The pro-hypertrophic basic helix-loop-helix protein p8 is degraded by the ubiquitin/proteasome system in a protein kinase B/Akt- and glycogen synthase kinase-3-dependent manner, whereas endothelin induction of p8 mRNA and renal mesangial cell hypertrophy require NFAT4.
Renal disease is a common complication of diabetes. The initiating events in diabetic nephropathy are triggered by hyperglycemia and, possibly, advanced glycation end products. Subsequently, excess levels of vasoactive peptides (especially endothelin-1 (ET-1)) accumulate in the diabetic kidney, and there is evidence that these peptides mediate many of the pathophysiological changes associated with diabetic renal disease. These changes include an excess deposition of extracellular matrix proteins into the glomerular basement membrane and renal mesangial cell hypertrophy. Our transcriptional profiling studies have revealed that the p8 gene, which encodes a putative basic helix-loop-helix protein, is strongly induced in ET-1-treated renal mesangial cells and in an animal model of diabetic nephropathy. RNA interference experiments indicated that the p8 gene is required for ET-1-induced mesangial cell hypertrophy. Here, we show that the p8 polypeptide is a phosphoprotein subject to constitutive degradation by the ubiquitin/proteasome system. This degradation is mediated by phosphatidylinositol 3-kinase and protein kinase B/Akt. By contrast, stabilization of the p8 protein requires glycogen synthase kinase-3. Finally, short interfering RNA-mediated RNA interference experiments indicated that ET-1-stimulated mesangial cell hypertrophy and p8 mRNA induction require the NFAT4 transcription factor. Thus, p8 levels in the cell are likely maintained by a balance between signal-dependent transcriptional induction and proteolysis.
Goruppi
Sandro
S
Molecular Cardiology Research Institute, Tufts-New England Medical Center and the Department of Medicine, Tufts University School of Medicine, 750 Washington Street, Boston, MA 02111, USA.
Kyriakis
John M
JM
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D018929:Cell Culture Techniques; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D003928:Diabetic Nephropathies / Q000235:genetics / Q000503:physiopathology; D004195:Disease Models, Animal; D016232:Endothelins / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D018257:Helix-Loop-Helix Motifs / Q000502:physiology; D009097:Multienzyme Complexes / Q000378:metabolism*; D050778:NFATC Transcription Factors; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism*
D051792:Basic Helix-Loop-Helix Proteins; D003546:Cysteine Endopeptidases; D004268:DNA-Binding Proteins; D016232:Endothelins; D038362:Glycogen Synthase Kinase 3; D009097:Multienzyme Complexes; D050778:NFATC Transcription Factors; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C477593:Nfatc4 protein, rat; C109741:Nupr1 protein, rat; C494920:Akt1 protein, rat