Aberrant Expression of the Maspin Gene Associated with Epigenetic Modification in Melanoma Cells

Abstract

Maspin, a mammary serine protease inhibitor, was originally reported to be a tumor suppressor gene in breast and prostate cancers. The expression pattern of the maspin gene differs among cancer types and normal tissue however, and its significance as a tumor suppressor has been questioned. In this study, maspin expression and/or allele-specific methylation status were investigated in five melanoma cell lines and a normal human epidermal melanocyte (NHEM) cell line, and 80 surgically resected tumors (40 melanomas and 40 melanocytic nevi). One (HMV-I) of five melanoma cell lines overexpressed maspin protein whereas the remaining four melanoma cell lines and NHEM did not. The 19 CpG sites of the maspin promoter region were extensively hypomethylated in HMV-I, a maspin-positive cell line, and those of the remaining four melanoma and NHEM cell lines were hypermethylated. Furthermore, maspin-negative cell lines exhibited activation after treatment with 5-aza-2'-deoxycytidine, a DNA demethylating agent. Immunoreactivity for maspin was negative in normal skin melanocytes and 40 melanocytic nevi, but five (12.5%) of 40 melanomas were positive. The methylation status judged by the methylation-specific PCR method was inversely correlated with maspin protein expression in vitro and in vivo. These results suggest that maspin expression in normal skin melanocytes and melanocytic nevi may be repressed in a cell-type-specific manner, whereas maspin is expressed aberrantly in a subset of melanoma cells by epigenetic modification. Further investigations are required to determine the significance of aberrant maspin expression.

Maspin expression and melanoma progression: a matter of sub-cellular localization

“…However, a high degree of variability was reported by different groups as for the frequency of protein expression, with maspin positivity ranging from 0 to 94% in primary tumors, and from 0 to 100% in metastases. 27,[29][30][31] Interestingly, when maspin expression was examined in clinical samples from various cancers, with tumor cells being analyzed in the context of host, stromal, and environmental influences, conflicting results were obtained, and the tumor-suppressive activity of maspin has been questioned. From these studies, it is becoming evident that not only protein expression, but also its sub-cellular localization, and consequently its putative interactors and functions, may influence its association with disease outcome and patient prognosis.…”

“…Although studies performed on melanoma tissues did not specifically investigate the sub-cellular location of maspin, published data report the protein as nuclear, 31 mixed nuclear and cytoplasmic, 30 and purely cytoplasmic. 29 To the best of our knowledge, this is the first study aimed at specifically examining the association of maspin expression and sub-cellular localization with disease progression in a large cohort of melanoma patients.…”

“…Wada et al found maspin in 38% thin primary melanomas but not in nevi nor in thick primaries. 29 The staining was reported to be cytoplasmic. The group of Vereecken observed a mixed nuclear-cytoplasmic maspin expression in 31% nevi, 100% thin and 92% thick primary melanomas, and 70% metastases.…”

Protease activated receptor-1 inhibits the Maspin tumor-suppressor gene to determine the melanoma metastatic phenotype

“…Previous reports have shown that early hypermethylation of the Maspin promoter might play a role in silencing Maspin. In addition, loss of Maspin was shown to correlate with increased tumor thickness (15)(16)(17).…”

“…Denk and colleagues found that metastatic melanoma cells had decreased expression levels of Maspin compared with normal human epidermal melanocytes (15). Moreover, Maspin expression is lost with increased tumor thickness in clinical specimens as the tumor progresses from nonmetastatic to metastatic melanoma (16,17). Previous reports have shown that early hypermethylation of the Maspin promoter might play a role in silencing Maspin.…”