Mps One Binder Kinase Activator (MOB)1A/1B are core components of the Hippo pathway that coactivate large tumor suppressor homolog (LATS) kinases. Mob1a/1b double deficiency in mouse liver (LMob1DKO) results in hyperplasia of oval cells and immature cholangiocytes accompanied by inflammatory cell infiltration and fibrosis. More than half of mutant mice die within 3 wk of birth. All survivors eventually develop liver cancers, particularly combined hepatocellular and cholangiocarcinomas (cHC-CCs) and intrahepatic cholangiocellular carcinomas (ICCs), and die by age 60 wk. Because this phenotype is the most severe among mutant mice lacking a Hippo signaling component, MOB1A/1B constitute the critical hub of Hippo signaling in mammalian liver. LMob1DKO liver cells show hyperproliferation, increased cell saturation density, hepatocyte dedifferentiation, enhanced epithelial–mesenchymal transition and cell migration, and elevated transforming growth factor beta(TGF-β)2/3 production. These changes are strongly dependent on Yes-Associated Protein-1 (Yap1) and partially dependent on PDZ-binding motif (Taz) and Tgfbr2, but independent of connective tissue growth factor (Ctgf). In human liver cancers, YAP1 activation is frequent in cHC-CCs and ICCs and correlates with SMAD family member 2 activation. Drug screening revealed that antiparasitic macrocyclic lactones inhibit YAP1 activation in vitro and in vivo. Targeting YAP1/TAZ with these drugs in combination with inhibition of the TGF-β pathway may be effective treatment for cHC-CCs and ICCs.

Head-and-neck squamous cell carcinoma (HNSCC) is the sixth most common group of cancers in the world, and patients have a poor prognosis. Here, we present data indicating that YAP1 may be a strong driver of the onset and progression of oral SCC (OSCC), a major subtype of HNSCC. Mice with tongue-specific deletion of Mob1a/b and thus endogenous YAP1 hyperactivation underwent surprisingly rapid and highly reproducible tumorigenesis, developing tongue carcinoma in situ within 2 weeks and invasive SCC within 4 weeks. In humans, precancerous tongue dysplasia displays YAP1 activation correlating with reduced patient survival. Combinations of molecules mutated in OSCC may increase and sustain YAP1 activation to the point of oncogenicity. Strikingly, siRNA or pharmacological inhibition of YAP1 blocks murine OSCC onset in vitro and in vivo. Our work justifies targeting YAP1 as therapy for OSCC and perhaps HNSCC, and our mouse model represents a powerful tool for evaluating these agents.

There is a consensus that portal venous pressure (PVP) modulation prevents portal hypertension (PHT) and consequent complications after adult-to-adult living donor liver transplantation (ALDLT). However, PVP-modulation strategies need to be updated based on the most recent findings. We examined our 10-year experience of PVP modulation and reevaluated whether it was necessary for all recipients or for selected recipients in ALDLT. In this retrospective study, 319 patients who underwent ALDLT from 2007 to 2016 were divided into 3 groups according to the necessity and results of PVP modulation: not indicated (n = 189), indicated and succeeded (n = 92), and indicated but failed (n = 38). Graft survival and associations with various clinical factors were investigated. PVP modulation was performed mainly by splenectomy to lower final PVP to ≤15 mm Hg. Successful PVP modulation improved prognosis to be equivalent to that of patients who did not need modulation, whereas failed modulation was associated with increased incidence of small-for-size syndrome (SFSS; P = 0.003) and early graft loss (EGL; P = 0.006). Among patients with failed modulation, donor age ≥ 45 years (hazard ratio [HR], 3.67; P = 0.02) and ABO incompatibility (HR, 3.90; P = 0.01) were independent risk factors for graft loss. Survival analysis showed that PVP > 15 mm Hg was related to poor prognosis in grafts from either ABO-incompatible or older donor age ≥ 45 years (P < 0.001), but it did not negatively affect grafts from ABO-compatible/identical and young donor age < 45 years (P = 0.27). In conclusion, intentional PVP modulation is not necessarily required in all recipients. Although grafts from both ABO-compatible/identical and young donors can tolerate PHT, lowering PVP to ≤15 mm Hg is a key to preventing SFSS and consequent EGL with grafts from either ABO-incompatible or older donors.

Hippo signaling is modulated in response to cell density, external mechanical forces, and rigidity of the extracellular matrix (ECM). The Mps one binder kinase activator (MOB) adaptor proteins are core components of Hippo signaling and influence Yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ), which are potent transcriptional regulators. YAP1/TAZ are key contributors to cartilage and bone development but the molecular mechanisms by which the Hippo pathway controls chondrogenesis are largely unknown. Cartilage is rich in ECM and also subject to strong external forces - two upstream factors regulating Hippo signaling. Chondrogenesis and endochondral ossification are tightly controlled by growth factors, morphogens, hormones, and transcriptional factors that engage in crosstalk with Hippo-YAP1/TAZ signaling. Here, we generated tamoxifen-inducible, chondrocyte-specific -deficient mice and show that hyperactivation of endogenous YAP1/TAZ impairs chondrocyte proliferation and differentiation/maturation, leading to chondrodysplasia. These defects were linked to suppression of SOX9, a master regulator of chondrogenesis, the expression of which is mediated by TEAD transcription factors. Our data indicate that a MOB1-dependent YAP1/TAZ-TEAD complex functions as a transcriptional repressor of SOX9 and thereby negatively regulates chondrogenesis.