Lipid Raft Association Restricts CD44-Ezrin Interaction and Promotion of Breast Cancer Cell Migration

Abstract

Cancer cell migration is an early event in metastasis, the main cause of breast cancer-related deaths. Cholesterol-enriched membrane domains called lipid rafts influence the function of many molecules, including the raft-associated protein CD44. We describe a novel mechanism whereby rafts regulate interactions between CD44 and its binding partner ezrin in migrating breast cancer cells. Specifically, in nonmigrating cells, CD44 and ezrin localized to different membranous compartments: CD44 predominantly in rafts, and ezrin in nonraft compartments. After the induction of migration (either nonspecific or CD44-driven), CD44 affiliation with lipid rafts was decreased. This was accompanied by increased coprecipitation of CD44 and active (threonine-phosphorylated) ezrin-radixin-moesin (ERM) proteins in nonraft compartments and increased colocalization of CD44 with the nonraft protein, transferrin receptor. Pharmacological raft disruption using methyl-β-cyclodextrin also increased CD44-ezrin coprecipitation and colocalization, further suggesting that CD44 interacts with ezrin outside rafts during migration. Conversely, promoting CD44 retention inside lipid rafts by pharmacological inhibition of depalmitoylation virtually abolished CD44-ezrin interactions. However, transient single or double knockdown of flotillin-1 or caveolin-1 was not sufficient to increase cell migration over a short time course, suggesting complex crosstalk mechanisms. We propose a new model for CD44-dependent breast cancer cell migration, where CD44 must relocalize outside lipid rafts to drive cell migration. This could have implications for rafts as pharmacological targets to down-regulate cancer cell migration.

A Systematic Analysis Reveals Heterogeneous Changes in the Endocytic Activities of Cancer Cells

“…15, 34). CD44 becomes more concentrated in flotillin-low or non-raft fractions, presumably corresponding to CLICs, in migrating breast cancer cells (35). Interestingly, CD44 is expressed in NSCLC, but not in small cell lung cancer (36).…”

Invariant Chain Complexes and Clusters as Platforms for MIF Signaling

“…The generation of such an membrane raft-enabled platform should foster the initiation of signal transduction processes as observed with model receptors such as the BCR [128]. It may be rewarding to also include molecules that function as co-receptors (CD44, CXCR2, CXCR4 and CXCR7) in the consideration of co-clustering receptors of MIF, because some of them appear to be associated with membrane rafts as well [129,130,131] and this might further support the formation of membrane raft-enabled signaling platforms.…”

Interleukin-1β-induced Reduction of CD44 Ser-325 Phosphorylation in Human Epidermal Keratinocytes Promotes CD44 Homomeric Complexes, Binding to Ezrin, and Extended, Monocyte-adhesive Hyaluronan Coats

“…Influence of CD44 Modifications on Ezrin Binding-Posttranslational modifications like phosphorylation and palmitoylation in the cytoplasmic and transmembrane domains of CD44 have been reported to influence its interaction with cytoskeleton (1,69). In macrophages, non-phosphorylated CD44 was associated with the cytoskeleton, whereas the phosphorylated form was not (60).…”

“…7A). For example, association of CD44 with membrane lipid rafts prevents its binding to ezrin (69). At the moment, the only known protein interacting with a peptide of CD44 containing phosphorylated Ser-325 is AMZ2 (archaemetzincin-2) (65) (Fig.…”