometrial cancer by downregulating MOB1B 5, while circFLNB suppresses colorectal cancer via the miR-3127-3p/MOB1B/Hippo axis 6. Conversely, degradation of MOB1B via CAND1-mediated ubiquitination suppresses Hippo signaling and promotes cardiomyocyte proliferation and heart regeneration after injury 7.