Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina, USA.
Departments of Molecular Genetics and of Microbiology and Neurosurgery, Duke University Medical Center, Durham, North Carolina, USA.
Mol Cell Biol. 2018 Sep 14;38(19). doi: 10.1128/MCB.00304-18. Print 2018 Oct 1.
Eukaryotic ribosomes contain the high-affinity protein kinase C βII (PKCβII) scaffold, receptor for activated C kinase (RACK1), but its role in protein synthesis control remains unclear. We found that RACK1:PKCβII phosphorylates eukaryotic initiation factor 4G1 (eIF4G1) at S1093 and eIF3a at S1364. We showed that reversible eIF4G(S1093) phosphorylation is involved in a global protein synthesis surge upon PKC-Raf-extracellular signal-regulated kinase 1/2 (ERK1/2) activation and in induction of phorbol ester-responsive transcripts, such as cyclooxygenase 2 (Cox-2) and cyclin-dependent kinase inhibitor (p21), or in 5' 7-methylguanosine (mG) cap-independent enterovirus translation. Comparison of mRNA and protein levels revealed that eIF4G1 or RACK1 depletion blocked phorbol ester-induced Cox-2 or p21 expression mostly at the translational level, whereas PKCβ inhibition reduced them both at the translational and transcript levels. Our findings reveal a physiological role for ribosomal RACK1 in providing the molecular scaffold for PKCβII and its role in coordinating the translational response to PKC-Raf-ERK1/2 activation.
真核核糖体含有高亲和力蛋白激酶 CβII（PKCβII）支架、激活的 C 激酶受体（RACK1），但其在蛋白质合成控制中的作用尚不清楚。我们发现 RACK1：PKCβII 在 S1093 处磷酸化真核起始因子 4G1（eIF4G1），在 S1364 处磷酸化 eIF3a。我们表明，可逆的 eIF4G（S1093）磷酸化参与 PKC-Raf-细胞外信号调节激酶 1/2（ERK1/2）激活后的全局蛋白质合成激增，以及诱导佛波酯反应性转录物，如环氧化酶 2（Cox-2）和细胞周期蛋白依赖性激酶抑制剂（p21），或 5' 7-甲基鸟苷（mG）帽非依赖性肠病毒翻译。mRNA 和蛋白质水平的比较表明，eIF4G1 或 RACK1 的耗竭主要在翻译水平上阻断佛波酯诱导的 Cox-2 或 p21 表达，而 PKCβ 抑制则在翻译和转录水平上均降低它们的表达。我们的研究结果揭示了核糖体 RACK1 在为 PKCβII 提供分子支架以及在协调 PKC-Raf-ERK1/2 激活的翻译反应中的生理作用。
