Characterization of alpha 2-macroglobulin binding to human trabecular meshwork cells: presence of the alpha 2-macroglobulin signaling receptor.
Direct binding of receptor-recognized alpha 2-macroglobulin (alpha 2M*) or a cloned receptor binding fragment from rat alpha 1-macroglobulin (RBF) to human trabecular meshwork cells demonstrated two classes of cell surface binding sites. One class has an apparent Kd of 5.0 nM and a receptor number of 31,800 receptors/cell. The other class has an apparent Kd of 20 pM and a receptor number of 1600 receptors/cell. Binding studies of alpha 2M* or RBF in the presence of a competitor for binding to low-density-lipoprotein receptor-related protein/alpha 2M* receptor (LRP/alpha 2MR) called receptor-associated protein (RAP) show that only the lower affinity class of binding sites is susceptible to competition with RAP. Uptake studies demonstrate specific internalization and degradation of alpha 2M* which is inhibitable by RAP. Exposure of the cells to alpha 2M* and RBF (40 nM) is associated with mean increases of 171 and 210%, respectively, in the intracellular calcium concentration, which is not inhibitable by RAP or pertussis toxin. These studies present the first characterization of alpha 2M* and RBF signaling in a primary human cell type and suggest a role for alpha 2M* in the physiology of the eye.
Howard
G C
GC
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Roberts
B C
BC
Epstein
D L
DL
Pizzo
S V
SV
D000368:Aged; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D026541:Heymann Nephritis Antigenic Complex; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011971:Receptors, Immunologic / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014129:Trabecular Meshwork / Q000166:cytology / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000235:genetics / Q000378:metabolism*
D026541:Heymann Nephritis Antigenic Complex; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins; D015544:Inositol 1,4,5-Trisphosphate; D004247:DNA; D002118:Calcium