Mol Cancer Res. 2012 Dec; 10(12):1597-606

Expression of Wnt3 activates Wnt/β-catenin pathway and promotes EMT-like phenotype in trastuzumab resistant HER2-overexpressing breast cancer cells.

Wu Y 1,3,4, Ginther C 2,4, Kim J 1,3, Mosher N 1,3, Chung S 1,3, Slamon D 2,4 and Vadgama JV 1,3,4

Divisions of 1Cancer Research and Training, and 2Hematology/Oncology, Department of Medicine, 3Charles R. Drew University of Medicine and Science; and 4University of California at Los Angeles, David Geffen School of Medicine, Los Angeles, California

 

ABSTRACT:

To understand the mechanisms leading to trastuzumab resistance in HER2-overexpressing breast tumors, we created trastuzumab-insensitive cell lines (SKBR3/100-8 and BT474/100-2). The cell lines maintain HER2 receptor overexpression and show increase in EGF receptor (EGFR). Upon trastuzumab treatment, SKBR3/100-8 and BT474/100-2 cell lines displayed increased growth rate and invasiveness. The trastuzumab resistance in SKBR3/100-8 and BT474/100-2 was accompanied with activation of the Wnt/β-catenin signaling pathway. Further investigation found that Wnt3 overexpression played a key role toward the development of trastuzumab resistance. The expression of Wnt3 in trastuzumab-resistant cells increased nuclear expression of β-catenin and transactivated expression of EGFR. The increased Wnt3 in the trastuzumab-resistant cells also promoted a partial EMT-like transition (epithelial-to-mesenchymal transition); increased N-cadherin, Twist, Slug; and decreased E-cadherin. Knockdown of Wnt3 by siRNA restored cytoplasmic expression of β-catenin and decreased EGFR expression in trastuzumab-resistant cells. Furthermore, the EMT markers were decreased, E-cadherin was increased, and the cell invasiveness was inhibited in response to the Wnt3 downregulation. Conversely, SKBR3 cells which had been stably transfected with full-length Wnt3 exhibited EMT-like transition. The Wnt3 transfectants, SKBR3/Wnt3-7 and SKBR3/Wnt3-9, showed a significant decrease in E-cadherin and increase in N-cadherin, Twist, and Slug. The cells were less sensitive to trastuzumab than parental SKBR3 and vector-transfected cells. In summary, our data suggest that Wnt3 overexpression activates Wnt/β-catenin signaling pathway that leads to transactivation of EGFR and promotes EMT-like transition. This could be an important mechanism leading to trastuzumab resistance in HER2-overexpressing breast cancer cells.

PMID: 23071104

 

SUPPLEMENT:

It is well established that HER2 overexpressing breast cancer patients have a poor outcome from their disease. Until the discovery of trastuzumab (Herceptin), no effective treatment was available. However, clinical data suggest that a large number of these patients receiving trastuzumab treatment will become resistant to trastuzumab. It is unclear what mechanisms may contribute to resistance to trastuzumab.

In this study we identified a novel mechanism that overexpression of Wnt3 in HER2-cells promotes epithelial to mesenchymal transition, transactivation of EGFR, and leads to trastuzumab resistance. Therefore Wnt3 could be critical target for reversing and/or preventing drug resistance and for target therapy.

 

ACKNOWLEDGEMENT:

This work was supported, in part, by grants from NIH/National Cancer Institute 1U54CA14393-01, U56 CA101599-01, CA15083-25S3; R25DK067015-01, and Department of Defense Breast Cancer Research Program grant BC043180 to J.V. Vadgama and pilot project to Y. Wu NIH-NIMHD U54 MD007598.
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