Identification of pleiotrophin in conditioned medium secreted from neural stem cells by SELDI-TOF and SELDI-tandem mass spectrometry.

Neural stem cells (NSCs) are multipotential progenitor cells that have self-renewal activity. Since the fates of the NSCs in situ depend on their niche containing growth factors and cytokines, we performed surface enhanced laser desorption/ionization time-of flight mass spectrometry (SELDI-TOF-MS) to screen for differentially secreted proteins in conditioned medium of neural stem cells and compared with that of NIH3T3 cells. A 15.3-kDa protein detected only in the conditioned medium of neural stem cells was determined as pleiotrophin (PTN) by SELDI-TOF-MS and ProteinChip-tandem MS systems. Identification of pleiotrophin was further confirmed by one-dimensional SDS gel electrophoresis and Edman degradation analysis. The mRNA transcripts of PTN and its receptors [receptor protein tyrosine phosphatase (RPTP) beta/zeta, N-syndecan and anaplastic lymphoma kinase (ALK)] were detected in neurosphere, suggesting that pleiotrophin signaling systems are present in the neural stem cells and are involved in the modulation of fate of neural stem cells.