The chemotherapeutic agent paclitaxel inhibits autophagy through two distinct mechanisms that regulate apoptosis.

Anti-mitotic agents such as paclitaxel and docetaxel are widely used for the treatment of breast, ovarian and lung cancers. Although paclitaxel induces apoptosis, this drug also modulates autophagy. How autophagy affects paclitaxel activity, is unclear. We discovered that paclitaxel inhibited autophagy through two distinct mechanisms dependent on cell cycle stage. In mitotic cells, paclitaxel blocked activation of the class III phosphatidyl inositol 3 kinase, Vps34, a critical initiator of autophagosome formation. In non-mitotic paclitaxel-treated cells, autophagosomes were generated but their movement and maturation was inhibited. Chemically or genetically blocking autophagosome formation diminished paclitaxel-induced cell death suggesting that autophagosome accumulation sensitized cells to paclitaxel toxicity. In line with these observations, we identified that primary breast tumors that expressed diminished levels of autophagy-initiating genes were resistant to taxane therapy, identifying possible mechanisms and prognostic markers of clinical chemotherapeutic resistance.

Apical localization of wingless transcripts is required for wingless signaling.

Many developing and adult tissues are comprised of polarized epithelia. Proteins that are asymmetrically distributed in these cells are thought to be localized by protein trafficking. Here we show that the distribution and function of the signaling protein Wingless is predetermined by the subcellular localization of its mRNA. High-resolution in situ hybridization reveals apical transcript localization in the majority of tissues examined. This localization is mediated by two independently acting elements in the 3' UTR. Replacement of these elements with non- or basolaterally localizing elements yields proteins with altered intracellular and extracellular distributions and reduced signaling activities. This novel aspect of the wingless signaling pathway is conserved and may prove to be a mechanism used commonly for establishing epithelial cell polarity.

FTZ-Factor1 and Fushi tarazu interact via conserved nuclear receptor and coactivator motifs.

To activate transcription, most nuclear receptor proteins require coactivators that bind to their ligand-binding domains (LBDs). The Drosophila FTZ-Factor1 (FTZ-F1) protein is a conserved member of the nuclear receptor superfamily, but was previously thought to lack an AF2 motif, a motif that is required for ligand and coactivator binding. Here we show that FTZ-F1 does have an AF2 motif and that it is required to bind a coactivator, the homeodomain-containing protein Fushi tarazu (FTZ). We also show that FTZ contains an AF2-interacting nuclear receptor box, the first to be found in a homeodomain protein. Both interaction motifs are shown to be necessary for physical interactions in vitro and for functional interactions in developing embryos. These unexpected findings have important implications for the conserved homologs of the two proteins.

Molecular interactions between Vestigial and Scalloped promote wing formation in Drosophila.

Scalloped (Sd) and Vestigial (Vg) are each needed for Drosophila wing development. We show that Sd is required for Vg function and that altering their relative cellular levels inhibits wing formation. In vitro, Vg binds directly to both Sd and its human homolog, Transcription Enhancer Factor-1. The interaction domains map to a small region of Vg that is essential for Vg-mediated gene activation and to the carboxy-terminal half of Sd. Our observations indicate that Vg and Sd function coordinately to control the expression of genes required for wing development, which implies that Vg is a tissue-specific transcriptional intermediary factor of Sd.

A genetic and molecular analysis of an invectedDominant mutation in Drosophila melanogaster.

