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Howard Hughes Medical Institute, Departments of Internal Medicine and Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242
The regulatory domain of
cystic fibrosis transmembrane conductance regulator (CFTR) regulates
channel activity when several serines are phosphorylated by
cAMP-dependent protein kinase. To further define the functional role of
individual phosphoserines, we studied CFTR containing previously
studied and new serine to alanine mutations. We expressed these
constructs in Fischer rat thyroid epithelia and measured
transepithelial Cl
current. Mutation of four in vivo
phosphorylation sites, Ser660, Ser737,
Ser795, and Ser813 (S-Quad-A), substantially
decreased cAMP-stimulated current, suggesting that these four sites
account for most of the phosphorylation-dependent response. Mutation of
either Ser660 or Ser813 alone significantly
decreased current, indicating that these residues play a key role in
phosphorylation-dependent stimulation. However, neither
Ser660 nor Ser813 alone increased current to
wild-type levels; both residues were required. Changing
Ser737 to alanine increased current above wild-type levels,
suggesting that phosphorylation of Ser737 may inhibit
current in wild-type CFTR. These data help define the functional role
of regulatory domain phosphoserines and suggest interactions between
individual phosphoserines.
Cl
channel; cystic fibrosis transmembrane conductance
regulator; regulatory domain; cystic fibrosis
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