Acquisition of Letrozole Resistance Through Activation of the p38/MAPK Signaling Cascade.

Abstract

Previous reports identified a global proteomic signature of estrogen-independent letrozole resistant breast cancer cells, however, it remains unclear how letrozole-resistance is impacted when cells remain estrogen receptor positive (ER+). To capture the protein expression profile associated with ER+ Aromatase inhibitor (AI) resistance, a global proteomic analysis was conducted using the letrozole-sensitive (T47Darom cells) and letrozole-resistant cells (T47DaromLR cells). To examine the molecular features associated with this phenotype Kaplan- Meier analysis, phospho-antibody arrays, proliferation and apoptosis assays were conducted. MAP3K6 was up-regulated in the T47DaromLR cells by 3.2-fold (p<0.01) which was associated with a decrease in relapse-free survival among breast cancer patients (p=0.0019). Members of the MAPK/p38 pathway (i.e., phospho-MKK6, phospho-p38, phospho-RSK1, phospho-RSK2, and p70S6K MAPK) were also increased in the T47DaromLR cells, while inhibiting p38 led to decreased proliferation and induction of apoptosis. Activation of the p38/MAPK pathway leads to ER+ AI-resistance.