CFTR Regulation by Phosphorylation

The cystic fibrosis transmembrane conductance regulator (CFTR) is a tightly regulated anion channel expressed in epithelial and other cells. It conducts chloride and bicarbonate ions through the plasma membrane and also influences the activity of other channels and transporters through unknown mechanisms. CFTR has two membrane domains (TM1, TM2), each comprised of six trans-membrane segments, two nucleotide-binding folds (NBD1, NBD2) that bind and hydrolyze ATP, and a central regulatory or “R” domain (1 ). Phosphorylation of the R domain by protein kinases Table 1 ) stimulates channel activity and may also enhance interactions of CFTR with other proteins. This chapter describes methods that we have found useful for studying the phosphorylation and dephosphorylation of CFTR. We emphasize simple approaches for the partial purification of CFTR and for assaying kinase and phosphatase activities using either CFTR or casein as substrate.