Rac1 contributes to actin organization in glomerular podocytes.
OBJECTIVE
The function of glomerular podocytes is closely associated with the actin cytoskeleton. In this study, we studied the role of the small Rho-GTPase, Rac1, in actin organization in podocytes.


METHODS
Conditionally immortalized mouse podocytes (MP) stably expressing nephrin or control plasmid were used.


RESULTS
In MP, Rac1 activity increased significantly at 1 week of differentiation. MP stably expressing nephrin showed Rac1 activity significantly higher and more sustained than vector-expressing control cells. Antibody-mediated cross-linking of nephrin also activated Rac1. Differentiated MP showed more distinct lamellipodia/cellular processes, as compared with undifferentiated cells, which was further augmented by nephrin expression. Transient transfection of constitutively active Rac1 markedly increased the number of lamellipodia/cellular processes in undifferentiated MP, while the Rac1 inhibitor caused actin cytoskeleton derangement in differentiating MP. In the rat model of puromycin aminonucleoside nephrosis, RhoA activity was increased at Day 7 (at the peak of proteinuria), while Rac1 activity increased significantly only at Day 14, when the recovery process had started.


CONCLUSIONS
Rac1 is activated in differentiating MP and nephrin potentiates Rac1 activation. Rac1 likely contributes to lamellipodia formation in differentiating MP and may contribute to process formation in podocytes recovering from injuries.
Attias
Ortal
O
Department of Medicine, McGill University Health Centre, Montreal, Que., Canada.
Jiang
Ruihua
R
Aoudjit
Lamine
L
Kawachi
Hiroshi
H
Takano
Tomoko
T
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000187:drug effects; D004789:Enzyme Activation; D007678:Kidney Glomerulus / Q000166:cytology* / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000494:pharmacology; D051379:Mice; D009401:Nephrosis / Q000139:chemically induced; D050199:Podocytes / Q000378:metabolism*; D011692:Puromycin Aminonucleoside; D051381:Rats; D017207:Rats, Sprague-Dawley; D020830:rac1 GTP-Binding Protein / Q000502:physiology*; D020703:ras GTPase-Activating Proteins / Q000502:physiology; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D000199:Actins; C101203:IQ motif containing GTPase activating protein 1; D008565:Membrane Proteins; C113267:nephrin; D020703:ras GTPase-Activating Proteins; D011692:Puromycin Aminonucleoside; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein