Role of EGF-induced tyrosine phosphorylation of reggie-1/flotillin-2 in cell spreading and signaling to the actin cytoskeleton.

Cholesterol and sphingolipid-rich membrane microdomains or rafts have been shown to be involved in signaling through many growth factor receptors but the molecular details of these processes are not well understood. The reggie/flotillin proteins are ubiquitously expressed proteins with a poorly characterized function. They are constitutively associated with membrane rafts by means of acylation and oligomerization. Previous studies have implicated reggies in signaling, regulation of actin cytoskeleton and in membrane transport processes. In this study, we analyzed the putative role of reggie-1/flotillin-2 in signaling through the epidermal growth factor receptor. We show that reggie-1 becomes phosphorylated by Src kinase at several tyrosines upon stimulation of cells with epidermal growth factor. In addition, Src and reggie-1 are present as a molecular complex. Epidermal growth factor stimulation of cells results in a Tyr163-dependent translocation of reggie-1 from the plasma membrane into endosomes. We also show that reggie-1 is capable of enhancing the spreading of cells, again in a tyrosine-dependent manner, and knockdown of reggie-1 interferes with spreading. Thus, we reveal a new function for reggie-1 in the regulation of cell adhesion and actin dynamics and in growth factor signaling.