Expression of T-cadherin in Basal keratinocytes of skin.

T-cadherin is a unique member of the cadherin superfamily that shares the ectodomain organization with classical cadherins, but lacks both transmembrane and cytoplasmic regions and is instead anchored to the plasma membrane through a glycosyl-phosphatidylinositol (GPI) moiety. The function of T-cadherin has not been revealed yet. The special structure of T-cadherin might endow this molecule with specific intracellular targeting properties and functions that are distinct from classical cadherins. T-cadherin was originally cloned from chicken embryo brain and then was also found in mouse and human nervous and cardiovascular systems; however, T-cadherin in the keratinocytes and skin tissue is still an unknown area that remains to be explored. To test whether the unusual truncated T-cadherin is expressed in keratinocytes, we performed the reverse transcriptase-polymerase chain reaction of T-cadherin, as well as several classical cadherins (E-, P-, and N-cadherin), on the mouse keratinocyte cell line Pam212, fibroblast NIH3T3, and melanoma cell B16. The result indicated that mouse keratinocytes expressed the mRNA of truncated T-cadherin apart from classical cadherins, E-, and P-cadherin. To confirm the expression of T-cadherin in mouse keratinocytes, immunocytochemistry staining was carried out on Pam212 cells by using rabbit anti-T-cadherin antibody and rat antimouse E- and P-cadherin antibody. The result of immunofluorescence staining proved that T-cadherin was expressed in mouse keratinocytes. In order to analyze the distribution patterns of T-cadherin and classical cadherins on the keratinocytes, 3D scanning was performed by using a confocal microscope. From the Z-sections and XZ-sections, it was clearly demonstrated that T-cadherin was distributed diffusely on the whole cell surface, while E- and P-cadherin were concentrated on the cell-cell contacts. To examine the expression and the localization of T-cadherin on skin tissue, the frozen sections of the mouse back skin were immunohistochemically labeled by using anti-T-cadherin antibody. It was found that T-cadherin was intensively expressed only on the basal cell layer of the mouse skin. Apart from mouse keratinocytes and mouse skin, we further examined the expression of T-cadherin in human keratinocytes and human skin by western blot, immunocytochemistry, and immunohistochemistry staining. The same results were achieved with human samples. In this study, we found and verified that T-cadherin was expressed on the mouse and human keratinocytes and specifically localized on the basal cell layer of skin. The nature of T-cadherin function and its mechanism of localization at the basal cell layer of skin are important issues to be addressed concerning this unique member of the cadherin family and its physiologic and pathologic roles in the skin.