Laboratorio de Biología Celular y Molecular-Instituto de Histología y Embriología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo-CONICET, Mendoza, Argentina.
Autophagy. 2010 Jan;6(1):110-25. doi: 10.4161/auto.6.1.10698.
Staphylococcus aureus is a pathogen that causes serious infectious diseases eventually leading to septic and toxic shock. Classically S. aureus has been considered an extracellular pathogen, but cumulative evidence indicates that it invades cells and replicates intracellularly leading to staphylococcal persistence and chronic disease. It has been previously shown that this pathogen localizes to LC3-labeled compartments and subverts the autophagy pathway. One of the key features of S. aureus infection is the production of a series of virulence factors, including secreted enzymes and toxins. In the present report we present evidence that the pore-forming toxin alpha-hemolysin (Hla) is a S. aureus secreted factor which participates in the activation of the autophagic pathway. In addition, our results indicate that although the toxin elicits an autophagic response this pathway is dysfunctional as indicated by the accumulation of the LC3-II form in cell lysates obtained from intoxicated cells. In addition, not only the purified Hla toxin but also the toxin-secreting pathogen prevented the maturation of autophagosomes. Interestingly, in cells infected with the wild-type strain of S. aureus the bacteria-containing compartments which recruited LC3 onto the limiting membrane did not accumulate the acidotropic probe LysoTracker. In contrast, those phagosomes containing the Hla(-) mutant (unable to produce the toxin) localized in an acidic compartment unlabeled by LC3. These results suggest that the LC3 protein is recruited only to those damaged vacuoles (i.e., perforated by the toxin), perhaps as an attempt to protect the cells. Furthermore, we have demonstrated that the toxin-dependent activation of autophagy (although it is regulated by calcium and requires Atg5) is independent of both PI3Kinase activity and Beclin 1 suggesting the involvement of a non-canonical autophagy pathway.
金黄色葡萄球菌是一种病原体，可导致严重的传染病，最终导致败血性和中毒性休克。经典地，金黄色葡萄球菌被认为是一种细胞外病原体，但累积的证据表明，它可以入侵细胞并在细胞内复制，导致金黄色葡萄球菌的持续存在和慢性疾病。先前已经表明，这种病原体定位于 LC3 标记的隔室，并颠覆了自噬途径。金黄色葡萄球菌感染的一个关键特征是产生一系列毒力因子，包括分泌酶和毒素。在本报告中，我们提供了证据表明，成孔毒素α-溶血素（Hla）是金黄色葡萄球菌分泌的一种因子，参与了自噬途径的激活。此外，我们的结果表明，尽管毒素引发了自噬反应，但该途径是功能性失调的，因为在来自中毒细胞的细胞裂解物中积累了 LC3-II 形式。此外，不仅纯化的 Hla 毒素，而且分泌毒素的病原体都阻止了自噬体的成熟。有趣的是，在感染金黄色葡萄球菌野生型菌株的细胞中，招募 LC3 到限膜上的含有细菌的隔室并没有积累酸性探针 LysoTracker。相比之下，那些含有 Hla(-)突变体（不能产生毒素）的吞噬体定位于未被 LC3 标记的酸性隔室。这些结果表明，LC3 蛋白仅被招募到那些受损的液泡（即被毒素穿孔），也许是为了保护细胞。此外，我们已经证明了依赖毒素的自噬的激活（尽管它受到钙的调节并且需要 Atg5）独立于 PI3Kinase 活性和 Beclin 1，表明涉及非典型自噬途径。
