title: Induction of serum- and glucocorticoid-induced kinase-1 (SGK1) by cAMP regulates increases in alpha-ENaC.
abstract: Alpha-ENaC expression and activity is regulated by a variety of hormones including beta-adrenergic agonists via the second messenger cAMP. We evaluated the early intermediate pathways involved in the up-regulation of SGK1 by DbcAMP and whether SGK1 is a prerequisite for induction of alpha-ENaC expression. Submandibular gland epithelial (SMG-C6) cells treated with DbcAMP (1 mM) induced both SGK1 mRNA and protein expression. DbcAMP-stimulated SGK1 mRNA expression was decreased by actinomycin D and mRNA and protein expressions were attenuated by PKA inhibitors (H-89 and KT5720). Inhibition of PI3-K with either LY294002 or dominant negative PI3-K reduced DbcAMP-stimulated SGK1 protein and mRNA levels, attenuated the phosphorylation of CREB (a cAMP-activated transcription factor) and decreased alpha-ENaC protein levels and Na(+) transport. In addition, the combination of PKA inhibitors with dominant negative PI3-K synergistically inhibited DbcAMP-induced Na(+) transport. Inhibition of SGK1 expression by siRNA decreased but did not obliterate DbcAMP-induced alpha-ENaC expression. Thus, in a cell line which endogenously exhibits minimal alpha-ENaC expression, induction of SGK1 by DbcAMP occurs via the PI3-K and PKA pathways. Increased alpha-ENaC levels and function are partly dependent upon the early induction of SGK1 expression.
authors.affiliation: Department of Pediatrics/Division of Neonatology, University of Texas Health Science Center, San Antonio, Texas 78229, USA. londonom@uthscsa.edu
authors.forename: Margarita M
authors.initials: MM
authors.lastname: Vasquez
authors.forename: Robert
authors.initials: R
authors.lastname: Castro
authors.forename: Steven R
authors.initials: SR
authors.lastname: Seidner
authors.forename: Barbara M
authors.initials: BM
authors.lastname: Henson
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ashton
authors.forename: Shamimunisa B
authors.initials: SB
authors.lastname: Mustafa
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology*; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D003513:Cycloheximide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D017874:Immediate-Early Proteins / Q000096:biosynthesis* / Q000235:genetics; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D003994:Bucladesine; D017362:Cyclic AMP Response Element-Binding Protein; D017868:Cyclic AMP-Dependent Protein Kinases; D003513:Cycloheximide; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010768:Phosphoserine; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D012964:Sodium; D000099184:Serum-Glucocorticoid Regulated Kinases