A novel receptor function for the heat shock protein Grp78: silencing of Grp78 gene expression attenuates alpha2M*-induced signalling.
The activated proteinase inhibitor alpha2-macroglobulin (alpha2M*) binds to two receptors, the low density lipoprotein receptor-related protein (LRP-1) and the alpha2M* signalling receptor (alpha2MSR). Silencing LRP-1 gene expression in macrophages by RNA interference does not block alpha2M* activation of signalling cascades. We now demonstrate that transfection of macrophages with a double-stranded RNA homologous in sequence to the Grp78 gene markedly decreased induction of inositol 1,4,5-trisphosphate (IP3) and subsequent IP3-dependent elevation of [Ca2+]i induced by alpha2M*. Concomitantly, alpha2M*-induced increase in [3H]thymidine uptake was abolished in these transfected cells. Insulin treatment significantly upregulates alpha2MSR and it also caused a marked increase in Grp78 expression which could be blocked by RNA interference. alpha2M* treatment of cells activates the Ras- and PI 3-kinase-dependent signalling pathways. Suppressing Grp78 expression leads to the loss of these activation events in transfected macrophages. We thus conclude that Grp78 is the alpha2M* signalling receptor.
Misra
Uma Kant
UK
Department of Pathology, Duke University Medical Center, Box 3712, Durham, NC 27710, USA.
Gonzalez-Gronow
Mario
M
Gawdi
Govind
G
Wang
Fang
F
Pizzo
Salvatore Vincent
SV
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D011905:Genes, ras / Q000502:physiology; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000378:metabolism*; D051379:Mice; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D034622:RNA Interference / Q000502:physiology; D012330:RNA, Double-Stranded / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D000511:alpha-Macroglobulins / Q000378:metabolism*
D002118:Calcium; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D015544:Inositol 1,4,5-Trisphosphate; D007328:Insulin; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D018832:Molecular Chaperones; D019869:Phosphatidylinositol 3-Kinases; D012330:RNA, Double-Stranded; D000511:alpha-Macroglobulins; C000717248:Hspa5 protein, mouse