Intravesicular epidermal growth factor receptor subject to retrograde trafficking drives epidermal growth factor-dependent migration

Abstract

The Epidermal Growth Factor Receptor (EGFR) is frequently mutated and overexpressed in metastatic cancer. Although EGFR is a transmembrane tyrosine kinase localized to the basolateral membrane in normal epithelium, it is frequently found intracellularly localized in transformed cells. We have previously demonstrated the epithelial adaptor protein mucin 1 (MUC1) alters trafficking of EGFR, inhibiting its degradation and promoting its translocation to the nucleus, where it can directly modulate gene transcription. Here, we demonstrate that MUC1 promotes the retention of EGF-bound EGFR in Early Endosome Antigen1 (EEA1)-positive vesicles while preventing its trafficking to the lysosome. These events result in the accumulation of endosomal vesicles harboring active receptor throughout the cell and a reorganization of the actin cytoskeleton. EGF-dependent cell migration and filopodia formation is reliant upon this altered trafficking, and can be prevented by blocking retrograde trafficking. Together, these results indicate that intracellular EGFR may play an essential role in cancer metastasis and a potential mechanism for the failure of therapeutic antibodies in EGFR-driven metastatic breast cancer.

Wrong place at the wrong time: how retrograde trafficking drives cancer metastasis through receptor mislocalization

“…Previously demonstrated in yeast that the retromer complex is involved in mammalian target of rapamycin (mTOR) signaling, high expression levels of mTOR have been similarly observed in GOLPH3-amplified human tumor tissues, resulting in increased pAKT activity [40] . Not only is increased pAKT associated with high metastatic potential in breast cancers, but mutations in an anchor protein such as GOLPH3 could result in endosomal retention of receptors by inhibiting their transition out of endosomes, leading to prolonged signal transduction and metastasis [41,42] .…”

“…An event frequently observed in cancers such as breast, pancreatic, and lung is the localization of activated receptor tyrosine kinases in the perinuclear space [43][44][45] . While not all of these receptors have been shown to pass through the Golgi, they do appear to be subject to retrotranslocation as many of them are found in the nucleus, including fibroblast growth factor receptor (FGFR), members of the ErbB family, and TGF-β receptor, all of which will be further discussed below [41,46,47] .…”

“…Nuclear EGFR has been found to be associated with more than 40 percent of breast cancer tumors and 35 percent of esophageal squamous cell cancers, correlated to shorter overall survival in patients and increased metastatic potential, respectively [93,94] . Nuclear EGFR also contributes to cetuximab and gefitinib resistance, likely due to the restricted access of the therapeutics to the target protein [41,85] . Finally, the role of retrotranslocated EGFR as a transcriptional co-factor further exemplifies its kinase-independent function, highlighting the need for therapeutically targeting this process.…”

“…This allows for signal transduction to remain unattenuated, resulting in a MUC1-dependent increase in breast cancer cell migration rates, an effect completely eliminated by the introduction of a retrograde trafficking inhibitor, Retro-2. Inhibiting retrotranslocation of EGFR, even in the presence of MUC1, results in a reduced migratory phenotype through cytoskeletal rearrangement and reduction of focal adhesion kinase (FAK)-positive structures [41] .…”

Glycosylation pathways of human corneal and conjunctival epithelial cell mucins

“…Typically, O-glycans are densely attached to Ser/Thr residues in tandem repeat sequences [6,19,20]. N-glycosylation sites (Asn-x-Ser/Thr) and N-glycans have also been found in mucins [21,22] and the cell surface-bound MUC1 associates with Tyr-kinase receptors that are N-glycosylated [13,14]. Mucin N-glycosylation plays a role in epitope exposure, barrier function and intracellular transport of mucins [23,24].…”