Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, USA.
Department of Breast Oncology, Juntendo University School of Medicine, Hongo 2-1-1, Bunyo-ku, Tokyo, 113-0033, Japan.
Breast Cancer. 2018 Jan;25(1):74-80. doi: 10.1007/s12282-017-0790-z. Epub 2017 Jun 22.
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.
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.
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.
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.
表皮生长因子受体（EGFR）在三阴性乳腺癌（TNBC）中常过度表达。然而，临床研究表明，针对 EGFR 的治疗在 TNBC 患者中并不有效。最近有报道称，EGFR 细胞外结构域的精氨酸 198/200 被 PRMT1 甲基化，这种甲基化使结直肠癌细胞对 EGFR 单克隆抗体西妥昔单抗产生耐药性。为了探讨 TNBC 中 EGFR 靶向治疗固有耐药的潜在机制，我们研究了 PRMT1 在 MDA-MB-468（468）TNBC 细胞中 EGFR 甲基化和信号转导中的作用。
我们通过 shRNA 敲低 468 细胞中的 PRMT1，并用 Western blot 分析检测 EGFR 激活及其下游分子。我们还评估了 PRMT1 敲低细胞的增殖和球体形成。最后，我们通过集落形成和软琼脂实验检测了泛 PRMT 抑制剂 AMI-1 对西妥昔单抗的影响。
与亲本细胞相比，PRMT1 敲低细胞的 EGFR 甲基化和活性显著降低。PRMT1 的敲低也降低了细胞增殖和球体形成。此外，AMI-1 使 468 细胞对西妥昔单抗敏感。
结果表明 PRMT1 对 468 细胞中 EGFR 的活性至关重要。我们的数据还表明，抑制 PRMT1 可使 TNBC 细胞对西妥昔单抗敏感。因此，抑制 PRMT1 可能是克服 TNBC 中对西妥昔单抗固有耐药的有效治疗策略。
