Relationship of GTP-binding proteins, phospholipase C, and PGE2 synthesis in rat glomerular mesangial cells.
We evaluated the role of GTP-binding proteins in the activation of phospholipase C, release of arachidonic acid, and synthesis of prostaglandin (PG) E2 in response to platelet-activating factor (PAF) and angiotensin II (ANG II) in cultured rat mesangial cells. Pretreatment with pertussis toxin (PT) decreased PGE2 formation and arachidonic acid release in response to PAF and ANG II but not that to A 23187. PT pretreatment also inhibited formation of inositol trisphosphate (IP3) in response to ANG II or PAF but did not significantly alter the rise in intracellular calcium detected by fura-2. PT catalyzed ADP ribosylation of two proteins of molecular mass approximately 40 and 41 kDa. Further evidence for involvement of GTP-binding protein in phospholipase C activation was that GTP-gamma S stimulated IP3 generation. Immunoblots with antibodies directed against different inhibitory alpha subunits of GTP-binding proteins showed that the major 40-kDa PT substrate reacted with an antibody directed against a decapeptide of the G protein subunit alpha i2 that is also found in leukocytes. This was further confirmed by Northern blot that showed the existence of mRNA in mesangial cells that hybridized with a cDNA probe for G alpha i2. In addition lesser amounts of mRNA hybridized with a restriction fragment cDNA probe for G alpha i3, which corresponds to the 41-kDa substrate for PT ribosylation. These results show that phospholipase C activation by PAF and ANG II in mesangial cells involves a specific G protein, most likely G alpha i2.(ABSTRACT TRUNCATED AT 250 WORDS)
Schlondorff
D
D
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Singhal
P
P
Hassid
A
A
Satriano
J A
JA
DeCandido
S
S
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D010972:Platelet Activating Factor / Q000494:pharmacology; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*
D007295:Inositol Phosphates; D010972:Platelet Activating Factor; D013873:Thionucleotides; D000804:Angiotensin II; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000001:Calcimycin; D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D015232:Dinoprostone