OX1 orexin receptors activate extracellular signal-regulated kinase in Chinese hamster ovary cells via multiple mechanisms: the role of Ca2+ influx in OX1 receptor signaling.
Activation of OX1 orexin receptors heterologously expressed in Chinese hamster ovary (CHO) cells led to a rapid, strong, and long-lasting increase in ERK phosphorylation (activation). Dissection of the signal pathways to ERK using multiple inhibitors and dominant-negative constructs indicated involvement of Ras, protein kinase C, phosphoinositide-3-kinase, and Src. Most interestingly, Ca2+ influx appeared central for the ERK response in CHO cells, and the same was indicated in recombinant neuro-2a cells and cultured rat striatal neurons. Detailed investigations in CHO cells showed that inhibition of the receptor- and store-operated Ca2+ influx pathways could fully attenuate the response, whereas inhibition of the store-operated Ca2+ influx pathway alone or the Ca2+ release was ineffective. If the receptor-operated pathway was blocked, an exogenously activated store-operated pathway could take its place and restore the coupling of OX1 receptors to ERK. Further experiments suggested that Ca2+ influx, as such, may not be required for ERK phosphorylation, but that Ca2+, elevated via influx, acts as a switch enabling OX1 receptors to couple to cascades leading to ERK phosphorylation, cAMP elevation, and phospholipase C activation. In conclusion, the data suggest that the primary coupling of orexin receptors to Ca2+ influx allows them to couple to other signal pathways; in the absence of coupling to Ca2+ influx, orexin receptors can act as signal integrators by taking advantage of other Ca2+ influx pathways.
Ammoun
Sylwia
S
Department of Neuroscience, Unit of Physiology, Uppsala University, SE-75123 Uppsala, Sweden.
Johansson
Lisa
L
Ekholm
Marie E
ME
Holmqvist
Tomas
T
Danis
Alexander S
AS
Korhonen
Laura
L
Sergeeva
Olga A
OA
Haas
Helmut L
HL
Akerman
Karl E O
KE
Kukkonen
Jyrki P
JP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism; D064446:Orexin Receptors; D000068797:Orexins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D002118:Calcium; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D010738:Type C Phospholipases