CDK7 Regulates the Mitochondrial Localization of a Tail-Anchored Proapoptotic Protein, Hid

SummaryThe mitochondrial outer membrane is a major site of apoptosis regulation across phyla. Human and C. elegans Bcl-2 family proteins and Drosophila Hid require the C-terminal tail-anchored (TA) sequence in order to insert into the mitochondrial membrane, but it remains unclear whether cytosolic proteins actively regulate the mitochondrial localization of these proteins. Here, we report that the cdk7 complex regulates the mitochondrial localization of Hid and its ability to induce apoptosis. We identified cdk7 through an in vivo RNAi screen of genes required for cell death. Although CDK7 is best known for its role in transcription and cell-cycle progression, a hypomorphic cdk7 mutant suppressed apoptosis without impairing these other known functions. In this cdk7 mutant background, Hid failed to localize to the mitochondria and failed to bind to recombinant inhibitors of apoptosis (IAPs). These findings indicate that apoptosis is promoted by a newly identified function of CDK7, which couples the mitochondrial localization and IAP binding of Hid

highroad Is a Carboxypetidase Induced by Retinoids to Clear Mutant Rhodopsin-1 in Drosophila Retinitis Pigmentosa Models

Rhodopsins require retinoid chromophores for their function. In vertebrates, retinoids also serve as signaling molecules, but whether these molecules similarly regulate gene expression in Drosophila remains unclear. Here, we report the identification of a retinoid-inducible gene in Drosophila, highroad, which is required for photoreceptors to clear folding-defective mutant Rhodopsin-1 proteins. Specifically, knockdown or genetic deletion of highroad blocks the degradation of folding-defective Rhodopsin-1 mutant, ninaE G69D . Moreover, loss of highroad accelerates the age-related retinal degeneration phenotype of ninaE G69D mutants. Elevated highroad transcript levels are detected in ninaE G69D flies, and interestingly, deprivation of retinoids in the fly diet blocks this effect. Consistently, mutations in the retinoid transporter, santa maria, impairs the induction of highroad in ninaE G69D flies. In cultured S2 cells, highroad expression is induced by retinoic acid treatment. These results indicate that cellular quality-control mechanisms against misfolded Rhodopsin-1 involve regulation of gene expression by retinoids. Folding-defective mutant rhodopsins undergo degradation in photoreceptors, but the underlying mechanism was unclear. Huang et al. identify highroad as a factor required for mutant Drosophila Rhodopsin-1 degradation. Loss of highroad accelerates retinal degeneration caused by mutant Rhodopsin-1, and highroad expression is dependent on retinoids.publishersversionpublishe

Ero1L, a thiol oxidase, is required for Notch signaling through cysteine bridge formation of the Lin12-Notch repeats in Drosophila melanogaster

Notch-mediated cell–cell communication regulates numerous developmental processes and cell fate decisions. Through a mosaic genetic screen in Drosophila melanogaster, we identified a role in Notch signaling for a conserved thiol oxidase, endoplasmic reticulum (ER) oxidoreductin 1–like (Ero1L). Although Ero1L is reported to play a widespread role in protein folding in yeast, in flies Ero1L mutant clones show specific defects in lateral inhibition and inductive signaling, two characteristic processes regulated by Notch signaling. Ero1L mutant cells accumulate high levels of Notch protein in the ER and induce the unfolded protein response, suggesting that Notch is misfolded and fails to be exported from the ER. Biochemical assays demonstrate that Ero1L is required for formation of disulfide bonds of three Lin12-Notch repeats (LNRs) present in the extracellular domain of Notch. These LNRs are unique to the Notch family of proteins. Therefore, we have uncovered an unexpected requirement for Ero1L in the maturation of the Notch receptor

Drosophila IAP antagonists form multimeric complexes to promote cell death

Self- and hetero-association of the pro-apoptotic proteins Reaper, Hid, and Grim is required for efficient induction of the cell death program

The role of apoptosis-induced proliferation for regeneration and cancer

Genes dedicated to killing cells must have evolved because of their positive effects on organismal survival. Positive functions of apoptotic genes have been well established in a large number of biological contexts, including their role in eliminating damaged and potentially cancerous cells. More recently, evidence has suggested that proapoptotic proteins-mostly caspases-can induce proliferation of neighboring surviving cells to replace dying cells. This process, that we will refer to as apoptosis-induced proliferation, may be critical for stem cell activity and tissue regeneration. Depending on the caspases involved, at least two distinct types of apoptosis-induced proliferation can be distinguished. One of these types have been studied using a model in which cells have initiated cell death, but are prevented from executing it because of effector caspase inhibition, thereby generating undead cells that emit persistent mitogen signaling and overgrowth. Such conditions are likely to contribute to certain forms of cancer. In this review, we summarize the current knowledge of apoptosis-induced proliferation and discuss its relevance for tissue regeneration and cancer

<i>xbp1_p>dsRed</i> is expressed in the salivary gland of <i>ire1 −/−</i> larva.

<p>(A) Shown are 48 – 72 hour larvae of the <i>ire1^f02170 −/−</i> (left three) and <i>ire1 −/+</i> (right two) genotypes. <i>xbp1_p>dsRed</i> was recombined to the <i>ire1^f02170</i> chromosome to facilitate genotyping. The <i>ire1+</i> chromosome is marked with GFP. No <i>ire1 −/−</i> larvae were found to grow beyond this 1^st instar larval stage. (B, C) A higher magnification view of an <i>ire1 −/−</i> larva. <i>xbp1_p>dsRed</i> expression in the salivary gland is visible (arrows) in the <i>ire1 −/−</i> zygotic (B), as well as maternal, zygotic mutants (C).</p

XBP1 regulatory sequence drives dsRed expression in developing secretory tissues.

<p>(A) Comparison of the <i>xbp1</i> locus sequence between <i>D. melanogaster, D. simulans, D. yakuba and D. erecta.</i> Sequence conservation is not only found in the coding sequence of genes (purple) and UTRs (light blue), but also in the intergenic region (red) that may encode enhancers and promoters. The bracket (<i>xbp1p</i>) indicates the intergenic sequence that was placed upstream of the dsRed reporter. (B) <i>xbp1</i> in situ hybridization in embryos. (C-E) <i>xbp1_p>dsRed</i> reporter expression in the embryo (C), the larval salivary gland (D) and the larval intestine (E). Images in (D, E) are composites of several frames taken with the 10x confocal microscope lens. There was no detectable <i>xbp1_p>dsRed</i> expression in the larval brain and imaginal discs (D). Abbreviations: Salivary Gland (SG), Mid Gut (MG).</p