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Tumor suppressor Nf2/merlin drives Schwann cell changes following electromagnetic field exposure through Hippo-dependent mechanisms

View Article: PubMed Central - PubMed

ABSTRACT

Previous evidence showed mutations of the neurofibromin type 2 gene (Nf2), encoding the tumor suppressor protein merlin, in sporadic and vestibular schwannomas affecting Schwann cells (SCs). Accordingly, efforts have been addressed to identify possible factors, even environmental, that may regulate neurofibromas growth. In this context, we investigated the exposure of SC to an electromagnetic field (EMF), which is an environmental issue modulating biological processes. Here, we show that SC exposed to 50 Hz EMFs changes their morphology, proliferation, migration and myelinating capability. In these cells, merlin is downregulated, leading to activation of two intracellular signaling pathways, ERK/AKT and Hippo. Interestingly, SC changes their phenotype toward a proliferative/migrating state, which in principle may be pathologically relevant for schwannoma development.

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ERK and AKT signaling pathways are activated in SCs following 10 min EMF exposure. (a) Representative immunoblots showing the variations in phosphorylated ERK 2 (pERK 2), total ERK 2 (tERK 2), both 42 KDa, phosphorylated AKT (pAKT), total AKT (tAKT), both 60 KDa, in SCs at 2 and 6 h following EMF exposure. The β-actin (43 KDa) was used as a housekeeping protein. (b) Quantitative data at 2 h showed that pERK levels significantly increased (***P<0.001), while tERK levels decreased (*P<0.05); the pERK/tERK ratio showed that ERK signaling was activated 2 h following EMF exposure (***P<0.001, white columns). Indeed, pERK levels significantly decreased at 6 h (***P<0.001), while tERK significantly increased at 6 h (***P<0.001); pERK/tERK ratio indicated that this signaling pathway was deactivated within 6 h following EMF exposure (***P<0.001). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). (c) Quantitative data at 2 h showing that pAKT levels significantly increased (***P<0.001), while tAKT levels were unchanged; the pAKT/tAKT ratio showed an activation trend, even not significant. At 6 h, pAKT levels did not change but tAKT levels were significantly rised (***P<0.001); pAKT/tAKT ratio revealed a significant deactivation within 6 h after EMF exposure (***P<0.001, white columns). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). One-way ANOVA using Tukey's post-test was used for all statistical analysis.
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fig4: ERK and AKT signaling pathways are activated in SCs following 10 min EMF exposure. (a) Representative immunoblots showing the variations in phosphorylated ERK 2 (pERK 2), total ERK 2 (tERK 2), both 42 KDa, phosphorylated AKT (pAKT), total AKT (tAKT), both 60 KDa, in SCs at 2 and 6 h following EMF exposure. The β-actin (43 KDa) was used as a housekeeping protein. (b) Quantitative data at 2 h showed that pERK levels significantly increased (***P<0.001), while tERK levels decreased (*P<0.05); the pERK/tERK ratio showed that ERK signaling was activated 2 h following EMF exposure (***P<0.001, white columns). Indeed, pERK levels significantly decreased at 6 h (***P<0.001), while tERK significantly increased at 6 h (***P<0.001); pERK/tERK ratio indicated that this signaling pathway was deactivated within 6 h following EMF exposure (***P<0.001). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). (c) Quantitative data at 2 h showing that pAKT levels significantly increased (***P<0.001), while tAKT levels were unchanged; the pAKT/tAKT ratio showed an activation trend, even not significant. At 6 h, pAKT levels did not change but tAKT levels were significantly rised (***P<0.001); pAKT/tAKT ratio revealed a significant deactivation within 6 h after EMF exposure (***P<0.001, white columns). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). One-way ANOVA using Tukey's post-test was used for all statistical analysis.

Mentions: Then we investigated the pathways involved in the SCs transformation and proliferation outcomes reported above. We found that both ERK (Ras/Raf/Mek/Erk) and AKT (PI3K/AKT) signaling pathways, which modulate biochemical pathways controlling cell growth and apoptosis, were activated. Quantitative immunoblots analysis confirmed that pERK significantly rose at 2 h (P<0.001), then significantly decreased at 6 h (P<0.001); tERK levels, indeed, showed a light but significant decrease at 2 h (P<0.05), then a significant increase at 6 h (P<0.001; Figure 4b). Analysis of pERK/tERK ratio confirmed that ERK signaling was activated at short time (2 h), and deactivated within 6 h after EMF exposure (P<0.001; Figure 4b).


