Potential role for heparan sulfate proteoglycans in regulation of transforming growth factor-beta (TGF-beta) by modulating assembly of latent TGF-beta-binding protein-1.
Latent transforming growth factor-beta-binding proteins (LTBPs) are extracellular matrix (ECM) glycoproteins that play a major role in storage of latent TGF-beta in the ECM and regulate its availability. We have previously identified fibronectin as a key molecule for incorporation of LTBP1 and TGF-beta into the ECM of osteoblasts and fibroblasts. Here we provide evidence that heparan sulfate proteoglycans may mediate binding between LTBP1 and fibronectin. We have localized critical domains in the N terminus of LTBP1 that are required for co-localization with fibronectin in osteoblast cultures and have identified heparin binding sites in the N terminus of LTBP1 between residues 345 and 487. Solid-phase binding assays suggest that LTBP1 does not bind directly to fibronectin but that the binding is indirect. Heparin coupled to bovine serum albumin (heparin-BSA) was able to mediate binding between fibronectin and LTBP1. Treatment of primary osteoblast cultures with heparin or heparin-BSA but not with chondroitin sulfate impaired LTBP1 deposition onto fibronectin without inhibiting expression of LTBP1. Inhibition of LTBP1 incorporation was accompanied by reduced incorporation of latent TGF-beta into the ECM, with increased amounts of soluble latent TGF-beta. Inhibition of attachment of glycosaminoglycans to the core proteins of proteoglycans by beta-d-xylosides also reduced incorporation of LTBP1 into the ECM. These studies suggest that heparan sulfate proteoglycans may play a critical role in regulating TGF-beta availability by controlling the deposition of LTBP1 into the ECM in association with fibronectin.
Chen
Qian
Q
Department of Oral Biology, School of Dentistry, University of Missouri at Kansas City, Kansas City, Missouri 64108, USA.
Sivakumar
Pitchumani
P
Barley
Craig
C
Peters
Donna M
DM
Gomes
Ronald R
RR
Farach-Carson
Mary C
MC
Dallas
Sarah L
SL
D000818:Animals; D002417:Cattle; D002461:Cell Line, Transformed; D002807:Chondroitin / Q000737:chemistry / Q000378:metabolism; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005353:Fibronectins / Q000737:chemistry / Q000378:metabolism*; D006027:Glycosides / Q000737:chemistry; D019812:Heparan Sulfate Proteoglycans / Q000737:chemistry / Q000378:metabolism*; D053779:Latent TGF-beta Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D012710:Serum Albumin, Bovine / Q000737:chemistry; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism*
D005353:Fibronectins; D006027:Glycosides; D019812:Heparan Sulfate Proteoglycans; C509032:LTBP1 protein, human; D053779:Latent TGF-beta Binding Proteins; D016212:Transforming Growth Factor beta; C010807:xylosides; D012710:Serum Albumin, Bovine; D002807:Chondroitin