PKC-beta1 mediates glucose-induced Akt activation and TGF-beta1 upregulation in mesangial cells.
Accumulation of glomerular matrix is a hallmark of diabetic nephropathy. The serine/threonine kinase Akt mediates glucose-induced upregulation of collagen I in mesangial cells through transactivation of the EGF receptor (EGFR). In addition, in renal tubular cells, glucose-induced secretion of TGF-beta requires phosphoinositide-3-OH kinase, suggesting a possible role for Akt in the modulation of TGF-beta expression, but the mechanisms of Akt activation and its involvement in TGF-beta regulation are unknown. Here, in primary mesangial cells, high glucose induced AktS473 phosphorylation, which correlates with its activation, in a protein kinase C beta (PKC-beta)-dependent manner. Glucose led to PKC-beta1 membrane translocation and association with Akt, and PKC-beta1 immunoprecipitated from glucose-treated cells phosphorylated recombinant Akt on S473. PKC is known to mediate glucose-induced TGF-beta1 upregulation through the transcription factor AP-1; here, inhibitors of phosphoinositide-3-OH kinase, PKC-beta and Akt, and dominant-negative Akt all prevented glucose-induced activation of AP-1 and upregulation of TGF-beta1. Finally, pharmacologic and dominant negative inhibition of EGFR blocked glucose-induced activation of PKC-beta1, phosphorylation of AktS473, activation of AP-1, and upregulation of TGF-beta1. In vivo, the PKC-beta inhibitor ruboxistaurin prevented Akt activation in the renal cortex of diabetic rats. In conclusion, PKC-beta1 is an Akt S473 kinase in glucose-treated mesangial cells, and TGF-beta1 transcriptional upregulation requires EGFR/PKC-beta1/Akt signaling. New therapeutic approaches for diabetic nephropathy may result from targeting components of this pathway, particularly the initial EGFR transactivation.
Wu
Dongcheng
D
Division of Nephrology, McMaster University, Hamilton, Ontario, Canada.
Peng
Fangfang
F
Zhang
Baifang
B
Ingram
Alistair J
AJ
Kelly
Darren J
DJ
Gilbert
Richard E
RE
Gao
Bo
B
Krepinsky
Joan C
JC
D000818:Animals; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000378:metabolism; D003928:Diabetic Nephropathies / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008301:Maleimides / Q000494:pharmacology; D050527:Mesangial Cells / Q000187:drug effects* / Q000378:metabolism*; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D064546:Protein Kinase C beta; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
D007211:Indoles; D008301:Maleimides; D047428:Protein Kinase Inhibitors; D011994:Recombinant Proteins; D018808:Transcription Factor AP-1; D053773:Transforming Growth Factor beta1; C099154:ruboxistaurin; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D005947:Glucose