Department of Pathology, Oslo University Hospital, Oslo, Norway; Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
Department of Pathology, Oslo University Hospital, Oslo, Norway.
Exp Cell Res. 2019 Sep 15;382(2):111473. doi: 10.1016/j.yexcr.2019.06.018. Epub 2019 Jun 21.
ErbB3, which belongs to the epidermal growth factor receptor (EGFR) or ErbB family of receptor tyrosine kinases, is involved in progression of several human cancers and a tight regulation of its expression is crucial. An important mechanism for regulation of ErbB proteins is endocytosis and we recently showed that ErbB3, contrary to other ErbB proteins, like EGFR and ErbB2, is constitutively internalized and degraded. Several studies show that protein kinase C (PKC) can regulate the activation, localization and stability of EGFR and ErbB2. Activation of PKC causes their down-regulation from the plasma membrane, but instead of being degraded the receptors accumulate in an endosomal recycling compartment. Since little is known about possible connections between ErbB3 and PKC, we have in the present study investigated effects PKC activity has on ErbB3 stability and intracellular trafficking. While PKC inhibition tends to increase ErbB3 degradation, activation of PKC causes ErbB3 stabilization. The stabilization was not due to inhibited internalization, on the contrary we find that expression of ErbB3 at the plasma membrane is reduced upon PMA-induced PKC activation. However, while endocytosed ErbB3 under normal conditions and upon PKC inhibition is found in early endosomal antigen 1 (EEA1) positive early endosomes and lysosomal-associated membrane protein 1 (LAMP1) positive late endosomes/lysosomes, indicating that it follows the classic degradative pathway, ErbB3 localizes to EEA1 and LAMP1 negative compartments upon PMA-induced activation of PKC. Altogether this shows that PKC regulates the stability of ErbB3, and knockdown experiments show that PKCδ is essential in this process. A likely explanation is that PKC regulates endosomal sorting of ErbB3 and that activated PKC sorts ErbB3 away from the degradative pathway.
ErbB3 属于表皮生长因子受体 (EGFR) 或 ErbB 家族受体酪氨酸激酶，参与多种人类癌症的进展，其表达的严密调控至关重要。ErbB 蛋白表达调控的一个重要机制是内吞作用，我们最近表明，与其他 ErbB 蛋白（如 EGFR 和 ErbB2）不同，ErbB3 是组成性内化和降解的。几项研究表明，蛋白激酶 C (PKC) 可以调节 EGFR 和 ErbB2 的激活、定位和稳定性。PKC 的激活导致它们从质膜下调，但受体不是被降解，而是在内体再循环隔室中积累。由于对 ErbB3 和 PKC 之间可能存在的联系知之甚少，我们在本研究中研究了 PKC 活性对 ErbB3 稳定性和细胞内转运的影响。虽然 PKC 抑制倾向于增加 ErbB3 的降解，但 PKC 的激活导致 ErbB3 的稳定。这种稳定不是由于抑制内化引起的，相反，我们发现 PMA 诱导的 PKC 激活会减少质膜上 ErbB3 的表达。然而，虽然在正常条件下和 PKC 抑制下内化的 ErbB3 位于早期内体抗原 1 (EEA1) 阳性早期内体和溶酶体相关膜蛋白 1 (LAMP1) 阳性晚期内体/溶酶体中，表明它遵循经典的降解途径，但在 PMA 诱导的 PKC 激活下，ErbB3 定位于 EEA1 和 LAMP1 阴性隔室。总的来说，这表明 PKC 调节 ErbB3 的稳定性，敲低实验表明 PKCδ 在这个过程中是必不可少的。一个可能的解释是 PKC 调节 ErbB3 的内体分选，而激活的 PKC 将 ErbB3 从降解途径中分选出来。
