Bradykinin stimulates the [erk_elk-1_fos/ap-1] pathway in mesangial
cells.
El-Dahr, Samir S., Susana Dipp, and William H. Baricos.
Section of Pediatric Nephrology, Department of Pediatrics; and
Department of Biochemistry, Tulane University School of Medicine, New
Orleans, Louisiana 70112
APStracts 5:0095F, 1998.
Among its diverse biologic actions, the vasoactive peptide bradykinin
(BK) induces the transcription factor AP-1 and proliferation of
mesangial cells (Kidney Int. 50: 1850-55, 1996). In the present
study, we examined the role of protein tyrosine phosphorylation and
the mitogen-activated protein kinases, ERK1/2, in mediating BK
-induced AP-1 and DNA replication in cultured rat mesangial cells. BK
(10-9 to 10-7 M) stimulated a rapid increase in tyrosine
phosphorylation of multiple proteins with an estimated MW of 120-130,
90-95, and 44-42 kDa. Immunoblots using antibodies specific for ERK
or tyrosine-phosphorylated ERK revealed a shifting of p42 ERK-2 to a
higher MW that correlated temporally with an increase in tyrosine
-phosphorylated ERK-2. Genistein, a specific tyrosine kinase
inhibitor, prevented the phosphorylation of ERK-2 by BK. In-gel
kinase assays indicated that BK-induced tyrosine phosphorylation of
ERK-2 is accompanied by 4-fold activation of its phosphotransferase
activity toward the substrate PHAS-I (p<0.05). Furthermore, BK
stimulated a 2.5-fold increase (p<0.05) in phosphorylation of Elk
-1, a transcription factor required for growth factor-induced c-fos
transcription. In accord with the stimulation of Elk-1
phosphorylation, BK induced c-fos gene expression and the production
of Fos/AP-1 complexes. In addition, thymidine incorporation into DNA
increased 2-fold (p<0.05) following BK stimulation. Each of these
effects was blocked by tyrosine kinase inhibition with genistein or
herbimycin A. Similarly, antisense oligodeoxynucleotide targeting of
ERK1/2 mRNA inhibited BK-stimulated DNA synthesis. In contrast, PKC
inhibition or depletion had no effect on BK-induced c-fos mRNA, AP-1
-DNA binding activity or DNA synthesis. Collectively, these data
demonstrate that BK activates the ERK_Elk-1_AP-1 pathway, and that BK
mitogenic signaling is critically dependent on protein tyrosine
phosphorylation.
Received 11 February 1998; accepted in final form 7 May 1998.
APS Manuscript Number F29-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 16 June 1998