Mechanisms of HER2-induced endothelial cell retraction.
BACKGROUND
HER2 overexpression imparts a metastatic advantage in breast cancer. We have shown that HER2 signaling in breast cancer cells induces adjacent endothelial cell (EC) retraction, disrupting endothelial integrity. Because endothelial integrity is dependent on the adherens junctions, we postulated that the mechanism of tumor cell-induced EC retraction involves dissociation of catenin proteins from vascular endothelial (VE) cadherin. In this study, we report a loss of VE-cadherin in tumor-associated EC. We also tested for a change of catenin dissociation from VE-cadherin by manipulating HER2 signaling in tumor cells.


METHODS
We tested confluent monolayers of human EC for downregulation of VE cadherin and dissociation of catenins from VE cadherin after exposure to breast cancer cells or conditioned media. Using immunoprecipitation, we quantitated the remaining complexed catenins to VE-cadherin in tumor-associated EC after different treatments to manipulate HER2 signaling.


RESULTS
Treatment of EC with conditioned media from MCF-7 cells expressing HER2 induced a loss of VE-cadherin expression, and time-dependent dissociation of catenins from VE cadherin. Catenin dissociation from VE-cadherin was enhanced by Heregulin beta1 (P < .05) stimulation and decreased by trastuzumab (P < .05) blockade of HER2 signaling in cancer cells. An increase in EC phosphoSrc (Tyr 416) was seen by 8 hours.


CONCLUSIONS
Our data suggest that HER2 induction of EC retraction involves both down-regulation of VE-cadherin and dissociation of catenins. HER2 signaling appears to regulate this potential metastatic mechanism. Further, Src phosphorylation suggests that this pathway may be involved in this mechanism.
Carter
W Bradford
WB
Don & Erika Wallace Comprehensive Breast Program at H. Lee Moffitt Cancer Center and Research Institute and Department of Interdisciplinary Oncology, University of South Florida, Tampa, FL, USA. Bradford.Carter@moffitt.org
Niu
Guilian
G
Ward
Michael D
MD
Small
Gregory
G
Hahn
Julianne E
JE
Muffly
Barbara J
BJ
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D015820:Cadherins / Q000378:metabolism; D051177:Catenins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000473:pathology; D017077:Culture Media, Conditioned; D015536:Down-Regulation / Q000502:physiology; D042783:Endothelial Cells / Q000473:pathology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D066298:In Vitro Techniques; D015398:Signal Transduction / Q000235:genetics
D015820:Cadherins; D051177:Catenins; D017077:Culture Media, Conditioned