Biochemistry and Molecular Biology Unit, Department of Biology, University of Girona, Girona 17071, Spain.
Int J Oncol. 2012 Sep;41(3):1128-38. doi: 10.3892/ijo.2012.1509. Epub 2012 Jun 6.
The deregulation of the epidermal growth factor receptor (EGFR) pathway plays a major role in the pathogenesis of prostate cancer (PCa). However, therapies targeting EGFR have demonstrated limited effectiveness in PCa. A potential mechanism to overcome EGFR blockade in cancer cells is the autocrine activation of alternative receptors of the human EGFR (HER) family through the overexpression of the HER receptors and ligands. In the present study, we were interested in analyzing if this intrinsic resistance mechanism might contribute to the inefficacy of EGFR inhibitors in PCa. To this end, we selected two androgen-independent human prostate carcinoma cell lines (DU145 and PC3) and established DU145 erlotinib-resistant cells (DUErR). Cells were treated with three EGFR inhibitors (cetuximab, gefinitib and erlotinib) and the sensitivity to each treatment was assessed. The gene expression of the four EGFR/HER receptors and seven ligands of the HER family was analyzed by real-time PCR prior to and after each treatment. The receptors expression and activation were further characterized by flow cytometry and western blot analysis. EGFR inhibition rapidly induced enhanced gene expression of the EGF, betacellulin and neuregulin-1 ligands along with HER2, HER3 and HER4 receptors in the DU145 cells. In contrast, slight changes were observed in the PC3 cells, which are defective in the phosphatase and tensin homolog (PTEN) tumor suppressor gene. In the erlotinib-resistant DUErR cells, the expression of HER2 and HER3 was increased at mRNA and protein levels together with neuregulin-1, leading to enhanced HER3 phosphorylation and the activation of the downstream PI3K/Akt survival pathway. HER3 blockage by a monoclonal antibody restored the cytostatic activity of erlotinib in DUErR cells. Our results confirm that the overexpression and autocrine activation of HER3 play a key role in mediating the resistance to EGFR inhibitors in androgen-independent PCa cells.
表皮生长因子受体 (EGFR) 通路的失调在前列腺癌 (PCa) 的发病机制中起着重要作用。然而，针对 EGFR 的治疗方法在 PCa 中的疗效有限。克服癌细胞中 EGFR 阻断的一个潜在机制是通过过度表达 HER 受体和配体，使 HER 家族的替代受体发生自分泌激活。在本研究中，我们感兴趣地分析这种内在耐药机制是否有助于 EGFR 抑制剂在 PCa 中的无效性。为此，我们选择了两种雄激素非依赖性人前列腺癌细胞系（DU145 和 PC3），并建立了 DU145 厄洛替尼耐药细胞（DUErR）。用三种 EGFR 抑制剂（西妥昔单抗、吉非替尼和厄洛替尼）处理细胞，并评估每种治疗的敏感性。在每种治疗之前和之后，通过实时 PCR 分析四个 EGFR/HER 受体和 HER 家族的七个配体的基因表达。通过流式细胞术和 Western blot 分析进一步表征受体表达和激活。EGFR 抑制迅速诱导 DU145 细胞中 EGF、betacellulin 和神经调节蛋白-1 配体以及 HER2、HER3 和 HER4 受体的基因表达增强。相比之下，在磷酸酶和张力蛋白同源物 (PTEN) 肿瘤抑制基因缺陷的 PC3 细胞中观察到轻微变化。在厄洛替尼耐药的 DUErR 细胞中，HER2 和 HER3 的表达在 mRNA 和蛋白水平上均增加，同时伴有神经调节蛋白-1 的表达增加，导致 HER3 磷酸化增强和下游 PI3K/Akt 存活途径的激活。HER3 阻断抗体恢复了 DUErR 细胞中厄洛替尼的细胞抑制活性。我们的结果证实，HER3 的过表达和自分泌激活在介导雄激素非依赖性 PCa 细胞对 EGFR 抑制剂的耐药性中起着关键作用。
