Prion Proteins (PRNP and PRND) are Over-Expressed in Osteosarcoma Vincenzo Sollazzo, 1 Marco Galasso, 2 Stefano Volinia, 3 Francesco Carinci 4 1 Orthopaedic Clinic, University of Ferrara, Ferrara, Italy, 2 Data Mining for Analysis of Microarrays, Department of Morphology and Embryology, Universita ` degli Studi, Ferrara, Ferrara, Italy, 3 Comprehensive Cancer Center, Ohio State University, Columbus, Ohio, 4 Maxillofacial Institute, University of Ferrara, Ferrara, Italy Received 23 July 2011; accepted 10 November 2011 Published online 6 December 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22034 ABSTRACT: Although osteosarcoma is the most common bone malignancy, the molecular and cellular mechanisms influencing its pathogenesis have remained elusive. Prion proteins (PRNP and PRND), known mostly for its involvement in neurodegenerative spongi- form encephalopathies, have been recently demonstrated to be involved in resistance to apoptosis, tumorigenesis, proliferation, and metastasis. The main aim of research was to study whether prion proteins were over-expressed in human osteosarcoma, and if prion proteins could have a role also in osteosarcomas. We evaluated differential gene expression between 22 cases of osteosarcoma and 40 cases of normal bone specimens through cDNA microarray analysis spanning a substantial fraction of the human genome. PRNP and PRND are significantly over-expressed in osteosarcoma. PRNP and PRND appear involved with some important genes related to tumorigenesis and apoptosis. PRNP is linked to PTK2, RBBP9, and TGFB1 while PRND is linked to TNFSF10, BCL2A1, NFKB2, and TP53RK. Increased expression on Affymetrix arrays of prion proteins seems to be associated with the development of osteosarcoma. Prions seem to induce a negative regulation of apoptosis, thus promoting osteosarcoma development and progression. Osteosarcoma is a very aggressive tumor and even after modern chemotherapy and excision of tumors efforts are needed to improve clinical outcome. Since Prion proteins seem to be related to osteosarcoma development, their inhibition could represent a new approach to the molecular treatment of osteosarcoma. ß 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1004–1012, 2012 Keywords: prion proteins; cancer; osteosarcoma; tumorigenesis; apoptosis Prion is an abbreviation devised by Stanley Prusiner for ‘‘proteinaceous infectious particle.’’ The prion protein, PrP c , is known mostly for its involvement in neurodegen- erative spongiform encephalopathies like Creutzfeldt– Jakob disease (CJD), Gerstmann–Straussler syndrome (GSS), kuru and fatal familial insomnia (FFI) in humans as well as scrapie and bovine spongiform encephalopathy in animals. 1 Prion diseases manifest as sporadic, genetic, or acquired disorders determined by the conformational conversion of PrP c (the normal cellular prion protein, where the superscript c stands for cellular) into scrapie prion protein (PrP sc ), where the superscript sc stands for scrapie, the prion disease that affects sheep. 2,3 Prions are characterized by their infectious properties and by the intrinsic ability of their secondary, tertiary, and quaternary structures to act as a template and convert the normal physiological PrP c into the pathological, disease causing form, PrP sc . 4 Several intriguing lines of evidence have recently emerged indicating that PrP c plays a funda- mental role not only in the nervous system, but also throughout the human body. This implies that PrP c may be involved in resistance to apoptosis, prolifera- tion, and metastasis of human cancer cells. 5 The resis- tance to cell death, particularly to apoptotic cell death, is an important aspect of both tumorigenesis and development of resistance to drugs used to treat cancer. 5,6 The expression levels of PRNP (the gene that encodes for PrP c ) may have a prognostic value in colorectal cancer, suggesting a role for the prion protein in colorectal cancer. 1 Moreover, PrP c over- expression may constitute a prognostic marker for disease recurrence and potentially a new target for anticancer therapy. 1 Recently, another prion protein, PRND, has been identified. PRND (prion protein 2 also called Doppel) is a membrane glycosylphosphatidylinositol-anchored glycoprotein that is found predominantly in testis. PRND gene is found on chromosome 20, approximately 20 kbp downstream of the gene encoding cellular prion protein, to which it is biochemically and structurally similar. Recently, it has been reported that Doppel is aberrantly expressed in astrocytic tumors where it dis- plays cellular localization and molecular properties dif- ferent from those of the corresponding testis protein. 7 Osteosarcoma is the most common type of solid bone cancer that predominantly develops in adoles- cents and young adults, 8 and can be histologically clas- sified into three types: osteoblastic, chondroblastic, and fibroblastic. 9,10 About six in every million children and two in every million adults will develop osteosar- coma. 11 They are very aggressive tumors and they often first develop in long bones (distal femur and proximal tibia). Even after the introduction of aggres- sive chemotherapy and wide excision of tumors, efforts are needed to improve clinical outcome. 12,13 Moreover, 20–30% of newly diagnosed cases presented with metastatic disease frequently localized at the lung but also locally at other sites within the bone. 14 Osteo- sarcoma is believed to arise from mesenchymal stem cells (MSCs) or osteoprogenitor cells due to a disruption in the osteoblast differentiation pathway. 15 Although osteosarcoma represents the most common bone malig- nancy, the molecular and cellular mechanisms Correspondence to: Vincenzo Sollazzo (T: þ39-532-236573; F: þ39-532-209250; E-mail: slv@unife.it) ß 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. 1004 JOURNAL OF ORTHOPAEDIC RESEARCH JUNE 2012