The effect of transforming growth factor beta 1 on mesangial cell fibronectin synthesis: increased incorporation into the extracellular matrix and reduced pI but no effect on alternative splicing.
Fibronectin is a multidomain glycoprotein which accumulates in mesangial proliferative glomerulonephritis (MPGN). Recent evidence has implicated transforming growth factor beta (TGF-beta) in the pathogenesis of experimental MPGN. We have, therefore, examined the influence of TGF-beta 1 on mesangial cell fibronectin synthesis. Considering, first, levels of mRNA, TGF-beta 1 increased steady-state fibronectin RNA in cultured mesangial cells by 1.9 times 24 hr after treatment of cycling mesangial cells and by 11.8 times in growth-arrested cells. There was, however, no alteration in fibronectin pre-mRNA splicing in either the EIIIA or IIICS regions. Fibronectin protein concentrations in cell culture supernatants, determined by immunoprecipitation of supernatants from cells labeled with [35S]methionine and by ELISA, were not increased by treatment with TGF-beta 1. Western blots and immunoprecipitation of metabolically labeled cells showed that fibronectin was increased, however, in the deoxycholate-insoluble extracellular matrix (ECM) of cells stimulated with TGF-beta 1. TGF-beta 1 altered the physicochemical properties of fibronectin in ECM and supernatant such that the isoelectric point of fibronectin, determined from Western blots of 2D SDS-PAGE gels, was reduced so that both became more acidic. These studies demonstrate, therefore, that in addition to increasing its synthesis, TGF-beta 1 increases incorporation of fibronectin into the ECM. Because fibronectin possesses binding sites for other ECM proteins, greater incorporation of fibronectin following TGF-beta 1 treatment may be an important pathogenetic mechanism in mesangial sclerosis. Moreover, the altered charge of fibronectin may increase localization of serum immunoglobulins to the mesangium.
McKay
N G
NG
Department of Medicine, University of Aberdeen, Scotland.
Khong
T F
TF
Haites
N E
NE
Power
D A
DA
D017398:Alternative Splicing / Q000502:physiology*; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D005109:Extracellular Matrix / Q000378:metabolism*; D005353:Fibronectins / Q000096:biosynthesis* / Q000235:genetics; D005920:Glomerular Mesangium / Q000378:metabolism*; D015432:Glomerulonephritis, Membranoproliferative / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016212:Transforming Growth Factor beta / Q000502:physiology*
D005353:Fibronectins; D016212:Transforming Growth Factor beta