Maspin expression inversely correlates with breast tumor progression in MMTV/TGF-alpha transgenic mouse model

Maspin is a novel serine protease inhibitor (serpin) with tumor suppressive activity. To date, despite the mounting evidence implicating the potential diagnostic/prognostic and therapeutic value of maspin in breast and prosta te carcinoma, the lack of a suitable animal model hampers the in vivo inves tigation on the role of maspin at different stages of tumor progression. In this study, we used MMTV/TGF-alpha transgenic mouse model to study the exp ression profile of maspin in mammary tumor progression. Histopathological e xaminations of MMTV/TGF-alpha transgenic mice revealed TGF-alpha expression leading to hyperproliferation, hyperplasia, and occasional carcinoma in ma mmary gland. Interestingly, when MMTV/TGF-alpha transgenic mice were breed to homozygocity, they also developed characteristic skin papillomas. Immuno histochemistry analysis of maspin expression in the breast tissues of TGF-o c transgenic mice showed a direct correlation between down-regulation of ma spin expression and tumor progression. The loss of maspin expression was co ncomitant with the critical transition from carcinoma in situ to invasive c arcinoma. Subsequent in-situ hybridization analyses suggest that the down-r egulation of maspin expression is primarily a transcriptional event. This d ata is consistent with the tumor suppressive role of maspin. Furthermore, o ur data suggests that MMTV/TGF-alpha transgenic mouse model is advantageous for in vivo evaluation of both the expression and the biological function of maspin during the slow multi-stage carcinogenesis of mammary gland.