TY - JOUR
T1 - Mechanism of inhibition of cAMP-dependent epithelial chloride secretion by phorbol esters
AU - Shen, Ben Quan
AU - Barthelson, Roger A.
AU - Skach, William
AU - Gruenert, Dieter C.
AU - Sigal, Elliott
AU - Mrsny, Randall J.
AU - Widdicombe, Jonathan H.
PY - 1993/9/5
Y1 - 1993/9/5
N2 - In T84 cells, we investigated how stimulation of protein kinase C leads to an inhibition of cAMP-dependent chloride secretion. Specifically, we tested the hypothesis that the inhibition was caused by loss of the cystic fibrosis transmembrane regulator (CFTR), an apical membrane chloride channel. As described by others (Trapnell, B. C., Zeitlin, P. L., Chu, C.-S., Yoshimura, K., Nakamura, H., Guggino, W. B., Bargon, J., Banks, T. C., Dalemans, W., Pavirani, A., Lecocq, J.-P., and Crystal, R. G. (1991) J. Biol. Chem. 266, 10319-10323), we found that treatment with the phorbol ester, phorbol myristate acetate (PMA), reduced CFTR mRNA levels by ∼80% with a t1/2 of ∼2 h. Chloride secretion, measured as forskolin-induced short circuit current, was also abolished by PMA with a t1/2 of ∼2 h. Levels of mature glycosylated CFTR measured by Western blotting also declined to 50 ± 8% (n = 7) of control after a 12-h PMA treatment. However, a 12-h exposure to PMA did not affect the forskolin-stimulated efflux of 125I into high potassium medium, a measure of apical membrane CFTR activity. We conclude that increased turnover of apical membrane CFTR in PMA-treated cells compensates for the decline in anion channel numbers. By contrast to its lack of effect on 125I effluxes, PMA reduced the cAMP-induced increase in 86Rb efflux, suggesting that it inhibits chloride secretion mainly by an action on basolateral potassium channels.
AB - In T84 cells, we investigated how stimulation of protein kinase C leads to an inhibition of cAMP-dependent chloride secretion. Specifically, we tested the hypothesis that the inhibition was caused by loss of the cystic fibrosis transmembrane regulator (CFTR), an apical membrane chloride channel. As described by others (Trapnell, B. C., Zeitlin, P. L., Chu, C.-S., Yoshimura, K., Nakamura, H., Guggino, W. B., Bargon, J., Banks, T. C., Dalemans, W., Pavirani, A., Lecocq, J.-P., and Crystal, R. G. (1991) J. Biol. Chem. 266, 10319-10323), we found that treatment with the phorbol ester, phorbol myristate acetate (PMA), reduced CFTR mRNA levels by ∼80% with a t1/2 of ∼2 h. Chloride secretion, measured as forskolin-induced short circuit current, was also abolished by PMA with a t1/2 of ∼2 h. Levels of mature glycosylated CFTR measured by Western blotting also declined to 50 ± 8% (n = 7) of control after a 12-h PMA treatment. However, a 12-h exposure to PMA did not affect the forskolin-stimulated efflux of 125I into high potassium medium, a measure of apical membrane CFTR activity. We conclude that increased turnover of apical membrane CFTR in PMA-treated cells compensates for the decline in anion channel numbers. By contrast to its lack of effect on 125I effluxes, PMA reduced the cAMP-induced increase in 86Rb efflux, suggesting that it inhibits chloride secretion mainly by an action on basolateral potassium channels.
UR - http://www.scopus.com/inward/record.url?scp=0027312715&partnerID=8YFLogxK
M3 - Article
C2 - 7689566
AN - SCOPUS:0027312715
SN - 0021-9258
VL - 268
SP - 19070
EP - 19075
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 25
ER -