Mohamed Raafat, Shajimoon Aravindra, Afroz Rizwana, Gabr Mai, Thomas Walter G, Little Peter J, Kamato Danielle
School of Pharmacy, Pharmacy Australia Centre of Excellence, The University of Queensland, Woolloongabba, Australia.
School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, Australia.
FEBS J. 2022 May;289(9):2642-2656. doi: 10.1111/febs.16297. Epub 2021 Dec 18.
Transforming growth factor (TGF)-β signalling commences with the engagement of TGF-β ligand to cell surface TGF-β receptors (TGFBR) stimulating Smad2 carboxyl-terminal phosphorylation (phospho-Smad2C) and downstream biological responses. In several cell models, G protein-coupled receptors (GPCRs) transactivate the TGF-β receptors type-1 (TGFBR1) leading to phospho-Smad2C, however, we have recently published that in keratinocytes thrombin did not transactivate the TGFBR1. The bulk of TGFBRs reside in the cytosol and in response to protein kinase B (Akt phosphorylation) can translocate to the cell surface increasing the cell's responsiveness to TGF-β. In this study, we investigate the role of Akt in GPCR transactivation of the TGFBR1. We demonstrate that angiotensin II and thrombin do not phosphorylate Smad2C in human vascular smooth muscle cells and in keratinocytes respectively. We used Akt agonist, SC79 to sensitise the cells to Akt and observed that Ang II and thrombin phosphorylate Smad2C via Akt/AS160-dependent pathways. We show that SC79 rapidly translocates TGFBRs to the cell surface thus increasing the cell's response to the GPCR agonist. These findings highlight novel mechanistic insight for the role of Akt in GPCR transactivation of the TGFBR1.
转化生长因子（TGF）-β信号传导始于TGF-β配体与细胞表面TGF-β受体（TGFBR）结合，刺激Smad2羧基末端磷酸化（磷酸化Smad2C）及下游生物学反应。在多个细胞模型中，G蛋白偶联受体（GPCR）可使I型TGF-β受体（TGFBR1）反式激活，导致磷酸化Smad2C，然而，我们最近发表的研究表明，在角质形成细胞中，凝血酶不会使TGFBR1反式激活。大部分TGFBR存在于胞质溶胶中，响应蛋白激酶B（Akt磷酸化）时可转运至细胞表面，增加细胞对TGF-β的反应性。在本研究中，我们探究了Akt在GPCR介导的TGFBR1反式激活中的作用。我们证明，血管紧张素II和凝血酶分别不会在人血管平滑肌细胞和角质形成细胞中使Smad2C磷酸化。我们使用Akt激动剂SC79使细胞对Akt敏感，观察到血管紧张素II和凝血酶通过Akt/AS160依赖性途径使Smad2C磷酸化。我们发现SC79可迅速将TGFBR转运至细胞表面，从而增强细胞对GPCR激动剂的反应。这些发现为Akt在GPCR介导的TGFBR1反式激活中的作用提供了新的机制性见解。
