Off-target response of a Wip1 chemical inhibitor in skin keratinocytes.

BACKGROUND: The wild type p53 inducible phosphatase (Wip1) plays an important role in modulating not only stress responses by various environmental stresses, but when overexpressed it also impairs the intrinsic tumor surveillance networks that are frequently found in a number of cancers including skin cancers. As a result, using a pharmacological inhibitor of Wip1 has been suggested to be a novel chemotherapeutic approach to recover the innate tumor surveillance in a variety of cancers. OBJECTIVE: We studied the effect of a pharmacological inhibitor of Wip1 in skin keratinocytes, under a ultra-violet (UV) stress condition. METHODS: A human keratinocyte cell line or human epidermal keratinocytes were exposed to UV, with or without the sole commercially available chemical inhibitor of Wip1, CCT007093; subsequently, we determined the diverse stress responses, including apoptosis and the activation of stress signaling. RESULTS: We demonstrate that the Wip1 inhibitor unexpectedly attenuated the UV-mediated apoptotic response in skin keratinocytes, as a consequence of attenuated JNK activation and reduced H2AX phosphorylation in both, skin keratinocytes and a Wip1-null cell model. On the other hand, the loss of Wip1 expression, either by knockout or knockdown in mice or human keratinocytes respectively, promoted apoptosis and potentiated H2AX phosphorylation following UV treatment. Of note, CCT007093 treatment appeared to promote apoptosis in breast cancer cells and skin transformed keratinocytes that ectopically expressed Wip1, demonstrating that the effect of CCT007093 differs based on the level of Wip1 expression. CONCLUSION: Thus, our studies suggest that the development of a more potent and specific Wip1 inhibitor is necessary to achieve the desired chemotherapeutic potential and to avoid off-target effects.