TGFbeta-induced RhoA activation and fibronectin production in mesangial cells require caveolae.

Abstract

Glomerular sclerosis of diverse etiologies is characterized by mesangial matrix accumulation, with transforming growth factor-beta (TGFbeta) an important pathogenic factor. The GTPase RhoA mediates TGFbeta-induced matrix accumulation in some settings. Here we study the role of the membrane microdomain caveolae in TGFbeta-induced RhoA activation and fibronectin upregulation in mesangial cells (MC). In primary rat MC, TGFbeta1 time dependently increased RhoA and downstream Rho kinase activation. Rho pathway inhibition blocked TGFbeta1-induced upregulation of fibronectin transcript and protein. TGFbeta1-induced RhoA activation was prevented by disrupting caveolae with cholesterol depletion and rescued by cholesterol repletion. Compared with wild types, RhoA/Rho kinase activation was absent in MC lacking caveolae. Reexpression of caveolin-1 (and caveolae) restored these responses. Phosphorylation of caveolin-1 on Y14, effected by Src kinases, has been implicated in signaling responses. Overexpression of nonphosphorylatable caveolin-1 Y14A prevented TGFbeta1-induced RhoA activation. TGFbeta1 also activated Src, and its inhibition blocked RhoA activation. Furthermore, TGFbeta1 led to association of RhoA and caveolin-1. This was prevented by Src or TGFbeta receptor I inhibition, and by caveolin-1 Y14A overexpression. Last, fibronectin upregulation by TGFbeta1 was blocked by Src inhibition, not seen in caveolin-1 knockout MC, and restored by caveolin-1 reexpression in the latter. TGFbeta1-induced collagen I accumulation also required caveolae. TGFbeta1-mediated Smad2/3 activation, however, did not require caveolae. We conclude that RhoA/Rho kinase mediates TGFbeta-induced fibronectin upregulation. This requires caveolae and caveolin-1 interaction with RhoA. Interference with caveolin/caveolae or RhoA signaling thus represents a potential target for the treatment of fibrotic renal disease.

• Authors: Fangfang Peng, Baifang Zhang, Dongcheng Wu, Alistair J Ingram, Bo Gao, Joan C Krepinsky
• Journal: American journal of physiology. Renal physiology (Am J Physiol Renal Physiol) Vol. 295 Issue 1 Pg. F153-64 (Jul 2008) ISSN: 1931-857X [Print] United States
• PMID: 18434385 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Fibronectins
• Indoles
• Receptors, Transforming Growth Factor beta
• SU 6656
• Sulfonamides
• Transforming Growth Factor beta
• rho-Associated Kinases
• rhoA GTP-Binding Protein

Topics

• Animals
• Caveolae (physiology)
• Enzyme Activation
• Fibronectins (biosynthesis)
• Indoles (pharmacology)
• Mesangial Cells (physiology)
• Mice
• Mice, Knockout
• Rats
• Rats, Sprague-Dawley
• Receptors, Transforming Growth Factor beta (physiology)
• Sulfonamides (pharmacology)
• Transforming Growth Factor beta (physiology)
• Up-Regulation
• rho-Associated Kinases (physiology)
• rhoA GTP-Binding Protein (metabolism)