Membrane receptor location defines receptor interaction with signaling proteins in a polarized epithelium

Signal transduction from receptors is mediated by the interaction of activa ted receptors with proximate downstream signaling proteins. In polarized ep ithelial cells, the membrane is divided into subdomains: the apical and bas olateral membranes. Membrane receptors may be present in one or both subdom ains. Using a combination of immunoprecipitation and Western blot analyses, we tested the hypothesis that a tyrosine kinase growth factor receptor, ep idermal growth factor receptor (EGFR), interacts with distinct signaling pr oteins when present at the apical vs. basolateral membrane of a polarized r enal epithelial cell. We report here that tyrosine phosphorylation of phosp holipase C-gamma (PLC-gamma) was induced only when basolateral EGFR was act ivated. In contrast, tyrosine phosphorylation of several other signaling pr oteins was increased by activation of receptor at either surface. All signa ling proteins were distributed diffusely throughout the cytoplasm; however, PLC-gamma protein also displayed a concentration at lateral cell borders. These results demonstrate that in polarized epithelial cells the array of s ignaling pathways initiated by activation of a membrane receptor is defined , at least in part, by the membrane location of the receptor.