Molecular mechanisms underlying Maspin biological activities

• Grant number: 12/00043-9
• Support Opportunities: Regular Research Grants
• Start date: April 01, 2012
• End date: September 30, 2014
• Field of knowledge: Biological Sciences - Biochemistry - Molecular Biology
• Principal Investigator: Nathalie Cella
• Grantee: Nathalie Cella
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Maspin (mammary serpin) is a tumor suppressor gene with diverse biological activities, among them regulation of cell adhesion, migration and death, oxidative stress response, gene transcription among others. Initially described in the mammary tissue, we now know that this protein is present in most epithelia and knockout mice do not survive beyond embryogenesis. Initial studies reported a strong correlation between loss of maspin expression and tumor progression. Recent data, however, suggest that maspin subcellular localization, and not expression levels, correlates with progression. Maspin is found in every cell compartment and presents several described ligands. Because there is only one gene and one transcript described for this protein, we looked for post-translational modifications that could regulate its diversity of functions, ligands and subcellular localizations. Using the MFC-10A model, a non-transformed human mammary epithelial cell line which endogenously expresses maspin, we identified four maspin forms, three of them were found phosphorylated on tyrosine residues. Inhibition of tyrosine phosphatase results in rapid increase in maspin protein levels, which accumulate in the cytoplasm (submitted manuscript attached). These data suggest that maspin phosphorylation may play a role in protein stability and subcellular localization. In addition, we observed that a short cell treatment with EGF (epithelial growth factor) results in decreased levels of maspin phosphorylation, suggesting that maspin is part of the EGF signaling pathway. The objectives of this proposal are (1) to determine the role of maspin phosphorylation on its subcellular localization; (2) to determine the role of maspin phosphorylation on its protein stability; (3) to determine maspin nuclear localization signal and (4) to investigate if cell adhesion regulates maspin phosphorylation and if maspin regulates EGF-induced cell migration. (AU)