Abstract
Protein kinase C (PKC)-δ is proapoptotic in human keratinocytes, and is downregulated or inactivated in keratinocytes expressing the activated Ha-ras oncogene, making it a candidate tumor suppressor gene for squamous cell carcinoma (SCC). We evaluated the significance of PKC-δ loss in transformed human keratinocytes using tumorigenic HaCaT Ras II-4 cells that have significantly reduced PKC-δ levels. Re-expression of PKC-δ by retrovirus transduction caused an increase in apoptosis and growth inhibition in culture. The growth inhibition induced by PKC-δ could be partially reversed by Bcl-xL expression, indicating that apoptosis was in part responsible for PKC-δ-induced growth inhibition. PKC-δ re-expression suppressed the tumorigenicity of HaCaT Ras II-4 cells in nude mice (P < 0.05), and the small tumors that did form contained elevated levels of activated caspase-3, indicating increased apoptosis. In addition, we found that 29% (12/42) of human Bowen's disease (squamous carcinoma in situ) or SCC cases had absent or reduced PKC-δ when compared to the surrounding normal epidermis. These results indicate that PKC-δ inhibits transformed keratinocyte growth by inducing apoptosis, and that PKC-δ may function as a tumor suppressor in human SCCs where its loss in cells harboring activated ras could provide a growth advantage by conferring resistance to apoptosis.
Original language | English (US) |
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Pages (from-to) | 378-386 |
Number of pages | 9 |
Journal | Oncogene |
Volume | 25 |
Issue number | 3 |
DOIs | |
State | Published - Jan 19 2006 |
Funding
We thank all members of the Skin Cancer Research Program for their help with this project, especially Jeffrey Panella for constructing the Ras (Q61) retroviral vector. We also thank Dr Divaker Choubey (Loyola University Medical Center, May-wood, IL, USA) for furnishing the Ras (Q61) cDNA, and Dr Norbert Fusenig (German Cancer Research Center, Heidelberg, Germany) and Mihaela Skobe (Harvard School of Medicine, Boston, MA, USA) for providing HaCaT cells and HaCaT Ras clones. This work was supported in part by a grant from the Potts Foundation (MFD), and NIH grants CA83784 (MFD) and AR47814 (BJN).
Keywords
- Protein kinase C-δ
- Skin cancer
- Squamous cell carcinoma
- Tumor suppressor gene
ASJC Scopus subject areas
- Genetics
- Molecular Biology
- Cancer Research