Autophagic proteins regulate cigarette smoke-induced apoptosis: protective role of heme oxygenase-1

Autophagy. 2008 Oct;4(7):887-95. doi: 10.4161/auto.6767. Epub 2008 Oct 12.

Abstract

Cigarette smoke-induced cell death contributes to the pathogenesis of chronic obstructive pulmonary disease, though the relative roles of apoptosis and autophagy remain unclear. The inducible stress protein heme oxygenase-1 (HO-1) confers cytoprotection against oxidative stress. We examined the relationships between these processes in human bronchial epithelial cells (Beas-2b) exposed to cigarette smoke extract (CSE). CSE induced morphological and biochemical markers of autophagy in Beas-2b cells and induced autophagosome formation as evidenced by formation of GFP-LC3 puncta and electron microscopic analysis. Furthermore, CSE increased the processing of microtubule-associated protein-1 light chain-3 (LC3B-I) to LC3B-II, within 1 hr of exposure. Increased LC3B-II was associated with increased autophagy, since inhibitors of lysosomal proteases and of autophagosome-lysosome fusion further increased LC3B-II levels during CSE exposure. CSE concurrently induced extrinsic apoptosis in Beas-2b cells involving early activation of death-inducing-signaling-complex (DISC) formation and downstream activation of caspases (-8,-9,-3). The induction of extrinsic apoptosis by CSE was dependent in part on autophagic proteins. Reduction of Beclin 1 levels with beclin 1 siRNA inhibited DISC formation and caspase-3/8 activation in response to CSE. LC3B siRNA also inhibited caspase-3/8 activation. The stress protein HO-1 protected against CSE-induced cell death by concurrently downregulating apoptosis and autophagy-related signaling. Adenoviral mediated expression of HO-1 inhibited DISC formation and caspase-3/9 activation in CSE-treated epithelial cells, diminished the expression of Beclin 1, and partially inhibited the processing of LC3B-I to LC3B-II. Conversely, transfection of Beas-2b with ho-1 siRNA augmented CSE-induced DISC formation and increased intracellular reactive oxygen species formation. HO-1 expression augmented CSE-induced phosphorylation of NFkappaB p65 in Beas-2b cells. Consistently, expression of IkappaB, the inhibitor of NFkappaB, increased CSE-induced DISC formation. LC3B siRNA also enhanced p65 phosphorylation. In fibroblasts from beclin 1 heterozygous knockout mice, p65 phosphorylation was dramatically upregulated, while CSE-induced DISC formation was inhibited, consistent with an anti-apoptotic role for NFkappaB and a pro-apoptotic role for Beclin 1. These studies demonstrated an interdependence of autophagic and apoptogenic signaling in CSE-induced cell death, and their coordinated downregulation by HO-1. An understanding of the regulation of cell death pathways during smoke exposure may provide therapeutic strategies in smoke-related illness.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis Regulatory Proteins
  • Apoptosis*
  • Autophagy*
  • Beclin-1
  • Cell Line
  • Heme Oxygenase-1 / metabolism*
  • Humans
  • Mice
  • Mice, Knockout
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • Necrosis
  • Proteins / genetics
  • Proteins / metabolism
  • Pulmonary Disease, Chronic Obstructive / chemically induced
  • Pulmonary Disease, Chronic Obstructive / pathology
  • RNA, Small Interfering / genetics
  • Respiratory Mucosa / drug effects*
  • Respiratory Mucosa / enzymology
  • Respiratory Mucosa / pathology*
  • Smoke
  • Tobacco / toxicity*
  • Transcription Factor RelA / metabolism

Substances

  • Apoptosis Regulatory Proteins
  • Beclin-1
  • Becn1 protein, mouse
  • Microtubule-Associated Proteins
  • Proteins
  • RNA, Small Interfering
  • Smoke
  • Transcription Factor RelA
  • light chain 3, human
  • Heme Oxygenase-1