Novel variants of muscle calpain 3 identified in human melanoma cells: cisplatin-induced changes in vitro and differential expression in melanocytic lesions.

Calpains are cysteine proteases comprising members ubiquitously expressed in human tissues and other tissue-specific isoforms. Alterations of calpain 3 (p94), the muscle-specific isoform that contains three peculiar sequences (NS, IS1 and IS2), are strictly associated to the limb-girdle muscular dystrophy type 2A, in which a myonuclear apoptosis has been documented. Our recent demonstration of a proapoptotic role of ubiquitous calpains in drug-induced apoptosis of melanoma cells prompted us to investigate the expression of calpain 3 in human melanoma cell lines undergoing apoptosis and in melanocytic lesions. In melanoma cell lines, we have identified two novel splicing variants of calpain 3 (hMp78 and hMp84): they have an atypical initiation exon and a putative nuclear localization signal, the shorter one lacks IS1 inset and both proteins are extremely unstable. Virtually, both isoforms (prevalently as cleavage forms) are localized in cytoplasm and in nucleoli. In cisplatin-treated preapoptotic cells, an increase of both transcription and autoproteolytic cleavage of the novel variants is observed; the latter event is prevented by the inhibitor of ubiquitous calpains, calpeptin, which is also able to protect from apoptosis. Interestingly, among melanocytic lesions, the expression of these novel variants is significantly downregulated, compared with benign nevi, in the most aggressive ones, i.e. in vertical growth phase melanoma and, even more, in metastatic melanoma cells, characterized by invasiveness properties and usually highly resistant to apoptosis. On the whole, our observations suggest that calpain 3 variants can play a proapoptotic role in melanoma cells and its downregulation, as observed in highly aggressive lesions, could contribute to melanoma progression.

Evaluation of tumour-infiltrating CD4+CD25+FOXP3+ regulatory T cells in human cutaneous benign and atypical naevi, melanomas and melanoma metastases.

BACKGROUND: CD4+CD25+FOXP3+ regulatory T cells (Tregs) are thought to induce immunotolerance in melanoma. They have not yet been investigated in the entire spectrum of melanocytic cutaneous lesions within a tumour site. OBJECTIVES: To evaluate CD4+CD25+FOXP3+ Tregs among tumour-infiltrating lymphocytes in cutaneous melanocytic lesions. METHODS: We analysed 128 lesions (10 benign junctional common naevi, 10 benign compound common naevi, 10 compound Spitz naevi, 10 junctional atypical naevi, 20 compound atypical naevi, 20 radial growth phase melanomas, 30 vertical growth phase melanomas and 18 melanoma metastases). Tregs were identified by CD25-FOXP3 double immunostains. RESULTS: This study indicates that CD4+/CD25+FOXP3+ Tregs are present in all groups of lesions. Junctional atypical naevi, compound atypical naevi and radial growth phase melanomas showed the highest percentages of CD4+CD25+FOXP3+ Tregs (junctional atypical naevi vs. junctional common naevi, compound common naevi, compound Spitz naevi, melanoma metastases: P < 0.0001; junctional atypical naevi vs. vertical growth phase melanomas: P = 0.001; compound atypical naevi vs. junctional common naevi, compound common naevi: P < 0.0001; compound atypical naevi vs. compound Spitz naevi, melanoma metastases: P = 0.002; compound atypical naevi vs. vertical growth phase melanomas: P = 0.02; radial growth phase melanomas vs. junctional common naevi, compound common naevi, compound Spitz naevi, melanoma metastases: P < 0.0001; radial growth phase melanomas vs. vertical growth phase melanomas: P = 0.008). CONCLUSIONS: The strong prevalence of CD25+FOXP3+ Tregs both in junctional and compound atypical naevi and radial growth phase melanomas, suggests that they induce immunotolerance early during melanoma genesis, favouring melanoma growth. Their evaluation within a tumour site could be useful for prognostic and therapeutic purposes.