Inhibition of histone deacetylase suppresses EGF signaling pathways by destabilizing EGFR mRNA in ER-negative human breast cancer cells.

Estrogen receptor alpha (ER)-negative human breast cancer cells frequently overexpress epidermal growth factor receptor (EGFR) and respond poorly to endocrine therapies. Our previous studies demonstrate that histone deacetylation plays a key role in ER gene silencing, and ER expression can be restored with histone deacetylase (HDAC) inhibitors in ER-negative human breast cancer cells. Whether inhibition of HDAC also alters epidermal growth factor (EGF) signaling pathways is not defined. Here we present evidence that reexpression of ER protein by a clinically available HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA or vorinostat), is coupled with loss of EGFR in ER-negative human breast cancer cells. Consistent with this observation, MDA-MB-231 cells, which are ER-negative and overexpress EGFR, that are engineered to express ER show a decrease in EGFR protein expression. Down-regulation of EGFR by SAHA results from attenuation of its mRNA stability. We also confirm that new protein synthesis is required for maintaining EGFR mRNA stability. Further experiments indicate that a decrease in EGFR abolished EGF-initiated signaling pathways including phosphorylated PAK1, p38MAPK and AKT. Thus, SAHA may not only reactivate silenced ER, but also simultaneously deplete EGFR expression. These data suggest that inhibition of HDAC is a promising epigenetic therapy for ER-negative human breast cancer.