A novel splice variant of the protein tyrosine phosphatase PTPRJ that encodes for a soluble protein involved in angiogenesis

// Anna Bilotta 1 , Vincenzo Dattilo 2 , Sabrina D'Agostino 1 , Stefania Belviso 1 , Stefania Scalise 1 , Mariaconcetta Bilotta 1 , Eugenio Gaudio 1, 3 , Francesco Paduano 1, 4 , Nicola Perrotti 2 , Tullio Florio 5 , Alfredo Fusco 6 , Rodolfo Iuliano 1 , Francesco Trapasso 1 1 Department of Medicina Sperimentale e Clinica, University Magna Graecia of Catanzaro, Catanzaro, Italy 2 Department of Scienze della Salute, University Magna Graecia of Catanzaro, Catanzaro, Italy 3 Lymphoma and Genomics Research Program, Institute of Oncology Research (IOR), Bellinzona, Switzerland 4 Tecnologica Research Institute, Biomedical Section, Crotone, Italy 5 Laboratory of Pharmacology, Dept. of Internal Medicine, and Center of Excellence for Biomedical Research (CEBR), University of Genova, Genova, Italy 6 Istituto di Endocrinologia e Oncologia Sperimentale - CNR c/o Dipartimento di Medicina Molecolare e Biotecnologie Mediche, University Federico II of Napoli, Napoli, Italy Correspondence to: Rodolfo Iuliano, email: iuliano@unicz.it Francesco Trapasso, email: trapasso@unicz.it Keywords: protein tyrosine phosphatase, soluble isoform, angiogenesis, glioblastoma, angiogenic factor Received: September 20, 2016 Accepted: December 13, 2016 Published: December 29, 2016 ABSTRACT PTPRJ is a receptor protein tyrosine phosphatase with tumor suppressor activity. Very little is known about the role of PTPRJ ectodomain, although recently both physiological and synthetic PTPRJ ligands have been identified. A putative shorter spliced variant, coding for a 539 aa protein corresponding to the extracellular N-terminus of PTPRJ, is reported in several databases but, currently, no further information is available. Here, we confirmed that the PTPRJ short isoform (named sPTPRJ) is a soluble protein secreted into the supernatant of both endothelial and tumor cells. Like PTPRJ, also sPTPRJ undergoes post-translational modifications such as glycosylation, as assessed by sPTPRJ immunoprecipitation. To characterize its functional activity, we performed an endothelial cell tube formation assay and a wound healing assay on HUVEC cells overexpressing sPTPRJ and we found that sPTPRJ has a proangiogenic activity. We also showed that sPTPRJ expression down-regulates endothelial adhesion molecules, that is a hallmark of proangiogenic activity. Moreover, sPTPRJ mRNA levels in human high-grade glioma, one of the most angiogenic tumors, are higher in tumor samples compared to controls. Further studies will be helpful not only to clarify the way sPTPRJ works but also to supply clues to circumvent its activity in cancer therapy.