Department of Biochemistry, University of Illinois, Urbana, IL, USA.
Department of Biochemistry, University of Illinois, Urbana, IL, USA; Cancer Center at Illinois, University of Illinois, Urbana, IL, USA.
Biochim Biophys Acta Mol Cell Res. 2020 Oct;1867(10):118765. doi: 10.1016/j.bbamcr.2020.118765. Epub 2020 Jun 2.
Accumulation of unfolded protein, or other stresses, activates the classical reactive unfolded protein response (UPR). In the recently characterized anticipatory UPR, receptor-bound estrogen, progesterone and other mitogenic hormones rapidly elicit phosphorylation of phospholipase C γ (PLCγ), activating the anticipatory UPR. How estrogen and progesterone activating their receptors couples to PLCγ phosphorylation and anticipatory UPR activation was unknown. We show that the oncogene c-Src is a rate-limiting regulator whose tyrosine kinase activity links estrogen and progesterone activating their receptors to anticipatory UPR activation. Supporting Src coupling estrogen and progesterone to anticipatory UPR activation, we identified extranuclear complexes of estrogen receptor α (ERα):Src:PLCγ and progesterone receptor:Src:PLCγ. Moreover, Src inhibition protected cancer cells against cell death. To probe Src's role, we used the preclinical ERα biomodulator, BHPI, which kills cancer cells by inducing lethal anticipatory UPR hyperactivation. Notably, Src inhibition blocked BHPI-mediated anticipatory UPR activation and the resulting rapid increase in intracellular calcium. After unbiased long-term selection for BHPI-resistant human breast cancer cells, 4/11 BHPI-resistant T47D clones, and nearly all MCF-7 clones, exhibited reduced levels of normally growth-stimulating Src. Notably, Src overexpression by virus transduction restored sensitivity to BHPI. Furthermore, in wild type cells, several-fold knockdown of Src, but not of ERα, strongly blocked BHPI-mediated UPR activation and subsequent HMGB1 release and necrotic cell death. Thus, Src plays a previously undescribed pivotal role in activation of the tumor-protective anticipatory UPR, thereby increasing the resilience of breast cancer cells. This is a new role for Src and the anticipatory UPR in breast cancer.
未折叠蛋白的积累或其他应激会激活经典的未折叠蛋白反应 (UPR)。在最近描述的预期 UPR 中，受体结合的雌激素、孕激素和其他有丝分裂激素会迅速引发磷脂酶 Cγ (PLCγ)的磷酸化，从而激活预期 UPR。雌激素和孕激素激活其受体如何与 PLCγ 磷酸化和预期 UPR 激活偶联尚不清楚。我们表明，癌基因 c-Src 是一种限速调节因子，其酪氨酸激酶活性将雌激素和孕激素与其受体偶联，从而激活预期 UPR。支持 Src 将雌激素和孕激素偶联到预期 UPR 激活，我们鉴定了雌激素受体α (ERα)的核外复合物：Src:PLCγ 和孕激素受体:Src:PLCγ。此外，Src 抑制可保护癌细胞免受细胞死亡。为了探究 Src 的作用，我们使用了临床前 ERα 生物调节剂 BHPI，它通过诱导致命的预期 UPR 过度激活来杀死癌细胞。值得注意的是，Src 抑制阻断了 BHPI 介导的预期 UPR 激活和随之而来的细胞内钙的快速增加。对 BHPI 耐药的人乳腺癌细胞进行无偏长期选择后，BHPI 耐药 T47D 克隆的 4/11 个和几乎所有 MCF-7 克隆均显示出通常刺激生长的 Src 水平降低。值得注意的是，病毒转导的 Src 过表达恢复了对 BHPI 的敏感性。此外，在野生型细胞中，Src 的几倍敲低，而不是 ERα 的敲低，强烈阻断了 BHPI 介导的 UPR 激活以及随后的 HMGB1 释放和坏死性细胞死亡。因此，Src 在激活肿瘤保护性预期 UPR 中发挥了以前未描述的关键作用，从而增加了乳腺癌细胞的弹性。这是 Src 和预期 UPR 在乳腺癌中的一个新作用。
