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Insulin Increases Sestrin 2 Content by Reducing Its Degradation through the PI 3 K/mTOR Signaling Pathway.

Chai D, Wang G, Zhou Z, Yang H, Yu Z - Int J Endocrinol (2015)

Bottom Line: Sestrin (SESN) is known as a cysteine sulfinic acid reductase.While mechanisms underlying the expression of SESN are not fully understood.Following SESN2 knockdown insulin-stimulated PKB phosphorylation was enhanced and accompanied by reduced PTEN content.

View Article: PubMed Central - PubMed

Affiliation: Fujian Key Laboratory of Chinese Materia Medica, Biomedical Drug Research and Development Center, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, China.

ABSTRACT
Sestrin (SESN) is known as a cysteine sulfinic acid reductase. Recently, nonredox functions of SESN in metabolic regulation and antitumor property have been recognized. While mechanisms underlying the expression of SESN are not fully understood. Here we report that insulin markedly increased SESN2 level in HepG2 cells through mTOR activation. To determine whether insulin affects SESN2 degradation, we assessed SESN2 turnover by applying the protein synthesis inhibitor, cycloheximide (CHX), and found that following insulin treatment SESN2 protein levels were reduced significantly slower than non-insulin-treated cells. Furthermore, the proteasomal inhibitor, MG132, dramatically increased SESN2 protein and its ubiquitination level while in the presence of MG132 insulin did not further increase SESN2 content, suggesting that insulin increases SESN2 content mainly via inhibiting its proteasomal degradation. We then explored the potential feedback role of SESN2 in insulin signaling by SESN2 siRNA knockdown in HepG2 cells. Following SESN2 knockdown insulin-stimulated PKB phosphorylation was enhanced and accompanied by reduced PTEN content. Taken together, our study suggests that insulin upregulates SESN2 content via the PI3K/mTOR signaling pathway and this effect is attributed to decreased SESN2 degradation. Furthermore, SESN2 via modulating PTEN plays a negative feedback role in insulin signaling.

No MeSH data available.


Related in: MedlinePlus

PI3K/mTOR signaling pathway is required for the upregulation of SESN2 level by insulin treatment. HepG2 cells were pretreated with indicated reagents at the indicated concentrations for 1 h, followed by an 18 h further treatment with 100 nM of insulin. Cells were harvested for western blotting. (a) to (c) are representative images of at least three independent experiments.
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fig2: PI3K/mTOR signaling pathway is required for the upregulation of SESN2 level by insulin treatment. HepG2 cells were pretreated with indicated reagents at the indicated concentrations for 1 h, followed by an 18 h further treatment with 100 nM of insulin. Cells were harvested for western blotting. (a) to (c) are representative images of at least three independent experiments.

Mentions: To identify the potential signaling pathways involved in insulin-stimulated SESN2 expression, HepG2 cells were pretreated with the PI3K inhibitor LY294002, the PKB inhibitor triciribine (TCN), and the mTOR inhibitor rapamycin, respectively, for 1 h followed by 100 nM insulin treatment for 18 h. All the three inhibitors either completely blocked or significantly attenuated insulin-stimulated SESN2 levels (Figures 2(a) and 2(b)). Insulin can also activate the MAP kinase signaling pathways including JNK, p38, and ERK [17]. In addition, it has been shown that JNK-activated dFoxO mediates dSESN upregulation in Drosophila [1]. We therefore examined the effects of the ERK inhibitor U0126, the p38 inhibitor SB202190, and the JNK inhibitor SP600125 on SESN2 levels in HepG2 cells and observed that none of them generated any appreciable inhibitory effect on insulin-stimulated SESN2 levels (Figure 2(c)). Together, these data suggest that insulin-regulated SESN2 expression is through the activation of PI3K/PKB/mTOR signaling but not the MAP kinase-mediated signaling.


Insulin Increases Sestrin 2 Content by Reducing Its Degradation through the PI 3 K/mTOR Signaling Pathway.

Chai D, Wang G, Zhou Z, Yang H, Yu Z - Int J Endocrinol (2015)

PI3K/mTOR signaling pathway is required for the upregulation of SESN2 level by insulin treatment. HepG2 cells were pretreated with indicated reagents at the indicated concentrations for 1 h, followed by an 18 h further treatment with 100 nM of insulin. Cells were harvested for western blotting. (a) to (c) are representative images of at least three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4352509&req=5

fig2: PI3K/mTOR signaling pathway is required for the upregulation of SESN2 level by insulin treatment. HepG2 cells were pretreated with indicated reagents at the indicated concentrations for 1 h, followed by an 18 h further treatment with 100 nM of insulin. Cells were harvested for western blotting. (a) to (c) are representative images of at least three independent experiments.
Mentions: To identify the potential signaling pathways involved in insulin-stimulated SESN2 expression, HepG2 cells were pretreated with the PI3K inhibitor LY294002, the PKB inhibitor triciribine (TCN), and the mTOR inhibitor rapamycin, respectively, for 1 h followed by 100 nM insulin treatment for 18 h. All the three inhibitors either completely blocked or significantly attenuated insulin-stimulated SESN2 levels (Figures 2(a) and 2(b)). Insulin can also activate the MAP kinase signaling pathways including JNK, p38, and ERK [17]. In addition, it has been shown that JNK-activated dFoxO mediates dSESN upregulation in Drosophila [1]. We therefore examined the effects of the ERK inhibitor U0126, the p38 inhibitor SB202190, and the JNK inhibitor SP600125 on SESN2 levels in HepG2 cells and observed that none of them generated any appreciable inhibitory effect on insulin-stimulated SESN2 levels (Figure 2(c)). Together, these data suggest that insulin-regulated SESN2 expression is through the activation of PI3K/PKB/mTOR signaling but not the MAP kinase-mediated signaling.

Bottom Line: Sestrin (SESN) is known as a cysteine sulfinic acid reductase.While mechanisms underlying the expression of SESN are not fully understood.Following SESN2 knockdown insulin-stimulated PKB phosphorylation was enhanced and accompanied by reduced PTEN content.

View Article: PubMed Central - PubMed

Affiliation: Fujian Key Laboratory of Chinese Materia Medica, Biomedical Drug Research and Development Center, Fujian University of Traditional Chinese Medicine, Fuzhou 350108, China.

ABSTRACT
Sestrin (SESN) is known as a cysteine sulfinic acid reductase. Recently, nonredox functions of SESN in metabolic regulation and antitumor property have been recognized. While mechanisms underlying the expression of SESN are not fully understood. Here we report that insulin markedly increased SESN2 level in HepG2 cells through mTOR activation. To determine whether insulin affects SESN2 degradation, we assessed SESN2 turnover by applying the protein synthesis inhibitor, cycloheximide (CHX), and found that following insulin treatment SESN2 protein levels were reduced significantly slower than non-insulin-treated cells. Furthermore, the proteasomal inhibitor, MG132, dramatically increased SESN2 protein and its ubiquitination level while in the presence of MG132 insulin did not further increase SESN2 content, suggesting that insulin increases SESN2 content mainly via inhibiting its proteasomal degradation. We then explored the potential feedback role of SESN2 in insulin signaling by SESN2 siRNA knockdown in HepG2 cells. Following SESN2 knockdown insulin-stimulated PKB phosphorylation was enhanced and accompanied by reduced PTEN content. Taken together, our study suggests that insulin upregulates SESN2 content via the PI3K/mTOR signaling pathway and this effect is attributed to decreased SESN2 degradation. Furthermore, SESN2 via modulating PTEN plays a negative feedback role in insulin signaling.

No MeSH data available.


Related in: MedlinePlus