Department of Immunobiology.
Asthma and Airway Disease Research Center, Tucson, Arizona.
Am J Respir Crit Care Med. 2021 Jun 1;203(11):1410-1418. doi: 10.1164/rccm.202006-2576OC.
CC16 (club cell secretory protein) is a pneumoprotein produced predominantly by pulmonary club cells. Circulating CC16 is associated with protection from the inception and progression of the two most common obstructive lung diseases (asthma and chronic obstructive pulmonary disease). Although exact mechanisms remain elusive, studies consistently suggest a causal role of CC16 in mediating antiinflammatory and antioxidant functions in the lung. We sought to determine any novel receptor systems that could participate in CC16's role in obstructive lung diseases. Protein alignment of CC16 across species led to the discovery of a highly conserved sequence of amino acids, leucine-valine-aspartic acid (LVD), a known integrin-binding motif. Recombinant CC16 was generated with and without the putative integrin-binding site. A mouse model and a fluorescent cellular adhesion assay were used to determine the impact of the LVD site regarding CC16 function during live infection and on cellular adhesion during inflammatory conditions. CC16 bound to integrin αβ), also known as the adhesion molecule VLA-4 (very late antigen 4), dependent on the presence of the LVD integrin-binding motif. During infection, recombinant CC16 rescued lung function parameters both when administered to the lung and intravenously but only when the LVD integrin-binding site was intact; likewise, neutrophil recruitment during infection and leukocyte adhesion were both impacted by the loss of the LVD site. We discovered a novel receptor for CC16, VLA-4, which has important mechanistic implications for the role of CC16 in circulation as well as in the lung compartment.
CC16（杯状细胞分泌蛋白）是一种主要由肺杯状细胞产生的肺蛋白。循环 CC16 与从哮喘和慢性阻塞性肺疾病（COPD）这两种最常见的阻塞性肺疾病的起始和进展中得到保护有关。尽管确切的机制仍不清楚，但研究一致表明 CC16 在介导肺部抗炎和抗氧化功能方面具有因果作用。我们试图确定任何可能参与 CC16 在阻塞性肺疾病中作用的新型受体系统。CC16 在物种间的蛋白比对导致发现了一个高度保守的氨基酸序列，亮氨酸-缬氨酸-天冬氨酸（LVD），这是一个已知的整合素结合基序。生成了带有和不带有假定整合素结合位点的重组 CC16。使用小鼠模型和荧光细胞黏附测定法来确定 LVD 位点在活感染期间以及在炎症条件下的细胞黏附期间对 CC16 功能的影响。CC16 依赖于 LVD 整合素结合基序与整合素 αβ（也称为黏附分子 VLA-4（非常晚期抗原 4））结合。在感染期间，重组 CC16 不仅在肺内给药时而且在静脉内给药时都能挽救肺功能参数，但只有在 LVD 整合素结合位点完整时才会这样；同样，感染期间的中性粒细胞募集和白细胞黏附都受到 LVD 位点缺失的影响。我们发现了 CC16 的一种新型受体 VLA-4，这对 CC16 在循环中以及在肺区的作用具有重要的机制意义。
