Coordinate regulation of the alpha(2)-macroglobulin signaling receptor and the low density lipoprotein receptor-related protein/alpha(2)-macroglobulin receptor by insulin.
We have studied insulin-dependent regulation of macrophage alpha(2)-macroglobulin signaling receptors (alpha(2)MSR) and low density lipoprotein receptor-related protein/alpha(2)M receptors (LRP/alpha(2)MR) employing cell binding of (125)I-alpha(2)M*, inhibition of binding by receptor-associated protein (RAP) or Ni(2+), LRP/alpha(2)MR mRNA levels, and generation of second messengers. 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 67,000 to 2,900 and 115,200 sites per cell, respectively. Neither RAP nor Ni(2+) blocked the binding of (125)I-alpha(2)M* to alpha(2)MSR on insulin- or buffer-treated cells, but they both blocked binding to LRP/alpha(2)MR. Insulin significantly increased LRP/alpha(2)MR mRNA levels in a dose- and time-dependent manner. Insulin-augmented (125)I-alpha(2)M* 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 generation of IP(3) and increased [Ca(2+)](i) levels upon receptor ligation. Incubation of macrophages with wortmannin, LY294002, PD98059, SB203580, rapamycin, or antibodies against insulin receptors before insulin treatment and alpha(2)M* stimulation significantly reduced the insulin-augmented increase in IP(3) and [Ca(2+)](i) levels. Pretreatment of cells with actinomycin D or cycloheximide blocked the synthesis of new alpha(2)MSR. In conclusion, we show here that insulin coordinately regulates macrophage alpha(2)MSR and LRP/alpha(2)MR, utilizing both the PI 3-kinase and Ras signaling pathways to induce new synthesis of these receptors.
Misra
U K
UK
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Gawdi
G
G
Gonzalez-Gronow
M
M
Pizzo
S V
SV
D000818:Animals; D002478:Cells, Cultured; D026541:Heymann Nephritis Antigenic Complex; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008264:Macrophages / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011971:Receptors, Immunologic / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D000511:alpha-Macroglobulins / Q000378:metabolism*
D026541:Heymann Nephritis Antigenic Complex; D007004:Hypoglycemic Agents; D007328:Insulin; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D000511:alpha-Macroglobulins