Inhibition of Basic Secretagogue-Induced Signaling in Mast Cells by Cell Permeable Gαi-Derived Peptides

BACKGROUND

Basic secretagogues of connective tissue mast cells act as receptor mimetic agents that trigger mast cells by activating G proteins. This leads to simultaneous propagation of two signaling pathways: one that culminates in exocytosis, while the other involves protein tyrosine phosphorylation and leads to release of arachidonic acid metabolites. We have previously shown that introduction of a peptide that comprises the C-terminal end of G alpha i3 into permeabilized mast cells inhibits basic secretagogue-induced exocytosis [Aridor et al., Science 1993;262:1569-1572]. We investigated whether cell-permeable peptides, composed of the C-terminus of G alpha i3 fused with importation sequences, affect mast cell function.

METHODS

Following preincubation with the fused peptides, rat peritoneal mast cells were activated by compound 48/80 and analyzed for histamine and prostaglandin D2 release and protein tyrosine phosphorylations.

RESULTS

We demonstrate that out of three importation sequences tested only G alpha i3 peptide fused with the Kaposi fibroblast growth factor importation sequence (ALL1) inhibited release of histamine. ALL1 as well as a cell-permeable peptide that corresponds to G alpha i2 also blocked compound 48/80-stimulated protein tyrosine phosphorylation, though the latter did not block histamine release. ALL1 effect was G protein-specific, as it was incapable of blocking protein tyrosine phosphorylation stimulated by pervanadate.

CONCLUSION

ALL1, a transducible G alpha i3-corresponding peptide, blocks the two signaling pathways in mast cells: histamine release and protein tyrosine phosphorylation. Cell permeable peptides that block these two signaling cascades may constitute a novel approach for preventing the onset of the allergic reaction.

Oxidation decreases low density lipoprotein association with the subendothelium extracellular matrix

Atherosclerosis is initiated by accumulation of low density lipoprotein (LDL) in the subendothelium extracellular matrix (ECM) followed by oxidation and scavenger receptor mediated uptake by the vessel wall recruited macrophages. The effect of oxidation on LDL association with the ECM is not yet clear. In the present study we examined the hypothesis that excessive oxidation of LDL results in decreased LDL association with ECM, thereby increasing its accessibility to the scavenger receptor on macrophages. We have studied the relative association of Cu+2 ion oxidized LDL to native LDL with the native or oxidized bovine corneal endothelial cells ECM. Oxidation of LDL decreased its binding to the ECM. The kinetic of this process was characterized by approximately 1 h lag phase followed by a significant decreased binding of 80% after 6.5 h oxidation. This kinetic more closely resembled the pattern of the oxidation product dienals accumulation rather than thiobarbituric acid reactive substance formation. Oxidation of ECM-bound LDL resulted in an increased LDL release from the ECM as a function of Cu+2 ion concentration with a maximal increase of 2-fold at 3 microM. ECM oxidation prior to exposure to LDL resulted in a 30% decrease in LDL binding to the ECM. In conclusion, these results suggest that oxidation processes in the vessel wall result in increased dissociation of ECM-bound LDL, which in turn makes this oxidized LDL more accessible for binding and uptake by macrophages leading to foam cell formation.