Our general goal is to identify the function of tumor suppressor genes relevant for disorders of the nervous system (MEN1, VHL, NF2) as well as to perform genetic and functional studies of these and other tumor-related genes in glial tumors of the CNS. In addition, we are interested in using the findings of protein expression and molecular genetics to identify routes to therapy. Potential important questions to pursue include: What is(are) the genetic event(s) which occur during tumorigenesis? For example, our current work has shown that the functional consequences of loss of heterozygosity (LOH) in VHL- and MEN1-associated tumors may be directly related to an effect of the inherited, mutated allele on the second, wild-type allele. Conversely, when a deletion occurs as the primary event (germline mutation), we have observed that the wild-type allele has become mutated in most cases and this seems to be associated with less intense expression of the clinical syndrome. Our long-range goal is to elucidate the mechanism(s) that underlies this phenomenon, to see if it is a common event with other tumor suppressor syndromes and to determine if it is a widespread event in tumorigenesis. Pathogenesis of MEN2-associated neuroendocrine tumors. We have recently shown that there may be an oncogene-related corollary to Knudson's tumor suppressor hypothesis. In Knudson's theory, two hits occur, one inherited mutated allele and a deletion as a second hit in the wild-type allele, which leads to development of tumors. Previously, we have cloned the gene responsible for papillary renal cell carcinoma, the c-met oncogene. In this tumor, we have identified a novel mechanism for tumorigenesis in which the first hit is an inherited mutation in the c-met oncogene and the second hit is duplication of the mutated allele (whereby duplication causes trisomy of the chromosome) which leads to a dominant effect and the development of tumor. This novel mechanism may underlie tumorigenesis in other types of tumors. More recently we have demonstrated that similar mechanisms are also applicable to other oncogenes, e.g. c-ret mutant allele duplication as an early event in MEN-2-associated pheochromocytoma. Pathogenesis of malignant glial tumors. Several years ago SNB created a primate model for glioma tumorigenesis using a radiation dose that is sufficient to initiate intracerebral tumors, but low enough to allow longterm survival. Morphologic analysis revealed the tumors to be de novo glioblastomas, sometimes occurring multifocally. Brain and tumor tissue from these monkeys may provide clues to a better understanding of human glioma tumorigenesis. In particular, atypical glial cells were identified in characteristic topographic areas in at least one brain that was unaffected by tumor. We are in the process of further neuropathologic evaluation of these radiation-induced gliomas and normal brain tissue and the procurement of tissues for further laboratory studies including morphology, immunohistochemistry and molecular genetic studies. Pathogenesis of VHL-associated hemangioblastomas. We have completed an extensive morphologic analysis of CNS and other tissue samples obtained at autopsy from patients with VHL disease. This provided a detailed spectrum of tumorigenesis and illustrated the earliest hemangioblastoma precursor lesions, as well as clinically relevant hemangioblastomas. The results indicate that early hemangioblastoma formation in VHL disease is restricted to specific anatomic areas in the spinal cord and cerebellum. The phenotype of the early precursor lesions is markedly different from that of larger tumors resected at surgery and may provide important clues about mechanisms of tumor progression. The lesions were further analyzed using specialized techniques to compare early lesions with clinically progressive hemangioblastomas. Further clues were obtained by detailed studies of surgically removed, progressively enlarging hemangioblastomas that revealed more intense activation of the HIF-1alpha signal transduction pathway and evidence for autocrine pathway activation of erythropoietin and its receptor. These studies provide strong evidence for a primary developmental origin of hemangioblastoma which may also broaden our understanding of other VHL-related tumors and other tumor-suppressor syndromes. In addition, we further evaluated tumors from patients of a single kindred with germline deletion and provided evidence that the second genetic hit is a random event, possibly associated with a more favorable clinical outcome. Further collaborations with other branches: Identification of HHV6 viral protein in epilepsy brain tissue via a new dissection technology (Steve Jacobson, NINDS) Detailed morphologic analysis of palatal myoclonus associated with olivary hypertrophy (Mark Hallett, NINDS) Detailed myeloarchitectonic analysis of brain tissue using up to date MRI technology (Alan Koretsky, NINDS) 2D protein analysis for protein expression profiling using neurons derived from patients with lipid storage diseases (Roscoe Brady, NINDS) Genetic analysis of NF2-associated retinal and optic nerve lesions. (Chi-Chao Chan, NEI) Morphologic evaluation of VHL knockout mouse tissue. (Bert Zbar, Laura Schmidt, NCI) Morphologic evaluation of various models of autoimmune encephalitis. (Roland Martin, NINDS) Morphologic characterization of motor neuropathy due to dynactin mutation. (Christy Ludlow, NINDS)
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