| Research Abstract |
We established a metallothionein-I (MT)/RET transgenic mouse line in which skin melanosis, benign melanocytic tumor and malignant melanoma develop stepwise. Malignant melanoma cells but not benign melanocytic tumor cells had metastatic ability in transgenic mice. In this study, we investigated the expression of several matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) including MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MT1-MMP, TIMP-1 and TIMP-2 in these tumors. Western and northern blot analyses revealed that malignant transformation of melanocytic tumors developed in MT/RET transgenic mice accompanied upregulation of MMP-9 and downregulation of TIMP-2. Expression of other MMP and TIMP genes examined was very low or undetectable in both benign and malignant tumors. Since activation of MMP-9 in malignant tumors was shown by gelatin zymography, these results suggest that imbalance of expression of the MMP-9 and TIMP-2 genes might be associated with metastatic ability of melanoma cells developed in MT/RET transgenic mice.
In addition, we generated transgenic mice by introducing the RET-MEN2A gene fused to Moloney murine leukemia virus long terminal repeat. Expression of the transgene and its product was detected at variable levels in a variety of tissues including thyroid, heart, liver, colon, parotid gland and brain. All of 29 mice analyzed developed thyroid C cell hyperplasia or medullary carcinoma, accompanying high levels of serum calcitonim. Moreover, development of mammary or parotid gland adenocarcinoma was observed in half of the transgenic mice. Mammary carcinoma but not thyroid carcinoma often metastasized to lung. Thus, this transgenic mouse line could provide a useful system to analyze the genes responsible for metastasis.
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