alpha(2B)-Adrenergic receptors activate MAPK and modulate proliferation of primary cultured proximal tubule cells.
In the rat proximal tubule, the alpha(2B)-adrenergic receptor (alpha(2B)-AR) enhances Na(+) reabsorption by increasing the activity of Na(+)/H(+) exchanger isoform NHE3. The mechanisms involved are unclear, and inhibition of cAMP production remains controversial. In this study, we reinvestigated alpha(2B)-AR signaling pathways using rat proximal tubule cells (PTC) in primary culture and LLC-PK(1) cells permanently transfected with the RNG gene (rat nonglycosylated alpha(2)-AR). Binding experiments indicated that PTC express substantial amounts of alpha(2B)-AR (130 fmol/mg protein), and only RNG transcripts were detected. In both cell types, the alpha(2B)-AR is coupled to G protein, and its stimulation by dexmedetomidine, but not by UK-14304, provoked a significant inhibition of the accumulation of cAMP induced by forskolin or parathyroid hormone. Exposure to alpha(2)-agonists increased arachidonic acid release and caused extracellular signal-regulated kinase (ERK)1/2 phosphorylation, which correlated with enhanced mitogen-activated protein kinse (MAPK) activity and nuclear translocation. MAPK phosphorylation was blunted by pertussis toxin but not by protein kinase C desensitization, and it coincided with transient phosphorylation of Shc. Finally, treatment with UK-14304 accelerated cell growth. Further studies will be necessary to clarify the precise mechanism of MAPK activation, but the present data suggest that alpha(2B)-AR may play a positive role during tubular regeneration.
Cussac
Daniel
D
Unit 388, Institut L. Bugnard, Centre Hospitalier Universitaire Rangueil, 31403 Toulouse Cedex 4, France.
Schaak
Stéphane
S
Gales
Céline
C
Flordellis
Christodoulos
C
Denis
Colette
C
Paris
Hervé
H
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D019329:Idazoxan / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000201:enzymology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D037342:Pertussis Toxin; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011807:Quinolizines / Q000378:metabolism; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D015398:Signal Transduction; D014316:Tritium; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
C547771:ADRA2B protein, human; C547773:Adra2b protein, rat; D000317:Adrenergic alpha-Antagonists; D007476:Ionophores; D011807:Quinolizines; D018341:Receptors, Adrenergic, alpha-2; D010566:Virulence Factors, Bordetella; D014316:Tritium; C054290:L 657743; D016718:Arachidonic Acid; D000001:Calcimycin; C058525:2-methoxyidazoxan; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases; D019329:Idazoxan; D004837:Epinephrine