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PDGF‐stimulated fibroblast proliferation is enhanced synergistically by receptor‐recognized α 2 ‐Macroglobulin
Author(s) -
Bonner James C.,
Badgett Annette,
OsornioVargas Alvaro R.,
Hoffman Maureane,
Brody Arnold R.
Publication year - 1990
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041450102
Subject(s) - platelet derived growth factor receptor , fibroblast , growth factor , platelet derived growth factor , alpha (finance) , cell growth , receptor , cell culture , medicine , microbiology and biotechnology , endocrinology , chemistry , biology , biochemistry , construct validity , nursing , patient satisfaction , genetics
α‐Macroglobulins derived from plasma or secreted by macrophages are plateletderived growth factor (PDGF) binding proteins that compete with cell‐surface receptors on fibroblasts for PDGF binding. α 2 ‐Macroglobulin (α 2 M) derived from bovine plasma was tested for its ability to modulate the PDGF‐induced proliferation of primary passage rat lung fibroblasts (RLFs) and a human skin fibroblast cell line (CRL 1508). Fibroblasts were grown in 10% fetal bovine serum (FBS) for 24 hr, then washed with serum‐free medium before adding serum‐free defined medium (SFDM) containing insulin and transferrin. To this medium were added varying concentrations of human plasma‐derived AB‐PDGF and α 2 M, alone or in combination. Receptor‐recognized α 2 M was prepared by treatment with methylamine. Both native α 2 M and the α 2 M‐methylamine (α 2 M‐MA) were tested for growth promoting activity in the absence or presence of PDGF. After 3 days, a concentration‐dependent growth curve of fibroblast proliferation was demonstrated for PDGF alone, with near maximal stimulation reached at 15–20 ng/ml PDGF. α 2 M and α 2 M‐MA alone had no effect on cell proliferation. However, α 2 M‐MA concentrations above 32 μg/ml synergistically enhanced PDGF‐stimulated proliferation >100% in the presence of 15 ng/ml PDGF. Native α 2 M enhanced PDGF‐stimulated growth 80–100% above PDGF controls only at low concentrations (32–64 μg/ml α 2 M). High concentrations of native α 2 M (128–256 μg/ml) either had no effect on growth or were inhibitory to PDGF‐stimulated growth, depending on the cell type tested. Rat lung fibroblasts were shown to secrete a factor(s) that inhibited the trypsin‐binding capacity of native α 2 M. We further demonstrated that early passage RLFs possess specific cell‐surface receptors for [ 125 I]‐PDGF and [ 125 I]‐α 2 M‐MA, and preincubation of RLFs with α 2 M‐MA increased the specific binding of [ 125 I]‐PDGF to the cell surface of these fibroblasts. Considered together, these data support the view that receptor‐recognized α 2 M synergistically enhances the proliferative capacity of PDGF. We postulate that receptor‐recognized αMs enhance PDGF‐stimulated growth by increasing the local concentration of PDGF at the cell surface, where the PDGF could be released in close proximity to its own receptors.