ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Recently, a new subfamily of nuclear retinoid receptors that is distinct from that of RARs has been identified and named Retinoid X receptors (RXRs). These receptors specifically bind 9-cis-retinoic acid (9cisRA), but not all-trans-retinoic acid (ATRA). We determined which RXR subtypes were expressed in B16 mouse melanoma cells and then studied the effect of ATRA, 8-bromo-cyclic AMP (8BrcA), and phorbol dibutyrate (PDB) on RXR mRNA levels. ATRA induces differentiation in these cells while 8BrcA and PDB antagonize the RA-induced differentiation of B16 melanoma cells. Northern analysis demonstrated the expression of RXRα and RXRβ mRNA in B16 cells, but RXRγ was not detectable. Further analysis using RT-PCR also failed to detect RXRγ in these cells. Longterm RA treatment decreased the expression of RXRα, but not RXRβ mRNAs. PDB did not alter the expression of either RXR mRNAs, however, 8BrcA treatment resulted in a time dependent decrease in the amount of RXRβ, but not RXRα mRNA. Inhibition of protein synthesis by cycloheximide resulted in a large increase in RXRα and RXRβ mRNA levels. This effect of cycloheximide was time and concentration dependent with maximal stimulation of RXRα and RXRβ mRNAs occurring at 4 h of treatment. Inhibition of transcription with actinomycin D completely abolished the cycloheximide-induced increase of RXRβ. In contrast to its effect on other genes, such as immediate response genes, cycloheximide treatment did not increase the half-life of RXRβ mRNA. Nucclear run-on assays showed that cycloheximide treatment of intact B16 melanoma cells stimulated the transcription rate of RXRβ, but not RXRα. These results suggest the presence of an unstable transcription factor that negatively regulates the expression of RXRβ in B16, melanoma cells. In addition, since RXRβ is the predominant isotype in B16 cells, 8BrcA may, at least partially, inhibit RA-induced differentiation through down-regulation of this RXR. © 1995 Wiley-Liss, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041650216
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