A novel functional target for tumor-promoting phorbol esters and lysophosphatidic acid. The p21rac-GTPase activating protein n-chimaerin.
Phorbol esters are potent tumor promoters widely used for investigating mechanisms of cell transformation with protein kinase C (PKC) generally considered as being their only protein target. Lysophosphatidic acid (LPA) can act as a mitogen, affecting cell shape and the actin cytoskeleton. There is no identified functional target for LPA. We have isolated a cDNA encoding a protein n-chimaerin that is a high affinity phorbol ester receptor and a p21rac-GTPase activating protein (rac-GAP). p21rac is a member of the ras superfamily of small molecular weight GTP-binding proteins, which stimulates actin microfilament formation in Swiss 3T3 cells and superoxide production by the neutrophil oxidase. We now show that the rac-GAP activity of n-chimaerin is stimulated by phosphatidylserine (PS) and phosphatidic acid (PA) and that phorbol esters can synergize with PS and PA. LPA, in contrast, was found to inhibit n-chimaerin. The phospholipid/phorbol ester modulation of the rac-GAP activity requires the PKC-like cysteine-rich domain of n-chimaerin. Thus, n-chimaerin is a novel functional target (distinct from PKC) for both phorbol esters and LPA. These data suggest that the physiological role of n-chimaerin is to link events initiating at the cell surface/membrane with p21rac effector pathways.
Institute of Molecular and Cell Biology, National University of Singapore.
S
S
Ahmed
J
J
Lee
R
R
Kozma
A
A
Best
C
C
Monfries
L
L
Lim
D000818:Animals; D002273:Carcinogens / Q000494:pharmacology*; D020848:Chimerin 1; D003001:Cloning, Molecular; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D007700:Kinetics; D008081:Liposomes; D008246:Lysophospholipids / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D010743:Phospholipids / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015183:Restriction Mapping; D020744:rac GTP-Binding Proteins; D020703:ras GTPase-Activating Proteins
D002273:Carcinogens; D020848:Chimerin 1; D020690:GTPase-Activating Proteins; D008081:Liposomes; D008246:Lysophospholipids; D009419:Nerve Tissue Proteins; D010703:Phorbol Esters; D010743:Phospholipids; D011506:Proteins; D011993:Recombinant Fusion Proteins; D020703:ras GTPase-Activating Proteins; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins