Down-regulated melanoma differentiation associated gene (mda-7) expression in human melanomas

Abstract

The melanoma differentiation associated gene-7 (mda-7) has a potential inhibitory role in melanoma progression, although the mechanisms underlying this effect are still unknown. mda-7 mRNA has been found to be present at higher levels in cultured normal melanocytes compared with metastatic melanoma cell lines. Furthermore, levels of mda-7 message have shown an inverse correlation with melanoma progression in human tumor samples, suggesting that mda-7 may be a novel tumor suppressor gene. We have designed this study to investigate MDA-7 protein expression in different stages of melanoma progression and to examine its antiproliferative effects in vitro. Our data demonstrate that MDA-7 protein can be found in normal melanocytes and early stage melanomas. It is also observed in smooth muscle cells in the skin. However, in keeping with a possible role as a tumor suppressor, MDA-7 expression is decreased in more advanced melanomas, with nearly undetectable levels in metastatic disease. We also investigated antitumor effects of overexpressed MDA-7 on human melanoma cells in vitro. A feature of malignant tumors that is considered therapeutically exploitable is the loss of cellular differentiation. This has lead to a search for tissue-specific differentiation factors that might be reintroduced into tumors in order to modify their growth and ability to metastasize. In the case of melanoma, several unique genes have been isolated by Jiang et al. 1 from a melanoma cell line induced to differentiate by interferon-␤ and mezerein. One of the most interesting and promising of these genes is the melanoma differentiation associated gene-7 (mda-7). Since its initial isolation from melanoma cells and subsequent molecular characterization, the mda-7 gene and MDA-7 protein have been studied in numerous other tumor types, some of which have included carcinoma of the lung, breast, prostate and cervix. 2 Experiments using an adenovirus/mda-7 vector construct (Ad-mda-7) to infect normal and malignant cells have consistently demonstrated growth-inhibitory effects on various tumor types, but no inhibitory effects on normal cells. 3,4 These findings have prompted the development of the Ad-mda-7 as a potential therapeutic agent, and plans for a phase I clinical trial are under way. Although the initial description of mda-7 occurred in melanoma, most of the clinically relevant research has focused on the more prevalent malignancies. Our results demonstrate that Ad-mda-7 induces apoptosis and G2/M cell cycle arrest in melanoma cellsOur laboratory has an ongoing interest in the development of prognostic tools and therapeutic interventions for advanced melanoma. We have therefore undertaken a study to better define the significance of MDA-7 in this disease. We describe in this paper our data from human tumors and cell lines demonstrating that MDA-7 protein can be found in normal melanocytes, early stage melanomas and smooth muscle cells. However, in keeping with a role as a tumor suppressor, MDA-7 expression is decreased in more advanced melanom...

Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells

“…Forced expression of E-cadherin in cultured cells, and transgenic mouse models of carcinogenesis, results in impaired metastatic and invasive phenotypes. 33,34 Here, we show that Herceptin, alone and in combination with Ad-mda7, is able to upregulate specifically E-cadherin in Her-2 þ cells, and to sequester its binding partner b-catenin to the plasma membrane (Figure 5a and b, left panel), thereby inhibiting its nuclear translocation and inhibiting b-catenin-induced transcriptional activation of cell migration and cell proliferation signals.…”

“…Differences in tumor size were analyzed for significance by the Student's t-test. Enhanced in vitro growth inhibitory and cytotoxic activity of Ad-mda7 and Herceptin in Her-2 þ breast cancer cells The antiproliferative effects of Ad-mda7 in various cancer cell types have been demonstrated in previous studies; [16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34]36 and the relevance of these findings to the clinical setting is supported by in vivo lung and breast xenograft models. 17,21 To corroborate that the Her-2 receptors expressed by the breast cancer cells are functional, we evaluated cell death in MDA-MB-453 and MCF-7 lines treated with increasing amounts of Herceptin (0-100 mg/ ml).…”

The cancer growth suppressing gene mda-7 induces apoptosis selectively in human melanoma cells

“…Temporal expression of mda-7 in normal human melanocytes and melanoma cells following Ad.mda-7 infection Mda-7 is expressed de novo in early passage normal and immortal FM516 melanocytes (Jiang et al, 1995a;Ekmekcioglu et al, 2001;Huang et al, 2001). In contrast, mda-7 is not detected, or is present at reduced levels, in most metastatic melanoma cell lines and in metastatic melanoma lesions from patients (Jiang et al, 1995a;Ekmekcioglu et al, 2001;Huang et al, 2001).…”

“…In contrast, mda-7 is not detected, or is present at reduced levels, in most metastatic melanoma cell lines and in metastatic melanoma lesions from patients (Jiang et al, 1995a;Ekmekcioglu et al, 2001;Huang et al, 2001). Previous studies document that treatment with IFNb+MEZ for 24 h results in growth suppression and induction or enhanced mda-7 mRNA expression in vitro in both primary and metastatic human melanoma cell lines (Jiang et al, 1995a;Huang et al, 2001).…”

Gene Therapy Progress and Prospects: cancer gene therapy using tumour suppressor genes

“…Subsequently, it was shown that adenoviral delivery of the mda-7 gene (Ad mda-7) is able to induce apoptosis in malignant cells but not normal epithelial cells in both melanoma 63 and NSCLC. 64 Work in the past 2 years has extended knowledge on this gene.…”