Lipid raft localization of EGFR alters the response of cancer cells to the EGFR tyrosine kinase inhibitor gefitinib

Abstract

Epidermal growth factor receptor (EGFR) is overexpressed in many cancer types including ∼30% of breast cancers. Several small molecule tyrosine kinase inhibitors (TKIs) targeting EGFR have shown clinical efficacy in lung and colon cancers, but no benefit has been noted in breast cancer. Thirteen EGFR expressing breast cancer cell lines were analyzed for response to EGFR TKIs. Seven were found to be EGFR TKI resistant; while shRNA knockdown of EGFR determined that four of these cell lines retained the requirement of EGFR protein expression for growth. Interestingly, EGFR localized to plasma membrane lipid rafts in all four of these EGFR TKI resistant cell lines, as determined by biochemical raft isolation and immunofluorescence. When lipid rafts were depleted of cholesterol using lovastatin, all four cell lines were sensitized to EGFR TKIs. In fact, the effects of the cholesterol biosynthesis inhibitors and gefitinib were synergistic. While gefitinib effectively abrogated phosphorylation of Akt and MAPK in an EGFR TKI sensitive cell line, phosphorylation of Akt persisted in two EGFR TKI resistant cell lines; however, this phosphorylation was abrogated by lovastatin treatment. Thus, we have shown that lipid raft localization of EGFR correlates with resistance to EGFR TKI-induced growth inhibition and pharmacological depletion of cholesterol from lipid rafts decreases this resistance in breast cancer cell lines. Furthermore, we have presented evidence to suggest that when EGFR localizes to lipid rafts, these rafts provide a platform to facilitate activation of Akt signaling in the absence of EGFR kinase activity.

Transforming Growth Factor-β1 (TGF-β1)-stimulated Fibroblast to Myofibroblast Differentiation Is Mediated by Hyaluronan (HA)-facilitated Epidermal Growth Factor Receptor (EGFR) and CD44 Co-localization in Lipid Rafts

“…Further examination of the localization of EGFR revealed that in both fibroblasts and myofibroblasts, EGFR was associated and co-localized with areas of high cholesterol content, otherwise known as cholesterol-rich microdomains or lipid rafts (48). These findings supported previous reports of EGFR being bound in lipid raft domains in other cell systems (49) and of lipid rafts as regulators of EGFR and other receptors (50,51,52). CD44 was found to co-localize with lipid raft domains after differentiation of fibroblasts to myofibroblasts, supporting the hypothesis that CD44 relocalization to lipid rafts containing EGFR was implicated in the differentiation pathway.…”

Pro‑metastatic signaling of the trans fatty acid elaidic acid is associated with lipid rafts

“…Statins have been reported to inhibit the growth of JAK2-mutated cells by inhibiting lipid rafts (23) and inducing apoptosis by inhibiting Rac1 (15). Thus, lipid rafts act as a platform for collecting multiple stimulants, receptors, and signals to activate cancer progression (24). The mechanism of integration of EA to cholesterol raft should be elucidated in further examinations; however, our data suggests that lipid rafts may be promising targets for anticancer treatment.…”

FAM83A confers EGFR-TKI resistance in breast cancer cells and in mice

“…In some EGFR-TKI-resistant breast cancers, Met and c-Src tyrosine kinases are overexpressed, hyperactivating EGFR even in the presence of the inhibitor (5). Furthermore, in EGFR-TKI-resistant breast cancer cell lines, EGFR is localized at lipid rafts even in the presence of the drug, leading to hyperactivation of the downstream Akt signaling (50). In the present study, we examined whether there were additional molecular modulations that confer EGFR-TKI resistance in breast cancer.…”