Haemophilus influenzae triggers autophagy in HEp-2 cells

The group A Streptococcus interleukin-8 protease SpyCEP promotes bacterial intracellular survival by evasion of autophagy

Autophagy serves an innate immune function in defending the host against invading bacteria, including group A Streptococcus (GAS). Autophagy is regulated by numerous host proteins, including the endogenous negative regulator calpain, a cytosolic protease. Globally disseminated serotype M1T1 GAS strains associated with high invasive disease potential express numerous virulence factors and resist autophagic clearance. Upon in vitro infection of human epithelial cell lines with representative wild-type GAS M1T1 strain 5448 (M1.5448), we observed increased calpain activation linked to a specific GAS virulence factor, the IL-8 protease SpyCEP. Calpain activation inhibited autophagy and decreased capture of cytosolic GAS in autophagosomes. In contrast, the serotype M6 GAS strain JRS4 (M6.JRS4), which is highly susceptible to host autophagy-mediated killing, expresses low levels of SpyCEP and does not activate calpain. Overexpression of SpyCEP in M6.JRS4 stimulated calpain activation, inhibited autophagy and significantly decreased bacterial capture in autophagosomes. These paired loss- and gain-of-function studies reveal a novel role for the bacterial protease SpyCEP in enabling GAS M1 evasion of autophagy and host innate immune clearance.

COPD-Related Modification to the Airway Epithelium Permits Intracellular Residence of Nontypeable Haemophilus influenzae and May Be Potentiated by Macrolide Arrest of Autophagy

Introduction

COPD is an inflammatory airway pathology associated with recurrent infection by nontypeable Haemophilus influenzae (NTHi) that is not effectively managed by macrolide antibiotic therapy. We hypothesised that NTHi is able to reside intracellularly within COPD-derived airway epithelial cells (AEC), and that the factors contained in cigarette smoke when coupled with exposure to erythromycin or azithromycin arrest autophagy, the principle mechanism responsible for clearing intracellular bacteria (called "xenophagy").

Methods

Cultures of bronchial airway epithelial cells derived from control and COPD participants were differentiated at an air-liquid interface and exposed to macrolide antibiotics, 10% cigarette smoke-extract (CSE) and NTHi. Markers of autophagic flux and intracellular NTHi were assessed using Western blot analysis and transmission electron microscopy.

Results

AEC treated with macrolide antibiotics or 10% CSE exhibited a block in autophagic flux as evidenced by a concomitant increase in LC3-II and Sequestosome abundance (vs control; both P < 0.01). While control AEC showed no clear evidence of intracellular NTHi, COPD-derived cultures exhibited abundant NTHi within the cytoplasm. Further, intracellular NTHi that were encapsulated within vesicles propagated from the apical epithelial layer to the basal cell layer.

Discussion

Taken together, our findings indicate that COPD, cigarette smoke and macrolide antibiotics potentiate the susceptibility to persistent intracellular NTHi. A major mechanism for this is arresting normal autophagic flux in airway epithelial cells. Hence, structural modifications that mitigate this off-target effect of macrolides have significant potential to clear intracellular NTHi and thereby reduce the influence of this pathogen in the airways afflicted by COPD.

Bacteria induce autophagy in a human ocular surface cell line

Autophagy protects cells from intracellular pathogens, but can be exploited by some infectious agents to their benefit. Currently it is not known if bacteria induce autohpagy in cells of the cornea. The goal of this study was to develop an ocular surface autophagy reporter cell line and determine whether ocular bacterial pathogens influence host responses through autophagy induction. The cell line was made using lentivirus transduction of an LC3-GFP fusion protein in human corneal limbal epithelial (HCLE) cells. LC3-GFP puncta in HCLEs were induced by rapamycin and ammonium chloride treatments, and prevented by the autophagy inhibitors 3-methyladenine (3'MA) and bafilomycin. Importantly, secretomes from Escherichia coli, Serratia marcescens, Staphylococcus aureus, methicillin sensitive (MSSA) and resistant (MRSA), were found to induce autophagy, whereas other bacteria, including Acinetobacter baumannii, Achromobacter xylosoxidans, Enterococcus faecalis, Klebsiella pneumoniae, Moraxella sp., and Stenotrophomonas maltophilia, did not. Our data indicates differences between tested ocular isolates of MRSA and MSSA in the activation of autophagy. HCLEs treated with 3'MA were slightly more susceptible to cytotoxic factors produced by S. marcescens and MRSA keratitis isolates, by contrast, bafilomycin A1 treatment caused no difference. This work demonstrates the successful development and validation of an autophagy reporter corneal cell line and indicates differences between ocular bacterial isolates in the activation of autophagy.

Downregulation of miRNA-26b inhibits cancer proliferation of laryngeal carcinoma through autophagy by targeting ULK2 and inactivation of the PTEN/AKT pathway

Laryngeal carcinoma is one of the most common tumors of the head and neck cancers, the pathogenesis of which remains yet unclear. It has been discovered through research that microRNAs (miRNAs) play an important role during the genesis of laryngeal carcinoma. In the present study we investigated the effect of miRNA-26b on the proliferation of laryngeal carcinoma and elucidated the potential underlying mechanisms in order to provide new targets for laryngeal carcinoma. Firstly, we found that miRNA-26b expression was significantly increased in patients with laryngeal carcinoma, compared with normal volunteers. The downregulation of miRNA-26b inhibited cell proliferation and induced apoptosis of Hep-2 cells. Furthermore, downregulation of the expression of miRNA‑26b promoted Bax, LC3 and p62 protein expression, decreased ULK2 mRNA and protein expression, as well as PTEN protein expression and increased phosphorylated‑AKT protein expression in Hep-2 cells as determined using quantification by real-time PCR and western blotting. The concomitant downregulation of ULK2 and miRNA-26b futher enhanced the miRNA‑26b-induced autophagy and apoptosis in addition to the miRNA-26b-inhibited cell proliferation of Hep-2 cells by targeting ULK2 and inactivating the PTEN/AKT pathway as determined by immunocytofluorescence. These findings revealed that miRNA-26b may play a key role in cell growth and death of laryngeal carcinoma through ULK2 and the PTEN/AKT pathway, and thus may be a new target for gene therapy in laryngeal carcinoma.