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Functional identification of Api5 as a suppressor of E2F-dependent apoptosis in vivo.

Morris EJ, Michaud WA, Ji JY, Moon NS, Rocco JW, Dyson NJ - PLoS Genet. (2006)

Bottom Line: Genetic interactions show that dE2F1-dependent apoptosis in vivo involves dArk/Apaf1 apoptosome-dependent activation of both initiator and effector caspases and is sensitive to levels of Drosophila inhibitor of apoptosis-1 (dIAP1).The strong genetic interaction between E2F and Api5/Aac11 suggests that elevated levels of Api5 may be selected during tumorigenesis to allow cells with deregulated E2F activity to survive under suboptimal conditions.Therefore, inhibition of Api5 function might offer a possible mechanism for antitumor exploitation.

View Article: PubMed Central - PubMed

Affiliation: Massachusetts General Hospital Cancer Center, Laboratory of Molecular Oncology, Charlestown, Massachusetts, United States of America.

ABSTRACT
Retinoblastoma protein and E2-promoter binding factor (E2F) family members are important regulators of G1-S phase progression. Deregulated E2F also sensitizes cells to apoptosis, but this aspect of E2F function is poorly understood. Studies of E2F-induced apoptosis have mostly been carried out in tissue culture cells, and the analysis of the factors that are important for this process has been restricted to the testing of a few candidate genes. Using Drosophila as a model system, we have generated tools that allow genetic modifiers of E2F-dependent apoptosis to be identified in vivo and developed assays that allow effects on E2F-induced apoptosis to be studied in cultured cells. Genetic interactions show that dE2F1-dependent apoptosis in vivo involves dArk/Apaf1 apoptosome-dependent activation of both initiator and effector caspases and is sensitive to levels of Drosophila inhibitor of apoptosis-1 (dIAP1). Using these approaches, we report the surprising finding that apoptosis inhibitor-5/antiapoptosis clone-11 (Api5/Aac11) is a critical determinant of dE2F1-induced apoptosis in vivo and in vitro. This functional interaction occurs in multiple tissues, is specific to E2F-induced apoptosis, and is conserved from flies to humans. Interestingly, Api5/Aac11 acts downstream of E2F and suppresses E2F-dependent apoptosis without generally blocking E2F-dependent transcription. Api5/Aac11 expression is often upregulated in tumor cells, particularly in metastatic cells. We find that depletion of Api5 is tumor cell lethal. The strong genetic interaction between E2F and Api5/Aac11 suggests that elevated levels of Api5 may be selected during tumorigenesis to allow cells with deregulated E2F activity to survive under suboptimal conditions. Therefore, inhibition of Api5 function might offer a possible mechanism for antitumor exploitation.

