Stimulation of HIRcB fibroblasts with insulin leads to accumulation of active components of
the mitogen-activated protein kinase cascade in endocytic compartments. However, the
factors that regulate the mobilization of these components through the endocytic pathway
and the relevance of this event to cellular signaling remain unclear. Here we report that Ras
proteins are associated with lipid rafts in resting HIRcB fibroblasts. Ras is rapidly
internalized into the endocytic compartment following stimulation with insulin. The …