The altered expression of α-smooth muscle actin in basal cell epithelioma and its surrounding stroma: with special reference to proliferating cell nuclear antigen expression and adenoid differentiation

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Abstract
Summary Altered expression of α-smooth muscle actin (α-SMA) is known to indicate the morphological, tumorigenic and immunological changes occurring in tumour and stromal cells. The purpose of this study was to analyse the dynamics of α-SMA expression in human basal cell epithelioma (BCE) cells and their surrounding stromal cells, in the process of differentiation towards cutaneous appendages such as hair, sebaceous, apocrine and eccrine glands. Using anti-α-SMA specific monoclonal antibody (MAb), 17 of 36 BCEs (47%) were shown to express α-SMA, despite the usual absence of α-SMA in all eukaryotic cells except muscle cells. Solid, adenoid and sclerosing types of BCE expressed α-SMA more frequently, and in greater amount, than cystic, keratotic and superficial types. Furthermore, the expression of α-SMA in BCE cells significantly paralleled the expression of proliferating cell nuclear antigen (PCNA) in these cells. Thus, the altered expression of α-SMA may reflect the growing properties of BCE cells under the specific cellular regulations for differentiation. In addition, we have found anti-α-SMA MAb-positive fibroblasts with smooth muscle differentiation (myofibroblasts) in desmoplastic stroma surrounding BCE nests in 13 of 36 cases (36%). Coincidental expression of α-SMA in both BCE cells and stromal cells was found in nine of the 13 cases (69%), indicating the possibility of the induction of myofibroblastic stromal changes in surrounding tissues by cytokines secreted from BCE cells [e.g. basic fibroblast growth factor (bFGF)-like factor].

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