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Aac11 Loss-of-Function Specifically Enhances Multiple dE2f1-Dependent Phenotypes In VivoThrough genetic screening, the P-element insertion l(2)k06710 was identified as a strong enhancer of the Act88F-Gal4;UAS-dE2f1 apoptotic wing phenotype (A). The arrow in (A) indicates enhanced ventral wing curvature and blistering in the l(2)k06710-enhanced dE2f1-dependent wing phenotype. In secondary screening, l(2)k06710 was found to enhance multiple dE2f1-dependent phenotypes in different tissues including a nos-Gal4;UAS-dE2f1 notum bristle phenotype (B–D) and a GMR-Gal4,UAS-dE2f1,UAS-dDp rough eye phenotype (E–H). The l(2)k06710 insertion enhanced bristle degeneration (compare arrows in [B] and [C]) and bristle stubble (arrowheads in [C]) induced by dE2f1 without inducing bristle phenotypes under heterozygous conditions alone (D). Expression of a UAS-Aac11 RNAi allele also enhanced the dE2f1-induced rough eye resulting in a blackened phenotype (I–K). Expression of the UAS-Aac11 RNAi allele under engrailed results in dominant posterior wing blistering which is enhanced by the l(2)k06710 P-insertion (L and M).
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pgen-0020196-g004: Aac11 Loss-of-Function Specifically Enhances Multiple dE2f1-Dependent Phenotypes In VivoThrough genetic screening, the P-element insertion l(2)k06710 was identified as a strong enhancer of the Act88F-Gal4;UAS-dE2f1 apoptotic wing phenotype (A). The arrow in (A) indicates enhanced ventral wing curvature and blistering in the l(2)k06710-enhanced dE2f1-dependent wing phenotype. In secondary screening, l(2)k06710 was found to enhance multiple dE2f1-dependent phenotypes in different tissues including a nos-Gal4;UAS-dE2f1 notum bristle phenotype (B–D) and a GMR-Gal4,UAS-dE2f1,UAS-dDp rough eye phenotype (E–H). The l(2)k06710 insertion enhanced bristle degeneration (compare arrows in [B] and [C]) and bristle stubble (arrowheads in [C]) induced by dE2f1 without inducing bristle phenotypes under heterozygous conditions alone (D). Expression of a UAS-Aac11 RNAi allele also enhanced the dE2f1-induced rough eye resulting in a blackened phenotype (I–K). Expression of the UAS-Aac11 RNAi allele under engrailed results in dominant posterior wing blistering which is enhanced by the l(2)k06710 P-insertion (L and M).

Mentions: The P-element insertion l(2)k06710 was a strong and specific enhancer of dE2F1-dependent phenotypes in the wing, eye, and bristles (Figure 4). The recessive-lethal l(2)k06710 insertion failed to complement the genomic deficiency Df(2L)H20, and a similar set of interactions were observed using this deletion (unpublished data). Df(2L)H20 spans 36A8–9 to 36F1 of Chromosome 2L and uncovers the l(2)k06710 insertion site within the first exon of the Drosophila Aac11 gene (Figure 5).


Functional identification of Api5 as a suppressor of E2F-dependent apoptosis in vivo.

Morris EJ, Michaud WA, Ji JY, Moon NS, Rocco JW, Dyson NJ - PLoS Genet. (2006)

Aac11 Loss-of-Function Specifically Enhances Multiple dE2f1-Dependent Phenotypes In VivoThrough genetic screening, the P-element insertion l(2)k06710 was identified as a strong enhancer of the Act88F-Gal4;UAS-dE2f1 apoptotic wing phenotype (A). The arrow in (A) indicates enhanced ventral wing curvature and blistering in the l(2)k06710-enhanced dE2f1-dependent wing phenotype. In secondary screening, l(2)k06710 was found to enhance multiple dE2f1-dependent phenotypes in different tissues including a nos-Gal4;UAS-dE2f1 notum bristle phenotype (B–D) and a GMR-Gal4,UAS-dE2f1,UAS-dDp rough eye phenotype (E–H). The l(2)k06710 insertion enhanced bristle degeneration (compare arrows in [B] and [C]) and bristle stubble (arrowheads in [C]) induced by dE2f1 without inducing bristle phenotypes under heterozygous conditions alone (D). Expression of a UAS-Aac11 RNAi allele also enhanced the dE2f1-induced rough eye resulting in a blackened phenotype (I–K). Expression of the UAS-Aac11 RNAi allele under engrailed results in dominant posterior wing blistering which is enhanced by the l(2)k06710 P-insertion (L and M).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1636698&req=5

