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Hypoxia-induced MIR155 is a potent autophagy inducer by targeting multiple players in the MTOR pathway.

Wan G, Xie W, Liu Z, Xu W, Lao Y, Huang N, Cui K, Liao M, He J, Jiang Y, Yang BB, Xu H, Xu N, Zhang Y - Autophagy (2013)

Bottom Line: MIR155 suppresses target-gene expression by directly interacting with their 3' untranslated regions (UTRs), mutations of the binding sites abolish their MIR155 responsiveness.Furthermore, by downregulating MTOR signaling, MIR155 also attenuates cell proliferation and induces G 1/S cell cycle arrest.Collectively, these data present a new role for MIR155 as a key regulator of autophagy via dysregulation of MTOR pathway.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences; Tsinghua University; Beijing, China; Key Lab in Healthy Science and Technology; Division of Life Science; Graduate School at Shenzhen; Tsinghua University; Shenzhen, China.

ABSTRACT
Hypoxia activates autophagy, an evolutionarily conserved cellular catabolic process. Dysfunction in the autophagy pathway has been implicated in an increasing number of human diseases, including cancer. Hypoxia induces upregulation of a specific set of microRNAs (miRNAs) in a variety of cell types. Here, we describe hypoxia-induced MIR155 as a potent inducer of autophagy. Enforced expression of MIR155 increases autophagic activity in human nasopharyngeal cancer and cervical cancer cells. Knocking down endogenous MIR155 inhibits hypoxia-induced autophagy. We demonstrated that MIR155 targets multiple players in MTOR signaling, including RHEB, RICTOR, and RPS6KB2. MIR155 suppresses target-gene expression by directly interacting with their 3' untranslated regions (UTRs), mutations of the binding sites abolish their MIR155 responsiveness. Furthermore, by downregulating MTOR signaling, MIR155 also attenuates cell proliferation and induces G 1/S cell cycle arrest. Collectively, these data present a new role for MIR155 as a key regulator of autophagy via dysregulation of MTOR pathway.

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Figure 7.MIR155 decelerates cell proliferation and cell cycle progression. (A) Overexpression of MIR155 inhibits cell proliferation. CNE or HeLa cells transfected with MIR155 or NC were cultured for 24, 48, and 72 h to determine cell proliferation rates. Data shown are means ± s.d. of independent experiments, n = 4, **P < 0.01, Student 2-tailed t test. (B) MIR155 induces G1/S cell cycle arrest. HeLa cells transfected with indicated miRNAs or siRNAs were synchronized at G1/S boundary by treatment with hydroxyurea. Cells were released from hydroxyurea block for 4 h, fixed and stained with propidium iodide (PI) for flow cytometry. Percentage of G1, S, and G2/M phase cells was quantified from flow cytometry analysis. Data shown are means ± s.d. from 3 independent experiments. (C) Proposed model of hypoxia-induced MIR155 in regulating autophagy, cell proliferation, and cell cycle progression. MIR155 is a hypoxia-inducible miRNA. MIR155 targets the expression of RHEB, RICTOR, and RPS6KB2, which in turns suppresses the activation of AKT and MTORC1. By deregulating the MTOR-AKT pathway, MIR155 induces autophagy and decelerates cell proliferation and cell cycle progression.
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Figure 7: Figure 7.MIR155 decelerates cell proliferation and cell cycle progression. (A) Overexpression of MIR155 inhibits cell proliferation. CNE or HeLa cells transfected with MIR155 or NC were cultured for 24, 48, and 72 h to determine cell proliferation rates. Data shown are means ± s.d. of independent experiments, n = 4, **P < 0.01, Student 2-tailed t test. (B) MIR155 induces G1/S cell cycle arrest. HeLa cells transfected with indicated miRNAs or siRNAs were synchronized at G1/S boundary by treatment with hydroxyurea. Cells were released from hydroxyurea block for 4 h, fixed and stained with propidium iodide (PI) for flow cytometry. Percentage of G1, S, and G2/M phase cells was quantified from flow cytometry analysis. Data shown are means ± s.d. from 3 independent experiments. (C) Proposed model of hypoxia-induced MIR155 in regulating autophagy, cell proliferation, and cell cycle progression. MIR155 is a hypoxia-inducible miRNA. MIR155 targets the expression of RHEB, RICTOR, and RPS6KB2, which in turns suppresses the activation of AKT and MTORC1. By deregulating the MTOR-AKT pathway, MIR155 induces autophagy and decelerates cell proliferation and cell cycle progression.

Mentions: Numerous studies demonstrate that MTOR signaling is essential for cell growth and proliferation. In this study, we discovered that overexpression of MIR155 could suppress the activation of MTORC1 and AKT. Thus, it is interesting to check whether MIR155 regulate cell proliferation and cell cycle progression. We observed that overexpression of MIR155 attenuated cell proliferation in both CNE and HeLa cells (Fig. 7A). Next, we examined the effect of MIR155 on cell cycle progression. HeLa cells transfected with NC or MIR155 were synchronized at G1/S boundary by treatment with hydroxyurea. At 4 h after release from G1 block, more than 70% of the control cells finished G1 and entered S phase. Similarly, MIR885-5P, a control miRNA had no effect on G1/S cell cycle progression. By contrast, both MIR155 and RHEB siRNA induced significant G1 phase arrest (Fig. 7B). Then we tested whether the effect of MIR155 on autophagy contributes to G1 phase cell cycle arrest. Cells were cotransfected with MIR155 and ATG5 siRNA. Interestingly, depletion of ATG5 relieved the inhibitory effect of MIR155 on G1/S cell cycle progression (Fig. 7B; Fig. S6). These data indicate a possible link between autophagy and cell cycle progression.


Hypoxia-induced MIR155 is a potent autophagy inducer by targeting multiple players in the MTOR pathway.

Wan G, Xie W, Liu Z, Xu W, Lao Y, Huang N, Cui K, Liao M, He J, Jiang Y, Yang BB, Xu H, Xu N, Zhang Y - Autophagy (2013)

Figure 7.MIR155 decelerates cell proliferation and cell cycle progression. (A) Overexpression of MIR155 inhibits cell proliferation. CNE or HeLa cells transfected with MIR155 or NC were cultured for 24, 48, and 72 h to determine cell proliferation rates. Data shown are means ± s.d. of independent experiments, n = 4, **P < 0.01, Student 2-tailed t test. (B) MIR155 induces G1/S cell cycle arrest. HeLa cells transfected with indicated miRNAs or siRNAs were synchronized at G1/S boundary by treatment with hydroxyurea. Cells were released from hydroxyurea block for 4 h, fixed and stained with propidium iodide (PI) for flow cytometry. Percentage of G1, S, and G2/M phase cells was quantified from flow cytometry analysis. Data shown are means ± s.d. from 3 independent experiments. (C) Proposed model of hypoxia-induced MIR155 in regulating autophagy, cell proliferation, and cell cycle progression. MIR155 is a hypoxia-inducible miRNA. MIR155 targets the expression of RHEB, RICTOR, and RPS6KB2, which in turns suppresses the activation of AKT and MTORC1. By deregulating the MTOR-AKT pathway, MIR155 induces autophagy and decelerates cell proliferation and cell cycle progression.
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Related In: Results  -  Collection

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Figure 7: Figure 7.MIR155 decelerates cell proliferation and cell cycle progression. (A) Overexpression of MIR155 inhibits cell proliferation. CNE or HeLa cells transfected with MIR155 or NC were cultured for 24, 48, and 72 h to determine cell proliferation rates. Data shown are means ± s.d. of independent experiments, n = 4, **P < 0.01, Student 2-tailed t test. (B) MIR155 induces G1/S cell cycle arrest. HeLa cells transfected with indicated miRNAs or siRNAs were synchronized at G1/S boundary by treatment with hydroxyurea. Cells were released from hydroxyurea block for 4 h, fixed and stained with propidium iodide (PI) for flow cytometry. Percentage of G1, S, and G2/M phase cells was quantified from flow cytometry analysis. Data shown are means ± s.d. from 3 independent experiments. (C) Proposed model of hypoxia-induced MIR155 in regulating autophagy, cell proliferation, and cell cycle progression. MIR155 is a hypoxia-inducible miRNA. MIR155 targets the expression of RHEB, RICTOR, and RPS6KB2, which in turns suppresses the activation of AKT and MTORC1. By deregulating the MTOR-AKT pathway, MIR155 induces autophagy and decelerates cell proliferation and cell cycle progression.
Mentions: Numerous studies demonstrate that MTOR signaling is essential for cell growth and proliferation. In this study, we discovered that overexpression of MIR155 could suppress the activation of MTORC1 and AKT. Thus, it is interesting to check whether MIR155 regulate cell proliferation and cell cycle progression. We observed that overexpression of MIR155 attenuated cell proliferation in both CNE and HeLa cells (Fig. 7A). Next, we examined the effect of MIR155 on cell cycle progression. HeLa cells transfected with NC or MIR155 were synchronized at G1/S boundary by treatment with hydroxyurea. At 4 h after release from G1 block, more than 70% of the control cells finished G1 and entered S phase. Similarly, MIR885-5P, a control miRNA had no effect on G1/S cell cycle progression. By contrast, both MIR155 and RHEB siRNA induced significant G1 phase arrest (Fig. 7B). Then we tested whether the effect of MIR155 on autophagy contributes to G1 phase cell cycle arrest. Cells were cotransfected with MIR155 and ATG5 siRNA. Interestingly, depletion of ATG5 relieved the inhibitory effect of MIR155 on G1/S cell cycle progression (Fig. 7B; Fig. S6). These data indicate a possible link between autophagy and cell cycle progression.

Bottom Line: MIR155 suppresses target-gene expression by directly interacting with their 3' untranslated regions (UTRs), mutations of the binding sites abolish their MIR155 responsiveness.Furthermore, by downregulating MTOR signaling, MIR155 also attenuates cell proliferation and induces G 1/S cell cycle arrest.Collectively, these data present a new role for MIR155 as a key regulator of autophagy via dysregulation of MTOR pathway.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences; Tsinghua University; Beijing, China; Key Lab in Healthy Science and Technology; Division of Life Science; Graduate School at Shenzhen; Tsinghua University; Shenzhen, China.

ABSTRACT
Hypoxia activates autophagy, an evolutionarily conserved cellular catabolic process. Dysfunction in the autophagy pathway has been implicated in an increasing number of human diseases, including cancer. Hypoxia induces upregulation of a specific set of microRNAs (miRNAs) in a variety of cell types. Here, we describe hypoxia-induced MIR155 as a potent inducer of autophagy. Enforced expression of MIR155 increases autophagic activity in human nasopharyngeal cancer and cervical cancer cells. Knocking down endogenous MIR155 inhibits hypoxia-induced autophagy. We demonstrated that MIR155 targets multiple players in MTOR signaling, including RHEB, RICTOR, and RPS6KB2. MIR155 suppresses target-gene expression by directly interacting with their 3' untranslated regions (UTRs), mutations of the binding sites abolish their MIR155 responsiveness. Furthermore, by downregulating MTOR signaling, MIR155 also attenuates cell proliferation and induces G 1/S cell cycle arrest. Collectively, these data present a new role for MIR155 as a key regulator of autophagy via dysregulation of MTOR pathway.

Show MeSH
Related in: MedlinePlus