Molecular determinants of Akt-induced keratinocyte transformation

Oncogene. 2006 Feb 23;25(8):1174-85. doi: 10.1038/sj.onc.1209155.

Abstract

The PI3K/PTEN/Akt signaling pathway has emerged in recent years as a main player in human cancers, increasing proliferation and decreasing apoptosis of transformed cells, and thus becoming a potential target for therapeutic intervention. Our previous data have demonstrated that Akt-mediated signaling is of a key relevance in the mouse skin carcinogenesis system, one of the best-known models of experimental carcinogenesis. Here, we investigated the involvement of several pathways as mediators of Akt-induced increased proliferation and tumorigenesis in keratinocytes. Tumors produced by subcutaneous injection of Akt-transformed keratinocytes showed increased Foxo3a phosphorylation, but no major alterations in p21(Cip1/WAF1), p27(Kip1) or mdm2 expression and/or localization. In contrast, we found increased expression and nuclear localization of DeltaNp63, beta-catenin and Lef1. Concomitantly, we also found increased expression of c-myc and CycD1, targets of the beta-catenin/Tcf pathway. Such increase is associated with increased phosphorylation and stabilization of c-myc protein as well as increased translation of c-myc and CycD1 due to mTOR activation. Using immunohistochemistry approaches in samples of oral dysplasias and human head and neck squamous cell carcinomas, we confirmed that increased Akt activation significantly correlates with increased DeltaNp63 and CycD expression, c-myc phosphorylation and nuclear accumulation of beta-catenin. Collectively, these results demonstrate that Akt is able to transform keratinocytes by specific mechanisms involving transcriptional and post-transcriptional processes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Proliferation
  • Cell Transformation, Neoplastic*
  • Cells, Cultured
  • Cyclin D1 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism
  • Female
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors / metabolism
  • Injections, Subcutaneous
  • Keratinocytes / metabolism*
  • Keratinocytes / pathology
  • Lymphoid Enhancer-Binding Factor 1 / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Nude
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Kinases / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Proto-Oncogene Proteins c-mdm2 / metabolism
  • Proto-Oncogene Proteins c-myc / metabolism
  • Signal Transduction
  • Skin Neoplasms / metabolism*
  • TOR Serine-Threonine Kinases
  • Trans-Activators / metabolism
  • beta Catenin / metabolism

Substances

  • Cdkn1a protein, mouse
  • Cyclin-Dependent Kinase Inhibitor p21
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • FoxO3 protein, mouse
  • Lef1 protein, mouse
  • Lymphoid Enhancer-Binding Factor 1
  • Phosphoproteins
  • Proto-Oncogene Proteins c-myc
  • Trans-Activators
  • Trp63 protein, mouse
  • beta Catenin
  • Cyclin D1
  • Cyclin-Dependent Kinase Inhibitor p27
  • Proto-Oncogene Proteins c-mdm2
  • Protein Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Proto-Oncogene Proteins c-akt