Effect of dexamethasone on the activity and expression of ornithine decarboxylase in rat liver and thymus.
A single intraperitoneal injection of the synthetic glucocorticoid dexamethasone into rats resulted in a marked stimulation (more than 60-fold) of hepatic ornithine decarboxylase (ODC) at 4 h after the injection, whereas the enzyme activity in thymus was almost totally (about 95%) depressed at the same time. The stimulation of ODC activity in liver was in all likelihood attributable to a greatly enhanced accumulation of mRNA species for the enzyme as revealed by Northern blot and dot-blot hybridization analyses. ODC activity in thymus, in response to dexamethasone, was only 5% of that found in control animals, but this decrease was apparently not accompanied by similar reductions of the levels of ODC message, which was in fact decreased only by 50% at the maximum. In addition to two mRNA species (2.1 and 2.6 kilobases; kb), typical to mouse cells, rat tissues seemed to contain a third hybridizable message for ODC, smaller (1.6 kb) than the above-mentioned species and not seen in samples obtained from mouse or human cells. Interestingly, these smaller poly(A)+ RNA sequences, hybridizable with cDNA complementary to mouse ODC mRNA, were apparently constitutively expressed, as the treatment with glucocorticoid altered the amount of these sequences only slightly.
Hirvonen
A
A
Department of Biochemistry, University of Helsinki, Finland.
Immonen
T
T
Leinonen
P
P
Alhonen-Hongisto
L
L
Jänne
O A
OA
Jänne
J
J
D000367:Age Factors; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D009955:Ornithine Decarboxylase / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D013950:Thymus Gland / Q000201:enzymology*
D012333:RNA, Messenger; D003907:Dexamethasone; D009955:Ornithine Decarboxylase