Modulation of proenkephalin A gene expression by cyclic AMP.
Regulation of proenkephalin A expression was studied in the human neuroblastoma SK-N-MC cell line with respect to mRNA-level, translation, posttranslational processing of the prohormone and secretion of the processed products into the culture medium. Cells were treated with either norepinephrine (NE), dexamethasone (DEX), dibutyryl-3',5'-cyclic AMP (dbcAMP) or the combination of NE and DEX. In an additional investigation, proenkephalin A mRNA levels were determined after 9 h of treatment with dbcAMP, NE, isoproterenol, NE + propranolol and dbcAMP + DEX. NE or dbcAMP for 1-48 h transiently elevated proenkephalin A mRNA 1.5-4.5 times compared to control. The effect of NE was partially blocked by the beta-adrenoceptor antagonist propranolol and was reproduced by the beta-adrenoceptor agonist isoproterenol, suggesting involvement of the beta-adrenoceptor. DEX alone had no significant effect. However it markedly antagonized the effect of NE but not that of dbcAMP suggesting an action on the beta-adrenoceptor. The intracellular content of Met-enkephalin-Arg6,Phe7 immunoreactivity was increased during drug treatment in parallel with changes in proenkephalin A mRNA. DEX gave no effect. No significant change in the ratio of low versus high molecular weight immunoreactive material could be detected in the cell extracts as determined at different time points. Secretion of immunoreactivity into the culture medium increased 5-fold after 18 h of treatment with NE, whereas dbcAMP gave a 2-fold increase. The proportion of low-molecular weight secreted material increased markedly. DEX alone did not induce any change but inhibited the effect of NE. Apparently, regulation of gene expression, prohormone processing and secretion are coordinated by a cAMP-dependent mechanism.
Folkesson
R
R
Department of Pharmacology, Uppsala University, Sweden.
Monstein
H J
HJ
Geijer
T
T
Terenius
L
L
D000242:Cyclic AMP / Q000494:pharmacology / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D004745:Enkephalins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D009447:Neuroblastoma; D009638:Norepinephrine / Q000494:pharmacology*; D011498:Protein Precursors / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism*
D004745:Enkephalins; D011498:Protein Precursors; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; C029992:proenkephalin; D003907:Dexamethasone; D000242:Cyclic AMP; D009638:Norepinephrine