Differential heparin inhibition of skeletal muscle alpha-dystroglycan binding to laminins.
The laminin binding properties of alpha-dystroglycan purified from rabbit skeletal muscle membranes were examined. In a solid phase microtiter assay, 125I-laminin (laminin-1) bound to purified alpha-dystroglycan in a specific and saturable manner with a half-maximal concentration of 8 nM. The binding of 125I- alpha-dystroglycan to native laminin and merosin (a mixture of laminin-2 and -4) was also compared using the solid phase assay. The absolute binding of 125I- alpha-dystroglycan to laminin (6955 +/- 250 cpm/well) was similar to that measured for merosin (7440 +/- 970 cpm/well). However, inclusion of 1 mg/ml heparin in the incubation medium inhibited 125I-alpha-dystroglycan binding to laminin by 84 +/- 4.3% but inhibited 125I-alpha-dystroglycan binding to merosin by only 17 +/- 5.2%. Similar results were obtained with heparan sulfate, while de-N-sulfated heparin, hyaluronic acid, and chondroitin sulfate had no differential effect. These results were confirmed by iodinated laminin and merosin overlay of electrophoretically separated and blotted dystrophin-glycoprotein complex. In contrast to the results obtained with skeletal muscle alpha-dystroglycan, both laminin and merosin binding to purified brain alpha-dystroglycan was significantly inhibited by heparin. Our data support the possibility that one or more heparan sulfate proteoglycans may specifically modulate the interaction of alpha-dystroglycan with different extracellular matrix proteins in skeletal muscle.
Pall
E A
EA
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
Bolton
K M
KM
Ervasti
J M
JM
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002809:Chondroitin Sulfates / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D049030:Dystroglycans; D016189:Dystrophin / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D006820:Hyaluronic Acid / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007700:Kinetics; D007797:Laminin / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D011865:Radioisotope Dilution Technique; D014407:Tumor Cells, Cultured
D003598:Cytoskeletal Proteins; D016189:Dystrophin; D007457:Iodine Radioisotopes; D007797:Laminin; D008562:Membrane Glycoproteins; D049030:Dystroglycans; D006820:Hyaluronic Acid; D006493:Heparin; D002809:Chondroitin Sulfates