Limits...
Dithiolethione compounds inhibit Akt signaling in human breast and lung cancer cells by increasing PP2A activity.

Switzer CH, Ridnour LA, Cheng RY, Sparatore A, Del Soldato P, Moody TW, Vitek MP, Roberts DD, Wink DA - Oncogene (2009)

Bottom Line: The effect of ACS-1 on Akt activation was not observed in the presence of the PP2A inhibitor okadaic acid.ACS-1 effects on PP2A activity were independent of ARE activation and cAMP formation.In addition to ACS-1, other dithiolethione compounds showed similar effects in reducing Akt activation, suggesting that this class of compounds may have other effects beyond chemoprevention.

View Article: PubMed Central - PubMed

Affiliation: Radiation Biology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.

ABSTRACT
The chemopreventative effects of dithiolethione compounds are attributed to their activation of antioxidant response elements (AREs) by reacting with the Nrf2/Keap1 protein complex. In this study, we show antiproliferative effects of the dithiolethione compound ACS-1 in human cancer cell lines (A549 and MDA-MB-231) by increasing the activity of the tumor suppressor protein phoshatase 2A (PP2A). ACS-1 inhibited epidermal growth factor (EGF)-induced cellular proliferation in a concentration- and time-dependent manner. Akt activation, as determined by serine-473 phosphorylation, was inhibited by ACS-1 in cells stimulated with either EGF or fibronectin. Furthermore, ACS-1 inhibited mammalian target of rapamycin signaling and decreased c-myc protein levels. ACS-1 did not proximally alter EGF receptor or integrin signaling, but caused a concentration-dependent increase in PP2A activity. The effect of ACS-1 on Akt activation was not observed in the presence of the PP2A inhibitor okadaic acid. ACS-1 effects on PP2A activity were independent of ARE activation and cAMP formation. In addition to ACS-1, other dithiolethione compounds showed similar effects in reducing Akt activation, suggesting that this class of compounds may have other effects beyond chemoprevention.

Show MeSH

Related in: MedlinePlus

ACS-1 inhibits Akt activation in FN-stimulated A549 cells. (A) FN, in a concentration-dependent manner, activates Akt in A549 cells. Serum starved A549 cells were plated into Petri dishes coated with differing amounts of FN and incubated for 2 hours. (B) ACS-1 inhibits FN-induced Akt and mTOR activation. ACS-1 treated A549 cells seeded onto FN-coated dishes and incubated for 2 hours. (C) ILK was immunoprecipitated from cells plated on FN in the presence of ACS-1 and ILK kinase activity was determined by recombinant Akt phosphorylation (ser 473).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3472634&req=5

Figure 4: ACS-1 inhibits Akt activation in FN-stimulated A549 cells. (A) FN, in a concentration-dependent manner, activates Akt in A549 cells. Serum starved A549 cells were plated into Petri dishes coated with differing amounts of FN and incubated for 2 hours. (B) ACS-1 inhibits FN-induced Akt and mTOR activation. ACS-1 treated A549 cells seeded onto FN-coated dishes and incubated for 2 hours. (C) ILK was immunoprecipitated from cells plated on FN in the presence of ACS-1 and ILK kinase activity was determined by recombinant Akt phosphorylation (ser 473).

Mentions: Mechanisms other than growth factor receptor activation mediate Akt signaling in human cancers. Extracellular matrix proteins (e.g. fibronectin, laminin) activate extracellular integrin complexes to initiate intracellular signaling via integrin linked kinase (ILK) activity, which directly activates Akt (Danen and Yamada, 2001; Persad and Dedhar, 2003). To address the effects of ACS-1 on Akt stimulation by integrin activation, A549 cells were plated on increasing concentrations of fibronectin (FN). Figure 4A demonstrates a FN-dependent increase in pAkt-(ser 473), which is concentration dependently suppressed by ACS-1 (Figure 4B). Moreover, ACS-1 also suppressed FN-mediated mTOR (ser 2448) activation (Figure 4B). ACS-1 had no effect on integrin signaling at the level of ILK activity (Figure 4C), which phosphorylates Akt ser473. ILK activity was unchanged with respect to ACS-1 concentration as determined by phosphorylation of recombinant Akt suggesting that ACS-1 targets are downstream of ILK.


