Flotillin-1/reggie-2 protein plays dual role in activation of receptor-tyrosine kinase/mitogen-activated protein kinase signaling.

Our previous work has shown that the membrane microdomain-associated flotillin proteins are potentially involved in epidermal growth factor (EGF) receptor signaling. Here we show that knockdown of flotillin-1/reggie-2 results in reduced EGF-induced phosphorylation of specific tyrosines in the EGF receptor (EGFR) and in inefficient activation of the downstream mitogen-activated protein (MAP) kinase and Akt signaling. Although flotillin-1 has been implicated in endocytosis, its depletion affects neither the endocytosis nor the ubiquitination of the EGFR.

Hetero-oligomerization of reggie-1/flotillin-2 and reggie-2/flotillin-1 is required for their endocytosis.

Reggie-1/flotillin-2 and reggie-2/flotillin-1 are membrane raft associated proteins which have been implicated in growth factor signaling, phagocytosis, regulation of actin cytoskeleton and membrane trafficking. Membrane and raft association of reggies is mediated by myristoylation, palmitoylation and oligomerization. We have shown that upon EGF stimulation of cells, reggie-1 is tyrosine phosphorylated by Src kinase and endocytosed into late endosomes.

Polarized transport of Alzheimer amyloid precursor protein is mediated by adaptor protein complex AP1-1B.

Alzheimer amyloid precursor protein (APP) is the precursor for the Abeta peptide involved in pathogenesis of Alzheimer's disease. The soluble ectodomain fragment of APP (sAPP) functions as a growth factor for epithelial cells, suggesting an important function for APP outside neuronal tissue. Previous studies have shown that in polarized epithelial cells, APP is targeted to the basolateral domain.

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.