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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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ERK7 mediates inhibition of dILP secretion upon disturbed ribosome biogenesis.Overexpression of ERK7 in the IPCs is sufficient to inhibit dILP2 (A, B) and dILP5 (C, D) secretion. Notably, dILP5 experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2K. Error bars represent standard deviation, (N≥10 brains). (E) ERK7 overexpression in the IPCs results in smaller pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (F) Overexpression of ERK7 in the IPCs leads to delayed pupation. Notably, this experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2L. Error bars represent standard deviation, (N = 4, 30 larvae/group). (G, H) Accumulation of dILP2 in the cell bodies of IPCs upon Rio2 depletion is suppressed by simultaneous knockdown of ERK7. Error bars represent standard deviation (N≥10 brains). (I) Knockdown of ERK7 in the IPCs partially suppresses the small pupal size caused by Rio2 depletion. Error bars represent standard deviation (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 or dILP5 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
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pgen-1004764-g005: ERK7 mediates inhibition of dILP secretion upon disturbed ribosome biogenesis.Overexpression of ERK7 in the IPCs is sufficient to inhibit dILP2 (A, B) and dILP5 (C, D) secretion. Notably, dILP5 experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2K. Error bars represent standard deviation, (N≥10 brains). (E) ERK7 overexpression in the IPCs results in smaller pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (F) Overexpression of ERK7 in the IPCs leads to delayed pupation. Notably, this experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2L. Error bars represent standard deviation, (N = 4, 30 larvae/group). (G, H) Accumulation of dILP2 in the cell bodies of IPCs upon Rio2 depletion is suppressed by simultaneous knockdown of ERK7. Error bars represent standard deviation (N≥10 brains). (I) Knockdown of ERK7 in the IPCs partially suppresses the small pupal size caused by Rio2 depletion. Error bars represent standard deviation (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 or dILP5 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).

Mentions: To this end, we decided to explore the functional relationship between ribosome surveillance, ERK7 and dILP secretion in the IPCs. We analyzed transgenic flies that specifically overexpress ERK7 in the IPCs (Figure S7). Indeed, ERK7 overexpression led to prominent accumulation of dILP2 and dILP5 in the IPCs (Figure 5A–5D). Consistently, ERK7 overexpression in the IPCs, but not in salivary glands, led to reduced pupal volume (Figure 5E and Figure S2) as well as delayed pupation (Figure 5F). To rule out the possibility that the ERK7-dependent dILP accumulation was due to elevated transcription, we used quantitative RT-PCR to measure dilp2 and dilp5 mRNA levels, which remained unchanged upon ERK7 overexpression (Figure S8). Thus, we conclude that elevated ERK7 expression is sufficient to inhibit dILP secretion cell autonomously in the IPCs. We also performed genetic epistasis experiments to test if ERK7 is essential to inhibit dILP2 secretion upon disturbed ribosome biogenesis. Indeed, ERK7 RNAi efficiently suppressed the dILP2 accumulation caused by Rio2 knockdown (Figure 5G, H). Similar suppression was observed in the case of dILP2 accumulation following dMyc depletion (Figure S9). Consistent with the effects on dILP2 secretion, IPC-specific depletion of ERK7 partially suppressed the impaired growth upon knockdown of Rio2, while having no effect on body size in the wild type background (Figure 5I).


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

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

ERK7 mediates inhibition of dILP secretion upon disturbed ribosome biogenesis.Overexpression of ERK7 in the IPCs is sufficient to inhibit dILP2 (A, B) and dILP5 (C, D) secretion. Notably, dILP5 experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2K. Error bars represent standard deviation, (N≥10 brains). (E) ERK7 overexpression in the IPCs results in smaller pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (F) Overexpression of ERK7 in the IPCs leads to delayed pupation. Notably, this experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2L. Error bars represent standard deviation, (N = 4, 30 larvae/group). (G, H) Accumulation of dILP2 in the cell bodies of IPCs upon Rio2 depletion is suppressed by simultaneous knockdown of ERK7. Error bars represent standard deviation (N≥10 brains). (I) Knockdown of ERK7 in the IPCs partially suppresses the small pupal size caused by Rio2 depletion. Error bars represent standard deviation (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 or dILP5 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
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Related In: Results  -  Collection

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pgen-1004764-g005: ERK7 mediates inhibition of dILP secretion upon disturbed ribosome biogenesis.Overexpression of ERK7 in the IPCs is sufficient to inhibit dILP2 (A, B) and dILP5 (C, D) secretion. Notably, dILP5 experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2K. Error bars represent standard deviation, (N≥10 brains). (E) ERK7 overexpression in the IPCs results in smaller pupal volume. Error bars represent standard deviation, (N = 3, 10 pupae/group). (F) Overexpression of ERK7 in the IPCs leads to delayed pupation. Notably, this experiment was done together with Rio2 knockdown and the control dataset is the same as in Figure 2L. Error bars represent standard deviation, (N = 4, 30 larvae/group). (G, H) Accumulation of dILP2 in the cell bodies of IPCs upon Rio2 depletion is suppressed by simultaneous knockdown of ERK7. Error bars represent standard deviation (N≥10 brains). (I) Knockdown of ERK7 in the IPCs partially suppresses the small pupal size caused by Rio2 depletion. Error bars represent standard deviation (N = 3, 10 pupae/group). For all confocal images, IPCs are marked by GFP (green) and dILP2 or dILP5 is shown as red. **p<0.01, ***p<0.001 (Student's t-test).
Mentions: To this end, we decided to explore the functional relationship between ribosome surveillance, ERK7 and dILP secretion in the IPCs. We analyzed transgenic flies that specifically overexpress ERK7 in the IPCs (Figure S7). Indeed, ERK7 overexpression led to prominent accumulation of dILP2 and dILP5 in the IPCs (Figure 5A–5D). Consistently, ERK7 overexpression in the IPCs, but not in salivary glands, led to reduced pupal volume (Figure 5E and Figure S2) as well as delayed pupation (Figure 5F). To rule out the possibility that the ERK7-dependent dILP accumulation was due to elevated transcription, we used quantitative RT-PCR to measure dilp2 and dilp5 mRNA levels, which remained unchanged upon ERK7 overexpression (Figure S8). Thus, we conclude that elevated ERK7 expression is sufficient to inhibit dILP secretion cell autonomously in the IPCs. We also performed genetic epistasis experiments to test if ERK7 is essential to inhibit dILP2 secretion upon disturbed ribosome biogenesis. Indeed, ERK7 RNAi efficiently suppressed the dILP2 accumulation caused by Rio2 knockdown (Figure 5G, H). Similar suppression was observed in the case of dILP2 accumulation following dMyc depletion (Figure S9). Consistent with the effects on dILP2 secretion, IPC-specific depletion of ERK7 partially suppressed the impaired growth upon knockdown of Rio2, while having no effect on body size in the wild type background (Figure 5I).

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