Expression of lumican, a small leucine-rich proteoglycan with antitumour activity, in human malignant melanoma

Background. The family of small leucine-rich proteoglycans (SLRPs), which includes decorin, lumican, biglycan and fibromodulin, constitutes an abundant component of the skin extracellular matrix. We previously demonstrated that human lumican inhibits melanoma growth and progression in a mouse experimental model, by regulating cell migration, proliferation and apoptosis. Aim. The aim of this study was to investigate the expression of lumican and decorin in human malignant melanoma and adjacent peritumoral tissue, to understand better their role in the control of growth and invasion of human melanoma. Methods. Expression of both proteoglycans was studied by immunohistochemistry using specific antibodies in 34 malignant melanomas, 12 Hutchinson's melanotic freckles and 4 cutaneous metastatic melanomas. Results. We showed that lumican and decorin are located in the dermis and in the peritumoral stroma of malignant melanoma, but are not found in melanoma cells or dense tumour tissue. In the healthy dermis, distant from the tumour, the increasing ratio of lumican to decorin was inversely correlated with the proliferation of the tumour cells ( P = 0.035). The comparison of the level of expression of lumican protein in superficial vs. nodular subtypes of malignant melanomas showed a decrease of lumican but not decorin in the peritumoral stroma of nodular subtypes. In the peritumoral stroma, the level of expression of lumican but not decorin decreased significantly ( P = 0.016) with increasing Clark levels. In addition, immunocytochemical and reverse transcription PCR analyses of malignant melanoma cell lines ( A-375, HT-144) and of MRC-5 and dermal fibroblasts from healthy donors in vitro confirmed that dermal fibroblasts are responsible for lumican and decorin synthesis in skin. Conclusions. Lumican may regulate vertical progression of human malignant melanoma, but further study is necessary to clarify the antitumour mechanism and the downstream signal transduction pathways involved.