Phosphatidylinositol 3 kinase (PI3K) modulates manganese homeostasis and manganese-induced cell signaling in a murine striatal cell line

Miles R. Bryan, Michael A. Uhouse, Kristen D. Nordham, Piyush Joshi, Daniel I.R. Rose, Michael T. O'Brien, Michael Aschner, Aaron B. Bowman

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

In a recent study, we found that blocking the protein kinase ataxia telangiectasia mutated (ATM) with the small molecule inhibitor (SMI) KU-55933 can completely abrogate Mn-induced phosphorylation of p53 at serine 15 (p-p53) in human induced pluripotent stem cell (hiPSC)-differentiated striatal neuroprogenitors. However, in the immortalized mouse striatal progenitor cell line STHdhQ7/Q7, a concentration of KU55933 far exceeding its IC50 for ATM was required to inhibit Mn-induced p-p53. This suggested an alternative signaling system redundant with ATM kinase for activating p53 in this cell line- one that was altered by KU55933 at these higher concentrations (i.e. mTORC1, DNApk, PI3K). To test the hypothesis that one or more of these signaling pathways contributed to Mn-induced p-p53, we utilized a set of SMIs (e.g. NU7441 and LY294002) known to block DNApk, PI3K, and mTORC1 at distinct concentrations. We found that the SMIs inhibit Mn-induced p-p53 expression near the expected IC50s for PI3K, versus other known targets. We hypothesized that inhibiting PI3K reduces intracellular Mn and thereby decreases activation of p53 by Mn. Using the cellular fura-2 manganese extraction assay (CFMEA), we determined that KU55933/60019, NU7441, and LY294002 (at concentrations near their IC50s for PI3K) all decrease intracellular Mn (∼50%) after a dual, 24-h Mn and SMI exposure. Many pathways are activated by Mn aside from p-p53, including AKT and mTOR pathways. Thus, we explored the activation of these pathways by Mn in STHdh cells as well as the effects of other pathway inhibitors. p-AKT and p-S6 activation by Mn is almost completely blocked upon addition of NU7441(5μM) or LY294002(7μM), supporting PI3K's upstream role in the AKT/mTOR pathway. We also investigated whether PI3K inhibition blocks Mn uptake in other cell lines. LY294002 exposure did not reduce Mn uptake in ST14A, Neuro2A, HEK293, MEF, or hiPSC-derived neuroprogenitors. Next, we sought to determine whether inhibition of PI3K blocked p53 phosphorylation by directly blocking an unknown PI3K/p53 interaction or indirectly reducing intracellular Mn, decreasing p-p53 expression. In-Cell Western and CFMEA experiments using multiple concentrations of Mn exposures demonstrated that intracellular Mn levels directly correlated with p-p53 expression with or without addition of LY294002. Finally, we examined whether PI3K inhibition was able to block Mn-induced p-p53 activity in hiPSC-derived striatal neuroprogenitors. As expected, LY294002 does not block Mn-induced p-p53 as PI3K inhibition is unable to reduce Mn net uptake in this cell line, suggesting the effect of LY294002 on Mn uptake is relatively specific to the STHdh mouse striatal cell line.

Original languageEnglish (US)
JournalNeuroToxicology
DOIs
StateAccepted/In press - 2017

Fingerprint

Phosphatidylinositol 3-Kinase
Cell signaling
Corpus Striatum
Manganese
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
Homeostasis
Cells
Cell Line
Induced Pluripotent Stem Cells
Ataxia Telangiectasia
Stem cells
Phosphorylation
Fura-2
Chemical activation
Assays
S 6
Molecules
Phosphatidylinositol 3-Kinases
Protein Kinases
Serine

Keywords

  • KU55933
  • KU60019
  • LY294002
  • Manganese
  • Manganese transport
  • Neurotoxicity
  • NU7441
  • P53
  • PI3K
  • STHdh

ASJC Scopus subject areas

  • Neuroscience(all)
  • Toxicology

Cite this

Bryan, M. R., Uhouse, M. A., Nordham, K. D., Joshi, P., Rose, D. I. R., O'Brien, M. T., ... Bowman, A. B. (Accepted/In press). Phosphatidylinositol 3 kinase (PI3K) modulates manganese homeostasis and manganese-induced cell signaling in a murine striatal cell line. NeuroToxicology. https://doi.org/10.1016/j.neuro.2017.07.026

Phosphatidylinositol 3 kinase (PI3K) modulates manganese homeostasis and manganese-induced cell signaling in a murine striatal cell line. / Bryan, Miles R.; Uhouse, Michael A.; Nordham, Kristen D.; Joshi, Piyush; Rose, Daniel I.R.; O'Brien, Michael T.; Aschner, Michael; Bowman, Aaron B.

In: NeuroToxicology, 2017.

Research output: Contribution to journalArticle

Bryan, Miles R. ; Uhouse, Michael A. ; Nordham, Kristen D. ; Joshi, Piyush ; Rose, Daniel I.R. ; O'Brien, Michael T. ; Aschner, Michael ; Bowman, Aaron B. / Phosphatidylinositol 3 kinase (PI3K) modulates manganese homeostasis and manganese-induced cell signaling in a murine striatal cell line. In: NeuroToxicology. 2017.
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TY - JOUR

T1 - Phosphatidylinositol 3 kinase (PI3K) modulates manganese homeostasis and manganese-induced cell signaling in a murine striatal cell line

AU - Bryan, Miles R.

AU - Uhouse, Michael A.

AU - Nordham, Kristen D.

AU - Joshi, Piyush

AU - Rose, Daniel I.R.

AU - O'Brien, Michael T.

AU - Aschner, Michael

AU - Bowman, Aaron B.

