Binding of receptor-recognized forms of α2-macroglobulin to the α2-macroglobulin signaling receptor activates phosphatidylinositol 3-kinase

Ligation of the alpha(2)-macroglobulin (alpha(2)M) signaling receptor by receptor-recognized forms of alpha(2)M (alpha(2)M*) initiates mitogenesis secondary to increased intracellular Ca2+. We report here that ligation of the alpha(2)M signaling receptor also causes a 1.5-2.5-fold increase in wortmannin-sensitive phosphatidylinositol 3-kinase (PI3K) activity as measured by the quantitation of phosphatidylinositol 3,4,5-trisphosphate (PIP3). PIP3 formation was alpha(2)M* concentration-dependent with a maximal response at similar to 50 pM ligand concentration. The peak formation of PIP3 occurred at 10 min of incubation. The alpha(2)M receptor binding fragment mutant K1370R which binds to the alpha(2)M signaling receptor activating the signaling cascade, increased PIP3 formation by 2-fold. The mutant K1374A, which binds very poorly to the alpha(2)M signaling receptor, did not cause any increase in PIP3 formation. alpha(2)M*-induced DNA synthesis was inhibited by wortmannin. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acetoxymethylester a chelator of intracellular Ca2+, drastically reduced alpha(2)M*-induced increases in PIP3 formation. We conclude that PI3K is involved in alpha(2)M*-induced mitogenesis in macrophages and intracellular Ca2+ plays a role in PI3K activation.