c‑Myc promotes cholangiocarcinoma cells to overcome contact inhibition via the mTOR pathway.

The loss of contact inhibition is a hallmark of a wide range of human cancer cells. Yet, the precise mechanism behind this process is not fully understood. c‑Myc plays a pivotal role in carcinogenesis, but its involvement in regulating contact inhibition has not been explored to date. Here, we report that c‑Myc plays an important role in abrogating contact inhibition in human cholangiocarcinoma (CCA) cells. Our data show that the protein level of c‑Myc obviously decreased in contact-inhibited normal biliary epithelial cells. However, CCA cells sustain high protein levels of c‑Myc and keep strong proliferation ability in confluent conditions. Importantly, the suppression of c‑Myc by inhibitor or siRNA induced G0/G1 phase cell cycle arrest in confluent CCA cells. We demonstrate that the inhibition of c‑Myc suppressed the activity of mammalian target of rapamycin (mTOR) in confluent CCA cells, and mTOR inhibition induced G0/G1 phase cell cycle arrest in confluent CCA cells. In confluent CCA cells, the activity of Merlin is downregulated, and Yes-associated protein (YAP) sustains high levels of activity. Furthermore, YAP inhibition not only induced G0/G1 phase cell cycle arrest, but also decreased c‑Myc expression in confluent CCA cells. These results indicate that Merlin/YAP/c‑Myc/mTOR signaling axis promotes human CCA cell proliferation by overriding contact inhibition. We propose that overriding c‑Myc‑mediated contact inhibition is implicated in the development of CCA.

[1]  Hong Zhou,et al.  Synergistic antitumor activity of the combination of salubrinal and rapamycin against human cholangiocarcinoma cells , 2016, Oncotarget.

[2]  Jin Chen,et al.  mTORC1 and mTORC2 in cancer and the tumor microenvironment , 2016, Oncogene.

[3]  M. Avila,et al.  New molecular interactions of c‐Myc in cholangiocarcinoma may open new therapeutic opportunities , 2016, Hepatology.

[4]  Shelly C. Lu,et al.  Deregulated methionine adenosyltransferase α1, c‐Myc, and Maf proteins together promote cholangiocarcinoma growth in mice and humans‡ , 2016, Hepatology.

[5]  Liu Cao,et al.  PI3K/Akt/mTOR signaling pathway and targeted therapy for glioblastoma , 2016, Oncotarget.

[6]  Javier León,et al.  Myc and cell cycle control. , 2015, Biochimica et biophysica acta.

[7]  R. Dai,et al.  Gankyrin drives malignant transformation of chronic liver damage-mediated fibrosis via the Rac1/JNK pathway , 2015, Cell Death and Disease.

[8]  P. Pontisso,et al.  SerpinB3 and Yap Interplay Increases Myc Oncogenic Activity , 2015, Scientific Reports.

[9]  M. Blagosklonny,et al.  Contact inhibition and high cell density deactivate the mammalian target of rapamycin pathway, thus suppressing the senescence program , 2014, Proceedings of the National Academy of Sciences.

[10]  G. Riggins,et al.  Increased activation of PI3K/AKT signaling pathway is associated with cholangiocarcinoma metastasis and PI3K/mTOR inhibition presents a possible therapeutic strategy , 2013, Tumor Biology.

[11]  D. Eick,et al.  Dose-dependent regulation of target gene expression and cell proliferation by c-Myc levels , 2013, Transcription.

[12]  K. Kinzler,et al.  Cancer Genome Landscapes , 2013, Science.

[13]  C. Hanemann,et al.  Merlin-deficient human tumors show loss of contact inhibition and activation of Wnt/β-catenin signaling linked to the PDGFR/Src and Rac/PAK pathways. , 2011, Neoplasia.

[14]  K. Ko,et al.  A mouse model of cholestasis-associated cholangiocarcinoma and transcription factors involved in progression. , 2011, Gastroenterology.

[15]  D. Hanahan,et al.  Hallmarks of Cancer: The Next Generation , 2011, Cell.

[16]  M. Giovannini,et al.  The Merlin/NF2 tumor suppressor functions through the YAP oncoprotein to regulate tissue homeostasis in mammals. , 2010, Developmental cell.

[17]  S. Thorgeirsson,et al.  Central role of c-Myc during malignant conversion in human hepatocarcinogenesis. , 2009, Cancer research.

[18]  A. Follis,et al.  Small-molecule perturbation of competing interactions between c-Myc and Max. , 2009, Bioorganic & medicinal chemistry letters.

[19]  D. Zhuang,et al.  c-Myc depletion inhibits proliferation of human tumor cells at various stages of the cell cycle , 2008, Oncogene.

[20]  Q. Zeng,et al.  The emerging role of the hippo pathway in cell contact inhibition, organ size control, and cancer development in mammals. , 2008, Cancer cell.

[21]  Li Li,et al.  Inactivation of YAP oncoprotein by the Hippo pathway is involved in cell contact inhibition and tissue growth control. , 2007, Genes & development.

[22]  D. Goss,et al.  Assembly of b/HLH/z proteins c-Myc, Max, and Mad1 with cognate DNA: importance of protein-protein and protein-DNA interactions. , 2005, Biochemistry.

[23]  G. Viglietto,et al.  Reduced E-cadherin expression contributes to the loss of p27kip1-mediated mechanism of contact inhibition in thyroid anaplastic carcinomas. , 2005, Carcinogenesis.

[24]  Chul-hak Yang,et al.  Determination of binding constant of transcription factor myc-max/max-max and E-box DNA: the effect of inhibitors on the binding. , 2004, Biochimica et biophysica acta.

[25]  James M. Roberts,et al.  CDK inhibitors: positive and negative regulators of G1-phase progression. , 1999, Genes & development.

[26]  S. Shurtleff,et al.  Overexpression of mouse D-type cyclins accelerates G1 phase in rodent fibroblasts. , 1993, Genes & development.

[27]  G. Sonenshein,et al.  Regulation of c-myc transcription and mRNA abundance by serum growth factors and cell contact. , 1986, The Journal of biological chemistry.

[28]  P. Nowell,et al.  Sequential expression of protooncogenes during lectin-stimulated mitogenesis of normal human lymphocytes. , 1986, Proceedings of the National Academy of Sciences of the United States of America.

[29]  H. Varmus,et al.  Amplification of N-myc in untreated human neuroblastomas correlates with advanced disease stage. , 1984, Science.

[30]  M. Abercrombie,et al.  Contact inhibition and malignancy , 1979, Nature.

[31]  S. Carter.  Tissue Homeostasis and the Biological Basis of Cancer , 1968, Nature.

[32]  H. Eagle,et al.  Growth Regulatory Effects of Cellular Interaction , 1967, Nature.

[33]  Heping Yang,et al.  AUTOIMMUNE, CHOLESTATIC AND BILIARY DISEASE Switch from Mnt-Max to Myc-Max Induces p53 and Cyclin D1 Expression and Apoptosis During Cholestasis in Mouse and Human Hepatocytes , 2009 .