Mammary serine protease inhibitor (maspin) is a non-inhibitory member of the serine protease inhibitor (serpin) superfamily and is involved in mammary gland development. Loss of maspin expression is commonly observed during breast cancer progression while re-expression of maspin confers tumor suppressive capabilities. Cellular localization of maspin within the cytosol, nucleus, and association in complexes at the plasma membrane confer different properties in cancer cells adding to the complexity of maspin function. The recombinant form of maspin (rMas) when added to growth media of maspin-null cancer cells recapitulates many of the effects of exogenous maspin re-expression including inhibition of invasion through 3D matrices. These effects highlight the potential of rMas for therapeutic development as a novel adjuvant therapy. The aim of this study was to characterize the uptake, processing and distribution of wild-type and mutated forms of rMas in cancer cells. Using the MDA-MB-231, BT549 and Hs578T breast cancer cell lines we demonstrate that rMas is directly internalized by cancer cells and degraded rapidly. Time-lapse confocal microscopy using Alexa Fluor 594 labeled rMas and nuclear/cytoplasmic extraction of rMas following cellular uptake demonstrate that rMas is predominantly localized and processed in the cytosol. Wild-type rMas inhibited cancer cell invasion through collagen based matrices and this effect was independent of nuclear localization. Interestingly, site-directed mutagenesis of rMas to induce reported polymorphisms (Ile to Val 66, Pro to Ser 176, Leu to Val 187, Ile to Val 319) abrogated the ability of rMas to inhibit invasion. These preliminary experiments contribute to the characterization of rMas following internalization by cancer cells and aid in the therapeutic development of rMas as a potential therapy. Additionally, mutational data from this study support growing evidence that mutations in the maspin gene alter functionality in vitro, and may correlate to clinical outcomes in patients in which maspin is expressed in tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 486A. doi:1538-7445.AM2012-486A