Fatty acid synthase phosphorylation: a novel therapeutic target in HER2-overexpressing breast cancer cells

Abstract

IntroductionThe 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.MethodsUsing 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.ResultsOur 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.ConclusionsFASN phosphorylation by HER2 plays an important role in breast cancer progression and may be a novel therapeutic target in HER2-overexpressing breast cancer cells.

Involvement of de novo synthesized palmitate and mitochondrial EGFR in EGF induced mitochondrial fusion of cancer cells

“…The relationship between de novo fatty acid synthesis and members of the EGFR family is especially close and bi-directional. 17,18 Our finding, pmEGFR signaling promotes mitochondrial fusion by interacting with/activating FASN to elevate the levels of de novo synthesized palmitate that in turn activates mtEGFR to promote mitochondrial fusion, further supports that FASN or de novo fatty acid synthesis is a part of EGFR's oncogenic machinery.…”

“…HER2 can activate FASN through physical interaction and phosphorylation. 18 EGFR was primarily found in the plasma membrane, where it is activated by its extracellular ligands such as EGF. Besides the plasma membrane, EGFR can also exist in the nucleus 19,20 and in the mitochondrion.…”

Organ-Specific Cancer Metabolism and Its Potential for Therapy

“…Additionally, the amplification/overexpression of the genetic driver HER2 defines fatty acid metabolism in one subtype of breast cancers: It has recently been suggested that HER2 directly phosphorylates and thereby activates fatty acid synthase [68]. Thus, fatty acid synthase inhibitors might be potent drugs in HER2 amplified breast tumors [68].…”

The Electronics of HER2/neu Positive Breast Cancer Cells

“…There is evidence that HER2 posphorylates FASN, which results in increased enzymatic activity. Blocking FASN phosphorylation and enzymatic activity by either lapatinib (HER2 specific tyrosine kinase inhibitor) or C75 (FASN inhibitor) suppressed invasion of SKBR3 and BT474 cells (Jin et al 2010). In order to sustain this lipogenic phenotype, the cells are in constant demand of cofactors that are essential for glycolysis and fatty acid synthesis.…”