G alpha(i-2) mediates renal LLC-PK1 growth by a Raf-independent activation of p42/p44 MAP kinase.
The protooncogene G alpha(i-2) plays a pivotal role in signaling pathways that control renal cell growth and differentiation. Mitogen-activated protein kinases (MAPKs) are potential downstream effectors for G alpha(i-2) in these pathways. In predifferentiated LLC-PK1 renal cells, the temporal maximal expression of G alpha(i-2) coincided with maximal activation of MAPK(p42/p44). By contrast, pertussis toxin treatment of these cells inhibited cell growth and reduced MAPK(p42/p44) activity by 30%. These findings reflected upstream activation of MAPK kinase (MEK1), as transient transfection of cells with a plasmid encoding a constitutively active form of MEK1 increased MAPK(p42/p44) activity and cell growth, whereas treatment with PD-098059, an inhibitor of MEK1 activity, reduced MAPK(p42/p44) activity and cell growth. Expression of a guanosinetriphosphatase (GTPase)-deficient G alpha(i-2) in these cells increased MAPK(p42/p44) activity and correspondingly reduced cell doubling time from 24 to 10 h without altering the activity of Raf-1 or c-Jun/stress-activated protein kinases (SAPKs). By contrast, expression of a GTPase-deficient G alpha(i-3) in these cells reduced both their cell doubling time by 30% and MAPK(p42/p44) activity by 60%. As the known MEKK isoforms (MEKK1, -2, and -3) can also activate SAPKs, these findings suggest the GTP-charged G alpha(i-2) subunit transduces growth signals in renal cells via activation of MAPK(p42/p44) and that such activation may be linked to pathways containing novel MEKK isoforms that preferentially activate MEKs.
Kinane
T B
TB
Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Kang
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I
Chu
A
A
Chin
S H
SH
Ercolani
L
L
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D007668:Kidney / Q000166:cytology* / Q000378:metabolism; D018374:LLC-PK1 Cells; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D037342:Pertussis Toxin; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D013552:Swine; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D011518:Proto-Oncogene Proteins; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins