Regulation of maspin phosphorylation by the EGFR pathway

Abstract

Maspin (mammary serpin) is a 42 kDa tumor suppressor protein which belongs to superfamily of serpins due to sequence homology, however, its mechanism of action does not depend on protease inhibition. This protein was identified in 1994 during a search for genes expressed in normal mammary epithelial cells but absent in breast tumors. Among maspin biological effects are modulation of cell adhesion, inhibition of tumor growth, invasion and angiogenesis, a pro-apoptotic effect and control of oxidative stress response. This functional diversity reflects maspin numerous ligands and its subcellular localization, since it is found on the plasma membrane, in the cytoplasm, nucleus and in mitochondria. Clinical studies indicate that the nuclear localization of maspin, rather than its expression levels correlates with good prognostic factors and overall survival in some types of cancer including breast cancer. Several studies indicate that maspin is regulated by posttranslational modification, yet, little is known about how these alterations regulate its biological activities, subcellular localization and the intracellular pathways involved. Using the non-transformed mammary epithelial cell line MCF-10A as a model system, we identified four different maspin forms and three of these forms were sensitive to acidic phosphatase treatment, suggesting that they are phosphorylated. Our results indicate that EGF-treatment increases maspin phosphorylation and nuclear accumulation, whereas autocrinally secreted amphiregulin regulates maspin phosphorylation only. This observation suggests that maspin phosphorylation and subcellular localization are regulated by EGFR ligands. The objective of this project is to identify downstream signals in EGFR pathway involved in maspin phosphorylation. (AU)