Met-enkephalin-containing peptides encoded by proenkephalin A mRNA expressed in activated murine thymocytes inhibit thymocyte proliferation.
Murine thymocytes activated with the mitogen Con A express proenkephalin A mRNA (PEA mRNA) and met-enkephalin and/or met-enkephalin-containing peptides ("enkephalins"). This Con A-induced expression of PEA mRNA is modulated by the delta opioid receptor agonist, deltorphin I, in a biphasic, dose-dependent manner. That is, 10(-13) M to 10(-11) M deltorphin enhanced PEA mRNA expression 3- to 3.5-fold over the level induced by Con A alone, and 10(-9) M to 10(-7) M deltorphin inhibited it 40 to 70%. delta opioid receptor antagonists recognizing the delta-2 (naltrindole (NTI) and naltriben (NTB)), but not the delta-1 (7-benzylidenenaltrexone (BNTX)), subtype of opioid receptor described in brain, reversed both the enhancing and inhibiting effects of deltorphin on Con A-induced PEA mRNA expression. In addition, the delta-2 receptor-specific antagonists, NTI and NTB, directly inhibited Con A-induced PEA mRNA expression. The function of the enkephalins expressed by thymocytes was examined by using 1) delta opioid receptor antagonists, 2) PEA mRNA-specific antisense cDNA, and 3) Ab to met-enkephalin, and measuring cell proliferation. All three reagents caused enhancement of Con A-induced proliferation, with effects ranging from two- to fourfold over the response to Con A alone. Again, the delta-2 subtype-specific antagonists, NTI and NTB, were functional and the delta-1 subtype-specific antagonist, BNTX, was not. The PEA mRNA-specific antisense cDNA blocked translation but not transcription of PEA mRNA. The data suggest that 1) endogenous enkephalins induced in thymocytes modulate their own expression through delta-2-like opioid receptors, and 2) these endogenous enkephalins function to inhibit the proliferation of activated thymocytes.
Linner
K M
KM
Minneapolis Medical Research Foundation, MN 55404, USA.
Quist
H E
HE
Sharp
B M
BM
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001483:Base Sequence; D015152:Blotting, Northern; D002455:Cell Division / Q000502:physiology*; D003208:Concanavalin A / Q000494:pharmacology; D016373:DNA, Antisense / Q000235:genetics; D004744:Enkephalin, Methionine / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D004745:Enkephalins / Q000235:genetics; D005260:Female; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D009842:Oligopeptides / Q000502:physiology; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011863:Radioimmunoassay; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors; D013950:Thymus Gland / Q000737:chemistry* / Q000166:cytology / Q000187:drug effects
D000911:Antibodies, Monoclonal; D016373:DNA, Antisense; D004745:Enkephalins; D009842:Oligopeptides; D011498:Protein Precursors; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; C029992:proenkephalin; D003208:Concanavalin A; C059567:deltorphin; D004744:Enkephalin, Methionine