title: The COOH terminus of megalin regulates gene expression in opossum kidney proximal tubule cells.
abstract: We recently reported that megalin is subjected to regulated intramembrane proteolysis (RIP) and includes 1) protein kinase C (PKC)-regulated, metalloprotease-mediated ectodomain shedding producing a membrane-bound megalin COOH-terminal fragment (MCTF) and 2) gamma-secretase-mediated cleavage of the MCTF producing a soluble megalin intracellular domain (MICD). Based on studies of RIP of other receptors, the MICD is predicted to target to the nucleus and regulate gene expression. To determine whether RIP of megalin regulates proximal tubule gene expression, we stably expressed the transfected MCTF (tMCTF) or transfected MICD (tMICD) in opossum kidney proximal tubule (OKP) cells and examined the resulting phenotype. Immunoblotting and immunocytochemical analysis of tMCTF cells showed the tMCTF was expressed and constitutively processed by gamma-secretase. Analysis of specific protein expression in tMCTF- and tMICD-transfected cells using Western blot showed endogenous megalin and Na(+)/H(+) exchanger 3 (NHE3) protein expression to be dramatically lower than that of control cells. Expression of other proteins including myosin VI, beta-adaptin, and the Na-K-ATPase appeared unchanged. Analysis of specific mRNA expression using quantitative real-time PCR showed megalin and NHE3 mRNA levels were significantly lower in tMCTF- and tMICD-transfected cells compared with controls. Inhibition of gamma-secretase activity in tMCTF cells resulted in an 8- to 10-fold recovery of megalin mRNA within 4 h. These data show that the COOH-terminal domain of megalin regulates expression of specific proteins in OKP cells and provides the first evidence that RIP of megalin may be part of a signaling pathway linking protein absorption and gene expression in proximal tubule.
authors.affiliation: Dept. of Internal Medicine, Section of Nephrology, Yale Univ. School of Medicine, 300 Cedar St., TAC S255, P.O. Box 208029, New Haven, CT 06520-8029, USA.
authors.forename: Yuanli
authors.initials: Y
authors.lastname: Li
authors.forename: Rong
authors.initials: R
authors.lastname: Cong
authors.forename: Daniel
authors.initials: D
authors.lastname: Biemesderfer
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation; D006056:Golgi Apparatus / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008871:Microvilli / Q000378:metabolism; D009893:Opossums; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011480:Protease Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D026561:Low Density Lipoprotein Receptor-Related Protein-2; D010446:Peptide Fragments; D011480:Protease Inhibitors; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C067713:lactacystin; D053829:Amyloid Precursor Protein Secretases; D000111:Acetylcysteine