Expression of smooth muscle-specific proteins in myoepithelium and stromal myofibroblasts of normal and malignant human breast tissue.

TLDR

The dual nature of myoepithelial cells and the phenotypic transition of fibroblasts to myofibroblasts exemplify differentiated cell plasticity. Immunofluorescence microscopy of frozen breast tissue sections with antibodies against smooth muscle and epithelial markers revealed that myoepithelial cells coexpress both marker types while luminal cells express only epithelial markers. Stromal myofibroblasts express all smooth muscle markers except high‑molecular‑weight caldesmon, and both myoepithelial cells and myofibroblasts display heterogeneous smooth‑muscle protein expression, indicating coordinated marker expression while preserving their distinct identities.

Abstract

The expression of several differentiation markers in normal human mammary gland myoepithelium and in certain stromal fibroblasts ("myofibroblasts") associated with breast carcinomas was studied by immunofluorescence microscopy of frozen sections. Several antibodies to smooth muscle-specific proteins (smooth muscle alpha-actin, smooth muscle myosin heavy chains, calponin, alpha 1-integrin, and high molecular weight caldesmon) and to epithelial-specific proteins (cytokeratins, E-cadherin, and desmoplakin) were used to show that myoepithelial cells concomitantly express epithelial and smooth muscle markers whereas adjacent luminal cells express only epithelial markers. The same antibodies were used to establish that stromal myofibroblasts exhibit smooth muscle phenotypic properties characterized by the expression of all the smooth muscle markers examined except for high molecular weight caldesmon. In addition, both myoepithelium and myofibroblasts show a significant degree of heterogeneity in smooth muscle protein expression. Thus, myoepithelial cells and stromal myofibroblasts are epithelial and mesenchymal cells, respectively, which coordinately express a set of smooth muscle markers while maintaining their specific original features. The dual nature of myoepithelial cells and the phenotypic transition of fibroblasts to myofibroblasts are examples of the plasticity of the differentiated cell phenotype.