PY - 2017

Y1 - 2017

N2 - In a recent study, we found that blocking the protein kinase ataxia telangiectasia mutated (ATM) with the small molecule inhibitor (SMI) KU-55933 can completely abrogate Mn-induced phosphorylation of p53 at serine 15 (p-p53) in human induced pluripotent stem cell (hiPSC)-differentiated striatal neuroprogenitors. However, in the immortalized mouse striatal progenitor cell line STHdhQ7/Q7, a concentration of KU55933 far exceeding its IC50 for ATM was required to inhibit Mn-induced p-p53. This suggested an alternative signaling system redundant with ATM kinase for activating p53 in this cell line- one that was altered by KU55933 at these higher concentrations (i.e. mTORC1, DNApk, PI3K). To test the hypothesis that one or more of these signaling pathways contributed to Mn-induced p-p53, we utilized a set of SMIs (e.g. NU7441 and LY294002) known to block DNApk, PI3K, and mTORC1 at distinct concentrations. We found that the SMIs inhibit Mn-induced p-p53 expression near the expected IC50s for PI3K, versus other known targets. We hypothesized that inhibiting PI3K reduces intracellular Mn and thereby decreases activation of p53 by Mn. Using the cellular fura-2 manganese extraction assay (CFMEA), we determined that KU55933/60019, NU7441, and LY294002 (at concentrations near their IC50s for PI3K) all decrease intracellular Mn (∼50%) after a dual, 24-h Mn and SMI exposure. Many pathways are activated by Mn aside from p-p53, including AKT and mTOR pathways. Thus, we explored the activation of these pathways by Mn in STHdh cells as well as the effects of other pathway inhibitors. p-AKT and p-S6 activation by Mn is almost completely blocked upon addition of NU7441(5μM) or LY294002(7μM), supporting PI3K's upstream role in the AKT/mTOR pathway. We also investigated whether PI3K inhibition blocks Mn uptake in other cell lines. LY294002 exposure did not reduce Mn uptake in ST14A, Neuro2A, HEK293, MEF, or hiPSC-derived neuroprogenitors. Next, we sought to determine whether inhibition of PI3K blocked p53 phosphorylation by directly blocking an unknown PI3K/p53 interaction or indirectly reducing intracellular Mn, decreasing p-p53 expression. In-Cell Western and CFMEA experiments using multiple concentrations of Mn exposures demonstrated that intracellular Mn levels directly correlated with p-p53 expression with or without addition of LY294002. Finally, we examined whether PI3K inhibition was able to block Mn-induced p-p53 activity in hiPSC-derived striatal neuroprogenitors. As expected, LY294002 does not block Mn-induced p-p53 as PI3K inhibition is unable to reduce Mn net uptake in this cell line, suggesting the effect of LY294002 on Mn uptake is relatively specific to the STHdh mouse striatal cell line.

AB - In a recent study, we found that blocking the protein kinase ataxia telangiectasia mutated (ATM) with the small molecule inhibitor (SMI) KU-55933 can completely abrogate Mn-induced phosphorylation of p53 at serine 15 (p-p53) in human induced pluripotent stem cell (hiPSC)-differentiated striatal neuroprogenitors. However, in the immortalized mouse striatal progenitor cell line STHdhQ7/Q7, a concentration of KU55933 far exceeding its IC50 for ATM was required to inhibit Mn-induced p-p53. This suggested an alternative signaling system redundant with ATM kinase for activating p53 in this cell line- one that was altered by KU55933 at these higher concentrations (i.e. mTORC1, DNApk, PI3K). To test the hypothesis that one or more of these signaling pathways contributed to Mn-induced p-p53, we utilized a set of SMIs (e.g. NU7441 and LY294002) known to block DNApk, PI3K, and mTORC1 at distinct concentrations. We found that the SMIs inhibit Mn-induced p-p53 expression near the expected IC50s for PI3K, versus other known targets. We hypothesized that inhibiting PI3K reduces intracellular Mn and thereby decreases activation of p53 by Mn. Using the cellular fura-2 manganese extraction assay (CFMEA), we determined that KU55933/60019, NU7441, and LY294002 (at concentrations near their IC50s for PI3K) all decrease intracellular Mn (∼50%) after a dual, 24-h Mn and SMI exposure. Many pathways are activated by Mn aside from p-p53, including AKT and mTOR pathways. Thus, we explored the activation of these pathways by Mn in STHdh cells as well as the effects of other pathway inhibitors. p-AKT and p-S6 activation by Mn is almost completely blocked upon addition of NU7441(5μM) or LY294002(7μM), supporting PI3K's upstream role in the AKT/mTOR pathway. We also investigated whether PI3K inhibition blocks Mn uptake in other cell lines. LY294002 exposure did not reduce Mn uptake in ST14A, Neuro2A, HEK293, MEF, or hiPSC-derived neuroprogenitors. Next, we sought to determine whether inhibition of PI3K blocked p53 phosphorylation by directly blocking an unknown PI3K/p53 interaction or indirectly reducing intracellular Mn, decreasing p-p53 expression. In-Cell Western and CFMEA experiments using multiple concentrations of Mn exposures demonstrated that intracellular Mn levels directly correlated with p-p53 expression with or without addition of LY294002. Finally, we examined whether PI3K inhibition was able to block Mn-induced p-p53 activity in hiPSC-derived striatal neuroprogenitors. As expected, LY294002 does not block Mn-induced p-p53 as PI3K inhibition is unable to reduce Mn net uptake in this cell line, suggesting the effect of LY294002 on Mn uptake is relatively specific to the STHdh mouse striatal cell line.

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KW - KU60019

KW - LY294002

KW - Manganese

KW - Manganese transport

KW - Neurotoxicity

KW - NU7441

KW - P53

KW - PI3K

KW - STHdh

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