In order to develop novel therapies for the treatment of childhood cancer and related diseases based on an understanding of signal transduction pathways controlling cell growth, differentiation and apoptosis, we use human pediatric tumors and their normal cellular counterparts as model systems to study the molecular events that regulate cell growth, differentiation and cell death. Retinoic acid (RA) induced differentiation of Neuroblastoma tumors continues to be our paradigm for studies that define signal transduction pathways that mediate control of cell growth, differentiation and cell death. Delineation of these pathways will not only enable a more efficacious clinical utilization of retinoids and their cogeners but has the possibility to identify novel molecules or pathways that may have the potential for therapeutic development in the treatment of neuroectodermal tumors. The focus of the CMBS is pediatric neuroectodermal tumors including neuroblastoma, brain tumors and the Ewing's sarcoma. We defined that NB cell lines express Trks and their ligands, the neurotrophins, which in normal neural cells activate survival and differentiation pathways. In NB tumors, Trks serve as tumor markers; Good prognosis tumors express TrkA while most poor prognosis tumors express TrkB and its ligand Brain-derived neurotrophic factor (BDNF). We first identified that although poor prognosis neuroblastomas express little TrkA or TrkB, retinoids induce TrkB in vitro. A major effort in the lab has focused on the isolation and biochemical characterization of the TrkB promoter and the mechanisms by which RA stimulates TrkB transcription. The induction of TrkB in tumor cells constitutively expressing BDNF leads to neurite extension and cell survival. Furthermore, BDNF stimulates invasiveness in NB cells. Recently published studies show that BDNF expression increases in drug resistant cell lines and BDNF stimulates resistance to the cytotoxic drug, vinblastine. Thus expression of BDNF and activation of the Trk signal transduction path stimulates cell invasion and chemoresistance, all properties that are found in a tumor with a poor prognosis. Current studies will define the signal transduction paths that mediate the alterations in chemosensitivity stimulated by BDNF and evaluate whether strategies aimed at decreasing BDNF expression will alter chemosensitivity. BDNF, as well as other neurotrophins are highly expressed in other embryonal tumors as well as brain tumors, and may serve similar roles in these tumors. In collaborative studies, we have determined that the peptide adrenomedullin is constitutively expressed in a number of tumor cell lines, including neuroblastoma, and ESFT and antibodies against this peptide inhibit cell proliferation. Adaptation to in vivo models is in progress. The CMBS has isolated a retinoid regulated gene named 37G1. Sequence analysis of 37G1 indicated it was most homologous to the ULIP gene (unc-33 like phophoprotein) a mouse gene that is highly expressed in developing brain and at the neuromuscular junction. 37G1 has been renamed hULIP. Mutation sin unc-33, lead to abnormalities in neuronal axon guidance and migration. We have developed an in vitro mode that will permit analysis of the function and regulation of hULIP. 15% of the CMBS's research is aimed at studying mechanisms of HIV transcription in neuroectodermal cells.
