Heat shock protein 27 is expressed in normal and malignant human melanocytes in vivo

Background: Heat shock proteins (HSPs) are a family of highly conserved proteins found ubiquitously in mammalian cells, believed to be regulators of normal cell physiology and the cellular stress response. In addition, the small 27-kDa heat shock protein (HSP27) has previously been found to be a differentiation marker for keratinocytes and a prognostic marker associated with increased survival in certain cancerous tumors. Methods: Using immunohistochemistry on routinely processed paraffin sections, we examined skin biopsies from 15 invasive melanomas, 13 intradermal nevi, and two compound nevi immunostained with a mouse monoclonal antibody to HSP27. In addition, cultured melanocytes were heat stressed at 45°C for 1 h and then fixed and immunostained in order to localize HSP27 expression intracellularly. Results: We found cytoplasmic and strong perinuclear staining of HSP27 in melanocytes in normal skin, in melanomas, and in nevi. Nuclear reactivity was absent. In addition, in cultured non-malignant melanocytes, HSP27 expression relocated from the cytoplasm to the nucleus with heat stress. Conclusions: To our knowledge, this investigation is the first to demonstrate that HSP27 is expressed in melanocytes in normal skin, in nevi, and in non-malignant cultured melanocytes.