A method for isolation of large, translationally active RNA species is presented. The procedure involves homogenization of cells or tissues in 5 M guanidine monothiocyanate followed by direct precipitation of RNA from the guanidinium by 4 M LiCl. Modifications are described for use with tissue culture cells, yeast, tissues, or isolated nuclei. The advantages of the procedure include speed, simplicity, avoidance of an ultracentrifugation, and its applicability to large numbers of small samples. The procedure yields large mRNA precursors up to 10 kb and mRNA species which translate very well. However, small (less than 300 nucleotides) RNA species are recovered with a poor yield.

The transcription of the progesterone receptor gene is induced by estrogens and decreased by progestins. Studies were performed to define the regions of the gene and the molecular mechanisms involved. No hormonal regulation could be observed using 5′ flanking regions of the gene up to −2762 in front of a heterologous gene. Estrogen and progestin regulation could be observed only when using fragments of the gene extending down to +788. Progressive deletions from the 5′ and 3′ ends, site‐directed mutagenesis and DNase protection experiments with purified estrogen receptor suggested that the biologically active estrogen responsive element (ERE) is present at +698/+723, overlapping the initiation of translation. An oligonucleotide was synthesized bearing this ERE and shown to impart estrogen inducibility to a heterologous gene. Its regulation by anti‐estrogens corresponded to that of the in situ progesterone receptor gene since tamoxifen was a partial agonist whereas ICI 164384 was a full antagonist. This ERE also mediated down‐regulation by progestins in the presence of the progesterone receptor, even though it has no progesterone receptor binding ability. DNase footprinting showed that this effect was not due to a decrease of estrogen receptor affinity for the ERE in the presence of progesterone receptor. Finally, use of deletion mutants of the progesterone receptor showed that the steroid binding and the DNA binding domains were necessary for down‐regulation whereas deletions of various parts of the N‐terminal domain were without effect.

Interleukin-1␤ (IL-1␤

The aryl hydrocarbon receptor (AhR) is involved in various processes such as cytochrome P450 (P450) 1A induction after xenobiotic exposure. It is also considered to play a major role in cell proliferation and differentiation. Recent evidences have suggested a cross-talk between AhR functions and the mitogen-activated protein kinase (MAPK) cascade. We now report that 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene (U0126), a specific inhibitor of MAPK kinase (MEK) MEK1/2, elicits a marked increase in CYP1A1 expression at both mRNA and protein levels associated with a significant increase of enzyme activity in primary rat hepatocytes and a human hepatoma cell line. This induction occurred independently of MEK/extracellular signal-regulated kinase (ERK) activation and in the absence of ERK1 and ERK2 expression. The effect of U0126 was mediated by its ability to transactivate xenobiotic responsive element (XRE)-driven genes, as demonstrated by transfection assays with an XRE-driven luciferase construct in the human B16A2 hepatoma cell line. CYP1A1 modulation was abolished by a cotreatment with resveratrol, an established AhR antagonist, arguing for AhR activation by U0126. Such an effect was demonstrated by direct in vitro ligand binding competition assays using rabbit liver cytosol, showing that this compound binds AhR with an EC 50 ϭ 25 ϫ 10 Ϫ6 M. Moreover, we demonstrated that U0126 is a substrate for several P450s including human CYP1A2, -1A1, and -1B1. We conclude that the widely used specific inhibitor of MEK/ ERK, U0126, also acts as a potent AhR activator and an inducer of related genes. Such effects on the AhR may have an impact on biological functions attributed previously to MAPK inhibition.2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and polycyclic aromatic hydrocarbons (PAH) are potent inducers of several genes, including some encoding "Phase I" and "Phase II" xenobiotic-metabolizing enzymes. These enzymes include cytochrome P450 (P450), glutathione transferases, NADPH: quinone reductases, and UDP-glucuronosyl transferases.TCDD and PAH effects are mediated by activation of the aryl hydrocarbon receptor (AhR), a cytosolic protein that forms complexes with two 90-kDa heat shock proteins and some other proteins. After ligand binding, the AhR is translocated and localized in the nucleus followed by an heterodimerization with the AhR nuclear translocator (Arnt) protein and acts as a transcriptional factor. Several reports have also shown constitutive activation of the AhR in the absence of exogenous ligand under certain conditions (Singh et al

PML (promyelocytic leukemia) is a protein involved in the t (15;17) translocation of promyelocytic leukemia and is mainly localized in nuclear bodies. Here we show that PML exerts a very powerful enhancing activity (up to 20-fold) on the transactivating properties of the progesterone receptor (PR) and has a similar effect on several other steroid hormone receptors. There is probably a direct or indirect interaction between PR and PML, because when the latter was expressed at high concentrations it shifted PR into the nuclear bodies. The use of deletion mutants showed that both activation functions (AF1 and AF2) of PR as well as the coiled coil and His-Cys-rich domains of PML were required for transcriptional enhancement. The fusion protein PML-RAR which is not localized in nuclear bodies, also enhanced the transactivating activity of PR, but this effect was totally suppressed by the administration of retinoic acid. PML, which is ubiquitously expressed, may thus be involved in the transactivation properties of steroid hormone receptors. This mechanism may also play a role in the oncogenic properties of PML-RAR and in their suppression by retinoic acid.

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