Lapatinib-Mediated Cyclooxygenase-2 Expression via Epidermal Growth Factor Receptor/HuR
Interaction Enhances the Aggressiveness of Triple-Negative Breast Cancer Cells
Te-Chun Hsia, Chih-Yen Tu, Yun-Ju Chen, Ya-Ling Wei, Meng-Chieh Yu, Wen-Shu Chen, Ming-Hsin Yeh, Mien-Chie Hung, and Wei-Chien Huang
Center for Molecular Medicine, China Medical University Hospital and Graduate Institute of Cancer Biology
Background & Aims
Lapatinib, a dual epidermal growth factor receptor (EGFR)/human epidermal growth factor receptor 2 (HER2) kinase inhibitor, showed clinical benefits in advanced HER2-positive breast cancer patients. Because some triple-negative breast cancers (TNBCs) frequently overexpress EGFR, the antitumor activity of lapatinib in such diseases was also tested. However, the results showed a worse event-free survival rate. It remains unknown whether and how lapatinib elicits the aggressiveness of such cancer cells
.
This study aimed to understand the therapeutic impact of lapatinib in TNBCs.Materials & Methods
Lapatinib-resistant cancer cell clones were established by treatment with gradually increasing concentrations of lapatinib for over 1 month. The protein and RNA expression in TNBCs and lapatinib-resistant clones with western blot and real-time PCR. In vitro cell viability was measured using an MTT assay. Migration and Invasion abilities of TNBCs and their lapatinib-resistant clones were determined by wound healing and transwell migration assays. The animal model was established by injection TNBCs into the mammary gland in NOD-SCID mices.
Results
The lapatinib-increased motility was attributed by the elevation of EGFR through the downregulation of microRNA-7 and by the subsequent overexpression of cyclooxygenase-2 (COX-2). Strikingly, independent of its kinase activity, the elevated EGFR at least partly stabilized COX-2 expression by enhancing the binding of HuR to COX-2 mRNA.
Figure 1. The effects of long-term treatment with lapatinib on migration and invasion of TNBC in vitro and in vivo.
Figure 2. The involvement of increased EGFR expression in cell migration and invasion of lapatinib-resistant TNBCs.
Figure 3. The involvement of has-miR-7 downregulation in the EGFR expression of lapatinib- resistant TNBCs.
Figure 4. The effects of elevation of COX-2 expression on the cell migration of lapatinb- resistant TNBCs.
Figure 6. The involvement of EGFR in the binding of HuR to COX-2 mRNA in lapatinib- resistant TNBCs.
Figure 5. The role of EGFR in the mRNA stability and promoter activity of COX-2 in lapatinib- resistant TNBCs.
Conclusion
These data not only provided a potential explanation for the worse clinical outcome of TNBC patients who receive lapatinib-based treatment, but also shed new light on the molecular mechanism of COX-2 mRNA stabilization by EGFR in a kinase-independent manner.
