Immunohistochemical analysis of the mammalian target of rapamycin signalling pathway in extramammary Paget's disease

Background We have previously observed that persistent activation of the serine/threonine kinase, protein kinase B (AKT) is a frequent event in extramammary Paget's disease (EMPD). AKT promotes cell proliferation by its ability to coordinate mitogenic signalling with energy- and nutrient-sensing pathways that control protein synthesis through the atypical serine/threonine kinase, mammalian target of rapamycin (mTOR). CDK2, a member of the serine/threonine kinase family of cyclin-dependent kinases, is a key regulator of G(1)-S cell cycle progression, and has recently been shown to be one of the targets of AKT. The AKT-mTOR-p70 ribosomal protein S6 kinase (p70S6K) pathway has been described in some human malignancies, but not in EMPD. Objective To investigate the immunohistochemical staining of the AKT-mTOR-p70S6K pathway in EMPD and to evaluate the relationships among the components. Methods Samples of primary EMPD tissue were subjected to immunohistological staining with phosphorylated (p)-AKT, p-mTOR, p-4E-binding protein 1 (p-4EBP1), p-p70S6K/S6K1, p-ribosomal protein S6 (p-S6) and CDK2. Ten normal skin samples served as a control. Results Of the 32 EMPD tissue samples, 29, 27, 26, 29, 26 and 32 samples were positive for p-AKT, p-mTOR, p-4EBP1, p-p70S6K/S6K1, p-S6 and CDK2 staining, respectively. All these cell signalling molecules showed higher positivity in invasive EMPD than in EMPD in situ. There were significant correlations between p-AKT, p-mTOR, p-4EBP1, p-p70S6K/S6K1 and p-S6 and CDK2. Conclusions The activation of the AKT-mTOR-p70S6K pathway may play an important role in the pathogenesis of EMPD. The high expression of the components of the pathway was highly correlated with CDK2 expression, suggesting that the AKT/mTOR pathway may induce the malignant transition through CDK2 in EMPD. The AKT-mTOR-p70S6K pathway might be a potential therapeutic target in EMPD.