Bergbower Emily, Boinot Clement, Sabirzhanova Inna, Guggino William, Cebotaru Liudmila
The Graduate Training Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Cell Physiol Biochem. 2018;45(2):639-655. doi: 10.1159/000487120. Epub 2018 Jan 29.
BACKGROUND/AIMS: The CFTR-Associated Ligand (CAL), a PDZ domain containing protein with two coiled-coil domains, reduces cell surface WT CFTR through degradation in the lysosome by a well-characterized mechanism. However, CAL's regulatory effect on ΔF508 CFTR has remained almost entirely uninvestigated.
In this study, we describe a previously unknown pathway for CAL by which it regulates the membrane expression of ΔF508 CFTR through arrest of ΔF508 CFTR trafficking in the endoplasmic reticulum (ER) using a combination of cell biology, biochemistry and electrophysiology.
We demonstrate that CAL is an ER localized protein that binds to ΔF508 CFTR and is degraded in the 26S proteasome. When CAL is inhibited, ΔF508 CFTR retention in the ER decreases and cell surface expression of mature functional ΔF508 CFTR is observed alongside of enhanced expression of plasma membrane scaffolding protein NHERF1. Chaperone proteins regulate this novel process, and ΔF508 CFTR binding to HSP40, HSP90, HSP70, VCP, and Aha1 changes to improve ΔF508 CFTR cell surface trafficking.
Our results reveal a pathway in which CAL regulates the cell surface availability and intracellular retention of ΔF508 CFTR.
背景/目的：CFTR相关配体（CAL）是一种含有两个卷曲螺旋结构域的PDZ结构域蛋白，通过一种已明确的机制在溶酶体中降解，从而减少细胞表面的野生型CFTR。然而，CAL对ΔF508 CFTR的调节作用几乎完全未被研究。
在本研究中，我们描述了一条此前未知的CAL作用途径，通过结合细胞生物学、生物化学和电生理学方法，CAL通过在内质网（ER）中阻止ΔF508 CFTR的转运来调节其膜表达。
我们证明CAL是一种定位于内质网的蛋白，它与ΔF508 CFTR结合并在26S蛋白酶体中降解。当CAL受到抑制时，ΔF508 CFTR在内质网中的滞留减少，同时观察到成熟功能性ΔF508 CFTR的细胞表面表达以及质膜支架蛋白NHERF1的表达增强。伴侣蛋白调节这一新过程，并且ΔF508 CFTR与HSP40、HSP90、HSP70、VCP及Aha1的结合发生变化，以改善ΔF508 CFTR的细胞表面转运。
我们的结果揭示了一条CAL调节ΔF508 CFTR细胞表面可用性和细胞内滞留的途径。
