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The Drosophila RASSF homolog antagonizes the hippo pathway.

Polesello C, Huelsmann S, Brown NH, Tapon N - Curr. Biol. (2006)

Bottom Line: Wts phosphorylates Yki and thus inhibits its activity and reduces expression of Yki target genes such as the caspase inhibitor DIAP1 and the micro RNA bantam.In this study, we show that the Drosophila RASSF ortholog (dRASSF) restricts Hpo activity by competing with Sav for binding to Hpo.In addition, we observe that dRASSF also possesses a tumor-suppressor function.

View Article: PubMed Central - PubMed

Affiliation: Apoptosis and Proliferation Control Laboratory, Cancer Research UK, London Institute, 44 Lincoln's Inn Fields, London, United Kingdom.

ABSTRACT
Correct organ size is determined by the balance between cell death and proliferation. Perturbation of this delicate balance leads to cancer formation . Hippo (Hpo), the Drosophila ortholog of MST1 and MST2 (Mammalian Sterile 20-like 1 and 2) is a key regulator of a signaling pathway that controls both cell death and proliferation . This pathway is so far composed of two Band 4.1 proteins, Expanded (Ex) and Merlin (Mer), two serine/threonine kinases, Hpo and Warts (Wts), the scaffold proteins Salvador (Sav) and Mats, and the transcriptional coactivator Yorkie (Yki). It has been proposed that Ex and Mer act upstream of Hpo, which in turn phosphorylates and activates Wts. Wts phosphorylates Yki and thus inhibits its activity and reduces expression of Yki target genes such as the caspase inhibitor DIAP1 and the micro RNA bantam. However, the mechanisms leading to Hpo activation are still poorly understood. In mammalian cells, members of the Ras association family (RASSF) of tumor suppressors have been shown to bind to MST1 and modulate its activity . In this study, we show that the Drosophila RASSF ortholog (dRASSF) restricts Hpo activity by competing with Sav for binding to Hpo. In addition, we observe that dRASSF also possesses a tumor-suppressor function.

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Tumour-Suppressor Function of dRASSF(A–C, E, and F) Scanning Electron Micrographs of Drosophila heads from control animals (A), animals bearing hpo42–47 clones (B), hpo42–48 clones (C), hpo42–47 clones in a dRASSF loss-of-function background (E), or hpo42–48 clones in a dRASSF loss-of-function background (F). The overgrowth phenotype elicited by the loss of hpo is enhanced by the removal of dRASSF. See Supplemental Experimental Procedures for genotypes.(D) Schematic representation of Hpo protein showing the different mutations used. The hpo42–47 allele causes a deletion of six amino acids in the kinase domain, and this deletion probably inhibits Hpo-ATP binding. The hpo42–48 allele is a deletion of 20 bp and gives rise to a premature stop codon. hpoKC203 changes G to A at the 5′ splicing site and the translation run into a stop codon in the intron.(G–H″) dRASSF rescues Ras1 loss of function. (G–G″) Ras1c40b clones (marked by a lack of GFP) are small. (H–H″) Rasc40b dRASSFX36 clones (marked by a lack of GFP) are larger than Rasc40b clones. dRASSF staining is in red (G′ and H′).
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fig4: Tumour-Suppressor Function of dRASSF(A–C, E, and F) Scanning Electron Micrographs of Drosophila heads from control animals (A), animals bearing hpo42–47 clones (B), hpo42–48 clones (C), hpo42–47 clones in a dRASSF loss-of-function background (E), or hpo42–48 clones in a dRASSF loss-of-function background (F). The overgrowth phenotype elicited by the loss of hpo is enhanced by the removal of dRASSF. See Supplemental Experimental Procedures for genotypes.(D) Schematic representation of Hpo protein showing the different mutations used. The hpo42–47 allele causes a deletion of six amino acids in the kinase domain, and this deletion probably inhibits Hpo-ATP binding. The hpo42–48 allele is a deletion of 20 bp and gives rise to a premature stop codon. hpoKC203 changes G to A at the 5′ splicing site and the translation run into a stop codon in the intron.(G–H″) dRASSF rescues Ras1 loss of function. (G–G″) Ras1c40b clones (marked by a lack of GFP) are small. (H–H″) Rasc40b dRASSFX36 clones (marked by a lack of GFP) are larger than Rasc40b clones. dRASSF staining is in red (G′ and H′).

Mentions: Though our results are consistent with biochemical data on mammalian RASSF family members [7, 16], they are at odds with the fact that RASSF genes are commonly silenced in tumor cells. Avruch and colleagues have proposed that one RASSF protein, Nore1, possesses a tumor-suppressor function that is independent of MST1 and MST2 [22]. We found two lines of evidence to support this notion. First, we made clones that are mutant for two hpo hypomorphic alleles, hpo42–48 ([19] compare Figures 4C and 4F), hpoKC203 ([23] not shown), that remove the SARAH domain in a dRASSF mutant background in the head by using the eyeless FLP system [24]. Interestingly, the overgrowth phenotype elicited by these hpo alleles was strongly enhanced by loss of dRASSF. By contrast, a hpo allele (hpo42–47[19]) bearing an inactivating deletion in the kinase domain but an intact SARAH domain was barely if at all enhanced by dRASSF loss of function (Figures 4B and 4E). This suggests that dRASSF may possess a tumor-suppressor function, which may be uncovered when the Hpo function is compromised.


The Drosophila RASSF homolog antagonizes the hippo pathway.

