Transforming growth factor-beta1 stimulates protein kinase A in mesangial cells.
We recently demonstrated that transforming growth factor-beta (TGF-beta) stimulates phosphorylation of the type I inositol 1,4, 5-trisphosphate receptor (Sharma, K., Wang, L., Zhu, Y., Bokkala, S., and Joseph, S. (1997) J. Biol. Chem. 272, 14617-14623), possibly via protein kinase A (PKA) activation in murine mesangial cells. In the present study, we evaluated whether TGF-beta stimulates PKA activation. Utilizing a specific PKA kinase assay, we found that TGF-beta increases PKA activity by 3-fold within 15 min of TGF-beta1 treatment, and the enhanced kinase activity was completely reversed by the inhibitory peptide for PKA (PKI; 1 microM). In mesangial cells transfected with a PKI expression vector, enhanced PKA activity could not be demonstrated with TGF-beta1 treatment. TGF-beta1 was also found to stimulate translocation of the alpha-catalytic subunit of PKA to the nucleus by Western analysis of nuclear protein as well as by confocal microscopy. TGF-beta1-mediated phosphorylation of cAMP response element-binding protein was completely reversed by H-89 (3 microM), a specific inhibitor of PKA. Stimulation of fibronectin mRNA by TGF-beta1 was also attenuated in cells overexpressing PKI. We thus conclude that TGF-beta stimulates the PKA signaling pathway in mesangial cells and that PKA activation contributes to TGF-beta stimulation of cAMP response element-binding protein phosphorylation and fibronectin expression.
Wang
L
L
Department of Medicine, Division of Nephrology, Thomas Jefferson University School of Medicine, Philadelphia, Pennsylvania 19107, USA.
Zhu
Y
Y
Sharma
K
K
D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005920:Glomerular Mesangium / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D015398:Signal Transduction / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D016212:Transforming Growth Factor beta; D017868:Cyclic AMP-Dependent Protein Kinases