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Query: UNIPROT:P06889 (Mol)
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Biological effects of retinoic acid (RA) are mediated through its binding to three closely related nuclear receptors (RAR alpha, RAR beta, and RAR gamma) belonging to the steroid-thyroid nuclear receptor family. RARs are able to modulate the transcription of specific genes by binding to responsive elements located in the promoter-enhancer region of these genes. As demonstrated by in situ hybridization, the distribution of each RAR type in the developing embryo, as well as in the adult, is not uniform. In this context, synthetic retinoids that would behave as selective ligands would be invaluable for studying the respective roles of each RAR type in cultured cells, whole animals, and embryos. Moreover, from a pharmacological point of view, such selective compounds may possess a higher therapeutic index and a lower teratogenic risk, because they might affect specific tissues and spare some others. As an approach to this problem, we have set up two complementary assays, (i) an in vitro binding assay to determine the Kd values of retinoids for RAR alpha, RAR beta, and RAR gamma and (ii) a functional assay in cultured cells to evaluate the potential of retinoids to transactivate, through their binding to one type of RAR, a reporter gene. The binding assay uses nuclear extracts of COS-7 cells transfected with vectors expressing RAR alpha, RAR beta, or RAR gamma. The functional assay is a measure of chloramphenicol acetyltransferase (CAT) activity in HeLa cells co-transfected with the expression vectors used in the binding assay and the reporter gene TRE-tk-CAT. Selective agonists for RAR alpha (Am80 and Am580) and RAR beta-RAR gamma (CD495 and CD564) were identified. However, compounds with pure RAR beta or RAR gamma selectivity have not yet been identified.
Mol Pharmacol 1991 Oct
PMID:Selective high affinity retinoic acid receptor alpha or beta-gamma ligands. 165 91

The ability of a retinoic acid (RA) response element (RARE) in the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter to mediate effects of either RA or thyroid hormone (T3) on gene expression was studied. Fusion gene constructs consisting of PEPCK promoter sequences ligated to the chloramphenicol acetyltransferase (CAT) reporter gene were used for this analysis. While T3 induced CAT expression to a small degree (about twofold) when such constructs were transiently transfected into H4IIE rat hepatoma cells, along with an expression vector encoding the alpha subtype of the T3 receptor (TR), this effect was mediated by promoter sequences distinct from the PEPCK RARE. Although TRs were capable of binding the PEPCK RARE in the form of putative monomers, dimers, and heterodimers with RA receptors (RARs), this element failed to mediate any positive effect of T3 on gene expression. In contrast, the PEPCK RARE mediated six- to eightfold induction of CAT expression by RA. When TRs were coexpressed along with RARs in transfected H4IIE cells, this RA induction was substantially blunted in a T3-independent manner. This inhibitory effect may be due to the binding of nonfunctional TRs or TR-RAR heterodimers to the PEPCK RARE. A model is proposed to explain the previously observed in vivo effects of T3 on PEPCK gene expression.
Mol Cell Biol 1991 Oct
PMID:Specificity of a retinoic acid response element in the phosphoenolpyruvate carboxykinase gene promoter: consequences of both retinoic acid and thyroid hormone receptor binding. 194 93

We used a series of cell clones from a human teratocarcinoma cell line, PA-1, to study the effect of transformation by an activated N-ras oncogene on the expression of genes involved in retinoic acid (RA)-induced differentiation and growth regulation. Recently, it has been shown that expression of human HOX 2 genes is sequentially activated by RA beginning from Hox 2.9 at the 3' end of the HOX 2 cluster (A. Simeone, D. Acampora, L. Arcioni, P. W. Andrews, E. Boncinelli, and F. Mavilio, Nature [London] 346:763-766, 1990). We now report that six different genes of the cluster HOX 1 are sequentially induced by RA in a similar temporal pattern, beginning with genes at the 3' end of the cluster. However, in N-ras-transformed cell clones, RA-induced expression of these homeobox genes is delayed. Hox 1.4 and Hox 1.3, genes abundantly induced in nontransformed clones after 3 days of RA treatment, are expressed in N-ras-transformed cells only after 10 days of RA treatment. At this time, the cells' growth is arrested at very high density, and no differentiated morphologic characteristics are observed. Constitutive expression of a transfected Hox 1.4 gene under the control of a simian virus 40 promotor leads to differentiated cell morphology similar to that of the RA-induced phenotype and restores the growth-inhibitory effects of RA in N-ras-transformed cells. These observations provide evidence that enhanced proliferation in N-ras-transformed cells compromises teratocarcinoma cell differentiation by a mechanism that transiently suppresses homeobox gene induction and implies a central role for homeobox genes in RA-induced cell differentiation. We conclude that stimulation of a putative growth factor signal pathway, associated with ras-induced proliferation, transiently suppresses the induction of transcription factors functionally involved in cell growth and differentiation.
Mol Cell Biol 1991 Jul
PMID:Alteration of homeobox gene expression by N-ras transformation of PA-1 human teratocarcinoma cells. 167 27

Thyroid hormone receptors are cellular homologues (c-erbAs) of the v-erbA oncoprotein of the avian erythroblastosis virus. Exclusive of the viral gag region, v-erbA differs from the chick c-erbA-alpha receptor by two amino acid changes N-terminal of the DNA binding domain, two amino acid changes in the DNA binding domain, nine amino acid changes in the C-terminal region corresponding to the ligand binding domain of c-erbA, and a nine-amino acid deletion near the C terminus. v-erbA does not bind thyroid hormone and when expressed in cells inhibits the activity of wild-type thyroid hormone receptors. We reported previously that mutants of chick c-erbA/thyroid hormone receptor which lack the DNA binding domain (DBD-) inhibit transcriptional activition by wild-type thyroid hormone and retinoic acid receptors (Forman, B. M., Yang, C.-R., Au, M., Casanova, J., Ghysdael, J., and Samuels, H. H. (1989) Mol. Endocrinol. 3, 1610-1626). This dominant negative activity mapped to a series of hydrophobic heptad motifs which are conserved in the C terminus of these receptors and have been suggested to play a role in receptor dimerization. In this study we show that unlike DBD- c-erbA, DBD- v-erbA does not block receptor activity, suggesting that v-erbA acts by competing for DNA response elements rather than by formation of nonfunctional v-erbA/c-erbA heterodimers. This difference in activity was localized to a single Pro to Ser change in v-erbA just N-terminal of the last heptad motif. Introduction of this Pro to Ser change into DBD- c-erbA resulted in a protein which was inactive both functionally and in blocking receptor dimer formation in vitro.
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PMID:Thyroid hormone receptor/and v-erbA. A single amino acid difference in the C-terminal region influences dominant negative activity and receptor dimer formation. 167 37

Retinoic acid (RA) has been shown to be required for the maintenance of epithelial differentiation. Vitamin A deficiency in hamsters induces the tracheal epithelial cells to undergo squamous metaplasia. Reversing the vitamin deficiency restores the tracheal epithelial cells to their normal morphology and function. Using a hamster tracheal epithelial (HTE) cell culture system which undergoes differentiation to predominantly secretory cells in vitro, we found that RA can convert flat, squamous-like cells to compact, cuboidal-like cells, and that it stimulated cell proliferation. The mitogenic response to RA was maximal at 10(-7) M and required at least 48 h of treatment to observe the effect. RNA levels of growth-related genes during the growth and differentiation phases of primary HTE cultures were examined by Northern analysis. RA maintained a high level of c-myc RNA expression in preconfluent cultures, whereas untreated cells had low amounts of c-myc RNA. Expression of RNA for the replication-dependent histone 3.2 followed a similar pattern, i.e., its level was high in retinoid-treated versus control preconfluent cultures. In confluent (fully differentiated) HTE cell cultures, both retinoid-treated and control cells had low RNA levels of c-myc and histone 3.2. c-fos RNA levels were undetectable in either control or treated cells at any stage during primary culture. The RNA level of c-Ha-ras was very low in both control and treated cultures and did not vary with the state of growth or differentiation, except that when RA-treated cultures reached confluence, no c-Ha-ras RNA was detected.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Respir Cell Mol Biol 1990 Apr
PMID:The effect of retinoic acid on growth and proto-oncogene expression in hamster tracheal epithelial cells. 169 Oct 8

The molecular mechanism of reduced incorporation of radioactively labeled mannose into hamster liver glycoconjugates during the progression of vitamin A deficiency was investigated. In particular the in vivo incorporation of [2-3H]mannose into GDP-mannose, dolichyl phosphate mannose (Dol-P-Man), lipid-linked oligosaccharides, and glycopeptides of hamster liver was examined. Hamsters maintained on a vitamin A-free diet showed a reduction in the incorporation of mannose into GDP-mannose about 10 days before clinical signs of vitamin A deficiency could be observed. The decrease in [2-3H]mannose incorporated into GDP-mannose was accompanied by a reduction in label incorporated into Dol-P-Man, lipid linked oligosaccharides and glycopeptides, which became more severe with the progression of vitamin A deficiency. By the time they reached a plateau stage of growth, hamsters fed the vitamin A-free diet showed a 50% reduction in the amount of [2-3H]mannose converted to GDP-mannose, and the radioactivity associated with Dol-P-Man and glycopeptides was reduced by approximately 60% as compared to retinoic acid-supplemented controls. These results strongly indicate that the reduced incorporation of mannose into lipidic intermediates and glycoproteins observed during vitamin A deficiency is due to impaired GDP-mannose synthesis.
Mol Cell Biochem 1990 Mar 27
PMID:Reduced mannose incorporation into GDP-mannose and dolichol-linked intermediates of N-glycosylation in hamster liver during vitamin A deficiency. 169 71

Human complement component C8 exhibits an unusual structure in that it contains three chains, two of which, alpha and beta, display high sequence homology to other complement and CTL pore-forming proteins. The third chain, C8 gamma, is covalently linked to C8 alpha by a disulfide linkage; it is demonstrated that Cys40 of C8 gamma is linked to Cys164 of C8 alpha, a unique cysteine located in a loop located between the cysteine-rich LDL-receptor class A module and the membrane-inserting region of C8 alpha. C8 gamma was recently identified as a member of the lipocalin protein family, in which all proteins were either shown to, or are believed to bind small hydrophobic ligands. The present results now demonstrate that C8 gamma incorporates retinol and retinoic acid in the presence of 2 M NaCl. Molecular modeling of C8 gamma, based on the crystal structure of the homologous beta-lactoglobulin, reveals a structure of eight antiparallel beta-strands, bearing a highly hydrophobic binding pocket. The residues participating in the pocket formation are highly conserved when compared with the structures of beta-lactoglobulin and retinol-binding protein, both of which are known to interact with retinol. It is therefore proposed that C8 gamma may act as a retinol transporting protein in plasma.
Mol Immunol
PMID:Structural and functional characterization of complement C8 gamma, a member of the lipocalin protein family. 170 34

In this study we demonstrate that retinoic acid (RA) increases the expression of transcription factor zif268 mRNA in primary cultures of fetal rat calvarial cells and in simian virus 40-immortalized clonal rat calvarial preosteoblastic cells (RCT-1), which differentiate in response to RA, but not in the more differentiated RCT-3 and ROS 17/2.8 cells. The increased expression of zif268 mRNA is rapid (maximal within 1 h), transient (returns to basal levels by 3 h), detectable at RA doses of 10(-12)M, and independent of protein synthesis. The relative stimulation of zif268 mRNA by RA was much larger than that of other early genes, including c-fos, c-jun, and junB. The rate of transcription of RA-stimulated RCT-1 cells, estimated by nuclear run-on assays, was elevated, suggesting that RA regulation of zif268 gene transcription was at least in part transcriptional. Moreover, RA stimulated the transcriptional activity of a Zif268CAT (chloramphenicol acetyltransferase) plasmid containing 632 bp of zif268 5' regulatory sequences in RCT-1 cells but not in the more differentiated RCT-3 cells. These in vitro data support the in vivo observations which localize zif268 and RA receptor-gamma transcripts to bone and cartilage during development, suggesting that both RA and zif268 may play a role in osteoblast differentiation.
Mol Cell Biol 1991 May
PMID:Retinoic acid increases zif268 early gene expression in rat preosteoblastic cells. 170 92

Differential screening of a human epidermal cDNA library led to the isolation of cDNA clones homologous to mRNAs specifically expressed in epidermis but weakly or not expressed in the undifferentiated squamous carcinoma cell line TR146. One of these 'differentiation-specific' cDNA clones, A8, hybridized with a 1.7 kb transcript among RNAs isolated from normal human epidermis, but with several transcripts ranging from 1.4 to 2.1 kb when mRNAs were isolated from cultured keratinocytes. We examined the effects of modulators of epidermal differentiation such as calcium and retinoic acid on the production of these transcripts. Their amount was found to increase in the presence of high calcium concentration, but to decrease in the presence of retinoic acid. These results strongly suggest that A8 messages are up-regulated during epidermal differentiation. The sequence of the 1371 bp of A8 cDNA shows a very high GC content. Because of its homology with the murine loricrin mRNA, A8 is likely to correspond either to the human loricrin or to a related protein.
Mol Biol Rep 1990 Nov
PMID:Isolation of a GC-rich cDNA identifying mRNA present in human epidermis and modulated by calcium and retinoic acid in cultured keratinocytes. Homology with murine loricrin mRNA. 171 17

cDNA probes for human retinoic acid receptors alpha and beta (RAR alpha and RAR beta) were modified for use as specific hybridization probes to study hepatocellular carcinomas (HCC) and cell lines, liver regeneration, and fetal development. RAR beta mRNA was detected at low levels in adult liver and rose markedly during the early phase of liver regeneration. RAR beta mRNA was present at very low levels in HCC and was not detected in fetal liver. In contrast, RAR alpha mRNA was present at low levels in normal liver, but showed a marked elevation in several HCCs and cell lines. Growth of cell lines was altered by retinoic acid (RA), but the effects could not be predicted by the levels of either RAR alpha or RAR beta mRNA. However, the response correlated with cell phenotype. Three cell lines with an adult phenotype (high albumin and low alpha-fetoprotein) were inhibited by RA, two undifferentiated lines showed moderate growth stimulation, and two of three cell lines that had high levels of alpha-fetoprotein were markedly stimulated by RA.
Mol Carcinog 1991
PMID:Expression of retinoic acid alpha and beta receptor genes in liver and hepatocellular carcinoma. 171 Apr 63


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