Bombesin and neuromedin B stimulate the activation of p42(mapk) and p74(raf-1) via a protein kinase C-independent pathway in Rat-1 cells.
The mechanisms by which seven transmembrane receptors activate p42-(mapk)/p44(mapk) are not well defined although p21ras- and protein kinase C (PKC)-dependent pathways have been implicated, typically for Gi- and Gq-coupled receptors, respectively. Here, we demonstrate that in Rat-1 cells transfected with the Gq-coupled bombesin/gastrin releasing peptide receptor, bombesin stimulated activation of p42(mapk) that was not inhibited by the specific PKC inhibitor GF 109203X or by down regulation of phorbol ester-sensitive PKC isoforms. In addition, bombesin rapidly stimulated p74(raf-1) activity that was also independent of PKC activity and insensitive to inhibition by pertussis toxin. Furthermore, addition of neuromedin B to Rat-1 cells transfected with the neuromedin B preferring receptor also activated p42(mapk) and p74(raf-1) in a PKC-independent and pertussis toxin-insensitive manner. Finally we show that addition of bombesin to Rat-1 cells stimulated the GTP loading of p21ras. Our results reveal a novel PKC-independent pathway in the action of Gq-coupled receptors and stress the importance of cell context in defining the signal transduction pathway(s) that link specific receptors to the activation of the mitogen-activated protein kinase cascade.
Charlesworth
A
A
Imperial Cancer Research Fund, London, UK.
Rozengurt
E
E
D000818:Animals; D001839:Bombesin / Q000187:drug effects / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D015638:Cytochalasin D / Q000494:pharmacology; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1; D015287:Neurokinin B / Q000031:analogs & derivatives* / Q000378:metabolism; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D018004:Receptors, Bombesin / Q000235:genetics; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018004:Receptors, Bombesin; D010566:Virulence Factors, Bordetella; D015638:Cytochalasin D; D006160:Guanosine Triphosphate; D015287:Neurokinin B; C038393:neuromedin B; D037342:Pertussis Toxin; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D001839:Bombesin