Non-melanoma skin cancer, the most common neoplasia after solid organ transplantation, causes serious morbidity and mortality and is related to sun exposure. Cyclosporin A (CsA) has been used widely to prevent rejection in organ transplantation. The mechanism of CsA action in causing cancer was thought to be well understood via immunosuppression. Here, we show that CsA promotes primary skin tumor growth in immune-deficient mice. CsA treatment at therapeutic plasma concentrations promotes growth and survival from removal of extracellular matrix or UVB radiation. CsA treatment enhances AKT activation following serum treatment and UVB radiation. Furthermore we found that PTEN expression, the negative regulator of AKT activation, is reduced significantly upon CsA treatment in human HaCaT and A431 cells and in mouse skin in vivo. Accordingly, the enhanced AKT activation in CsA-treated cells upon UVB radiation is observed in PTEN knockdown keratinocytes. CsA-induced PTEN suppression is critical for increased AKT activation. Inhibition of AKT activation abolishes CsA-promoted growth and survival, indicating that AKT hyperactivation is essential for the enhanced growth and survival of CsA-treated cells. In addition, mTOR signaling as a known AKT downstream target is required for CsA-enhanced growth and survival. Taken together, we have identified PTEN/AKT pathway as new molecular targets of CsA in epidermal keratinocytes, suggesting a previously unknown mechanism in CsA-enhanced skin carcinogenesis. Our findings challenge assumptions about how CsA-associated tumors arise in skin.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 341.

©2010 American Association for Cancer Research
2010