Document Detail

Superinduction of P-glycoprotein messenger RNA in vivo in the presence of transcriptional inhibitors.
MedLine Citation:
PMID:  12724855     Owner:  NLM     Status:  MEDLINE    
P-Glycoprotein (P-gp) is comprised of a small family of plasma membrane proteins, and its presence in high amounts often correlates with multidrug resistance in cultured cells. Dramatically increased levels of a single member of P-gp mRNA (pgp2) have been observed in experimental liver carcinogenesis models, during liver regeneration, upon culturing of hepatocytes and in the uterus of pregnant animals. In all cases, the increase in mRNA level appears to be the result of an increase in mRNA half-life (stability). Previously, we have used transcriptional inhibitors alpha-amanitin and actinomycin D to measure P-gp mRNA half-life in normal liver and in liver tumors. We showed that the level of all three P-gp mRNAs decreased with time in the presence of transcriptional inhibitors, yielding measured half-lives of less than 2 h in liver but greater than 12 h in liver tumors. This observation raised the possibility that regulation of P-gp mRNA stability plays a role in liver carcinogenesis. In the present study, we measured P-gp mRNA half-life in other normal tissues to determine if a short P-gp mRNA half-life is unique to the liver. Our study reveals that in contrast to liver, measured P-gp mRNA half-lives in most tissues examined are greater than 12 h. Moreover, we observed an unexpected, marked increase in the level of pgp2 mRNA with time after injection of transcriptional inhibitors. This can only be explained if the transcriptional inhibitors directly or indirectly inhibit the normally high degradation rate of pgp2 mRNA, resulting in the superinduction of this mRNA. These findings have implications for our understanding of the regulation of P-gp gene expression and drug resistance in vivo.
Chow H Lee; Victor Ling
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of experimental therapeutics & oncology     Volume:  3     ISSN:  1359-4117     ISO Abbreviation:  J. Exp. Ther. Oncol.     Publication Date:    2003 Jan-Feb
Date Detail:
Created Date:  2003-05-02     Completed Date:  2004-02-02     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9604933     Medline TA:  J Exp Ther Oncol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  14-26     Citation Subset:  IM    
Chemistry Program, University of Northern British Columbia, Prince George, BC, Canada.
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MeSH Terms
Amanitins / pharmacology*
Dactinomycin / pharmacology*
Injections, Intraperitoneal
Intestine, Small / metabolism
Kidney / metabolism
Liver / metabolism
Lung / metabolism
Myocardium / metabolism
Nucleic Acid Synthesis Inhibitors / pharmacology*
P-Glycoproteins / biosynthesis*,  genetics
RNA, Messenger / biosynthesis*
Rats, Inbred F344
Spleen / metabolism
Transcription, Genetic / drug effects
Reg. No./Substance:
0/Amanitins; 0/Nucleic Acid Synthesis Inhibitors; 0/P-Glycoproteins; 0/P-glycoprotein 2; 0/RNA, Messenger; 50-76-0/Dactinomycin

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