Abstract
Excess presence of the human epidermal growth factor receptor 2 (HER2) as well as of the focal adhesion protein complexes are associated with increased proliferation, migratory, and invasive behavior of cancer cells. A cross-regulation between HER2 and integrin signaling pathways has been found, but the exact mechanism remains elusive. Here, we investigated whether HER2 colocalizes with focal adhesion complexes on breast cancer cells overexpressing HER2. For this purpose, vinculin or talin green fluorescent protein (GFP) fusion proteins, both key constituents of focal adhesions, were expressed in breast cancer cells. HER2 was either extracellularly or intracellularly labeled with fluorescent quantum dots nanoparticles (QDs). The cell-substrate interface was analyzed at the location of the focal adhesions by means of total internal reflection fluorescent microscopy or correlative fluorescence- and scanning transmission electron microscopy. Expression of HER2 at the cell-substrate interface was only observed upon intracellular labeling, and was heterogeneous with both HER2-enriched and -low regions. In contrast to an expected enrichment of HER2 at focal adhesions, an anti-correlated expression pattern was observed for talin and HER2. Our findings suggest a spatial anti-correlation between HER2 and focal adhesion complexes for adherent cells.
Highlights
human epidermal growth factor receptor 2 (HER2), named ErbB2, belongs to the epidermal growth factor receptor (EGFR) family, and is overexpressed in 20–30% of breast cancer cases [1]
To analyze HER2 expression within the proximity of focal adhesions, a labeling protocol was developed for SKBR3 breast cancer cells
Focal adhesions were tagged by transfection of eGFPvinculin (Fig 2A and 2B) that allows labeling of integral proteins of the adhesion complex [22]
Summary
HER2, named ErbB2, belongs to the epidermal growth factor receptor (EGFR) family, and is overexpressed in 20–30% of breast cancer cases [1]. High HER2 expression promotes proliferation, migration, and invasiveness of cancer cells, whereby HER2 is preferentially found at the plasma membranes in so-called ruffles [2,3,4] These cellular processes are enhanced by the adhesion of tumor cells to their surrounding environment, the extracellular matrix (ECM). It has been established that integrin- and HER2-signaling are functionally linked by sharing common signaling pathways that actively modulate cellular responses involved in cancer cell invasion [6,7,8,9,10]. It was found, for instance, that focal
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