TURNOVER OF THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR (CFTR) - SLOW DEGRADATION OF WILD-TYPE AND DELTA-F508 CFTR IN SURFACE-MEMBRANE PREPARATIONS OF IMMORTALIZED AIRWAY EPITHELIAL-CELLS
Xf. Wei et al., TURNOVER OF THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR (CFTR) - SLOW DEGRADATION OF WILD-TYPE AND DELTA-F508 CFTR IN SURFACE-MEMBRANE PREPARATIONS OF IMMORTALIZED AIRWAY EPITHELIAL-CELLS, Journal of cellular physiology, 168(2), 1996, pp. 373-384
The protein product of the cystic fibrosis (CF) gene, termed the cysti
c fibrosis transmembrane conductance regulator (CFTR), is known to fun
ction as an apical chloride channel at the surface of airway epithelia
l cells. It has been proposed that CFTR has additional intracellular f
unctions and that there is altered precessing of mutant forms. In exam
ining these functions we found a stable form of CFTR with slow turnove
r in surface membrane preparations from CF and non-CF immortalized air
way epithelial cell lines. The methods used to study the turnover of C
FTR were pulse/chase experiments utilizing saturation labeling of [S-3
5]Met with chase periods of 5-24 h in the presence of 8 mM Met and cel
l fractionation techniques. Preparations of morphologically identifiab
le surface membranes were compared to total cell membrane preparations
containing intracellular membranes. Surface membrane CFTR had lower t
urnover defined by pulse/chase ratios than that of the total cell memb
rane preparations. Moreover, mutant CFTR was stable in the surface mem
brane fraction with little degradation even after a 24 h chase, wherea
s wild-type CFTR had a higher pulse/chase ratio at 24 h. In the presen
ce of 50 mu M castanospermine, which is an inhibitor of processing alp
ha-glucosidases, a more rapid turnover of mutant CFTR was found in the
total cell membrane preparation, whereas wild-type CFTR had a lower r
esponse. The results are compatible with a pool of CFTR in or near the
surface membranes which has an altered turnover in CF and a glycosyla
tion-dependent alteration in the processing of mutant CFTR. (C) 1996 W
iley-Liss, Inc.