Cystic fibrosis (CF) is the most common Caucasian autosomal recessive disease. It is due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding the CFTR protein, which is a chloride (Cl(-)) channel. The most common mutation leads to a missing phenylalanine at position 508 (DeltaF508). The DeltaF508-CFTR protein is misfolded and retained in the endoplasmic reticulum and may trigger the unfolded protein response (UPR). Furthermore, CF is accompanied by inflammation and infection, which are also involved in the UPR. To date, the UPR transducer ATF6 and ER stress sensor Grp78 have been used as UPR markers. Therefore, our aim was to study the activation of ATF6 and Grp78 in transfected human epithelial cells expressing the DeltaF508-CFTR protein, and we showed that they are activated in these cells. We investigated the effect of exogenous UPR inducers thapsigargin (Tg) and tunicamycin (Tu) on Grp78 and ATF6 expression. Whereas the cells reacted to the UPR induction, we show a difference in the electrophoretic pattern of ATF6. The Grp78/ATF6 complex was previously described, but its stability during UPR is controversial. Using co-immunoprecipitation we show that it is stable in DeltaF508-CFTR-expressing cells and is maintained under UPR conditions. Finally, using siRNA, we show that decreased ATF6 expression induces increased cAMP-dependent halide flux through DeltaF508-CFTR due to its increased membrane localization. Therefore, our results suggest that UPR may be triggered in CF and that ATF6 may be a therapeutic target.

The cystic fibrosis transmembrane conductance regulator (CFTR) functions as a cAMP-activated chloride channel, which is regulated by protein-protein interactions. The extent to which CFTR is regulated by these interactions remains unknown. Annexin V is overexpressed in cystic fibrosis (CF), and given the functional properties of annexin V and CFTR we considered whether they are associated and if so whether this has implications for CFTR function. Using co-immunoprecipitation and overlay experiments, we show that annexin V is associated with nucleotide-binding domain 1 (NBD1) of CFTR. Surface plasmon resonance (SPR) indicated different KD values in the absence and presence of both calcium and ATP, suggesting that this interaction is calcium- and ATP-dependent. Using an siRNA approach and overexpression, we showed that CFTR chloride channel function and its localization in the cell membranes were dependent on annexin V expression. We concluded that annexin V is necessary for normal CFTR chloride channel activity. Furthermore, we show that CFTR and annexin V are partially co-distributed in normal epithelial cells in human bronchi. In conclusion, we show for the first time that annexin V is associated with CFTR and is involved in its function.

The idea of a virtual sensor is to extract information of parameters that cannot be measured directly, or at least would require very costly sensors, by only using available information. Virtual sensors are described for the friction between road and tire, the tire inflation pressure and wheel imbalance. There are certain interconnections between these virtual sensors so they are preferably implemented in one unit. Results from a real-time implementation, using mainly sensor information from the CAN bus, are given.