Receptor tyrosine kinase ERBB4 mediates acquired resistance to ERBB2 inhibitors in breast cancer cells

Approximately 25% of breast cancers overexpress and depend on the receptor tyrosine kinase ERBB2, one of 4 ERBB family members. Targeted therapies directed against ERBB2 have been developed and used clinically, but many patients continue to develop resistance to such therapies. Although much effort has been focused on elucidating the mechanisms of acquired resistance to ERBB2-targeted therapies, the involvement of ERBB4 remains elusive and controversial. We demonstrate that genetic ablation of ERBB4, but not ERBB1-3, led to apoptosis in lapatinib-resistant cells, suggesting that the efficacy of pan-ERBB inhibitors was, at least in part, mediated by the inhibition of ERBB4. Moreover, ERBB4 was upregulated at the protein level in ERBB2+ breast cancer cell lines selected for acquired lapatinib resistance <i>in vitro</i> and in <i>MMTV-Neu</i> mice following prolonged lapatinib treatment. Knockdown of ERBB4 caused a decrease in AKT phosphorylation in resistant cells but not in sensitive cells, suggesting that ERBB4 activated the PI3K/AKT pathway in lapatinib-resistant cells. Importantly, ERBB4 knockdown triggered apoptosis not only in lapatinib-resistant cells but also in trastuzumab-resistant cells. Our results suggest that although ERBB4 is dispensable for naïve ERBB2+ breast cancer cells, it may play a key role in the survival of ERBB2+ cancer cells after they develop resistance to ERBB2 inhibitors, lapatinib and trastuzumab.约25%的乳腺癌会过表达并依赖于受体酪氨酸激酶ERBB2（ERBB2），该激酶属于ERBB家族的4个成员之一。针对ERBB2的靶向治疗已被开发并应用于临床，但诸多患者仍会对这类治疗产生耐药性。尽管学界已投入大量精力阐明ERBB2靶向治疗获得性耐药的机制，但ERBB4在其中的作用仍不甚明确且存在争议。我们的研究证实，仅特异性敲除ERBB4（而非ERBB1至ERBB3）即可诱导拉帕替尼耐药细胞发生细胞凋亡，这提示泛ERBB抑制剂的疗效至少部分是通过抑制ERBB4介导的。此外，在体外筛选获得拉帕替尼耐药的ERBB2阳性乳腺癌细胞系，以及经长期拉帕替尼处理的MMTV-Neu小鼠体内，ERBB4的蛋白水平均出现上调。对ERBB4进行基因敲低可降低耐药细胞中AKT的磷酸化水平，但对敏感细胞无此效果，这表明ERBB4可在拉帕替尼耐药细胞中激活PI3K/AKT信号通路。值得注意的是，敲低ERBB4不仅可诱导拉帕替尼耐药细胞发生细胞凋亡，还可诱导曲妥珠单抗耐药细胞凋亡。我们的研究结果表明，尽管ERBB4对未经药物处理的ERBB2阳性乳腺癌细胞并非必需，但在ERBB2阳性癌细胞对ERBB2抑制剂拉帕替尼和曲妥珠单抗产生耐药性后，ERBB4可能在其存活过程中发挥关键作用。