University of Vermont COBRE 2 (P20 RR016435)
"Center for Neuroscience Excellence"

Research Project 4: "Role of Dipeptidyl Peptidase IV (DPPIV) in Peripheral Neurogenesis and Neuroblastomas"
Investigator: Umadevi Wesley, Ph.D.

The normal process of differentiation plays a key role in generation of various cell types, in the correct number and sequence, during neuronal development. Perturbed differentiation leads to various pathological conditions including development of malignant tumors, such as neuroblastomas (NB). NB is a pediatric tumor that originates from neural precursor cells of the sympathetic nervous system. About 50% of the children diagnosed with NB die from the disease emphasizing the need for identification of critical genetic and molecular changes involved in NB. It is evident that growth factors including basic fibroblast growth factor (bFGF) and Notch signaling play central roles in proper temporal and spatial neuronal differentiation. The cell surface protease, dipeptidyl peptidase IV (DPPIV) is a differentiation antigen that regulates the activities of many growth factors by proteolytic cleavage. DPPIV is expressed in normal mammalian neurons but its expression is lost in NB that exhibit characteristics of embryonic neural stem cells. Thus, regulated expression of DPPIV appears to be essential for sustaining normal neural development and maintenance. Our previous work shows that DPPIV is highly expressed in differentiated melanocytes that originate from neural crest cells but not in its malignant counterpart melanomas that are highly proliferative and migratory. Restoration of DPPIV in these cells inhibits their proliferation by promoting differentiation and by decreasing the levels of bFGF. Importantly, DPPIV abrogates the survival and tumorigenic potential of melanoma cells. Our preliminary studies show that restoration of DPPIV expression in NB cells leads to their morphological differentiation and growth inhibition. These data support our hypothesis that DPPIV is required for induction and maintenance of the differentiated phenotype of peripheral neurons. Specifically, DPPIV decreases the levels of bFGF and Notch signaling, thereby promoting the peripheral neural differentiation and inhibiting the growth stimulatory signals required for proliferation and survival of neural crest precursor cells. This hypothesis will be tested by examining the role of DPPIV in peripheral neural development and differentiation using an in vitro cell culture system and in vivo mouse model. We will specifically examine whether DPPIV modulates bFGF and Notch signaling pathways. The set of molecular and biochemical assays employed will include morphometric analysis, cell proliferation, apoptosis, and migration assays using time-lapse deconvolution microscopy, confocal microscopy, immunoanalyses, real time RT-PCR, and RNA interference technique. The long term goal is to further elucidate the role of cell surface proteases in regulating the molecular mechanisms involved in peripheral neural and NB development that may open up new directions for developing novel therapeutic approaches for NB, which still remains a major cause of cancer related deaths in children.