Compartmentalization of integrin α6β4 signaling in lipid rafts

Abstract

Integrin α6β4 signaling proceeds through Src family kinase (SFK)–mediated phosphorylation of the cytoplasmic tail of β4, recruitment of Shc, and activation of Ras and phosphoinositide-3 kinase. Upon cessation of signaling, α6β4 mediates assembly of hemidesmosomes. Here, we report that part of α6β4 is incorporated in lipid rafts. Metabolic labeling in combination with mutagenesis indicates that one or more cysteine in the membrane-proximal segment of β4 tail is palmitoylated. Mutation of these cysteines suppresses incorporation of α6β4 in lipid rafts, but does not affect α6β4-mediated adhesion or assembly of hemidesmosomes. The fraction of α6β4 localized to rafts associates with a palmitoylated SFK, whereas the remainder does not. Ligation of palmitoylation-defective α6β4 does not activate SFK signaling to extracellular signal–regulated kinase and fails to promote keratinocyte proliferation in response to EGF. Thus, compartmentalization in lipid rafts is necessary to couple the α6β4 integrin to a palmitoylated SFK and promote EGF-dependent mitogenesis.

Curcumin Inhibition of the Functional Interaction between Integrin α6β4 and the Epidermal Growth Factor Receptor

“…Therefore, it is possible that curcumin may affect one of the signaling pathways responsible for the phosphorylation of these Ser residues. Alternatively, palmitoylation of membrane proximal Cys residues of b4 integrin is required for lipid raft localization of a6b4 (20). On the basis of our data, which show that curcumin shifts a6b4 from lipid raft to nonlipid raft fractions (Fig.…”

“…Mobilization of a6b4 from HDs to leading edges of migrating carcinoma cells is thought to increase the localization of a6b4 into lipid rafts (16), where lots of other signaling receptors are located in the near vicinity so that a6b4 acts as a signal amplifier of these receptors (20,21,31). Therefore, we tested whether curcuminmediated a6b4 sequestration in HDs affects localization of a6b4 in lipid rafts (Fig.…”

“…The localization of a6b4 to actin filament-rich structures such as lamellipodia and filopodia has an important implication for cancer cell motility and invasion, because integrins can harness traction forces through association with F-actin and their ability to engage the extracellular matrix (18,19). In addition, localization of a6b4 in the leading edge is thought to increase the level of a6b4 in lipid rafts (20). Lipid rafts are sphingolipid and cholesterol-rich microdomains of the plasma membrane (21,22).…”

“…Lipid rafts are sphingolipid and cholesterol-rich microdomains of the plasma membrane (21,22). Lipid rafts can act as "signaling platforms," in which signaling initiation and amplification occur more efficiently by recruiting signaling receptors into close proximity (20)(21)(22)(23). Once a6b4 localizes in lipid rafts, it is assumed that its signaling function is enhanced through interaction with other signaling receptors such as EGFR (20,21).…”

Bisecting GlcNAc Residues on Laminin-332 Down-regulate Galectin-3-dependent Keratinocyte Motility

“…Thus, galectin-3 might play an important role in the ternary complex formation in lipid rafts. Compartmentalization of lipid rafts is necessary to couple ␣6␤4 integrin and EGFR to active Src family kinase, which both prevents incorporation of ␣6␤4 integrin into hemidesmosomes and promotes cell migration (42,44,57). Some studies have reported that integrins are localized in the so-called glycosphingolipid-enriched microdomain rather than existing in lipid rafts on the cell surface.…”