title: Epac1-mediated, high glucose-induced renal proximal tubular cells hypertrophy via the Akt/p21 pathway.
abstract: The mechanisms involved in tubular hypertrophy in diabetic nephropathy are unclear. We investigated the role of exchange protein activated by cAMP 1(Epac1), which activates Rap-family G proteins in cellular hypertrophy. Epac1 is expressed in heart, renal tubules, and in the HK-2 cell line. In diabetic mice, increased Epac1 expression was observed, and under high glucose ambience (HGA), HK-2 cells also exhibited increased Epac1 expression. We isolated a 1614-bp DNA fragment upstream of the initiation codon of Epac1 gene, inclusive of glucose response elements (GREs). HK-2 or COS7 cells transfected with the Epac1 promoter revealed a dose-dependent increase in its activity under HGA. Mutations in GRE motifs resulted in decreased promoter activity. HK-2 cells exhibited a hypertrophic response and increased protein synthesis under HGA, which was reduced by Epac1-siRNA or -mutants, whereas the use of a protein kinase A inhibitor had minimal effect. Epac1 transfection led to cellular hypertrophy and increased protein synthesis, which was accentuated by HGA. HGA increased the proportion of cells in the G0/G1 cell-cycle phase, and the expression of pAkt and the cyclin-dependent kinase inhibitors p21 and p27 was increased while the activity of cyclin-dependent kinase 4 decreased. These effects were reversed following transfection of cells with Epac1-siRNA or -mutants. These data suggest that HGA increases GRE-dependent Epac1 transcription, leading to cell cycle arrest and instigation of cellular hypertrophy.
authors.affiliation: Departments of Pathology and Medicine, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Sun
authors.forename: Vinay K
authors.initials: VK
authors.lastname: Kondeti
authors.forename: Ping
authors.initials: P
authors.lastname: Xie
authors.forename: Kirtee
authors.initials: K
authors.lastname: Raparia
authors.forename: Yashpal S
authors.initials: YS
authors.lastname: Kanwar
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000473:pathology; D020869:Gene Expression Profiling; D005947:Glucose / Q000494:pharmacology*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006984:Hypertrophy; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology*; D051379:Mice; D009928:Organ Specificity / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013311:Streptozocin
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D013311:Streptozocin; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose