Gi proteins use a novel beta gamma- and Ras-independent pathway to activate extracellular signal-regulated kinase and mobilize AP-1 transcription factors in Jurkat T lymphocytes.
Receptors coupled to pertussis toxin (PTX)-sensitive Gi proteins regulate T lymphocyte cytokine secretion, proliferation, and chemotaxis, yet little is known about the molecular mechanisms of Gi protein signaling in mammalian lymphocytes. Using the Jurkat T lymphocyte cell line, we found that a stably expressed Gi protein-coupled receptor (the delta-opioid receptor (DOR1)) stimulates MEK-1 and extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2) and transcriptional activity by an ERK target, Elk-1, via a mechanism requiring a PTX-sensitive Gi protein. Levels of beta-adrenergic receptor kinase-1 C-terminal fragment that inhibited signaling by Gi protein beta gamma subunits in these cells had no effect on DOR1 stimulation of either MEK-1- or Elk-1-dependent transcription, indicating that this pathway is independent of beta gamma. Analysis of this betagamma-independent pathway indicates a role for a herbimycin A-sensitive tyrosine kinase. Unlike beta gamma-mediated pathways, the beta gamma-independent pathway was insensitive to RasN17, inhibitors of phosphatidylinositol 3-kinase (PI 3-kinase), and constitutive PI 3-kinase activity. The beta gamma-independent pathway regulates downstream events, since blocking it abrogated both Elk-1-dependent transcription and mobilization of the mitogenic transcription factor, AP-1, in response to DOR1 signaling. These results characterize a novel, Ras- and PI 3kinase-independent pathway for ERK activation by Gi protein signaling that is distinct from ERK activation by beta gamma and may therefore be mediated by the alphai subunit.
Hedin
K E
KE
Department of Immunology, The Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA. hedin@mayo.edu
Bell
M P
MP
Huntoon
C J
CJ
Karnitz
L M
LM
McKean
D J
DJ
D016227:Benzoquinones; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D019169:Jurkat Cells; D047029:Lactams, Macrocyclic; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D011809:Quinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins / Q000378:metabolism*
D016227:Benzoquinones; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D019204:GTP-Binding Proteins; D047029:Lactams, Macrocyclic; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D011809:Quinones; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; D017828:Rifabutin; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella; D051552:beta-Adrenergic Receptor Kinases; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins; C494112:ELK1 protein, human; C020754:herbimycin; C482125:MAP2K1 protein, human