Axl promotes cutaneous squamous cell carcinoma survival through negative regulation of pro-apoptotic Bcl-2 family members

J Invest Dermatol. 2011 Feb;131(2):509-17. doi: 10.1038/jid.2010.326. Epub 2010 Nov 11.

Abstract

Expression of Axl, a receptor tyrosine kinase, is increased in cutaneous squamous cell carcinoma (SCC). Examination of a series of cutaneous SCC tumors revealed positive phospho-Akt (P-Akt) staining accompanied by weak TUNEL staining in Axl-positive tumors, suggesting an anti-apoptotic role for Axl in SCC survival. The role of Axl in UV-induced apoptosis was investigated in a cutaneous SCC cell line using retroviral short hairpin RNA sequences enabling stable Axl knock-down. We show that, although Axl knock-down has no effect on cell proliferation, it sensitizes cells to UV-induced apoptosis through increased activation of the pro-apoptotic protein Bad, a change in the conformation of Bax and Bak, release of cytochrome c into the cytosol, and activation of caspases. These events are accompanied by faster Akt dephosphorylation in UV-treated Axl knock-down cells and correlate with the degree of Axl knock-down. Treatment with the pan-caspase inhibitor zVAD-fmk partially rescued cells from UV-induced apoptosis but did not affect Bid cleavage or cytochrome c release, suggesting that cells die via the mitochondrial-mediated pathway. Thus, Axl confers resistance of SCC cells to apoptosis and displays potential as a target for therapeutic intervention in cutaneous SCC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / physiology
  • Apoptosis / radiation effects
  • Axl Receptor Tyrosine Kinase
  • Carcinoma, Squamous Cell / metabolism*
  • Carcinoma, Squamous Cell / pathology*
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Survival
  • Cytochromes c / metabolism
  • Humans
  • PTEN Phosphohydrolase / metabolism
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Receptor Protein-Tyrosine Kinases / metabolism*
  • Signal Transduction / physiology
  • Skin Neoplasms / metabolism*
  • Skin Neoplasms / pathology*
  • Ultraviolet Rays / adverse effects
  • bcl-2 Homologous Antagonist-Killer Protein / metabolism
  • bcl-2-Associated X Protein / metabolism
  • bcl-Associated Death Protein / metabolism

Substances

  • BAD protein, human
  • BAK1 protein, human
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2 Homologous Antagonist-Killer Protein
  • bcl-2-Associated X Protein
  • bcl-Associated Death Protein
  • Cytochromes c
  • Receptor Protein-Tyrosine Kinases
  • Proto-Oncogene Proteins c-akt
  • PTEN Phosphohydrolase
  • PTEN protein, human
  • Axl Receptor Tyrosine Kinase
  • AXL protein, human