Background: Epidermal growth factor receptor (EGFR) is often overexpressed in triple-negative breast cancer (TNBC). However, clinical studies have shown that therapies against EGFR are not effective in patients with TNBC. Recently, it has been reported that arginine 198/200 in EGFR extracellular domain is methylated by PRMT1 and that the methylation confers resistance to EGFR monoclonal antibody cetuximab in colorectal cancer cells. To explore a potential mechanism underlying intrinsic resistance to anti-EGFR therapy in TNBC, we investigated the role of PRMT1 in EGFR methylation and signaling in MDA-MB-468 (468) TNBC cells.
Methods: We knocked down PRMT1 in 468 cells by shRNA, and subjected the cell lysates to Western blot analysis to examine EGFR activation and its downstream molecules. We also evaluated cell proliferation and sphere formation of PRMT1-knockdown cells. Finally, we examined the effects of pan-PRMT inhibitor, AMI-1, on cetuximab by colony formation and soft agar assays.
Results: EGFR methylation and activity was significantly reduced in PRMT1-knockdown cells compared to the parental cells. Knockdown of PRMT1 also reduced cell proliferation and sphere formation. Moreover, AMI-1 sensitized 468 cells to cetuximab.
Conclusion: The results indicate that PRMT1 is critical for EGFR activity in 468 cells. Our data also suggest that inhibition of PRMT1 sensitizes TNBC cells to cetuximab. Thus, inhibition of PRMT1 may be an effective therapeutic strategy to overcome intrinsic resistance to cetuximab in TNBC.
Keywords: Arginine methylation; EGFR; PRMT1; Triple-negative breast cancer.