Nef stimulates proliferation of glomerular podocytes through activation of Src-dependent Stat3 and MAPK1,2 pathways.
In collapsing focal segmental glomerulosclerosis (FSGS) of HIV-associated nephropathy (HIVAN), podocytes exhibit a high proliferation rate and loss of differentiation markers. We have found previously that the nef gene of HIV-1 is responsible for these changes. Here, we investigated the signaling pathways induced by Nef and its role in the pathogenesis of HIVAN. Using conditionally immortalized podocytes after differentiation, we found that infection of podocytes with nef increased Src kinase activity and signal transducer and activator of transcription 3 (Stat3) phosphorylation and activated the Ras-c-Raf-MAPK1,2 pathway. A dominant negative mutant of Src abolished the Nef effect, whereas inhibition of MAPK1,2 or dominant negative Stat3 reduced Nef effects partially. Reducing the expression of Nef with small interference RNA reversed the Nef effect. Mutation of Nef in the PxxP or R105R106 motifs diminished Nef signaling and the phenotypic changes in podocytes. Both phospho-MAPK1,2 and phospho-Stat3 staining increased in podocytes of kidneys from HIV-1 transgenic mice compared with their littermates and in podocytes of kidneys from HIVAN patients compared with HIV patients with non-HIVAN kidney diseases or non-HIV patients with idiopathic FSGS, classic FSGS, or minimal-change disease. These data suggest that Nef-induced activation of Stat3 and Ras-MAPK1,2 via Src-dependent pathways is responsible for podocyte proliferation and dedifferentiation, a characteristic finding in collapsing FSGS of HIVAN.
He
John Cijiang
JC
Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA. cijiang.he@mssm.edu
Husain
Mohammad
M
Sunamoto
Masaaki
M
D'Agati
Vivette D
VD
Klotman
Mary E
ME
Iyengar
Ravi
R
Klotman
Paul E
PE
D000818:Animals; D002455:Cell Division / Q000502:physiology; D019927:Cyclin E / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015693:Gene Products, nef / Q000378:metabolism*; D007678:Kidney Glomerulus / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D010766:Phosphorylation; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
D019927:Cyclin E; D004268:DNA-Binding Proteins; D015693:Gene Products, nef; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D019061:src-Family Kinases; D019950:Mitogen-Activated Protein Kinase 1