Binding of rat alpha 1-inhibitor-3-methylamine to the alpha 2-macroglobulin signaling receptor induces second messengers.
Binding of receptor-recognized forms of tetrameric human alpha 2-macroglobulin (alpha 2M*) to a macrophage signaling receptor induces cAMP synthesis, increases in inositol 1,4,5-triphosphate (IP3) synthesis, and a concomitant rise in cytosolic free calcium ([Ca2+]i). The alpha 2M* signaling receptor is coupled to a pertussis-toxin insensitive G protein. Binding of alpha 2M* also occurs to the low density lipoprotein receptor-related protein/alpha 2M receptor (LRP/alpha 2MR), but this binding does not induce signal transduction. Rat alpha 1-inhibitor-3 (alpha 1I3) is a monomeric member of the alpha-macroglobulin/complement superfamily. Like alpha 2M, it can react with proteinases or methylamine which induces a conformational change causing activated alpha 1I3 to bind to LRP/alpha 2MR. We now report that alpha 1I3-methylamine binds to the macrophage alpha 2M* signaling receptor inducing a rapid rise in the synthesis of IP3 with a subsequent 1.5- to 3-fold rise in [Ca2+]i. alpha 1I3-methylamine binding to macrophages also caused a statistically significant elevation in cAMP. Native alpha 1I3, like alpha 2M, was unable to induce signal transduction. alpha 1I3 forms a complex with alpha 1-microglobulin, which has a distinct conformation from alpha 1I3 and is recognized by LRP/alpha 2MR. This complex also induces an increase in [Ca2+]i comparable to the effect of alpha 1I3-methylamine on macrophages. It is concluded that activation of alpha 1I3 by methylamine or binding of alpha 1-microglobulin causes similar conformational changes in the inhibitor, exposing the receptor recognition site for the alpha 2M* signaling receptor, as well as for LRP/alpha 2MR.
Misra
U K
UK
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Gawdi
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G
Pizzo
S V
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D000209:Acute-Phase Proteins / Q000378:metabolism*; D000510:Alpha-Globulins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011971:Receptors, Immunologic / Q000502:physiology*; D015398:Signal Transduction; D013047:Specific Pathogen-Free Organisms
D000209:Acute-Phase Proteins; D000510:Alpha-Globulins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; C017894:alpha 1-inhibitor 3; C016001:alpha-1-microglobulin; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium