Differences in metallothionein expression in transplantable mouse mammary tumor lines

In order to elucidate a possible role of metallothionein (MT) in mammary ca rcinogenesis, MT and sex hormone receptor (estrogen receptor, ER; progester one receptor, PR) expressions were investigated immunohistochemically in a transplantable pregnancy-dependent mouse mammary tumor (TPDMT-4) and relate d autonomous tumor sublines (T4-OI96, T4-OI165 and T4-OI320CY) recovered fr om pregnant and virgin DDD mice. TPDMT-4 showed MT expression in tumor cell s, while the expression was less evident in T4-OI165 and T4-OI96 among the autonomous tumor lines; in T4-OI320CY, the MT expression was similar to tha t in TPDMT-4. Chromatographic study of MT contents in the tumor lines confi rmed the results of the immunohistochemical examination. PR and ER were loc alized in the tumor cells of TPDMT-4, but not in those of autonomous tumor sublines. In TPDMT-4, a significant correlation was observed between MT and ER expressions (r = 0.83, P < 0.01), but not between MT and PR expressions (r = 0.26, P > 0.4), also between MT expression and mitotic activity (r = -0.34, P > 0.3). Since T4-OI96 and T4-OI165 are known to be more malignant than T4-OI320CY. the present study indicates a negative correlation between the MT positivity and progression of the transplantable mammary tumor in m ice. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.