Dithiolethione compounds inhibit Akt signaling in human breast and lung cancer cells by increasing PP2A activity.

Switzer CH, Ridnour LA, Cheng RY, Sparatore A, Del Soldato P, Moody TW, Vitek MP, Roberts DD, Wink DA - Oncogene (2009)

ACS-1 inhibits Akt activation in FN-stimulated A549 cells. (A) FN, in a concentration-dependent manner, activates Akt in A549 cells. Serum starved A549 cells were plated into Petri dishes coated with differing amounts of FN and incubated for 2 hours. (B) ACS-1 inhibits FN-induced Akt and mTOR activation. ACS-1 treated A549 cells seeded onto FN-coated dishes and incubated for 2 hours. (C) ILK was immunoprecipitated from cells plated on FN in the presence of ACS-1 and ILK kinase activity was determined by recombinant Akt phosphorylation (ser 473).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472634&req=5

Figure 4: ACS-1 inhibits Akt activation in FN-stimulated A549 cells. (A) FN, in a concentration-dependent manner, activates Akt in A549 cells. Serum starved A549 cells were plated into Petri dishes coated with differing amounts of FN and incubated for 2 hours. (B) ACS-1 inhibits FN-induced Akt and mTOR activation. ACS-1 treated A549 cells seeded onto FN-coated dishes and incubated for 2 hours. (C) ILK was immunoprecipitated from cells plated on FN in the presence of ACS-1 and ILK kinase activity was determined by recombinant Akt phosphorylation (ser 473).
Mentions: Mechanisms other than growth factor receptor activation mediate Akt signaling in human cancers. Extracellular matrix proteins (e.g. fibronectin, laminin) activate extracellular integrin complexes to initiate intracellular signaling via integrin linked kinase (ILK) activity, which directly activates Akt (Danen and Yamada, 2001; Persad and Dedhar, 2003). To address the effects of ACS-1 on Akt stimulation by integrin activation, A549 cells were plated on increasing concentrations of fibronectin (FN). Figure 4A demonstrates a FN-dependent increase in pAkt-(ser 473), which is concentration dependently suppressed by ACS-1 (Figure 4B). Moreover, ACS-1 also suppressed FN-mediated mTOR (ser 2448) activation (Figure 4B). ACS-1 had no effect on integrin signaling at the level of ILK activity (Figure 4C), which phosphorylates Akt ser473. ILK activity was unchanged with respect to ACS-1 concentration as determined by phosphorylation of recombinant Akt suggesting that ACS-1 targets are downstream of ILK.

Bottom Line: The effect of ACS-1 on Akt activation was not observed in the presence of the PP2A inhibitor okadaic acid.ACS-1 effects on PP2A activity were independent of ARE activation and cAMP formation.In addition to ACS-1, other dithiolethione compounds showed similar effects in reducing Akt activation, suggesting that this class of compounds may have other effects beyond chemoprevention.

View Article: PubMed Central - PubMed

Affiliation: Radiation Biology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.

ABSTRACT
The chemopreventative effects of dithiolethione compounds are attributed to their activation of antioxidant response elements (AREs) by reacting with the Nrf2/Keap1 protein complex. In this study, we show antiproliferative effects of the dithiolethione compound ACS-1 in human cancer cell lines (A549 and MDA-MB-231) by increasing the activity of the tumor suppressor protein phoshatase 2A (PP2A). ACS-1 inhibited epidermal growth factor (EGF)-induced cellular proliferation in a concentration- and time-dependent manner. Akt activation, as determined by serine-473 phosphorylation, was inhibited by ACS-1 in cells stimulated with either EGF or fibronectin. Furthermore, ACS-1 inhibited mammalian target of rapamycin signaling and decreased c-myc protein levels. ACS-1 did not proximally alter EGF receptor or integrin signaling, but caused a concentration-dependent increase in PP2A activity. The effect of ACS-1 on Akt activation was not observed in the presence of the PP2A inhibitor okadaic acid. ACS-1 effects on PP2A activity were independent of ARE activation and cAMP formation. In addition to ACS-1, other dithiolethione compounds showed similar effects in reducing Akt activation, suggesting that this class of compounds may have other effects beyond chemoprevention.

Show MeSH
Related in: MedlinePlus