Study of metallopeptidase PHEX in tumor cells and bone mineralization process

• Grant number: 12/22480-1
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: October 01, 2013
• End date: August 31, 2017
• Field of knowledge: Biological Sciences - Biochemistry - Enzymology
• Principal Investigator: Nilana Meza Tenório de Barros Jaggi
• Grantee: Raquel Leão Neves
• Host Institution: Escola Paulista de Medicina (EPM). Universidade Federal de São Paulo (UNIFESP). Campus São Paulo. São Paulo , SP, Brazil

Abstract

The PHEX gene (phosphate-regulating gene with homologies to endopeptidase on the X chromosome) was identified in 1995 as the mutated gene in patients with a prevalent form (1: 20.000) of hereditary human ricket, called XLH (X-linked hypophosphataemia ). The XLH is characterized by defects in the reabsorption of phosphate and vitamin D metabolism, and disorders such as rickets, osteomalacia and in bone mineralization defects. The PHEX gene expression results in a membrane metallopeptidase mainly associated with bone and teeth. Recently, using different methodologies and murine model of XLH (Hyp mice), we described the first protein substrate for PHEX, osteopontin (OPN) (Barros et al., 2012). The OPN is a multifunctional phosphoprotein with tissue-specific activities, that among the functions, may act as an inhibitor of bone mineralization (Addison et al., 2010; Boskey et al., 2012), and in tumors, as a promoter of the progression ( reviewed by Bellahcène et al., 2008, Chen et al., 2012). In addition, we reported that the absence of functional Phex in Hyp mouse results in the accumulation of OPN fragments in the bone of in this animal (Barros et al., 2012).Data resulting from our work showed that PHEX also has high expression (mRNA) in human tumor cells (squamous cell carcinoma -SCC). Following, SCC cells were silenced for PHEX (SCC-shRNA-PHEX), giving this proposal to investigate the role of PHEX in tumoral processes and characterization of physiological substrates, not only in bone tissue, but also in tumors SCC. The results could represent a major breakthrough in functional characterization of PHEX, going beyond function primarily related to bones and teeth described in the literature.Finally, considering another data from our group indicating that PHEX could be at the extracellular matrix during mineralization, and to continue the studies related to bone, we also propose a detailed study of the cellular distribution of PHEX in mineralization, using as models MC-3T3 (mouse) and MG-63 (human) osteoblasts.