9-cis-retinoic acid is more effective than all-trans-retinoic acid in upregulating expression of the alpha-fetoprotein gene.
In McA-RH 8994 rat hepatoma cells, all-trans-retinoic acid (t-RA) induces expression of the alpha-fetoprotein (AFP) and albumin genes and results in a phenotype similar to differentiated fetal hepatocytes. The present study elucidated the mechanism involved in AFP gene regulation mediated by retinoic acid. Northern blot analyses demonstrated that 9-cis-retinoic acid (c-RA), a ligand for retinoid x receptors (RXRs), also induced expression of the AFP gene in McA-RH 8994 cells. The induction was time- and dose-dependent. Northern blots and transfection assays using the 7.3 kb full-length regulatory region of the AFP gene demonstrated that c-RA was more effective than t-RA in regulating expression of the AFP gene. At 10(-7) M, c-RA increased AFP mRNA 5-fold and chloramphenicol acetyltransferase (CAT) activity 2.5-fold. In contrast, t-RA at a concentration of 10(-7) M exerted no significant effect; 10(-6) to 10(-5) M t-RA was needed to affect AFP gene expression. These data suggested that activation of RXRs is essential for the regulation of the AFP gene. Co-transfection experiments revealed that over-expression of RXR alpha in McA-RH 8994 cells further enhanced the CAT activity induced by c-RA. In addition, c-RA did not alter the half-life of AFP mRNA. Thus, RXR alpha may play a crucial role in transcriptional regulation of the AFP gene and in controlling hepatocyte phenotype.
Wan
Y J
YJ
Department of Pathology, Harbor-UCLA Medical Center, Torrance 90509, USA.
Pan
T
T
Wang
L
L
Locker
J
J
Wu
T C
TC
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D047488:Retinoid X Receptors; D013237:Stereoisomerism; D014157:Transcription Factors / Q000378:metabolism; D014212:Tretinoin / Q000737:chemistry / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D000509:alpha-Fetoproteins / Q000235:genetics*
D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D000509:alpha-Fetoproteins; D014212:Tretinoin; D015500:Chloramphenicol O-Acetyltransferase