Airway epithelium, which forms the first barrier towards environmental insults, is disturbed by cigarette smoking, a major risk factor for developing chronic obstructive pulmonary disease (COPD). A-kinase anchoring proteins (AKAP) maintain endothelial barrier function and coordinate subcellular localization of protein kinase A (PKA). However, the role of AKAPs in epithelial barrier function is unknown. We studied the role of AKAPs in regulating human bronchial epithelial (Hogg JC, Timens W. Annu Rev Pathol 4: 435-459, 2009; HBE) barrier. Cigarette smoke extract (CSE) reduced barrier function in 16HBE cells and the expression of the adhesion molecule E-cadherin specifically at the cell membrane. In addition, CSE reduced the protein expression of the AKAP family member AKAP9 at the cell membrane. The expression of AKAP5 and AKAP12 was unaffected by CSE. AKAP9 interacted and colocalized with E-cadherin at the cell membrane, suggesting that the reduction of both proteins may be related. Interestingly, disruption of AKAP-PKA interactions by st-Ht31 prevented the CSE-induced reduction of Ecadherin and AKAP9 protein expression and subsequent loss of barrier function. Silencing of AKAP9 reduced the functional epithelial barrier and prevented the ability of st-Ht31 to restore membrane localization of E-cadherin. Our data suggest the possibility of a specific role for AKAP9 in the maintenance of the epithelial barrier. E-cadherin, but not AKAP9, protein expression was reduced in lung tissue from COPD patients compared with controls. However, AKAP9 mRNA expression was decreased in primary bronchial epithelial cells from current smokers compared with non/ex-smokers. In conclusion, our results indicate that AKAP proteins, most likely AKAP9, maintain the bronchial epithelial barrier by regulating the E-cadherin expression at the cell membrane.

The epithelial barrier is a protective layer against unwanted particles, present in cigarette smoke (CS), a risk factor for developing chronic obstructive pulmonary disease. cAMP, a second messenger, increases barrier properties in endothelial cells, but the role of cAMP in the epithelial barrier is not known. The cAMP effectors, PKA and Epac, may be involved, next to compartmentalization of cAMP signalling by A‐kinase anchoring proteins (AKAPs). Our hypothesis is that AKAPs are involved in CS‐induced effects on the maintenance of the barrier dysfunction. We studied the effect of cigarette smoke extract (CSE) on the barrier function by electrical cell‐substrate impedance sensing (ECIS) and by analyzing the main cell‐cell contact molecule E‐cadherin. CSE‐induced reduction of the functional epithelial barrier is independently of both PKA and Epac. Addition of Ht31 (AKAP‐inhibitor) prevented the effects of CSE on the barrier, strongly suggesting that compartmentalization of cAMP by AKAPs maintains the barrier properties. In addition CSE delocalizes E‐cadherin and AKAP9 from the membrane and reduces the expression of these proteins. Ht31 relocalizes and restores E‐cadherin and AKAP9 levels. Similar results on AKAP9 were obtained in primary epithelial cells from current smokers. In conclusion, AKAPs contribute to CSE‐induced disturbance of the epithelial barrier by translocation of E‐cadherin from the cell membrane. (NAF grant 3.2.09.034)