Nuclear localization of beta-catenin in the hair matrix cells and differentiated keratinocytes.

Beta-catenin is a structural component of adherens junctions and also a downstream effector of Wnt signaling pathway. Beta-catenin has been detected in the adherens junctions in almost all normal tissues including the epidermis. Only in some malignant tumor cells was it found in the cytoplasm and nuclei. Recently pilomatricoma was found to be caused by mutations of amino-terminal segment of beta-catenin, normally involved in phosphorylation-dependent ubiquitin-mediated degradation of the protein. Since nuclear beta-catenin has not been detected in pilomatricoma or any other benign follicular tumors, we investigated localization of beta-catenin in the normal hair follicle, follicular tumor cells, normal and psoriatic epidermis by using immunohistochemical method with a high temperature antigen unmasking technique. The nuclear localization of beta-catenin was detected not only in the matrix cells of follicular tumors including pilomatricoma but also in the normal hair matrix cells and the differentiated keratinocytes of the upper layers of the epidermis. Cell membrane staining of beta-catenin and E-cadherin was decreased in these differentiated keratinocytes. This coincided with the emergence of nuclear beta-catenin. The present immunohistochemical method has revealed hitherto unproven nuclear localization of beta-catenin in hair matrix cells. Our results also provided evidence suggesting that beta-catenin plays an important role in keratinocyte differentiation.