Cheng Yi-Lin, Wu Yan-Wei, Kuo Chih-Feng, Lu Shiou-Ling, Liu Fu-Tong, Anderson Robert, Lin Chiou-Feng, Liu Yi-Ling, Wang Wan-Yu, Chen Ying-Da, Zheng Po-Xing, Wu Jiunn-Jong, Lin Yee-Shin
Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
Department of Microbiology and Immunology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
mBio. 2017 Jul 25;8(4):e00899-17. doi: 10.1128/mBio.00899-17.
Group A streptococcus (GAS) is an important human pathogen that causes a wide variety of cutaneous and systemic infections. Although originally thought to be an extracellular bacterium, numerous studies have demonstrated that GAS can trigger internalization into nonimmune cells to escape from immune surveillance or antibiotic-mediated killing. Epithelial cells possess a defense mechanism involving autophagy-mediated targeting and killing of GAS within lysosome-fused autophagosomes. In endothelial cells, in contrast, we previously showed that autophagy is not sufficient for GAS killing. In the present study, we showed higher galectin-3 (Gal-3) expression and lower Gal-8 expression in endothelial cells than in epithelial cells. The recruitment of Gal-3 to GAS is higher and the recruitment of Gal-8 to GAS is lower in endothelial cells than in epithelial cells. We further showed that Gal-3 promotes GAS replication and diminishes the recruitment of Gal-8 and ubiquitin, the latter of which is a critical protein for autophagy sequestration. After knockdown of Gal-3 in endothelial cells, the colocalization of Gal-8, parkin, and ubiquitin-decorated GAS is significantly increased, as is the interaction of Gal-8 and parkin, an E3 ligase. Furthermore, inhibition of Gal-8 in epithelial cells attenuates recruitment of parkin; both Gal-8 and parkin contribute to ubiquitin recruitment and GAS elimination. Animal studies confirmed that Gal-3-knockout mice develop less-severe skin damage and that GAS replication can be detected only in the air pouch and not in organs and endothelial cells. These results demonstrate that Gal-3 inhibits ubiquitin recruitment by blocking Gal-8 and parkin recruitment, resulting in GAS replication in endothelial cells. In epithelial cells, GAS can be efficiently killed within the lysosome-fused autophaosome compartment. However, we previously showed that, in spite of LC-3 recruitment, the autophagic machinery is not sufficient for GAS killing in endothelial cells. In this report, we provide the first evidence that Gal-3, highly expressed in endothelial cells, blocks the tagging of ubiquitin to GAS by inhibiting recruitment of Gal-8 and parkin, leading to an enhancement of GAS replication. We also provide the first demonstration that Gal-8 can interact with parkin, the critical E3 ligase, for resistance to intracellular bacteria by facilitating the decoration of bacteria with ubiquitin chains. Our findings reveal that differential levels of Gal-3 and Gal-8 expression and recruitment to GAS between epithelial cells and endothelial cells may contribute to the different outcomes of GAS elimination or survival and growth of GAS in these two types of cells.
A组链球菌(GAS)是一种重要的人类病原体,可引起多种皮肤和全身感染。尽管最初被认为是一种胞外细菌,但大量研究表明,GAS可触发内化进入非免疫细胞,以逃避免疫监视或抗生素介导的杀伤。上皮细胞具有一种防御机制,涉及自噬介导的在溶酶体融合自噬体内靶向和杀伤GAS。相比之下,在内皮细胞中,我们之前表明自噬不足以杀伤GAS。在本研究中,我们发现内皮细胞中半乳糖凝集素-3(Gal-3)的表达高于上皮细胞,而Gal-8的表达低于上皮细胞。在内皮细胞中,Gal-3向GAS的募集高于上皮细胞,而Gal-8向GAS的募集低于上皮细胞。我们进一步表明,Gal-3促进GAS复制,并减少Gal-8和泛素的募集,后者是自噬隔离的关键蛋白。在内皮细胞中敲低Gal-3后,Gal-8、帕金和泛素标记的GAS的共定位显著增加,Gal-8和E3连接酶帕金的相互作用也显著增加。此外,在上皮细胞中抑制Gal-8会减弱帕金的募集;Gal-8和帕金都有助于泛素的募集和GAS的清除。动物研究证实,Gal-3基因敲除小鼠的皮肤损伤较轻,并且仅在气腔中可检测到GAS复制,而在器官和内皮细胞中未检测到。这些结果表明,Gal-3通过阻断Gal-8和帕金的募集来抑制泛素募集,从而导致内皮细胞中GAS的复制。在上皮细胞中,GAS可在溶酶体融合自噬体区室中被有效杀伤。然而,我们之前表明,尽管有LC-3的募集,但自噬机制在内皮细胞中不足以杀伤GAS。在本报告中,我们提供了首个证据,即在内皮细胞中高表达的Gal-3通过抑制Gal-8和帕金的募集来阻断泛素与GAS的结合,从而导致GAS复制增强。我们还首次证明,Gal-8可与关键的E3连接酶帕金相互作用,通过促进细菌被泛素链修饰来抵抗细胞内细菌。我们的研究结果表明,上皮细胞和内皮细胞之间Gal-3和Gal-8表达及向GAS募集的差异水平可能导致这两种细胞中GAS清除或存活及生长的不同结果。