Stimulation of alpha2-adrenergic receptor inhibits cholangiocarcinoma growth through modulation of Raf-1 and B-Raf activities.
Growth factor signaling, mediated by the mitogen-activated protein kinase (MAPK) cascade, induces cell mitosis. Adenosine 3',5'-monophosphate (cAMP) may inhibit or stimulate mitosis (depending on the cell type) through the activation of MAPK and Raf proteins. Among Raf proteins, Raf-1 and B-Raf differentially regulate mitosis. Our aims were to evaluate the role and mechanisms of action of the alpha(2)-adrenergic agonist UK14,304 in the regulation of growth of the human cholangiocarcinoma cell line Mz-ChA-1. Immunocytochemistry and immunoblotting for alpha(2A)-, alpha(2B)-, or alpha(2C)-adrenergic receptor subtypes showed positive reaction in Mz-ChA-1 cells. We found that physiological concentrations of UK14,304 increased cAMP levels and inhibited proliferation and MAPK activity in Mz-ChA-1 cells. Mz-ChA-1 cells expressed Raf-1 and B-Raf. Epidermal growth factor (EGF) immediately and transiently stimulated Raf-1 activity, whereas B-Raf activity was increased with prolonged EGF stimulation. EGF-stimulated Raf-1 and B-Raf activities were both inhibited by UK14,304. UK14,304 did not affect Ras activity. In Mz-ChA-1 cells, alpha(2)-adrenoreceptor stimulation causes up-regulation of cAMP, which inhibits EGF-induced MAPK activity through an acute increase of Raf-1 and sustained activation of B-Raf. In conclusion, because alpha(2)-AR inhibition of growth occurred downstream of Ras, adrenergic stimulation or other stimulants of cAMP may overcome the Ras mutations and offer a new therapeutic approach for patients with cholangiocarcinoma.
Kanno
Noriatsu
N
Department of Internal Medicine, Scott & White Hospital and The Texas A&M University System, HSC COM, 76504, USA.
Lesage
Gene
G
Phinizy
Jo Lynne
JL
Glaser
Shannon
S
Francis
Heather
H
Alpini
Gianfranco
G
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D001650:Bile Duct Neoplasms; D001653:Bile Ducts, Intrahepatic; D015153:Blotting, Western; D000068438:Brimonidine Tartrate; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D018281:Cholangiocarcinoma; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf / Q000032:analysis / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D000068438:Brimonidine Tartrate; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins