Ca2+-mediated activation of ERK in hepatocytes by norepinephrine and prostaglandin F2 alpha: role of calmodulin and Src kinases.
BACKGROUND
Previous studies have shown that several agents that stimulate heptahelical G-protein coupled receptors activate the extracellular signal regulated kinases ERK1 (p44mapk) and ERK2 (p42mapk) in hepatocytes. The molecular pathways that convey their signals to ERK1/2 are only partially clarified. In the present study we have explored the role of Ca2+ and Ca2+-dependent steps leading to ERK1/2 activation induced by norepinephrine and prostaglandin (PG)F2alpha.


RESULTS
Pretreatment of the cells with the Ca2+ chelators BAPTA-AM or EGTA, as well as the Ca2+ influx inhibitor gadolinium, resulted in a partial decrease of the ERK response. Furthermore, the calmodulin antagonists W-7, trifluoperazine, and J-8 markedly decreased ERK activation. Pretreatment with KN-93, an inhibitor of the multifunctional Ca2+/calmodulin-dependent protein kinase, had no effect on ERK activation. The Src kinase inhibitors PP1 and PP2 partially diminished the ERK responses elicited by both norepinephrine and PGF2alpha.


CONCLUSIONS
The present data indicate that Ca2+ is involved in ERK activation induced by hormones acting on G protein-coupled receptors in hepatocytes, and suggest that calmodulin and Src kinases might play a role in these signaling pathways.
Melien
Oyvind
O
Department of Pharmacology, Faculty of Medicine, University of Oslo, Box 1057 Blindern, N-0316, Oslo, Norway. oyvind.melien@c2i.net
Nilssen
Laila S
LS
Dajani
Olav F
OF
Sand
Kristin Larsen
KL
Iversen
Jens-Gustav
JG
Sandnes
Dagny L
DL
Christoffersen
Thoralf
T
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology*; D007476:Ionophores / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*
D002147:Calmodulin; D007476:Ionophores; D000001:Calcimycin; D015237:Dinoprost; D019061:src-Family Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium; D009638:Norepinephrine