PKC-alpha modulates TGF-beta signaling and impairs podocyte survival.
BACKGROUND
Progressive loss of podocytes has been documented as an early lesion in the development of glomerular disease. In a variety of glomerular diseases, including diabetic nephropathy the activation of transforming growth factor-beta (TGF-beta) has been demonstrated to promote podocyte death and the development of glomerulosclerosis. In this manuscript we analyzed the role of PKC-alpha (PKCalpha) on TGF-beta1 induced apoptosis in podocytes.


METHODS
To accomplish this we generated stable murine PKCalpha deficient podocyte cell lines and examined survival- and pro-apoptotic signaling signatures as well as caspase activation after stimulation with TGF-beta.


RESULTS
After stimulation with TGF-beta we can demonstrate an enhanced and prolonged activation of PI3K/AKT and ERK1/2 in PKCalpha-knockout (PKCalpha-/-) podocytes compared to PKCalpha-wildtype (PKCalpha+/ +) podocytes, whereas proapoptotic signaling via p38MAPK is significantly reduced. Interestingly, activation of the Smad-pathway is also prolonged in the PKCalpha-/-podocytes. When we analyzed the underlying mechanisms we found a TGF-beta inducible interaction of PKCalpha with the TGF-beta-type-I-receptor (TGFbetaRI). Moreover, endocytosis assays showed that the TGFbetaRI is less internalized in PKCalpha-/- podocytes.


CONCLUSIONS
Since we can demonstrate a key role for PKCalpha in the signaling response after stimulation with TGF-beta we conclude that PKCalpha might be an interesting target molecule as a "podocyte protective" therapy.
Tossidou
Irini
I
Department of Medicine, Hannover Medical School, Germany.
Starker
Gabriele
G
Kruger
Janna
J
Meier
Matthias
M
Leitges
Michael
M
Haller
Hermann
H
Schiffer
Mario
M
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D004705:Endocytosis; D055786:Gene Knockout Techniques; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D050199:Podocytes / Q000201:enzymology*; D051571:Protein Kinase C-alpha / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D018125:Receptors, Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051571:Protein Kinase C-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048051:p38 Mitogen-Activated Protein Kinases