P2X5 and P2X7 receptors in human warts and CIN-612 organotypic raft cultures of human papillomavirus infected keratinocytes

Purinergic receptors, which bind adenosine 5′-triphosphate (ATP), are expressed on human cutaneous keratinocytes and in squamous cell carcinomas. Studies on normal human epidermis and primary keratinocyte cultures have suggested that P2X5 receptors are likely to be involved in keratinocyte differentiation and P2X7 receptors are likely to be part of the machinery of end stage terminal differentiation/apoptosis of keratinocytes. P2X7 receptor agonists can significantly reduce primary keratinocyte cell numbers in culture. Human papillomaviruses are increasingly recognised as important human carcinogens in the development of non-melanoma skin cancers. In our study, immunohistochemical analysis for P2X5 and P2X7 receptors was performed on paraffin sections of normal human skin, warts, raft cultures of normal human keratinocytes and raft cultures of CIN 612 cells, a model of keratinocytes infected with human papillomavirus type 31. In warts there was up-regulation of the expression of P2X5 receptors. A similar pattern was seen in the CIN 612 raft cultures. Both P2X5 and P2X7 receptors were found in the nuclei of koilocytes, abnormal keratinocytes characteristic of human papillomavirus infection. P2X5 and P2X7 receptors may provide a new focus for therapeutic research into treatments for warts because these receptors can induce cell differentiation and cell death.