Fatty acid synthase phosphorylation: a novel therapeutic target in HER2-overexpressing breast cancer cells
- Equal contributors
1 Department of Breast Medical Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
2 Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
3 Department of Molecular Pathology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
4 Department of General Internal Medicine, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA
5 The University of Texas Graduate School of Biomedical Sciences at Houston, 6767 Bertner Ave., Houston, TX 77030, USA
6 Current address: Laboratory of Individualized Therapies, M. D. Anderson International España, Calle de Arturo Soria, 28033 Madrid, Spain
Breast Cancer Research 2010, 12:R96 doi:10.1186/bcr2777
See related letter by Oliveras-Ferraros et al., http://breast-cancer-research.com/content/13/1/401Published: 16 November 2010
The human epidermal growth factor receptor 2 (HER2) is a validated therapeutic target in breast cancer. Heterodimerization of HER2 with other HER family members results in enhanced tyrosine phosphorylation and activation of signal transduction pathways. HER2 overexpression increases the translation of fatty acid synthase (FASN), and FASN overexpression markedly increases HER2 signaling, which results in enhanced cell growth. However, the molecular mechanism and regulation of HER2 and FASN interaction are not well defined. Lapatinib is a small-molecule tyrosine kinase inhibitor that blocks phosphorylation of the epidermal growth factor receptor and HER2 in breast cancer cells, resulting in apoptosis. We hypothesized that FASN is directly phosphorylated by HER2, resulting in enhanced signaling and tumor progression in breast cancer cells.
Using mass spectrometry, we identified FASN as one of the proteins that is dephosphorylated by lapatinib in SKBR3 breast cancer cells. Immunofluorescence, immunoprecipitation, Western blotting, a kinase assay, a FASN enzymatic activity assay, an invasion assay, a cell viability assay and zymography were used to determine the role of FASN phosphorylation in invasion of SKBR3 and BT474 cells. The FASN inhibitor C75 and small interfering RNA were used to downregulate FASN expression and/or activity.
Our data demonstrated that FASN is phosphorylated when it is in complex with HER2. FASN phosphorylation was induced by heregulin in HER2-overexpressing SKBR3 and BT474 breast cancer cells. Heregulin-induced FASN phosphorylation resulted in increased FASN enzymatic activity, which was inhibited by lapatinib. The FASN inhibitor C75 suppressed FASN activity by directly inhibiting HER2 and FASN phosphorylation. Blocking FASN phosphorylation and activity by lapatinib or C75 suppressed the activity of matrix metallopeptidase 9 and inhibited invasion of SKBR3 and BT474 cells.
FASN phosphorylation by HER2 plays an important role in breast cancer progression and may be a novel therapeutic target in HER2-overexpressing breast cancer cells.