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Metallothionein expression in transplantable mouse mammary tumors.

BACKGROUND
The metal binding protein, metallothionein (MT) is involved in various physiological processes. In various human tumors, moreover, MT is reported to play an important role in carcinogenesis.


MATERIALS AND METHODS
MT expression was investigated immunohistochemically and chromatographically in a transplantable pregnancy-dependent mouse mammary tumor (TPDMT-4) and related autonomous tumor sublines (T4-OI320 and -OI320CY).


RESULTS
All tumor lines showed MT expression in the nucleus and/or cytoplasm of tumor cells. However, adenoacanthomatous T4-OI320 whose structure was different histopathologically from the remaining adenocarcinomas showed over-expression of MT in the basal layer of squamous metaplastic nodules. Cell proliferation activity estimated by the BrdU labeling method (BrdU index) was highest in the squamous nodules and correlated with the degree of MT expression (r = 0.96). By contrast, the BrdU index in T4-OI320CY was inversely correlated with the MT index (r = -0.91).


CONCLUSIONS
The present investigation suggests expression of isotype MT in the transplantable mouse mammary tumors which may be involved in the carcinogenesis.