pgen-0020196-g004: Aac11 Loss-of-Function Specifically Enhances Multiple dE2f1-Dependent Phenotypes In VivoThrough genetic screening, the P-element insertion l(2)k06710 was identified as a strong enhancer of the Act88F-Gal4;UAS-dE2f1 apoptotic wing phenotype (A). The arrow in (A) indicates enhanced ventral wing curvature and blistering in the l(2)k06710-enhanced dE2f1-dependent wing phenotype. In secondary screening, l(2)k06710 was found to enhance multiple dE2f1-dependent phenotypes in different tissues including a nos-Gal4;UAS-dE2f1 notum bristle phenotype (B–D) and a GMR-Gal4,UAS-dE2f1,UAS-dDp rough eye phenotype (E–H). The l(2)k06710 insertion enhanced bristle degeneration (compare arrows in [B] and [C]) and bristle stubble (arrowheads in [C]) induced by dE2f1 without inducing bristle phenotypes under heterozygous conditions alone (D). Expression of a UAS-Aac11 RNAi allele also enhanced the dE2f1-induced rough eye resulting in a blackened phenotype (I–K). Expression of the UAS-Aac11 RNAi allele under engrailed results in dominant posterior wing blistering which is enhanced by the l(2)k06710 P-insertion (L and M).
Mentions: The P-element insertion l(2)k06710 was a strong and specific enhancer of dE2F1-dependent phenotypes in the wing, eye, and bristles (Figure 4). The recessive-lethal l(2)k06710 insertion failed to complement the genomic deficiency Df(2L)H20, and a similar set of interactions were observed using this deletion (unpublished data). Df(2L)H20 spans 36A8–9 to 36F1 of Chromosome 2L and uncovers the l(2)k06710 insertion site within the first exon of the Drosophila Aac11 gene (Figure 5).

Bottom Line: Genetic interactions show that dE2F1-dependent apoptosis in vivo involves dArk/Apaf1 apoptosome-dependent activation of both initiator and effector caspases and is sensitive to levels of Drosophila inhibitor of apoptosis-1 (dIAP1).The strong genetic interaction between E2F and Api5/Aac11 suggests that elevated levels of Api5 may be selected during tumorigenesis to allow cells with deregulated E2F activity to survive under suboptimal conditions.Therefore, inhibition of Api5 function might offer a possible mechanism for antitumor exploitation.

View Article: PubMed Central - PubMed

Affiliation: Massachusetts General Hospital Cancer Center, Laboratory of Molecular Oncology, Charlestown, Massachusetts, United States of America.

ABSTRACT
Retinoblastoma protein and E2-promoter binding factor (E2F) family members are important regulators of G1-S phase progression. Deregulated E2F also sensitizes cells to apoptosis, but this aspect of E2F function is poorly understood. Studies of E2F-induced apoptosis have mostly been carried out in tissue culture cells, and the analysis of the factors that are important for this process has been restricted to the testing of a few candidate genes. Using Drosophila as a model system, we have generated tools that allow genetic modifiers of E2F-dependent apoptosis to be identified in vivo and developed assays that allow effects on E2F-induced apoptosis to be studied in cultured cells. Genetic interactions show that dE2F1-dependent apoptosis in vivo involves dArk/Apaf1 apoptosome-dependent activation of both initiator and effector caspases and is sensitive to levels of Drosophila inhibitor of apoptosis-1 (dIAP1). Using these approaches, we report the surprising finding that apoptosis inhibitor-5/antiapoptosis clone-11 (Api5/Aac11) is a critical determinant of dE2F1-induced apoptosis in vivo and in vitro. This functional interaction occurs in multiple tissues, is specific to E2F-induced apoptosis, and is conserved from flies to humans. Interestingly, Api5/Aac11 acts downstream of E2F and suppresses E2F-dependent apoptosis without generally blocking E2F-dependent transcription. Api5/Aac11 expression is often upregulated in tumor cells, particularly in metastatic cells. We find that depletion of Api5 is tumor cell lethal. The strong genetic interaction between E2F and Api5/Aac11 suggests that elevated levels of Api5 may be selected during tumorigenesis to allow cells with deregulated E2F activity to survive under suboptimal conditions. Therefore, inhibition of Api5 function might offer a possible mechanism for antitumor exploitation.

Show MeSH
Related in: MedlinePlus