The invected gene of Drosophila melanogaster is a homeobox-containing gene that is closely related to engrailed. A dominant gain of function allele, invectedDominant, was derived from mutagenesis of a dominant allele of vestigial, In(2R)vgW. A careful analysis of the phenotype of invectedDominant shows that it is associated with a transformation of the anterior compartment of the wing to a posterior fate. This transformation is normally limited to the wing blade itself and does not involve the remaining tissues derived from the wing imaginal disc, including the wing hinge and dorsal thorax of the fly. The ectopic expression of invected protein associated with invectedDominant correlates spatially with the normal expression pattern of vestigial in the wing imaginal disc, suggesting that control elements of vestigial are driving ectopic invected expression. This was confirmed by sequence analysis that shows that the dominant vestigial activity was eliminated by a deletion that removes the 3' portion of the vestigial coding region. This leaves a gene fusion wherein the vestigial enhancer elements are still juxtaposed immediately 5' to the invected transcriptional start site, but with the vg sequences harboring an additional lesion. Unlike recessive invected alleles, the invectedDominant allele produces an observable phenotype, and as such should prove useful in determining the role of invected in patterning the wing imaginal disc. Genetic analysis has shown that mutations of polyhomeotic, a gene involved in regulating engrailed expression, cause a reproducible alteration in the invectedDominant phenotype. Finally, the invectedDominant allele should prove valuable for identifying and characterizing genes that are activated within the posterior compartment. A screen using various lacZ lines that are asymmetrically expressed in an anterior-posterior manner in the wing imaginal disc isolated one line that shows posterior-specific expression within the transformed anterior compartment.

Distinguishable functions for engrailed and invected in anterior-posterior patterning in the Drosophila wing.

Subdivision of the limb primordia into compartments initiates pattern formation in the developing limbs. Interaction between distinctly specific cells in adjacent compartments leads to localized expression of the secreted signalling molecules Wingless (Wg) or Decapentaplegic (Dpp), which in turn organize pattern and control growth of the limbs. The homeobox gene engrailed has been implicated in specification of posterior cell fate, whereas the LIM/homeobox gene, apterous, specifies dorsal fate. Removing apterous activity causes a complete transformation from dorsal to ventral fate and leads to the formation of an ectopic dorsal-ventral boundary organizer. By contrast, removing engrailed activity causes incomplete morphological transformation from posterior to anterior fate in the wing, and fails to produce an ectopic anterior-posterior organizer (reviewed in ref.2). Complete transformation can only be effected by simultaneously eliminating activity of engrailed and its homologue invected. Here we show that invected functions principally to specify posterior cell fate. Thus establishment of the anterior-posterior organizer and control of compartment identity are genetically distinguishable, and invected may perform a discrete subset of functions previously ascribed to engrailed.

Development of an assay for the estimation of N10-propargyl-5,8-dideazafolic acid polyglutamates in tumor cells.

A method is described herein for the isolation and quantitation of polyglutamates of the thymidylate synthase (TS) inhibitor N10-propargyl-5,8-dideazafolic acid (CB3717) in tumor cells exposed to the drug in vitro. Cells were incubated with 50 microM 3H-CB3717 for 12 h and then disrupted by sonication. CB3717 and its polyglutamates were extracted by boiling in 0.01 M Tris-HCl pH 10. The extract was concentrated by lyophilization and analyzed by reverse phase HPLC (10 x 0.46-cm Polygosil 5-micron C18 column) using linear gradient elution (5-16% acetonitrile in 0.1 M sodium acetate, pH 5, over 15 min, 2 ml/min). Recovery of radioactivity at each stage of the method was greater than 70%. CB3717 and its polyglutamates were identified by co-chromatography with synthetic standards and by inhibition of partially purified TS. Quantitation was by means of radiochemical analysis. The 3H-CB3717 used in these studies was prepared by catalytic tritiation of diethyl-(2-chloro-4-nitrobenzoyl)-L-glutamate followed by consecutive alkylation with propargyl bromide and 2-amino-6-bromomethyl-3,4-dihydro-4-oxoquinazoline hydrobromide. The free diacid was prepared as required by hydrolysis in sodium hydroxide and purified by HPLC. Tritiation in only one position was confirmed by 3H NMR. Following the exposure of L1210 leukemia cells to 50 microM 3H-CB3717 for 12 h the total cellular radioactivity level was approximately 7 microM, of which 27% was present as polyglutamated metabolites with four and five glutamate residues.