Abstract: Maspin is a novel serine protease inhibitor (serpin) that does not act as a classical serine protease inhibitor. Our lab demonstrated that maspin directly inhibits the serine protease-like enzyme, histone deacetylase 1 (HDAC1), which is a major deacetylase up-regulated in many types of cancers. To our knowledge, maspin is the only endogenous polypeptide inhibitor of HDAC1 identified thus far. Interestingly, the differential regulation of maspin during tumor progression is characterized by changes in overall expression and subcellular distribution. In particular, a significant shift in maspin subcellular localization from the nucleus to the cytosol has been observed at the transition from benign epithelial cells to precancerous or low grade carcinoma cells. Accumulated clinical evidence suggests that nuclear retention of maspin is correlated with better overall patient survival. We propose that hypothesized that the configuration and conformation of maspin coded by its primary sequence, i.e. cis elements are the key determinants for where maspin may be retained in a given molecular context. We noted that at the C-terminal end of the RCL sequence is an Aspartate 346 (D346) which is also unique among all maspin homologs and orthologs. In the current study, using the mutagenesis approach, we aimed to determine whether D346 acts as the cis element essential for maspin subcellular localization and function. We showed that in comparison to the maspinWT, which is distributed in both cytosol and nuclei of cancer cells, maspinD346E is predominantly localized in the nuclei of cancer cells. In addition, maspinD346E had an increased affinity towards HDAC1 and it was more effective inhibitor of HDAC1 as compared to the maspinWT. These findings led to a novel molecular model that explains how maspin may be disregulated during tumor progression resulting in loss of its tumor suppressive potential.

Citation Format: Sijana H. Dzinic, Alexander Kaplun, Xiaohua Li, Margarida M. Bernardo, Ivory Dean, Fulvio Lonardo, Shijie Sheng. Identification of an intrinsic determinant critical for maspin subcellular localization and function. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5203. doi:10.1158/1538-7445.AM2013-5203