YAP-dependent induction of UHMK1 supports nuclear enrichment of the oncogene MYBL2 and proliferation in liver cancer cells.

The oncogene yes-associated protein (YAP) is a key modifier of liver homeostasis and regulates mitosis in hepatocytes as well as in malignantly transformed cells. However, the question of how YAP supports cell proliferation in hepatocellular carcinoma (HCC) is not well understood. Here we identified U2AF momology motif kinase 1 (UHMK1) as a direct transcriptional target of YAP and the transcription factor forkhead box M1 (FOXM1), which supports HCC cell proliferation but not migration. Indeed, UHMK1 stimulates the expression of genes that are specific for cell cycle regulation and which are known downstream effectors of YAP. By using BioID labeling and mass spectrometry, the dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex constituent MYB proto-oncogene like 2 (MYBL2, B-MYB) was identified as a direct UHMK1 interaction partner. Like YAP, UHMK1 stimulates nuclear enrichment of MYBL2, which is associated HCC cell proliferation and the expression of the cell cycle regulators CCNB1, CCNB2, KIF20A, and MAD2L1. The association between YAP, UHMK1, MYBL2, and proliferation was confirmed in YAPS127A-transgenic mice and human HCC tissues. In summary, we provide a model by which YAP supports cell proliferation through the induction of important cell cycle regulators in a UHMK1- and MYBL2-dependent manner.

Cytoplasmic localization of the cell polarity factor scribble supports liver tumor formation and tumor cell invasiveness.

The loss of epithelial cell polarity plays an important role in the development and progression of liver cancer. However, the specific molecular mechanisms supporting tumor initiation and progression are poorly understood. In this study, transcriptome data and immunofluorescence stains of tissue samples derived from hepatocellular carcinoma (HCC) patients revealed that overexpression associated with cytoplasmic localization of the basolateral cell polarity complex protein scribble (Scrib) correlated with poor prognosis of HCC patients. In comparison with HCC cells stably expressing wild-type Scrib (ScribWT ), mutated Scrib with enforced cytoplasmic enrichment (ScribP305L ) induced AKT signaling through the destabilization of phosphatase and tensin homolog (PTEN) and PH domain and leucine-rich repeat protein phosphatase 1 (PHLPP1). Cytoplasmic ScribP305L stimulated a gene signature and a phenotype characteristic for epithelial to mesenchymal transition (EMT) and HCC cell invasiveness. ScribP305L -dependent invasion was mediated by the activator protein 1 (AP-1) constituents ATF2 and JunB through induction of paracrine-acting secreted protein acidic and cysteine-rich (SPARC). Coexpression of ScribP305L and the oncogene c-MYC through hydrodynamic gene delivery in mouse livers promoted tumor formation and increased abundance of pAKT, pATF2, and SPARC in comparison with controls. Finally, cytoplasmic Scrib localization correlated with AKT and ATF2 phosphorylation in human HCC tissues, and the ScribP305L -dependent gene signature was enriched in cancer patients with poor prognosis. CONCLUSION: Perturbation of hepatocellular polarity due to overexpression and cytoplasmic enrichment of Scrib supports tumor initiation and HCC cell dissemination through specific molecular mechanisms. Biomarker signatures identified in this study can be used for the identification of HCC patients with higher risk for the development of metastasis. (Hepatology 2018;67:1842-1856).