BRADYKININ INDUCES TUBULIN PHOSPHORYLATION AND NUCLEAR TRANSLOCATION OF MAP KINASE IN MESANGIAL CELLS

Glomerular hypertension and glomerular hypertrophy act early and syner gistically to promote glomerular injury in diabetes. We have previousl y shown that increased renal kinin production contributes to the glome rular hemodynamic abnormalities associated with diabetes. Glomeruloscl erosis, characterized by mesangial cell proliferation and matrix expan sion, is the final pathway leading to renal failure. The signal(s) ini tiating mesangial cell proliferation is ill defined. In the present st udy, we utilized immunofluorescence, immunoprecipitation, and immunobl otting techniques to identify substrates that are tyrosine phosphoryla ted in response to bradykinin action in mesangial cells. Immunofluores cence microscopy of mesangial cells stained with anti-phosphotyrosine (anti-PY) antibodies following bradykinin treatment (10(-9)-10(-6) M) revealed a dose-dependent increase in the labeling of cytoplasmic and nuclear proteins. Immunoprecipitation with anti-PY, followed by immuno blot revealed bradykinin-induced tyrosyl phosphorylation of tubulin an d mitogen-activated protein kinase (MAPK). Confocal microscopy of mesa ngial cells stained for MAPK indicated that bradykinin stimulation res ulted in translocation of MAPK from the cytoplasm to the nucleus by 2 h. These data demonstrate that bradykinin action results in the tyrosi ne phosphorylation of cellular proteins in mesangial cells and suggest a role for tubulin and MAPK in the signaling cascade of bradykinin le ading to altered mesangial function.