title: Akt recruits Dab2 to albumin endocytosis in the proximal tubule.
abstract: Proximal tubule epithelial cells have a highly sophisticated endocytic machinery to retrieve the albumin in the glomerular filtrate. The megalin-cubilin complex and the endocytic adaptor disabled-2 (Dab2) play a pivotal role in albumin endocytosis. We previously demonstrated that protein kinase B (Akt) regulates albumin endocytosis in the proximal tubule through an interaction with Dab2. Here, we examined the nature of Akt-Dab2 interaction. The pleckstrin homology (PH) and catalytic domains (CD) of Akt interacted with the proline-rich domain (PRD) of Dab2 based on yeast-two hybrid (Y2H) experiments. Pull-down experiments utilizing the truncated constructs of Dab2 demonstrated that the initial 11 amino acids of Dab2-PRD were sufficient to mediate the interaction between Akt and Dab2. Endocytosis experiments utilizing Akt1- and Akt2-silencing RNA revealed that both Akt1 and Akt2 mediate albumin endocytosis in proximal tubule epithelial cells; therefore, Akt1 and Akt2 may play a compensatory role in albumin endocytosis. Furthermore, both Akt isoforms phosphorylated Dab2 at Ser residues 448 and 449. Ser-to-Ala mutations of these Dab2 residues inhibited albumin endocytosis and resulted in a shift in location of Dab2 from the peripheral to the perinuclear area, suggesting the physiological relevance of these phosphorylation sites in albumin endocytosis. We conclude that both Akt1 and Akt2 are involved in albumin endocytosis, and phosphorylation of Dab2 by Akt induces albumin endocytosis in proximal tubule epithelial cells. Further delineation of how Akt affects expression/phosphorylation of endocytic adaptors and receptors will enhance our understanding of the molecular network triggered by albumin overload in the proximal tubule.
authors.affiliation: Division of Nephrology, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: Kelly
authors.initials: K
authors.lastname: Koral
authors.affiliation: Division of Renal-Electrolyte, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania; and.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Division of Nephrology, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania;
authors.forename: Nandita
authors.initials: N
authors.lastname: Ganesh
authors.affiliation: Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Morris J
authors.initials: MJ
authors.lastname: Birnbaum
authors.affiliation: Division of Renal-Electrolyte, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania; and.
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Hallows
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio; Elif.Erkan@cchmc.org.
authors.forename: Elif
authors.initials: E
authors.lastname: Erkan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000418:Albumins / Q000378:metabolism*; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D004705:Endocytosis; D057809:HEK293 Cells; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000201:enzymology*; D008297:Male; D018345:Mice, Knockout; D010766:Phosphorylation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D051057:Proto-Oncogene Proteins c-akt / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000418:Albumins; D051017:Apoptosis Regulatory Proteins; C102885:DAB2 protein, human; C478773:Dab2 protein, mouse; D025521:Tumor Suppressor Proteins; C494918:AKT1 protein, human; C494921:AKT2 protein, human; C514862:Akt1 protein, mouse; C494922:Akt2 protein, mouse; D051057:Proto-Oncogene Proteins c-akt
keywords: albumin; endocytosis; proximal tubule epithelial cells