Distinct Retinoid X Receptor-Retinoic Acid Receptor Heterodimers Are Differentially Involved in the Control of Expression of Retinoid Target Genes in F9 Embryonal Carcinoma Cells

Abstract

The F9 murine embryonal carcinoma cell line represents a well-established system for the study of retinoid signaling in vivo. We have investigated the functional specificity of different retinoid X receptor (RXR)-retinoic acid (RA) receptor (RAR) isotype pairs for the control of expression of endogenous RA-responsive genes, by using wild-type (WT), RXR␣ -RAR␥؊/؊ F9 cells, as well as panRXR and RAR isotype (␣, ␤, and ␥)-selective retinoids. We show that in these cells the control of expression of different sets of RA-responsive genes is preferentially mediated by distinct RXR-RAR isotype combinations. Our data support the conclusion that RXR-RAR heterodimers are the functional units transducing the retinoid signal and indicate in addition that these heterodimers exert both specific and redundant functions on the expression of particular sets of RA-responsive genes. We also show that the presence of a given receptor isotype can hinder the activity of another isotype and therefore that functional redundancy between retinoid receptor isotypes can be artifactually generated by gene knockouts.The F9 murine embryonal carcinoma (EC) cell line, a wellestablished model system for the analysis of retinoid signaling, differentiates upon retinoic acid (RA) treatment into three distinct extraembryonic (primitive, parietal, and visceral) endodermal cell types, depending on the culture conditions (for reviews, see references 16, 17, and 40). Retinoid-induced differentiation is accompanied by an apoptotic response and a decrease in the rate of proliferation (references 1, 9, and 38 and references therein), as well as by the induction of expression of a number of genes (references 2, 16, and 38 and references therein). F9 cells express all RA receptor isotypes (RAR␣, RAR␤, and RAR␥), activated by either all-trans retinoic acid (tRA) or its 9-cis isomer (9c-RA), as well as all retinoid X receptor isotypes (RXR␣, RXR␤, and RXR␥), activated by 9c-RA only (30,44,45). RXR-RAR heterodimers bind much more efficiently in vitro to RA response elements (RAREs) than do their respective homodimers (references 5, 6, 13-15, 18, 21, 24, 27, and 28 and references therein), and several lines of evidence support the idea that these heterodimers represent the functional units transducing the retinoid signal in vivo (references 6 and 19 and references therein). For instance, we have previously shown that a combination of a pan-RXR agonist and suboptimal concentrations of RAR isotype-selective agonists synergistically induce the expression of several endogenous RA-responsive genes in F9 and P19 EC cells (37, 43), which indeed strongly suggests that RXR-RAR heterodimers are the functional units responsible for transducing the retinoid signal which triggers the expression of RAresponsive genes in vivo.We have recently engineered F9 cells lacking either RXR␣ and RAR␣ or RXR␣ and RAR␥ and shown that different RXR-RAR pairs exert both specific and redundant functions in differentiation, proliferation, and apoptosis of these cells We show that distinct R...

RAR-mediated epigenetic control of the cytochrome P450 Cyp26a1 in embryocarcinoma cells

“…By using antibodies specifically recognizing either RARa or RARb2 overexpressed in COS-1 cells (Figure 2a), we found that RARa specifically binds the P19 RARb2 region encompassing the RARE, but not two flaking regions, one upstream (À1 Kb) and one downstream ( þ 1 Kb) of the RARE-containing region (ChIP anti-RARa, Figure 2b, left). Upon RARb2 induction in response to RA (1 mM, for 24 h), RARb2 binds not only its own RARE region (ChIP anti-RARb, Figure 2b, middle), as expected since RARb2 regulates its own transcription (Chiba et al, 1997), but also the Cyp26a1 RARE (ChIP anti-RARb, Figure 2b, right). Thus, RARb2 binds Cyp26a1 in response to RA.…”

Ubiquitinated or sumoylated retinoic acid receptor alpha determines its characteristic and interacting model with retinoid X receptor alpha in gastric and breast cancer cells

“…4A). It is well known that the RAR/RXR heterodimer is a functional unit that preferentially transduces the retinoic acid signal in vivo and in vitro (Zhang et al 1992, Kastner et al 1995, Clifford et al 1996, Chiba et al 1997a,b, Wu et al 1997a.…”

Maintenance of spermatogenesis requires TAF4b, a gonad-specific subunit of TFIID

“…These include genes involved in retinoic acid signaling that are known to impact male fertility (Livera et al 2002). Retinoic acid receptor ␥, which has been shown to control expression of Stra8 (Chiba et al 1997), is expressed at lower levels in Taf4b-null testis (Fig. 6C).…”

“…Stra8, a RAR␥-responsive gene, (Chiba et al 1997) is the most dramatically down-regulated gene in Taf4b-null testes by semiquantitative RT-PCR. Stra8 is deficient as early as the day of birth, when Taf4b-null testes have comparable numbers of germ cells compared to wild type and heterozygous littermates.…”