Coordinate regulation of the alpha(2)-macroglobulin signaling receptor andthe low density lipoprotein receptor-related protein/alpha(2)-macroglobulin receptor by insulin

We have studied insulin-dependent regulation of macrophage alpha(2)-macrogl obulin signaling receptors (alpha(2)MSR) and low density lipoprotein recept or-related protein/ alpha(2)M receptors (LRP/alpha(2)MR) employing cell bin ding of I-125-alpha(2)M*, inhibition of binding by receptor-associated prot ein (RAP) or Ni2+, LRP/alpha(2)MR mRNA levels, and generation of second mes sengers. Insulin treatment increased the number of alpha(2)M* high (alpha(2 )MSR) and low (LRP/ alpha(2)MR) affinity binding sites from 1,600 and 67,00 0 to 2,900 and 115,200 sites per cell, respectively. Neither RAP nor Ni2+ b locked the binding of I-125-alpha(2)M* to alpha(2)MSR on insulin- or buffer -treated cells, but they both blocked binding to LRP/alpha(2)MR, Insulin si gnificantly increased LRP/alpha(2)MR mRNA levels in a dose- and time-depend ent manner. Insulin-augmented I-125-alpha(2),MX binding to macrophages was severely reduced by wortmannin, LY294002, PD98059, SB203580, or rapamycin, The increase in alpha(2)MSR receptor synthesis was reflected by augmented g eneration of IP3 and increased [Ca2+](i) levels upon receptor ligation. Inc ubation of macrophages with wortmannin, LY294002, PD98059, SB203580, rapamy cin, or antibodies against insulin receptors before insulin treatment and a lpha(2)M* stimulation significantly reduced the insulin-augmented increase in IP3 and [Ca2+](i) levels. Pretreatment of cells with actinomycin D or cy cloheximide blocked the synthesis of new alpha(2)MSR, In conclusion, we sho w here that insulin coordinately regulates macrophage alpha(2)MSR and LRP/a lpha(2)MR, utilizing both the PI 3-kinase and Pas signaling pathways to ind uce new synthesis of these receptors.