Loss of protein phosphatase 6 in mouse keratinocytes increases susceptibility to ultraviolet-B-induced carcinogenesis

Cancer Lett. 2015 Sep 1;365(2):223-8. doi: 10.1016/j.canlet.2015.05.022. Epub 2015 Jun 5.


We previously reported that deficiency in the gene encoding the catalytic subunit of protein phosphatase 6 (Ppp6c) predisposes mouse skin tissue to papilloma formation initiated by DMBA. Here, we demonstrate that Ppp6c loss acts as a tumor promoter in UVB-induced squamous cell carcinogenesis. Following UVB irradiation, mice with Ppp6c-deficient keratinocytes showed a higher incidence of skin squamous cell carcinoma than did control mice. Time course experiments showed that following UVB irradiation, Ppp6c-deficient keratinocytes upregulated expression of p53, PUMA, BAX, and cleaved caspase-3 proteins. UVB-induced tumors in Ppp6c-deficient keratinocytes exhibited a high frequency of both p53- and γH2AX-positive cells, suggestive of DNA damage. Epidemiological and molecular data strongly suggest that UVB from sunlight induces p53 gene mutations in keratinocytes and is the primary causative agent of human skin cancers. Our analysis suggests that PP6 deficiency underlies molecular events that drive outgrowth of initiated keratinocytes harboring UVB-induced mutated p53. Understanding PP6 function in preventing UV-induced tumorigenesis could suggest strategies to prevent and treat this condition.

Keywords: PUMA; Protein phosphatase; UV-induced carcinogenesis; apoptosis; p53; γH2AX.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / radiation effects
  • Apoptosis Regulatory Proteins / biosynthesis
  • Carcinogenesis / genetics
  • Carcinogenesis / radiation effects*
  • Carcinoma, Squamous Cell / genetics*
  • Caspase 3 / metabolism
  • Cell Proliferation
  • DNA Damage / genetics
  • Histones / biosynthesis
  • Keratinocytes / metabolism*
  • Mice
  • Mice, Knockout
  • Phosphoprotein Phosphatases / genetics*
  • Skin / pathology
  • Skin / radiation effects
  • Tumor Suppressor Protein p53 / biosynthesis
  • Tumor Suppressor Proteins / biosynthesis
  • Ultraviolet Rays / adverse effects*
  • bcl-2-Associated X Protein / biosynthesis


  • Apoptosis Regulatory Proteins
  • Histones
  • PUMA protein, mouse
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • bcl-2-Associated X Protein
  • gamma-H2AX protein, mouse
  • Phosphoprotein Phosphatases
  • protein phosphatase 6
  • Caspase 3