Expression of the nuclear factor-κB inhibitor A20 is altered in the cystic fibrosis epithelium

A20 is a lipopolysaccharide (LPS)-inducible, cytoplasmic zinc finger protein, which
inhibits Toll-like receptor-activated nuclear factor (NF)-kB signalling by deubiquitinating tumour
necrosis factor receptor-associated factor (TRAF)-6. The action of A20 is facilitated by complex
formation with ring finger protein (RNF)-11, Itch and TAX-1 binding protein-1 (TAX1BP1). This
study investigated whether the expression of A20 is altered in the chronically inflamed cystic
fibrosis (CF) airway epithelium.
Nasal epithelial cells from CF patients (F508del homozygous), non-CF controls and immortalised
epithelial cells (16HBE14o- and CFBE41o-) were stimulated with LPS. Cytoplasmic expression of
A20 and expression of NF-kB subunits were analysed. Formation of the A20 ubiquitin editing
complex was also investigated.
In CFBE41o-, peak LPS-induced A20 expression was delayed compared with 16HBE14o- and
fell significantly below basal levels 12–24 h after LPS stimulation. This was confirmed in primary
CF airway cells. Additionally, a significant inverse relationship between A20 and p65 expression
was observed. Inhibitor studies showed that A20 does not undergo proteasomal degradation in
CFBE41o-. A20 interacted with TAX1BP1, RNF11 and TRAF6 in 16HBE14o- cells, but these
interactions were not observed in CFBE41o-.
The expression of A20 is significantly altered in CF, and important interactions with complex
members and target proteins are lost, which may contribute to the state of chronic NF-kB-driven
inflammation.