Which of the following statements best explains how this deletion will affect the CFTR protein?

When CFTR is defective other channels, including the outwardly rectifying chloride channel (ORCC), the epithelial sodium channel (ENaC), a potassium channel known as ROMK1 and a chloride/bicarbonate exchanger, do not work properly. In addition, other chloride channels present on the surface of epithelial cells may be affected in the CF airways. These “alternative” chloride channels have been proposed as a therapeutic target to enhance chloride transport.

The ORCC is found on the surface of many epithelial cells. Normal CFTR facilitates the transport of adenosine triphosphate (ATP), an energy-carrying molecule, to the outside of the cell, activating ORCC. It is unknown whether CFTR itself or an associated channel actually transports the ATP. However, the mutant CFTR is not able to perform the function of transporting ATP.

The ENaC, a sodium channel found on the surface of epithelial cells, is made up of four subunits: two alpha, one beta and one gamma. Each subunit consists of two transmembrane helices. CFTR also influences the function of ENaC in the lung by decreasing its activity, however, the mechanism by which this occurs is unclear.

As suggested by its name, the chloride/bicarbonate exchanger transports one bicarbonate molecule out the cell for every chloride that it transports into the cell. The chloride is derived from the efflux of chloride through CFTR. Therefore, if CFTR is not functional the activity of this channel will be greatly reduced.

Several other chloride channels are present on the cell surface. The one that may be most influenced by CFTR is the CaCC or calcium-activated chloride channel. The exact protein that creates this channel has yet to be defined. However, it is known that the channel is modulated by the P2Y2 receptor which is activated by ATP. Therefore, the activity of this channel could be influenced by decreased ATP associated with mutant CFTR..

Which of the following statements best explains how this deletion will affect the CFTR protein?

CFTR regulates the function of other ion channels located within the cell membrane.

*Reference is also in this collection.

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Page 2

Summary of CFTR coding regions according to historical and current nomenclature

ExonHistorical exon nameStartEndLengthExonStartEndLength
Exon 1Exon 1117,120,017117,120,201185Intron 1-2117,120,202117,144,30624,105
Exon 2Exon 2117,144,307117,144,417111Intron 2-3117,144,418117,149,0874670
Exon 3Exon 3117,149,088117,149,196109Intron 3-4117,149,197117,170,95221,756
Exon 3Exon 3117,170,953117,171,168216Intron 4-5117,171,169117,174,3293161
Exon 5Exon 5117,174,330117,174,41990Intron 5-6117,174,420117,175,301882
Exon 6Exon 6a117,175,302117,175,465164Intron 6-7117,175,466117,176,6011136
Exon 7Exon 6b117,176,602117,176,727126Intron 7-8117,176,728117,180,1533426
Exon 8Exon 7117,180,154117,180,400247Intron 8-9117,180,401117,182,0691669
Exon 9Exon 8117,182,070117,182,16293Intron 9-10117,182,163117,188,6946532
Exon 10Exon 9117,188,695117,188,877183Intron 10-11117,188,878117,199,51710,640
Exon 11Exon 10117,199,518117,199,709192Intron 11-12117,199,710117,227,79228,083
Exon 12Exon 11117,227,793117,227,88795Intron 12-13117,227,888117,230,4062519
Exon 13Exon 12117,230,407117,230,49387Intron 13-14117,230,494117,231,9871494
Exon 14Exon 13117,231,988117,232,711724Intron 14-15117,232,712117,234,9832272
Exon 15Exon 14a117,234,984117,235,112129Intron 15-16117,235,113117,242,8797767
Exon 16Exon 14b117,242,880117,242,91738Intron 16-17117,242,918117,243,585668
Exon 17Exon 15117,243,586117,243,836251Intron 17-18117,243,837117,246,7272891
Exon 18Exon 16117,246,728117,246,80780Intron 18-19117,246,808117,250,5723765
Exon 19Exon 17a117,250,573117,250,723151Intron 19-20117,250,724117,251,634911
Exon 20Exon 17b117,251,635117,251,862228Intron 20-21117,251,863117,254,6662804
Exon 21Exon 18117,254,667117,254,767101Intron 21-22117,254,768117,267,57512,808
Exon 22Exon 19117,267,576117,267,824249Intron 22-23117,267,825117,282,49114,667
Exon 23Exon 20117,282,492117,282,647156Intron 23-24117,282,648117,292,89510,248
Exon 24Exon 21117,292,896117,292,98590Intron 24-25117,292,986117,304,74111,756
Exon 25Exon 22117,304,742117,304,914173Intron 25-26117,304,915117,305,512598
Exon 26Exon 23117,305,513117,305,618106Intron 26-27117,305,619117,306,9611343
Exon 27Exon 24117,306,962117,308,7151754