Overexpression of the multidrug resistance gene product in adult rat hepatocytes during primary culture.
Expression of P-glycoprotein (P-gp), the product of multidrug resistance gene(s), was investigated in primary cultures of normal adult rat hepatocytes. Levels of P-gp mRNAs determined by Northern blotting and of P-gp measured by immunoblotting increased in parallel with time in culture. As in normal liver, P-gp was found to be localized on the membrane of bile canaliculus-like structures. This increased expression of P-gp was associated with decreased intracellular retention of doxorubicin, which could be restored by compounds such as verapamil and cyclosporin; doxorubicin (and also vincristine) was more cytotoxic to early than to late cultures. As in preneoplastic and neoplastic liver, overexpression of P-gp in cultured hepatocytes was associated with differential changes in drug-metabolizing enzymes, including increased glutathione S-transferase 7-7. Functional P-gp over-expression was observed in the absence of xenobiotic exposure or cell division; it could be linked to cellular stress occurring during cell isolation and plating. Increased expression of P-gp was blocked by actinomycin D, indicating its dependence on increased transcription, while cycloheximide led to a superinduction suggesting negative regulation by a protein factor.
Unité de Recherches Hépatologiques, Institut National de la Santé de la Recherche Médicale, Rennes, France.
O
O
Fardel
D
D
Ratanasavanh
P
P
Loyer
B
B
Ketterer
A
A
Guillouzo
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000639:Amitriptyline / Q000494:pharmacology; D000818:Animals; D015152:Blotting, Northern; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D004317:Doxorubicin / Q000378:metabolism* / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics*; D015870:Gene Expression; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology; D014750:Vincristine / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D000639:Amitriptyline; D014750:Vincristine; D004317:Doxorubicin; D016572:Cyclosporine; D014700:Verapamil; D009543:Nifedipine; D011802:Quinidine