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Autophagy and modular restructuring of metabolism control germline tumor differentiation and proliferation in C. elegans.

Gomes LC, Odedra D, Dikic I, Pohl C - Autophagy (2016)

Bottom Line: To understand how autophagy plays this dual role in cancer, in vivo models are required.Fasting of animals with fully developed tumors leads to a doubling of their life span, which depends on modular changes in transcription including switches in transcription factor networks and mitochondrial metabolism.Hence, our results suggest that metabolic restructuring, cell-type specific regulation of autophagy and neuronal differentiation constitute central pathways preventing growth of heterogeneous tumors.

View Article: PubMed Central - PubMed

Affiliation: a Buchmann Institute for Molecular Life Sciences, Goethe University , Frankfurt (Main) , Germany.

ABSTRACT
Autophagy can act either as a tumor suppressor or as a survival mechanism for established tumors. To understand how autophagy plays this dual role in cancer, in vivo models are required. By using a highly heterogeneous C. elegans germline tumor, we show that autophagy-related proteins are expressed in a specific subset of tumor cells, neurons. Inhibition of autophagy impairs neuronal differentiation and increases tumor cell number, resulting in a shorter life span of animals with tumors, while induction of autophagy extends their life span by impairing tumor proliferation. Fasting of animals with fully developed tumors leads to a doubling of their life span, which depends on modular changes in transcription including switches in transcription factor networks and mitochondrial metabolism. Hence, our results suggest that metabolic restructuring, cell-type specific regulation of autophagy and neuronal differentiation constitute central pathways preventing growth of heterogeneous tumors.

No MeSH data available.


Related in: MedlinePlus

Inhibition of autophagy impairs neuronal differentiation within germline tumors. (A) LGG-1-expressing cells in germline tumors are neurons that coexpress UNC-119. Left panels: Maximum projections of merged z-planes of gld-1 RNAi gonads at d 1, 3 and 5 of adulthood. Right panels: Confocal planes showing LGG-1 (top) and UNC-119 (bottom). Scale bar: 20 μm. (B) UNC-119::mCherry expression in the gonad of gld-1, gld-1+lgg-3 and gld-1+atg-7 RNAi-treated animals (d 1.5 of adulthood). Representative gonad arm reconstructed from maximum projections. Asterisks mark neuronal cells in germline tumors. Top: The region reconstructed is depicted in the schema (boxed area). Scale bar: 20 μm. (C) Area occupied by UNC-119 expressing cells per gonad arm normalized by gld-1 RNAi-treated animals. Qualitative scoring of the gonadal area occupied by UNC-119 expressing cells was performed blindly using maximum z-projections covering whole gonad arms (d 1.5 to 2.5 of adulthood. Data represent mean ± SEM of 3 independent experiments, n = 3 to 6 (6 to 12 gonad arms), per experiment.
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f0004: Inhibition of autophagy impairs neuronal differentiation within germline tumors. (A) LGG-1-expressing cells in germline tumors are neurons that coexpress UNC-119. Left panels: Maximum projections of merged z-planes of gld-1 RNAi gonads at d 1, 3 and 5 of adulthood. Right panels: Confocal planes showing LGG-1 (top) and UNC-119 (bottom). Scale bar: 20 μm. (B) UNC-119::mCherry expression in the gonad of gld-1, gld-1+lgg-3 and gld-1+atg-7 RNAi-treated animals (d 1.5 of adulthood). Representative gonad arm reconstructed from maximum projections. Asterisks mark neuronal cells in germline tumors. Top: The region reconstructed is depicted in the schema (boxed area). Scale bar: 20 μm. (C) Area occupied by UNC-119 expressing cells per gonad arm normalized by gld-1 RNAi-treated animals. Qualitative scoring of the gonadal area occupied by UNC-119 expressing cells was performed blindly using maximum z-projections covering whole gonad arms (d 1.5 to 2.5 of adulthood. Data represent mean ± SEM of 3 independent experiments, n = 3 to 6 (6 to 12 gonad arms), per experiment.

Mentions: gld-1 germline tumors do not only comprise germ cells but also ectopically differentiated somatic cells, such as muscle, neurons and intestinal cells (Fig. 1A and S1A).2 We observed that the morphology of cells expressing autophagy markers within the germline tumor resembles the morphology of neuronal cells (Figs. 1 and 2C). Therefore, we used a C. elegans strain expressing a pan-neuronal marker (UNC-119::mCherry) and GFP::LGG-1. Confocal microscopy of germline tumors induced by gld-1 RNAi, showed that LGG-1 is expressed in cells differentiating as neurons (Fig. 4A). Concomitantly, we examined differentiation of other somatic cell types in gld-1 germline tumors, by knocking down gld-1 in reporter strains expressing GFP or mCherry under the control of tissue-specific—neuronal (unc-119), muscle (myo-3) or pharyngeal (pha-4)—promoters. Although gld-1-deficient germ cells reprogram mainly as neurons, we also observed—to a lesser extent—differentiation of muscle and pharynx cells (Fig. S1A). Consistently, transcriptome analysis showed that neuronal-specific genes are consistently upregulated in gld-1-depleted animals (Fig. S1B) and, to a lesser extent, muscle- and pharynx-specific genes are also upregulated (Fig. S1B). Hence, the concurrence of neuronal differentiation and high-level expression of autophagy pathway genes suggests that both processes might depend on each other.Figure 4.


