Plasma membrane domain organization regulates EGFR signaling in tumor cells

Abstract

Macromolecular complexes exhibit reduced diffusion in biological membranes; however, the physiological consequences of this characteristic of plasma membrane domain organization remain elusive. We report that competition between the galectin lattice and oligomerized caveolin-1 microdomains for epidermal growth factor (EGF) receptor (EGFR) recruitment regulates EGFR signaling in tumor cells. In mammary tumor cells deficient for Golgi β1,6N-acetylglucosaminyltransferase V (Mgat5), a reduction in EGFR binding to the galectin lattice allows an increased association with stable caveolin-1 cell surface microdomains that suppresses EGFR signaling. Depletion of caveolin-1 enhances EGFR diffusion, responsiveness to EGF, and relieves Mgat5 deficiency–imposed restrictions on tumor cell growth. In Mgat5+/+ tumor cells, EGFR association with the galectin lattice reduces first-order EGFR diffusion rates and promotes receptor interaction with the actin cytoskeleton. Importantly, EGFR association with the lattice opposes sequestration by caveolin-1, overriding its negative regulation of EGFR diffusion and signaling. Therefore, caveolin-1 is a conditional tumor suppressor whose loss is advantageous when β1,6GlcNAc-branched N-glycans are below a threshold for optimal galectin lattice formation.

Role of N-glycosylation in trafficking of apical membrane proteins in epithelia

“…As a consequence, the rate of constitutive endocytosis of the mutant subunit would increase. Interactions of lectins with N-glycans attached to other membrane proteins have been shown to be important for their retention in the plasma membrane in several different cell types (11,47,64,65,68).…”

Bidirectional control of the inner dynamics of focal adhesions promotes cell migration

“…These studies showed that Mgat5-dependent recruitment of cytokine receptors (EGFR) to the galectin lattice enhances signaling potential by downregulating receptor endocytosis. 22,23 Further work, including the study described here, demonstrated that Mgat5-dependent recruitment of glycosylated integrins promotes their clustering, decreases local exchange of FA proteins, and favors subsequent FA turnover 8,24 (Fig. 1A).…”

“…Our studies highlight a novel membrane domain, the "Cav1 scaffold", and explain how this non-caveolar Cav1 domain regulates receptor signaling and dynamics. 23 Although the functions of Cav1 outside caveolae remain poorly understood, they are the subject of intensive study. 26,32 For example, Cav1 molecules have been detected in cells lacking caveolae and in non-caveolar regions of cells such as cytoplasm, focal adhesions, the Golgi apparatus, the extracellular milieu, and the nucleus, suggesting potential functions for Cav1 in a variety of cell signaling and mechanotransduction phenomena.…”

“…This interaction produces a expressed at levels below the threshold for caveolae formation. 23 Caveolin-1 has been proposed to interact with integrins, most probably outside of caveolae. 34,35 Cav1 is also a substrate of Src kinase 36 and our studies show an association of Cav1 with cell transformation and tumor progression, although its exact role here remains unclear.…”

Membrane dynamics in mammalian embryogenesis: Implication in signal regulation

“…Cell surface receptors, such as epidermal growth factor receptor (EGFR), is also shown to be associated with the plasma membrane microdomain, where their tyrosine kinases become inactivated (Couet et al, 1997;Waugh et al, 1999;Lajoie et al, 2007). In addition to the signaling cascades involving the secreted extracellular ligands, a class of cell surface resident molecules is also known to be preferentially associated with the membrane microdomain.…”