HDL3 binds to glycosylphosphatidylinositol-anchored proteins to activate signalling pathways.
Previous studies have indicated that in HepG2 cells HDL3-signalling involves glycosylphosphatidylinositol (GPI) anchored proteins. HDL3-binding to HepG2 cells was found to be enhanced by cellular preincubation with PI-PLC inhibitors and sensitive to a cellular preincubation with exogenous PI-PLC, suggesting that HDL3 binds directly on GPI-anchored proteins to initiate signaling. Moreover HDL3-binding was found to be partly inhibited by antibodies against the HDL-binding protein (AbHBP). HDL3, when binding to HepG2 cells, promoted the release in the culture medium of a 110 kDa protein that binds AbHBP, while a cellular preincubation with antibodies against the inositol-phosphoglycan (IPG) moiety of GPI-anchor (AbIPG), used to block lipolytic cleavage of the GPI-anchor, inhibits HDL3-induced release of the 110 kDa protein in the culture medium. In [3H]-PC prelabeled HepG2 cells, AbHBP were found to stimulate PC-hydrolysis and DAG generation within 5 min as did HDL3 stimulation. Cellular preincubation with AbIPG was found to inhibit only the HDL3-signal and not the AbHBP-signal, while a prior cellular pretreatment with PI-PLC from Bacillus cereus was found to inhibit the HDL3-and AbHBP-signal. Moreover cellular preincubation with AbHBP for 1 h at 37 degrees C was found to inhibit HDL3-signalling pathways. Our results suggest that in HepG2 cells a 110 kDa protein, which could be HBP, can be anchored to the membrane via GPI, and can function in HDL3-signalling pathways as binding sites.
Nazih-Sanderson
F
F
Unité INSERM 325, Institut Pasteur, Lille, France.
Lestavel
S
S
Nion
S
S
Rouy
D
D
Denefle
P
P
Fruchart
J C
JC
Clavey
V
V
Delbart
C
C
D000906:Antibodies / Q000494:pharmacology; D001665:Binding Sites; D002352:Carrier Proteins; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010740:Phospholipases / Q000037:antagonists & inhibitors; D016601:RNA-Binding Proteins; D018110:Receptors, Lipoprotein / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D000906:Antibodies; D002352:Carrier Proteins; D017261:Glycosylphosphatidylinositols; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D016601:RNA-Binding Proteins; D018110:Receptors, Lipoprotein; C031616:high density lipoprotein receptors; C075197:high density lipoprotein binding protein; D010740:Phospholipases