Russell T. Matthews, Ph.D. - US grants

DESCRIPTION (provided by applicant): Primary tumors of the central nervous system, gliomas, are notoriously difficult to control, due in large measure to their highly invasive behavior. The ability of cells to migrate through tissue depends, in part, on the composition of the tissues extracellular matrix (ECM). Understanding the molecular composition of the extracellular environment of brain tumors is one approach to developing methods to prevent tumor invasion. BEHAB/brevican, a recently identified brain-specific ECM protein, is markedly upregulated in human glioma and in experimental models of glioma. In human glioma BEHAB/brevican expression is 700 percent over that in the normal adult human brain and expression is not detected in any non-glial derived tumor, even when these tumors grow within the brain. Our work during the previous funding period has provided evidence that BEHAB/brevican plays a role in glioma invasion. The experiments proposed here will test this hypothesis and, in addition, will test the possibility that BEHAB/brevican may provide a novel therapeutic target for glioma. In experimental glioma cel models, BEHAB/brevican expression is induced by a brain-specific factor. The first specific aim of this application is to characterize the mechanism of BEHAB/brevican induction and to identify potential inducing factors. Several converging lines of evidence suggest that proteolytic processing is required for BEHAB/brevican function in glioma invasion. The second specific aim of this application is to characterize BEHAB/brevican Droteolytic cleava2e in glioma. Slowing or preventing glioma cell motility could increase the efficacy of regional therapies; the third specific aim of this application is to determine whether inhibitors of BEHAB/brevican cleavage can slow tumor invasion and, therefore, might provide a new therapeutic avenue foi glioma. Our work has led to the hypothesis that production, cleavage, and turnover of BEHAB/brevican together modulate the ECM and can regulate cell motility. Our final specific aim is to test a role for BEHAB/brevican turnover in glioma invasion. Our long-term goal is to determine if functional reduction or elimination of BEHAB could slow the progression of primary brain tumor.

DESCRIPTION (provided by applicant): Mutations in enzymes involved in protein O-mannosyl glycosylation produce a group of devastating diseases characterized by congenital muscular dystrophy (CMD), type II lissencephaly, and eye abnormalities. Previous studies using animal models have demonstrated that hypoglycosylation of a-dystroglycan critically contributes to the pathogenesis of these disorders. A growing body of evidence, however, suggests that other substrates for O-mannosyl glycosylation likely contribute to particular brain abnormalities found both in animal models and in patients with CMDs. Unfortunately, previous studies have failed to identify the additional neural substrates of O-mannosylation that contribute to these brain pathologies. Using an animal model of CMD in which the glycosyltransferase POMGnT1 is knocked out we identified RPTP? as another important substrate for O-mannosyl glycosylation in the brain. Receptor tyrosine phosphatase zeta/beta is a receptor phosphatase that is found predominately in the central nervous system and is highly expressed during key stages of neural development. Both membrane-bound receptor and secreted variants of the protein are expressed in the brain and are high affinity ligands for a number of developmentally important adhesion molecules, growth factors and extracellular matrix proteins. We hypothesize that the hypoglycosylation of RPTP6 due to disrupted O-mannosylation alters the interactions of RPTP? with these key ligands and contributes to abnormal brain development. Consistent with this hypothesis we found that cortical neuron development in cultured cells from POMGnT1 knockouts is abnormal when they are plated on a subset of known RPTP? ligands. In this proposal we investigate the hypothesis that the hypoglycosylaton of RPTP? in O-mannosyl glycosylation mutant animals alters its ligand-binding characteristics thereby leading to aberrant cellular interactions and abnormal brain development. The proposal is focused on the following 3 specific aims: 1) To determine whether altered glycosylation of RPTP? modulates its ligand binding characteristics. 2) To determine whether disrupted glycosylation of RPTP? alter cell development. And 3) To identify the 1-dystroglycan-independent neural abnormalities in animal models of CMDs and to determine if these abnormalities are due to altered RPTP?/phosphacan glycosylation. To explore these questions, we will utilize a variety of genetic mouse model systems in which we will disrupt O-mannosyl glycosylation, a-dystrglycan expression or RPTP?expression. Studies will be conducted both in vitro and in vivo to determine how O-mannosyl glycans modulate RPTP? function and if this contributes to brain abnormalities found in animal models of CMDs. These studies will determine if RPTP? is an important contributor to CMD pathogenesis and will provide important insights into the pathomechanisms of the neural phenotypes in these disorders. PUBLIC HEALTH RELEVANCE: Altered protein glycosylation is a well-known cause of congenital muscular dystrophies. However, all the protein targets of altered glycosylation in these disorders are not known. In this proposal we investigate RPTP? as an important new target of the disrupted glycosylation in congenital muscular dystrophies in investigate its role in animals models of these disorders.