Carcinogenesis Advance Access originally published online on April 21, 2009
Carcinogenesis 2009 30(6):960-967; 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
Department of Physiopathology, Experimental Medicine and Public Health, Section of General Pathology
1 Department of Human Pathology and Oncology, Section of Pathological Anatomy
2 Department of Clinical Medicine and Immunological Sciences, Section of Dermatology, University of Siena, via A. Moro, 53100 Siena, Italy
* To whom correspondence should be addressed. Tel: +39 0577 234006; Fax: +39 0577 234009; Email: maellaro{at}unisi.it
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.
Abbreviations: cDNA, complementary DNA; EDTA, ethylenediaminetetraacetic acid; mRNA, messenger RNA; NLS, nuclear localization sequence; PBS, phosphate-buffered saline; PCR, polymerase chain reaction; RGPM, radial growth phase melanoma; VGPM, vertical growth phase melanoma
Received January 15, 2009; revised March 27, 2009; accepted April 16, 2009.