Polesello C, Huelsmann S, Brown NH, Tapon N - Curr. Biol. (2006)

Tumour-Suppressor Function of dRASSF(A–C, E, and F) Scanning Electron Micrographs of Drosophila heads from control animals (A), animals bearing hpo42–47 clones (B), hpo42–48 clones (C), hpo42–47 clones in a dRASSF loss-of-function background (E), or hpo42–48 clones in a dRASSF loss-of-function background (F). The overgrowth phenotype elicited by the loss of hpo is enhanced by the removal of dRASSF. See Supplemental Experimental Procedures for genotypes.(D) Schematic representation of Hpo protein showing the different mutations used. The hpo42–47 allele causes a deletion of six amino acids in the kinase domain, and this deletion probably inhibits Hpo-ATP binding. The hpo42–48 allele is a deletion of 20 bp and gives rise to a premature stop codon. hpoKC203 changes G to A at the 5′ splicing site and the translation run into a stop codon in the intron.(G–H″) dRASSF rescues Ras1 loss of function. (G–G″) Ras1c40b clones (marked by a lack of GFP) are small. (H–H″) Rasc40b dRASSFX36 clones (marked by a lack of GFP) are larger than Rasc40b clones. dRASSF staining is in red (G′ and H′).
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Related In: Results  -  Collection

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fig4: Tumour-Suppressor Function of dRASSF(A–C, E, and F) Scanning Electron Micrographs of Drosophila heads from control animals (A), animals bearing hpo42–47 clones (B), hpo42–48 clones (C), hpo42–47 clones in a dRASSF loss-of-function background (E), or hpo42–48 clones in a dRASSF loss-of-function background (F). The overgrowth phenotype elicited by the loss of hpo is enhanced by the removal of dRASSF. See Supplemental Experimental Procedures for genotypes.(D) Schematic representation of Hpo protein showing the different mutations used. The hpo42–47 allele causes a deletion of six amino acids in the kinase domain, and this deletion probably inhibits Hpo-ATP binding. The hpo42–48 allele is a deletion of 20 bp and gives rise to a premature stop codon. hpoKC203 changes G to A at the 5′ splicing site and the translation run into a stop codon in the intron.(G–H″) dRASSF rescues Ras1 loss of function. (G–G″) Ras1c40b clones (marked by a lack of GFP) are small. (H–H″) Rasc40b dRASSFX36 clones (marked by a lack of GFP) are larger than Rasc40b clones. dRASSF staining is in red (G′ and H′).
Mentions: Though our results are consistent with biochemical data on mammalian RASSF family members [7, 16], they are at odds with the fact that RASSF genes are commonly silenced in tumor cells. Avruch and colleagues have proposed that one RASSF protein, Nore1, possesses a tumor-suppressor function that is independent of MST1 and MST2 [22]. We found two lines of evidence to support this notion. First, we made clones that are mutant for two hpo hypomorphic alleles, hpo42–48 ([19] compare Figures 4C and 4F), hpoKC203 ([23] not shown), that remove the SARAH domain in a dRASSF mutant background in the head by using the eyeless FLP system [24]. Interestingly, the overgrowth phenotype elicited by these hpo alleles was strongly enhanced by loss of dRASSF. By contrast, a hpo allele (hpo42–47[19]) bearing an inactivating deletion in the kinase domain but an intact SARAH domain was barely if at all enhanced by dRASSF loss of function (Figures 4B and 4E). This suggests that dRASSF may possess a tumor-suppressor function, which may be uncovered when the Hpo function is compromised.

Bottom Line: Wts phosphorylates Yki and thus inhibits its activity and reduces expression of Yki target genes such as the caspase inhibitor DIAP1 and the micro RNA bantam.In this study, we show that the Drosophila RASSF ortholog (dRASSF) restricts Hpo activity by competing with Sav for binding to Hpo.In addition, we observe that dRASSF also possesses a tumor-suppressor function.

View Article: PubMed Central - PubMed

Affiliation: Apoptosis and Proliferation Control Laboratory, Cancer Research UK, London Institute, 44 Lincoln's Inn Fields, London, United Kingdom.

ABSTRACT
Correct organ size is determined by the balance between cell death and proliferation. Perturbation of this delicate balance leads to cancer formation . Hippo (Hpo), the Drosophila ortholog of MST1 and MST2 (Mammalian Sterile 20-like 1 and 2) is a key regulator of a signaling pathway that controls both cell death and proliferation . This pathway is so far composed of two Band 4.1 proteins, Expanded (Ex) and Merlin (Mer), two serine/threonine kinases, Hpo and Warts (Wts), the scaffold proteins Salvador (Sav) and Mats, and the transcriptional coactivator Yorkie (Yki). It has been proposed that Ex and Mer act upstream of Hpo, which in turn phosphorylates and activates Wts. Wts phosphorylates Yki and thus inhibits its activity and reduces expression of Yki target genes such as the caspase inhibitor DIAP1 and the micro RNA bantam. However, the mechanisms leading to Hpo activation are still poorly understood. In mammalian cells, members of the Ras association family (RASSF) of tumor suppressors have been shown to bind to MST1 and modulate its activity . In this study, we show that the Drosophila RASSF ortholog (dRASSF) restricts Hpo activity by competing with Sav for binding to Hpo. In addition, we observe that dRASSF also possesses a tumor-suppressor function.

Show MeSH
Related in: MedlinePlus