Eccrine sweat glands: expression of transforming growth factor-beta and bone morphogenetic protein type I receptors and their intracellular signalling Smad proteins.

The transforming growth factor-beta superfamily is thought to be involved in the regulation and control of growth and differentiation. These growth factors signal through transmembrane serine/threonine kinase receptors. The activation of type I receptor kinase phosphorylates a family of intracellular signalling proteins called Smads. In the present study, we wanted to localize type I and type II receptors and Smad proteins in human eccrine sweat glands. Expression of transforming growth factor-beta type I receptor was restricted to myoepithelial cells only, whereas bone morphogenetic protein receptor IA was found selectively within the duct epithelium of both the dermal portion and the acrosyringium. Bone morphogenetic protein receptor IB antibody gave a faint staining of secretory epithelium and myoepithelial cells. Smad proteins were identified in different parts of the eccrine sweat gland apparatus. In particular, Smad 1 and Smad 3 were localized within myoepithelial cells, whereas coils were stained weakly for Smad 1 and Smad 3. Smad 3 protein was also expressed by the duct epithelium. Smad 2, Smad 4, Smad 5, Smad 6 and Smad 7 were not identified in eccrine sweat gland epithelia. Our data provide evidence for transforming growth factor-beta/bone morphogenetic protein signalling in the eccrine sweat gland and the selective expression of Smad proteins. Myoepithelial cells and duct cells have been identified as major targets of the transforming growth factor-beta pathway. Possible functions are growth inhibition and control of myoepithelial differentiation.