Molecular mechanisms underlying forskolin-mediated up-regulation of human dopamine D2L receptors.
1. Human dopamine (DA) D2long (hD2L) receptors, expressed by Ltk- cells, can be up-regulated by treating the cells with forskolin for 16 hr (Johansson and Westlind-Danielsson, 1994). We have examined some of the molecular mechanisms underlying this forskolin-mediated up-regulation. 2. Forskolin (100 microM, 16 hr), but not 1,9-dideoxyforskolin, a forskolin analogue that is unable to activate adenylyl cyclase and raise intracellular cAMP concentrations, up-regulates the hD2L receptor population by 43%. The implication of a cAMP-dependent increase in the receptor up-regulation was further substantiated by treating the cells with 8-bromo-cAMP or prostaglandin E1 (PGE1). The forskolin-mediated rise in receptor number was blocked by cycloheximide or an antisense phosphorothioate oligodeoxynucleotide (ODN) directed toward the hD2L mRNA. KT5720, a specific protein kinase A (PKA) inhibitor, completely blocked the receptor rise, whereas pertussis toxin (PTX) attenuated the increase considerably. Forskolin also produced an increase in the level of the DA hD2short (hD2S) receptor expressed by Ltk- cells. This increase was 2.5-fold higher than that found for the hD2L receptor. 3. The forskolin-mediated hD2L receptor rise is dependent on de novo protein synthesis, a rise in cAMP levels, PKA activation, and, at least partially, PTX-sensitive G proteins. 4. Long-term increases in intracellular cAMP levels may change the sensitivity of a DA receptor expressing cell to DA by increasing D2 receptor density through enhanced cAMP-dependent transcription.
Wanderoy
M H
MH
Department of Biochemistry, CNS Preclinical R&D, Astra Arcus AB, Södertälje, Sweden.
Westlind-Danielsson
A
A
D037361:Adenylate Cyclase Toxin; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018492:Dopamine Antagonists / Q000494:pharmacology; D005347:Fibroblasts / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D010446:Peptide Fragments / Q000502:physiology; D037342:Pertussis Toxin; D020891:Raclopride; D017448:Receptors, Dopamine D2 / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D012457:Salicylamides / Q000494:pharmacology; D014162:Transfection; D014316:Tritium; D015854:Up-Regulation / Q000187:drug effects*; D010566:Virulence Factors, Bordetella
D037361:Adenylate Cyclase Toxin; D018492:Dopamine Antagonists; D010446:Peptide Fragments; D017448:Receptors, Dopamine D2; D012457:Salicylamides; D010566:Virulence Factors, Bordetella; D014316:Tritium; D005576:Colforsin; D020891:Raclopride; D000242:Cyclic AMP; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins