HIF-1α has an anti-apoptotic effect in human airway epithelium that is mediated via Mcl-1 gene expression

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) and myeloid cell leukemia-1 (Mcl-1) proteins have been shown to regulate apoptosis in some cell systems but have not been studied in this context in airway epithelium. Using a model of anoxia/reoxygenation (A/R), the present study employed RNA interference (RNAi) targeting HIF-1 alpha and Mcl-1 to evaluate their possible anti-apoptotic effects on HBE1 cells, an immortalized human bronchial epithelial cell line. The cells were either Cultured under normoxic conditions or were transfected with small interfering RNA (siRNA) duplexes targeting HIFI 1 alpha or Mcl-1 mRNA and then immediately exposed to A/R. As controls, non-transfected HBE1 cells and cells transfected with scrambled RNA duplexes were subjected to A/R. Apoptosis was evaluated by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and RNAi was assessed by knockdown of HIF-1 alpha and Mcl-1 mRNA and protein expression using real-time quantitative RT-PCR (Q-PCR), immunohistochemistry, and Western blots. HBE1 cells transfected with siRNA duplexes targeting either HIF-1 alpha or Mcl-1 and Subjected to A/R manifested considerable apoptosis, a finding not observed in either non-transfected cells or cells transfected with scrambled RNA duplexes. Specific knockdown of mRNA and protein expression by RNAi in HBE1 cells after A/R was shown for siRNA duplexes targeting either HIF-1 alpha or Mcl-1. Unexpectedly, knockdown of HIF-1 alpha induced parallel knockdown of Mcl-1 mRNA and protein expression, whereas Mcl-1 knockdown had no noticeable effect on HIF-1 alpha expression. Thus, although both of these proteins were shown to be anti-apoptotic, the action of HIF-1 alpha appeared to be mediated in part via Mcl-1.