title: Insulin is involved in transcriptional regulation of NKCC and the CFTR Cl(-) channel through PI3K activation and ERK inactivation in renal epithelial cells.
abstract: It is is well known that insulin stimulates glucose transport and epithelial Na(+) channel (ENaC)-mediated Na(+) reabsorption; however, the action of insulin on Cl(-) secretion is not fully understood. In this study, we investigated the action of insulin on Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-mediated Cl(-) secretion in epithelial A6 cells. Interestingly, insulin treatment remarkably enhanced the forskolin-stimulated Cl(-) secretion associated with an increase in apical Cl(-) conductance by upregulating mRNA expression of both CFTR and NKCC, although insulin treatment alone had no effect on the basal Cl(-) secretion or apical Cl(-) conductance without forskolin application. We next elucidated a role of phosphoinositide 3-kinase (PI3K) in the insulin-induced enhancement of the Cl(-) secretion, since insulin actually activated PI3K, resulting in activation of Akt, a downstream molecule of PI3K. LY294002 (a PI3K inhibitor) reduced the Cl(-) secretion by suppressing mRNA expression of NKCC, whereas insulin still had a stimulatory action on mRNA expression of CFTR even in the presence of LY294002. On the other hand, we found that a MEK inhibitor (PD98059) further enhanced the insulin-stimulated CFTR mRNA expression and the Cl(-) secretion in forskolin-stimulated A6 cells and that insulin induced slight, transient activation of ERK followed by significant inactivation of ERK. These observations suggest that: (1) insulin respectively upregulates mRNA expression of NKCC and CFTR through activation of PI3K and inactivation of ERK; (2) insulin signals on mRNA expression of NKCC and CFTR are not enough to stimulate transepithelial Cl(-) secretion, but enhance the stimulatory action of cAMP on transepithelial Cl(-) secretion.
authors.affiliation: Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan.
authors.forename: Hongxin
authors.initials: H
authors.lastname: Sun
authors.forename: Naomi
authors.initials: N
authors.lastname: Niisato
authors.forename: Toshio
authors.initials: T
authors.lastname: Inui
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Marunaka
mesh_terms: D000818:Animals; D002460:Cell Line; D018118:Chloride Channels / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D005576:Colforsin / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D064466:Solute Carrier Family 12, Member 1 / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects; D014982:Xenopus laevis
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D007328:Insulin; D012333:RNA, Messenger; D064466:Solute Carrier Family 12, Member 1; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases