We have compared the expression of alpha and beta retinoic acid receptors (RAR-alpha and RAR-beta) in different rat tissues. The two cDNA probes for RAR-alpha and RAR-beta each specifically detect two different transcripts. RAR-alpha was expressed in all tissues examined, but, in contrast, the expression of RAR-beta was undetectable in some tissues. The data do not support the idea that RAR-beta is specific to epithelial tissues.

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The objective of this study was to compare the properties of 9-cis and all-trans retinoic acid with respect to the induction of expression of retinoic acid receptor beta (RAR-beta) and cellular retinoic acid-binding protein (CRABP) II in human neuroblastoma SH SY 5Y cells. RAR-beta and CRABP II mRNA was induced by both all-trans and 9-cis retinoic acid in SH SY 5Y cells. Induction was rapid, detectable within 2-4 h, and inhibited by actinomycin D. Time-courses of induction for RAR-beta and CRABP II differed: RAR-beta mRNA levels reached a maximum 4-6 h after adding all-trans or 9-cis retinoic acid, whereas CRABP II mRNA levels increased over at least 18 h. These differences were attributed to the longer half-life of CRABP II mRNA (20 h) compared with RAR-beta mRNA (3.9 h). The dose-response characteristics of all-trans and 9-cis retinoic acid were different: all-trans was effective at nanomolar concentrations, whereas 10-fold higher levels of 9-cis retinoic acid were required to achieve comparable induction of RAR-beta and CRABP II. Conversely, at high concentrations, 9-cis retinoic acid gave a greater induction of RAR-beta and CRABP II than all-trans. The induction of RAR-beta and CRABP II by all-trans retinoic acid was maintained in the subsequent absence of all-trans retinoic acid, whereas induction by 9-cis retinoic acid was dependent on its continued presence in the culture medium. These results suggest that, at high concentrations, 9-cis retinoic acid may produce its transcriptional effects via retinoid X receptor (RXR) homodimers. This has implications for the cellular functions of 9-cis retinoic acid and its use as a biological response modifier.

Retinoic acid, one of the most potent of the naturally occurring retinoids (retinol and derivatives), is required in vivo for the maintenance of epithelial cell growth. This study describes the pattern of expression of nuclear retinoic acid receptors (RARs and RXRs), and cellular binding proteins for retinol and retinoic acid (CRBP I, CRABP I and II), in endometrial epithelial cells. The effects of retinoic acid on the expression of these receptors in endometrial epithelial cells have also been studied and compared with its effects in endometrial stromal cells. Messenger RNA for RAR-alpha, RAR-beta, RAR-gamma, RXR-alpha, CRBP I and CRABP II was detected by Northern blotting of total RNA extracted from cultured epithelial cells. In comparison with stromal cell RNA that was used as an internal standard, CRBP I appeared to be more abundant in epithelial cells, whereas CRABP II appeared to be more abundant in the stromal cells. This implies that the intracellular concentration of retinoic acid may be maintained at higher levels in epithelial cells compared to stromal cells. In addition, the response of the two cell types to retinoic acid differs: RAR-beta is induced in stromal cells treated with all-trans retinoic acid but not in epithelial cells. From these data we suggest that retinoid physiology differs between endometrial epithelial and stromal cells. Furthermore, by analogy with other studies, we propose that retinoic acid may be maintained at a higher intracellular concentration in endometrial epithelial cells to facilitate differentiation to a glandular phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Ring glands or brain-ring gland complexes from third-instar Drosophila melanogaster larvae secreted ecdysone [(22R)-2j3,3,,14a,22,25-pentahydroxy-5i3-cholest-7-en-6-oneJ and two less polar ecdysteroids (LP1 and LP2) in vitro. Radioimmunoassay with different antisera indicated that LP1 and LP2 are side-chain-modified analogues of ecdysone. In high-performance liquid chromatography, the retention time of LP2 was equivalent to that of a precursor of makisterone A [(20R,22R)-2fi,3fi,l4a,20,22,25-hexahydroxy-24-methyl-5p-cholest-7-en-6-one] secreted by Dysdercusfasciatus prothoracic glands in vitro. LP2 was metabolized in vitro by the fat body of DrosophilM larvae to a product with the characteristics of iakisterone A when analyzed by gas chromatography/mass spectrometry (selected ion nionitoring). Evidence was obtained for the presence of mikisterone A in. Drosophila larvae. These data suggest that LP2 is 20-deoxymakisterone A (24-methylecdysone) and that makisterone A could function as an additional moulting hormone in Drosophila, although 20-deoxymakisterone A production is apparently dependent on the sterol composition of the diet. LP1 has not been identified.The insect steroid ecdysone, a C27 ecdysteroid [(22R)-2p,3,8 14a,22,25-pentahydroxy-5p-cholest-7-en-6-one], is secreted by the prothoracic glands (1) or, in cyclorrhaphous Diptera, by the ring gland (2). Ecdysone is hydroxylated at C-20 by monooxygenase enzyme systems in the fat body, gut, and Malpighian tubules to give the biologically active moulting hormone 20-hydroxyecdysone [(20R,22R)-2P,3,8,14a,20,22,25-hexahydroxy-5/3-cholest-7-en-6-oneI (3).Recently, the moulting hormone in Dysdercus fasciatus (4) and some other species of phytophagous Hemiptera (5) has been identified as a C28 ecdysteroid, makisterone A [(20R,22R)-2(,3(3,14a,20,22,25-hexahydroxy-24-methyl-5f3-cholest-7-en-6-one], which differs from 20-hydroxyecdysone in the presence of an additional methyl group at C-24 of the ecdysteroid side chain. By analogy with other insects (1), the prothoracic glands of these hemipterans would be expected to secrete the 24-methylated analogue of ecdysone, 20-deoxymakisterotle A (24-methylecdysone).In a previous study, it was shown that Drosophila ring glands secrete ecdysteroids in vitro and that the rate of secretion rea'ches a maximum towards the end of the last larval instar (6). Sarcophaga ring glands secrete ecdysone in vitro (2), and the experiments reported here were initially designed (7) were used.Yeast RNA was replaced with uridine and inosine, and lecithin was replaced with choline chloride (7). The medium constituents were purchased from Sigma [uridine, nicotinic acid, thiamine HCl, calcium pantothenate, pyridoxine, biotin, and ergosterol (ergosta-5,7,22E-trien-3,8-ol) Organ Culture. Ring glands or brain-ring gland complexes from third-instar Drosophila larvae with partially or fully bloated larval salivary glands were dissected and cultured (three to six ring glands or brain-ring gland complexes per culture) in Grace's medium (Flow La...

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Muscle wasting is a common and prominent feature of advanced cancer, including lung cancer. Evidence from animal experiments suggests that accelerated proteolysis via the ubiquitin--proteasome pathway is the primary cause of cancer-related cachexia. However, there are few data on the role of this pathway in determining muscle wasting in human cancer. The present study was designed to measure whether skeletal muscle gene expression of components of the ubiquitin-proteasome pathway and/or the lysosomal proteolytic pathway was increased in patients with early lung cancer. A total of 36 patients with lung cancer referred for curative resection and 10 control subjects had biopsies of latissimus dorsi muscle taken at operation. mRNA levels of four components of the ubiquitin-proteasome pathway, i.e. polyubiquitin, C2 alpha proteasome subunit, 14 kDa ubiquitin-carrier protein and ubiquitin-activating protein, and of two lysosomal proteolytic enzymes, i.e. cathepsin B and cathepsin D, were measured using quantitative Northern blotting. mRNA levels for cathepsin B, but not for components of the ubiquitin--proteasome pathway, were higher in patients with cancer compared with controls (P=0.01). Among lung cancer patients, cathepsin B mRNA levels correlated with fat-free mass index (r = -0.57, P=0.003) and tumour stage (r(s)=0.45, P=0.03), and were higher in smokers (P=0.04). Thus gene expression of the lysosomal protease cathepsin B is increased in the skeletal muscle of patients with early lung cancer, and the strong inverse relationship with fat-free mass suggests that cathepsin B may have a role in inducing muscle wasting in the early stages of lung cancer.