Tumor suppressor Nf2/merlin drives Schwann cell changes following electromagnetic field exposure through Hippo-dependent mechanisms
ERK and AKT signaling pathways are activated in SCs following 10 min EMF exposure. (a) Representative immunoblots showing the variations in phosphorylated ERK 2 (pERK 2), total ERK 2 (tERK 2), both 42 KDa, phosphorylated AKT (pAKT), total AKT (tAKT), both 60 KDa, in SCs at 2 and 6 h following EMF exposure. The β-actin (43 KDa) was used as a housekeeping protein. (b) Quantitative data at 2 h showed that pERK levels significantly increased (***P<0.001), while tERK levels decreased (*P<0.05); the pERK/tERK ratio showed that ERK signaling was activated 2 h following EMF exposure (***P<0.001, white columns). Indeed, pERK levels significantly decreased at 6 h (***P<0.001), while tERK significantly increased at 6 h (***P<0.001); pERK/tERK ratio indicated that this signaling pathway was deactivated within 6 h following EMF exposure (***P<0.001). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). (c) Quantitative data at 2 h showing that pAKT levels significantly increased (***P<0.001), while tAKT levels were unchanged; the pAKT/tAKT ratio showed an activation trend, even not significant. At 6 h, pAKT levels did not change but tAKT levels were significantly rised (***P<0.001); pAKT/tAKT ratio revealed a significant deactivation within 6 h after EMF exposure (***P<0.001, white columns). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). One-way ANOVA using Tukey's post-test was used for all statistical analysis.
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fig4: ERK and AKT signaling pathways are activated in SCs following 10 min EMF exposure. (a) Representative immunoblots showing the variations in phosphorylated ERK 2 (pERK 2), total ERK 2 (tERK 2), both 42 KDa, phosphorylated AKT (pAKT), total AKT (tAKT), both 60 KDa, in SCs at 2 and 6 h following EMF exposure. The β-actin (43 KDa) was used as a housekeeping protein. (b) Quantitative data at 2 h showed that pERK levels significantly increased (***P<0.001), while tERK levels decreased (*P<0.05); the pERK/tERK ratio showed that ERK signaling was activated 2 h following EMF exposure (***P<0.001, white columns). Indeed, pERK levels significantly decreased at 6 h (***P<0.001), while tERK significantly increased at 6 h (***P<0.001); pERK/tERK ratio indicated that this signaling pathway was deactivated within 6 h following EMF exposure (***P<0.001). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). (c) Quantitative data at 2 h showing that pAKT levels significantly increased (***P<0.001), while tAKT levels were unchanged; the pAKT/tAKT ratio showed an activation trend, even not significant. At 6 h, pAKT levels did not change but tAKT levels were significantly rised (***P<0.001); pAKT/tAKT ratio revealed a significant deactivation within 6 h after EMF exposure (***P<0.001, white columns). Experiments were normalized for β-actin, and expressed as percentage versus controls (CONTR, black columns). The values are means±S.D. (N=3). One-way ANOVA using Tukey's post-test was used for all statistical analysis.
Mentions: Then we investigated the pathways involved in the SCs transformation and proliferation outcomes reported above. We found that both ERK (Ras/Raf/Mek/Erk) and AKT (PI3K/AKT) signaling pathways, which modulate biochemical pathways controlling cell growth and apoptosis, were activated. Quantitative immunoblots analysis confirmed that pERK significantly rose at 2 h (P<0.001), then significantly decreased at 6 h (P<0.001); tERK levels, indeed, showed a light but significant decrease at 2 h (P<0.05), then a significant increase at 6 h (P<0.001; Figure 4b). Analysis of pERK/tERK ratio confirmed that ERK signaling was activated at short time (2 h), and deactivated within 6 h after EMF exposure (P<0.001; Figure 4b).

View Article: PubMed Central - PubMed

ABSTRACT

Previous evidence showed mutations of the neurofibromin type 2 gene (Nf2), encoding the tumor suppressor protein merlin, in sporadic and vestibular schwannomas affecting Schwann cells (SCs). Accordingly, efforts have been addressed to identify possible factors, even environmental, that may regulate neurofibromas growth. In this context, we investigated the exposure of SC to an electromagnetic field (EMF), which is an environmental issue modulating biological processes. Here, we show that SC exposed to 50&thinsp;Hz EMFs changes their morphology, proliferation, migration and myelinating capability. In these cells, merlin is downregulated, leading to activation of two intracellular signaling pathways, ERK/AKT and Hippo. Interestingly, SC changes their phenotype toward a proliferative/migrating state, which in principle may be pathologically relevant for schwannoma development.

No MeSH data available.


Related in: MedlinePlus