Inhibition of platelet-derived growth factor-BB-induced fibroblast proliferation by plasmin-activated alpha 2-macroglobulin is mediated via an alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein-dependent mechanism.
alpha 2-Macroglobulin (alpha 2M) is a potentially important regulator of platelet-derived growth factor-BB (PDGF-BB)-stimulated cell growth due to our previous observation that PDGF-BB binds to alpha 2M noncovalently (Bonner, J. C., Goodell, A. L., Lasky, J. A., and Hoffman, M. R. (1992) J. Biol. Chem. 267, 12837-12844). We examined the in vitro effect of native and plasmin-activated (receptor-recognized) alpha 2M on the PDGF-BB-induced proliferation of mouse Swiss 3T3 and rat lung fibroblasts. Nondenaturing polyacrylamide gel electrophoresis showed that plasmin converted alpha 2M to its electrophoretically "fast" form at a 2:1 molar ratio and that 125I-PDGF-BB bound both alpha 2M and alpha 2M-plasmin. PDGF-BB-induced growth was not affected by native alpha 2M (0.3 microM) or plasmin (0.6 microM). The combination of plasmin and alpha 2M (2:1 molar ratio) inhibited PDGF-BB-induced cell proliferation 80-90%. Complexes of PDGF-BB.alpha 2M purified by gel filtration chromatography retained growth promoting activity, but the PDGF-BB.alpha 2M-plasmin complex did not. Preincubation of fibroblasts (37 degrees C for 24 h) with alpha 2M-plasmin did not change 125I-PDGF-BB binding or affect gene expression of the 6.5-kilobase PDGF-alpha receptor or 5.2-kilobase PDGF-beta receptor mRNA. However, preincubation with alpha 2M-plasmin (0-4 degrees C for 4 h) increased 125I-PDGF-BB binding 2-fold, and this increase was blocked by a receptor-associated protein antagonist of the alpha 2M-receptor/low density lipoprotein receptor-related protein. The receptor-associated protein antagonist blocked 125I-alpha 2M-methylamine binding, inhibited PDGF-BB-alpha 2M-plasmin uptake from fibroblast-cultured supernatants, and abolished the inhibitory effect of alpha 2M-plasmin on PDGF-stimulated growth. These data suggest that inhibition of PDGF-stimulated proliferation by alpha 2M-plasmin is mediated in part by clearance of PDGF-BB-alpha 2M-plasmin through the lipoprotein receptor-related protein.
Bonner
J C
JC
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Badgett
A
A
Hoffman
M
M
Lindroos
P M
PM
D000818:Animals; D000077214:Becaplermin; D002417:Cattle; D002455:Cell Division / Q000187:drug effects*; D002478:Cells, Cultured; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D005341:Fibrinolysin / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008168:Lung / Q000166:cytology; D010982:Platelet-Derived Growth Factor / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011971:Receptors, Immunologic / Q000502:physiology*; D011973:Receptors, LDL / Q000502:physiology*; D017479:Receptors, Platelet-Derived Growth Factor / Q000096:biosynthesis / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D000511:alpha-Macroglobulins; D000077214:Becaplermin; D017479:Receptors, Platelet-Derived Growth Factor; D005341:Fibrinolysin