No abstract

The t(15;17) chromosomal translocation, specific for acute promyelocytic leukemia (APL), fuses thePML gene to the retinoic acid receptor a (RARa) gene, resulting in expression of a PML-RARa hybrid protein. In this report, we analyzed the nature of PML-RARa-containing complexes in nuclear protein extracts of t(15;17)-positive cells. We show that endogenous PML-RARa can bind to DNA as a homodimer, in contrast to RARa that requires the retinoid X receptor (RXR) dimerization partner. In addition, these cells contain oligomeric complexes of PML-RARa and endogenous RXR Treatment with retinoic acid results in a decrease of PML-RARa protein levels and, as a consequence, of DNA binding by the different complexes. Using responsive elements from various hormone signaling pathways, we show that PML-RARa homodimers have altered DNA-binding characteristics when compared to RARaRXRa heterodimers. In transfected Drosophila SL-3 cells that are devoid of endogenous retinoid receptors PML-RARa inhibits transactivation by RARa-RXRa heterodimers in a dominant fashion. In addition, we show that both normal retinoid receptors and the PML-RARa hybrid bind and activate the peroxisome proliferator-activated receptor responsive element from the AcylCoA oxidase gene, indicating that retinoids and peroxisome proliferator receptors may share common target genes. These properties of PML-RARa may contribute to the transformed phenotype of APL cells.The consistent expression of PML-retinoic acid receptor a (RARa) in the majority of cases of acute promyelocytic leukemia (APL) suggests an important role for the fusion protein during transformation of these cells. Since PML-RARa retains most of the functional domains of both PML and RARa, it may interfere with the normal function of either of the parental proteins. Retinoid receptors are ligand-inducible transcription factors that belong to the nuclear receptor superfamily. Two families of retinoid receptors have been described, each consisting of three genes. RARa, -13, and -y bind both all-trans-and 9-cis-retinoic acid (RA), whereas the three retinoid X receptors (RXRs) (a,1, and y) bind only the 9-is isomer. RARs bind with high affinity to RA responsive elements [RAREs; consisting of a directly repeated (A/G)G(T/G)TCA consensus sequence] as a heterodimer with RXRs. RXR also heterodimerizes with several other nuclear receptors, such as the vitamin D3 receptor, the thyroid hormone receptor, and the peroxisome proliferatoractivated receptor (PPAR), indicating its pivotal role in different hormone signaling pathways. When compared to normal receptors, the transactivating properties of PMLRARa are altered.

We describe a novel approach for the insertion of an insecticidal toxin gene into a resident plasmid in Bacillus thuringiensis (Bt). A gene encoding a coleopteran-specific toxin was cloned within a fragment of IS232 and inserted into a plasmid thermosensitive for replication in Bt. The plasmid was used to transform a Bt strain toxic to lepidoptera, and the transformants were then selected at non-permissive temperature for clones in which the vector had integrated into a copy of IS232 present on a resident plasmid. A second recombination event was selected such that the vector was eliminated and the newly introduced toxin gene was conserved. The resulting strain contained only DNA of Bt origin, and displayed insecticidal activity against both lepidoptera and coleoptera.