Autophagy and modular restructuring of metabolism control germline tumor differentiation and proliferation in C. elegans.

Gomes LC, Odedra D, Dikic I, Pohl C - Autophagy (2016)

Inhibition of autophagy impairs neuronal differentiation within germline tumors. (A) LGG-1-expressing cells in germline tumors are neurons that coexpress UNC-119. Left panels: Maximum projections of merged z-planes of gld-1 RNAi gonads at d 1, 3 and 5 of adulthood. Right panels: Confocal planes showing LGG-1 (top) and UNC-119 (bottom). Scale bar: 20 μm. (B) UNC-119::mCherry expression in the gonad of gld-1, gld-1+lgg-3 and gld-1+atg-7 RNAi-treated animals (d 1.5 of adulthood). Representative gonad arm reconstructed from maximum projections. Asterisks mark neuronal cells in germline tumors. Top: The region reconstructed is depicted in the schema (boxed area). Scale bar: 20 μm. (C) Area occupied by UNC-119 expressing cells per gonad arm normalized by gld-1 RNAi-treated animals. Qualitative scoring of the gonadal area occupied by UNC-119 expressing cells was performed blindly using maximum z-projections covering whole gonad arms (d 1.5 to 2.5 of adulthood. Data represent mean ± SEM of 3 independent experiments, n = 3 to 6 (6 to 12 gonad arms), per experiment.
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f0004: Inhibition of autophagy impairs neuronal differentiation within germline tumors. (A) LGG-1-expressing cells in germline tumors are neurons that coexpress UNC-119. Left panels: Maximum projections of merged z-planes of gld-1 RNAi gonads at d 1, 3 and 5 of adulthood. Right panels: Confocal planes showing LGG-1 (top) and UNC-119 (bottom). Scale bar: 20 μm. (B) UNC-119::mCherry expression in the gonad of gld-1, gld-1+lgg-3 and gld-1+atg-7 RNAi-treated animals (d 1.5 of adulthood). Representative gonad arm reconstructed from maximum projections. Asterisks mark neuronal cells in germline tumors. Top: The region reconstructed is depicted in the schema (boxed area). Scale bar: 20 μm. (C) Area occupied by UNC-119 expressing cells per gonad arm normalized by gld-1 RNAi-treated animals. Qualitative scoring of the gonadal area occupied by UNC-119 expressing cells was performed blindly using maximum z-projections covering whole gonad arms (d 1.5 to 2.5 of adulthood. Data represent mean ± SEM of 3 independent experiments, n = 3 to 6 (6 to 12 gonad arms), per experiment.
Mentions: gld-1 germline tumors do not only comprise germ cells but also ectopically differentiated somatic cells, such as muscle, neurons and intestinal cells (Fig. 1A and S1A).2 We observed that the morphology of cells expressing autophagy markers within the germline tumor resembles the morphology of neuronal cells (Figs. 1 and 2C). Therefore, we used a C. elegans strain expressing a pan-neuronal marker (UNC-119::mCherry) and GFP::LGG-1. Confocal microscopy of germline tumors induced by gld-1 RNAi, showed that LGG-1 is expressed in cells differentiating as neurons (Fig. 4A). Concomitantly, we examined differentiation of other somatic cell types in gld-1 germline tumors, by knocking down gld-1 in reporter strains expressing GFP or mCherry under the control of tissue-specific—neuronal (unc-119), muscle (myo-3) or pharyngeal (pha-4)—promoters. Although gld-1-deficient germ cells reprogram mainly as neurons, we also observed—to a lesser extent—differentiation of muscle and pharynx cells (Fig. S1A). Consistently, transcriptome analysis showed that neuronal-specific genes are consistently upregulated in gld-1-depleted animals (Fig. S1B) and, to a lesser extent, muscle- and pharynx-specific genes are also upregulated (Fig. S1B). Hence, the concurrence of neuronal differentiation and high-level expression of autophagy pathway genes suggests that both processes might depend on each other.Figure 4.

Bottom Line: To understand how autophagy plays this dual role in cancer, in vivo models are required.Fasting of animals with fully developed tumors leads to a doubling of their life span, which depends on modular changes in transcription including switches in transcription factor networks and mitochondrial metabolism.Hence, our results suggest that metabolic restructuring, cell-type specific regulation of autophagy and neuronal differentiation constitute central pathways preventing growth of heterogeneous tumors.

View Article: PubMed Central - PubMed

Affiliation: a Buchmann Institute for Molecular Life Sciences, Goethe University , Frankfurt (Main) , Germany.

ABSTRACT
Autophagy can act either as a tumor suppressor or as a survival mechanism for established tumors. To understand how autophagy plays this dual role in cancer, in vivo models are required. By using a highly heterogeneous C. elegans germline tumor, we show that autophagy-related proteins are expressed in a specific subset of tumor cells, neurons. Inhibition of autophagy impairs neuronal differentiation and increases tumor cell number, resulting in a shorter life span of animals with tumors, while induction of autophagy extends their life span by impairing tumor proliferation. Fasting of animals with fully developed tumors leads to a doubling of their life span, which depends on modular changes in transcription including switches in transcription factor networks and mitochondrial metabolism. Hence, our results suggest that metabolic restructuring, cell-type specific regulation of autophagy and neuronal differentiation constitute central pathways preventing growth of heterogeneous tumors.

No MeSH data available.


Related in: MedlinePlus