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p53- and ERK7-dependent ribosome surveillance response regulates Drosophila insulin-like peptide secretion.

Hasygar K, Hietakangas V - PLoS Genet. (2014)

Bottom Line: A downstream effector of this growth inhibitory response is an atypical MAP kinase ERK7 (ERK8/MAPK15), which is upregulated in the IPCs following impaired ribosome biogenesis as well as starvation.Moreover, we provide evidence that p53 and ERK7 contribute to the inhibition of dILP secretion upon starvation.Thus, we conclude that a cell autonomous ribosome surveillance response, which leads to upregulation of ERK7, inhibits dILP secretion to impede tissue growth under limiting dietary conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences & Institute of Biotechnology, University of Helsinki, Helsinki, Finland.

ABSTRACT
Insulin-like signalling is a conserved mechanism that coordinates animal growth and metabolism with nutrient status. In Drosophila, insulin-producing median neurosecretory cells (IPCs) regulate larval growth by secreting insulin-like peptides (dILPs) in a diet-dependent manner. Previous studies have shown that nutrition affects dILP secretion through humoral signals derived from the fat body. Here we uncover a novel mechanism that operates cell autonomously in the IPCs to regulate dILP secretion. We observed that impairment of ribosome biogenesis specifically in the IPCs strongly inhibits dILP secretion, which consequently leads to reduced body size and a delay in larval development. This response is dependent on p53, a known surveillance factor for ribosome biogenesis. A downstream effector of this growth inhibitory response is an atypical MAP kinase ERK7 (ERK8/MAPK15), which is upregulated in the IPCs following impaired ribosome biogenesis as well as starvation. We show that ERK7 is sufficient and essential to inhibit dILP secretion upon impaired ribosome biogenesis, and it acts epistatically to p53. Moreover, we provide evidence that p53 and ERK7 contribute to the inhibition of dILP secretion upon starvation. Thus, we conclude that a cell autonomous ribosome surveillance response, which leads to upregulation of ERK7, inhibits dILP secretion to impede tissue growth under limiting dietary conditions.

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p53 mediates dILP2 accumulation upon inhibited ribosome biogenesis.(A, B) Overexpression of p53 in the IPCs is sufficient to inhibit dILP2 secretion. Error bars represent standard deviation, (N≥10 brains). (C) Overexpression of p53 in the IPCs leads to reduced pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (D, E) Knockdown of p53 suppresses dILP2 accumulation following Rio2 depletion. Error bars represent standard deviation, (N≥10 brains). (F) Knockdown of p53 leads to partial rescue of pupal volume phenotype observed upon Rio2 depletion. Error bars represent standard deviation, (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
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pgen-1004764-g003: p53 mediates dILP2 accumulation upon inhibited ribosome biogenesis.(A, B) Overexpression of p53 in the IPCs is sufficient to inhibit dILP2 secretion. Error bars represent standard deviation, (N≥10 brains). (C) Overexpression of p53 in the IPCs leads to reduced pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (D, E) Knockdown of p53 suppresses dILP2 accumulation following Rio2 depletion. Error bars represent standard deviation, (N≥10 brains). (F) Knockdown of p53 leads to partial rescue of pupal volume phenotype observed upon Rio2 depletion. Error bars represent standard deviation, (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).

Mentions: How is the ribosome biogenesis pathway coupled to dILP secretion? We hypothesised that one of the ribosome biogenesis surveillance pathways might link secretion to the status of ribosome biogenesis in specialised secretory cells like the IPCs. As p53 is the best-established surveillance factor for the ribosome biogenesis pathway [14], [15], [37], we wanted to explore, whether it is involved in the regulation of dILP secretion. Indeed, overexpression of p53 in the IPCs revealed that p53 is sufficient to cause dILP2 accumulation (Figure 3A, B). To analyse the possible impact of transcriptional regulation, we measured dilp2 mRNA levels by quantitative RT-PCR. p53 overexpression caused modest downregulation of dilp2 mRNA levels (Figure S4), ruling out the possibility of transcriptional activation as a cause for p53-dependent dILP2 accumulation. To assess the contribution of p53-mediated dILP regulation on growth, we analyzed pupal volume, which is a sensitive means to measure changes in total body size [22]. In our hands, pupal volume data is consistent with the adult weight, but displays less random variation. In accordance with the immunofluorescence data suggesting inhibited dILP2 secretion, p53 overexpression in the IPCs strongly reduced the pupal volume (Figure 3C). In contrast, overexpression of p53 in the salivary glands caused no growth impairment (Figure S2). In sum, our data is consistent with the idea that p53 expression in the IPCs is sufficient to prevent dILP secretion and consequently inhibit tissue growth.


p53- and ERK7-dependent ribosome surveillance response regulates Drosophila insulin-like peptide secretion.

