The experiments in this section of the application are designed to examine the molecular basis of the angiogenic switch observed during gliomagenesis. Biochemical and genetic methods will be used to determine the mechanisms whereby the Id transcription factors and one of their potential target-effectors, the alpha6 beta4 integrin, promote the growth of blood vessels into gliomas and to examine if these proteins are suitable targets for drug intervention. Loss of function of Id proteins suppresses the growth and metastasis of tumor cells injected subcutaneously in mice because these proteins are required for the mobilization of endothelial cell precursors from the bone marrow and their proper differentiation in angiogenic endothelial cells. A central aim of this section of the proposal will be to determine if the Id proteins are also required for blood vessel development into gliomas induced either by stereotactic injection ofglioma cells or by transduction ofoncogenes using the tv-a /RCAS system. Recent evidence indicates that loss of Id leads to a loss of expression of alpha6beta4 in endothelial cells suggesting that this integrin may in part mediate the effects of Id. A targeted deletion of the signaling segment of beta4 cytoplasmic domain inhibits postnatal angiogenesis, indicating that alpha6 beta4 signaling is required during angiogenesis. We will thereby use genetic methods to examine if loss of alpha6beta 4 signaling prevents glioma angiogenesis and to identify the signaling pathways involved. Finally, we will examine the expression of Id proteins and alpha6 beta4 integrin in human gliomas and seek proof of principle that inhibition of these proteins may be of therapeutic advantage.
