Carcinogenesis Advance Access published online on April 21, 2009
Carcinogenesis, doi:10.1093/carcin/bgp098
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Published by Oxford University Press 2009.
Novel variants of muscle calpain 3 identified in human melanoma cells: cisplatin-induced changes in vitro and differential expression in melanocytic lesions
1 Dept. Physiopathology, Experimental Medicine and Public Health, Sec. General Pathology, University of Siena, 53100 Siena - Italy
2 Dept. Human Pathology and Oncology, Sec. Pathological Anatomy, University of Siena
3 Dept. Clinical Medicine and Immunological Sciences, Sec. Dermatology, University of Siena
* Corresponding author: Prof. Emilia Maellaro, University of Siena, Dept. Physiopathology, Experimental Medicine and Public Health, via A. Moro – 53100 Siena (Italy), e-mail: maellaro{at}unisi.it, tel.: +39 0577 234006, fax: +39 0577 234009
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 which 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 pro-apoptotic 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 pre-apoptotic cells an increase of both transcription and (auto)proteolytic 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 down-regulated, compared to 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 pro-apoptotic role in melanoma cells and its down-regulation, as observed in highly aggressive lesions, could contribute to melanoma progression.
Key Words: Calpain 3 • Apoptosis • Cisplatin • Melanoma cells • Melanocytic lesions
Received January 15, 2009; revised March 27, 2009; accepted April 16, 2009.