Heat shock protein 70 enhances vascular bone morphogenetic protein-4 signaling by binding matrix Gla protein.
BACKGROUND
Matrix Gla protein (MGP) is a calcification inhibitor, which binds and inhibits bone morphogenetic protein (BMP)-2 and -4.


OBJECTIVE
The objective was to determine whether MGP also binds other proteins, which could interfere with its function.


RESULTS
We transfected bovine aortic endothelial cells with N-terminally FLAG-tagged MGP and used immunoprecipitation and liquid chromatographic-tandem mass spectrometric analysis to identify MGP-binding proteins. Heat shock protein (HSP)70, a stress-induced protein expressed in atherosclerotic lesions and soluble in serum, was identified as a novel MGP-binding protein. The interaction between MGP and HSP70 was confirmed by coimmunoprecipitation and chemical crosslinking, and blocked the interaction between MGP and BMP-4. In endothelial cells, HSP70 enhanced BMP-4-induced proliferation and tube formation, and in calcifying vascular cells, HSP70 enhanced BMP-induced calcium deposition. In addition, HSP70 mediated the procalcific effect of interleukin-6 on calcifying vascular cells. In apolipoprotein E-null mice, a model for atherosclerosis, levels of BMP-4, HSP70, MGP, and interleukin-6 were elevated in the aortic wall. Levels of BMP-4, HSP70, and interleukin-6 were also elevated in serum, and anti-HSP70 antibodies diminished its procalcific effect on calcifying vascular cells.


CONCLUSIONS
HSP70 binds MGP and enhances BMP activity, thereby functioning as a potential link between cellular stress, inflammation, and BMP signaling.
Yao
Yucheng
Y
Division of Cardiology, David Geffen School of Medicine at UCLA, Box 951679, Los Angeles, CA 90095-1679, USA.
Watson
Andrew D
AD
Ji
Sheng
S
Boström
Kristina I
KI
D000818:Animals; D001011:Aorta / Q000378:metabolism* / Q000473:pathology; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism; D050197:Atherosclerosis / Q000235:genetics / Q000378:metabolism*; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism; D055415:Bone Morphogenetic Protein 4 / Q000235:genetics / Q000378:metabolism*; D002114:Calcinosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding / Q000235:genetics; D000097568:Matrix Gla Protein
D001057:Apolipoproteins E; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D018840:HSP70 Heat-Shock Proteins; D000097568:Matrix Gla Protein; C525718:BMP2 protein, human; C525809:BMP4 protein, human; C525719:Bmp2 protein, mouse; C525810:Bmp4 protein, mouse