Transformation of cells by Rous sarcoma virus is dependent on the expression of virus encoded src gene. Experiments using microinjection or co-expression of dominant negative ras or raf genes has suggested that the mechanism by which v-src transforms cells involves ras and raf mediated signal transduction. But these conditions not only suppress v-src induced cell transformation, they also suppress normal cell proliferation. An alternative view is that v-src functions through its interaction with molecules involved in cell adhesion and determination of cell shape. The difficulty with this view is that there is little functional data to support it and the potential mechanisms by which cell adhesion may alter cell gene expression and cell proliferation are at a very early stage of development. The objective of this proposal is to fill this void and test the hypothesis that v-src operates by interfering with normal cell signaling pathways which are linked to cell adhesion and particularly to integrin family receptors. To test this proposition, we will reexamine two old model systems for cell transformation from the perspective of a possible link between v-src dependent cell proliferation and v-src mediated modulation of integrin mediated cell adhesion. (i) Deprivation of serum causes cells to arrest in Go. Activation of v-src in the arrested cells induces cell proliferation. The role of integrins in the establishment of the quiescent state and the potential requirement for integrin modulation to reinitiate cell proliferation will be tested. Does v-src induced proliferation depend on its effect to weaken integrin extracellular matrix links? (ii) Transformed fibroblasts are able to proliferate in suspension whereas normal fibroblasts require an adhesive substrate. The role of integrins in supplying this adhesion signal and the possibility that v-src disrupts this signal will be examined using cell cycle analysis, functional analysis of adhesion requirements and genetic manipulation.
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