A novel anti-apoptotic role for apolipoprotein L2 in IFN-γ-induced cytotoxicity in human bronchial epithelial cells.
Airway epithelium functions not only as a physical barrier, but also a regulator of lung inflammation. IFN-γ plays a critical role in airway inflammation associated with respiratory viral infection. We investigated differential protein profiling in IFN-γ-stimulated normal human bronchial epithelial cells (HBEC) using a 2-dimensional gel electrophoresis followed by MALDI-TOF-MS/MS. IFN-γ markedly stimulated apolipoprotein L2 (ApoL2) protein expression in normal HBEC. ApoL2 mRNA expression was also elevated in normal human lung fibroblasts and smooth muscle cells stimulated with IFN-γ, in lung tissues from an IFN-γ-predominant influenza A virus-infected mouse lung injury model, and in cancer lung tissues from human patients. Normal HBEC showed strong resistance to IFN-γ-induced cytotoxicity. ApoL2 knockdown by siRNA promoted IFN-γ-induced cytotoxicity as revealed by a significant drop in cell viability using MTT and CyQUANT NF cell proliferation assays, and a marked increase in hypodiploid sub-G1 cell population in cell cycle analysis. Furthermore, depletion of ApoL2 facilitated IFN-γ-induced membrane damage and chromatin condensation as observed in Hoechst and propidium iodide-double staining and in transmission electron microscopy, and DNA fragmentation using a DNA laddering assay, in a caspase-dependent manner. Our results reveal a novel function for ApoL2 in conferring anti-apoptotic ability of human bronchial epithelium to the cytotoxic effects of IFN-γ, in maintaining airway epithelial layer integrity.
Liao
Wupeng
W
Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Goh
Fera Y
FY
Betts
Richard J
RJ
Kemeny
D Michael
DM
Tam
John
J
Bay
Boon-Huat
BH
Wong
W S Fred
WS
D000818:Animals; D001053:Apolipoproteins / Q000235:genetics / Q000378:metabolism*; D000075943:Apolipoproteins L; D017209:Apoptosis / Q000187:drug effects*; D001980:Bronchi / Q000166:cytology*; D002478:Cells, Cultured; D053938:DNA Fragmentation; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000473:pathology*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D008075:Lipoproteins, HDL / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology; D013058:Mass Spectrometry; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology*
C543112:APOL2 protein, human; D001053:Apolipoproteins; D000075943:Apolipoproteins L; D008075:Lipoproteins, HDL; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D007371:Interferon-gamma