Hasygar K, Hietakangas V - PLoS Genet. (2014)

p53 mediates dILP2 accumulation upon inhibited ribosome biogenesis.(A, B) Overexpression of p53 in the IPCs is sufficient to inhibit dILP2 secretion. Error bars represent standard deviation, (N≥10 brains). (C) Overexpression of p53 in the IPCs leads to reduced pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (D, E) Knockdown of p53 suppresses dILP2 accumulation following Rio2 depletion. Error bars represent standard deviation, (N≥10 brains). (F) Knockdown of p53 leads to partial rescue of pupal volume phenotype observed upon Rio2 depletion. Error bars represent standard deviation, (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4230838&req=5

pgen-1004764-g003: p53 mediates dILP2 accumulation upon inhibited ribosome biogenesis.(A, B) Overexpression of p53 in the IPCs is sufficient to inhibit dILP2 secretion. Error bars represent standard deviation, (N≥10 brains). (C) Overexpression of p53 in the IPCs leads to reduced pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (D, E) Knockdown of p53 suppresses dILP2 accumulation following Rio2 depletion. Error bars represent standard deviation, (N≥10 brains). (F) Knockdown of p53 leads to partial rescue of pupal volume phenotype observed upon Rio2 depletion. Error bars represent standard deviation, (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
Mentions: How is the ribosome biogenesis pathway coupled to dILP secretion? We hypothesised that one of the ribosome biogenesis surveillance pathways might link secretion to the status of ribosome biogenesis in specialised secretory cells like the IPCs. As p53 is the best-established surveillance factor for the ribosome biogenesis pathway [14], [15], [37], we wanted to explore, whether it is involved in the regulation of dILP secretion. Indeed, overexpression of p53 in the IPCs revealed that p53 is sufficient to cause dILP2 accumulation (Figure 3A, B). To analyse the possible impact of transcriptional regulation, we measured dilp2 mRNA levels by quantitative RT-PCR. p53 overexpression caused modest downregulation of dilp2 mRNA levels (Figure S4), ruling out the possibility of transcriptional activation as a cause for p53-dependent dILP2 accumulation. To assess the contribution of p53-mediated dILP regulation on growth, we analyzed pupal volume, which is a sensitive means to measure changes in total body size [22]. In our hands, pupal volume data is consistent with the adult weight, but displays less random variation. In accordance with the immunofluorescence data suggesting inhibited dILP2 secretion, p53 overexpression in the IPCs strongly reduced the pupal volume (Figure 3C). In contrast, overexpression of p53 in the salivary glands caused no growth impairment (Figure S2). In sum, our data is consistent with the idea that p53 expression in the IPCs is sufficient to prevent dILP secretion and consequently inhibit tissue growth.

Bottom Line: A downstream effector of this growth inhibitory response is an atypical MAP kinase ERK7 (ERK8/MAPK15), which is upregulated in the IPCs following impaired ribosome biogenesis as well as starvation.Moreover, we provide evidence that p53 and ERK7 contribute to the inhibition of dILP secretion upon starvation.Thus, we conclude that a cell autonomous ribosome surveillance response, which leads to upregulation of ERK7, inhibits dILP secretion to impede tissue growth under limiting dietary conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences & Institute of Biotechnology, University of Helsinki, Helsinki, Finland.

ABSTRACT
Insulin-like signalling is a conserved mechanism that coordinates animal growth and metabolism with nutrient status. In Drosophila, insulin-producing median neurosecretory cells (IPCs) regulate larval growth by secreting insulin-like peptides (dILPs) in a diet-dependent manner. Previous studies have shown that nutrition affects dILP secretion through humoral signals derived from the fat body. Here we uncover a novel mechanism that operates cell autonomously in the IPCs to regulate dILP secretion. We observed that impairment of ribosome biogenesis specifically in the IPCs strongly inhibits dILP secretion, which consequently leads to reduced body size and a delay in larval development. This response is dependent on p53, a known surveillance factor for ribosome biogenesis. A downstream effector of this growth inhibitory response is an atypical MAP kinase ERK7 (ERK8/MAPK15), which is upregulated in the IPCs following impaired ribosome biogenesis as well as starvation. We show that ERK7 is sufficient and essential to inhibit dILP secretion upon impaired ribosome biogenesis, and it acts epistatically to p53. Moreover, we provide evidence that p53 and ERK7 contribute to the inhibition of dILP secretion upon starvation. Thus, we conclude that a cell autonomous ribosome surveillance response, which leads to upregulation of ERK7, inhibits dILP secretion to impede tissue growth under limiting dietary conditions.

Show MeSH
Related in: MedlinePlus