Differential regulation of multiple gap junction transcripts and proteins during rat liver regeneration.
The mRNA and protein expression of alpha 1 (connexin 43), beta 1 (connexin 32), and beta 2 (connexin 26) gap junction genes were examined in the regenerating rat liver after 70% partial hepatectomy (PH). Expression of beta 1 and beta 2 steady-state mRNA levels changed minimally until 12 h after PH when both transcripts decreased to approximately 15% of baseline values. A similar decrease in assembled connexin levels was detected by immunoblot and indirect immunofluorescence at 18 h after PH. Both transcripts simultaneously increased between 24 and 42 h and again rapidly decreased by 48 h post-PH. beta 1 and beta 2 assembled gap junction protein expression increased at 48 h post-PH and rapidly decreased by 56 h. By 72 to 84 h post-PH, beta 1 and beta 2 mRNA and assembled protein expression returned to near baseline levels and were maintained. Interestingly, inhibition of protein synthesis with cycloheximide completely inhibited disappearance of the beta 2 transcript, in contrast to beta 1 mRNA which was unaffected. Nuclear run-on assays showed no change in transcriptional rates for either gene during the regenerative period. However, both beta 1 and beta 2 transcripts exhibited significantly decreased mRNA half-lives at 12 h post-PH (3.8 and 3.7 h, respectively) relative to those at 0 h (10.9 and 6.1 h, respectively). Surprisingly, although the transcriptional rate for alpha 1 was similar to that observed for beta 2, no alpha 1 transcripts were detectable by northern or RNase protection analysis. The results suggest that in the regenerating rat liver, beta 1 and beta 2 gap junction genes are not regulated at the transcriptional level. Rather, the cyclical modulation of their steady-state transcripts is regulated primarily by posttranscriptional events of which mRNA stability is at least one critical factor in the control process.
Kren
B T
BT
Department of Medicine, University of Minnesota Medical School, Minneapolis 55455.
Kumar
N M
NM
Wang
S Q
SQ
Gilula
N B
NB
Steer
C J
CJ
D000818:Animals; D015152:Blotting, Northern; D000072259:Connexin 26; D018031:Connexin 43 / Q000096:biosynthesis; D017630:Connexins / Q000096:biosynthesis*; D003513:Cycloheximide / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D007365:Intercellular Junctions / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008115:Liver Regeneration; D008297:Male; D016253:Microscopy, Immunoelectron; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic; D000097002:Gap Junction beta-1 Protein
D000072259:Connexin 26; D018031:Connexin 43; D017630:Connexins; D003513:Cycloheximide; D012333:RNA, Messenger; D000097002:Gap Junction beta-1 Protein; C000607044:Gjb2 protein, rat