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A novel immunosuppressive agent FTY720 induced Akt dephosphorylation in leukemia cells
Yumiko Matsuoka1, Yukitoshi Nagahara, Masahiko Ikekita
1Division of Radio Isotopes and Biosafety Research, National Research Institute for Child Health and Development, 3-35-31 Taishido, Setagaya-ku, Tokyo 154-8567, Japan.
Abstract:
1. Our previous studies revealed that the immunosuppressive agent, FTY720, mainly induces mitochondria-involved apoptosis in some types of cancer cells, since Bcl-2 overexpression prevents the FTY720-induction of apoptotic stimuli. Furthermore, FTY720 induces G0/G1 cell cycle arrest. The present study further examines the correlation between intracellular signaling kinases with FTY720-induced mitochondria-involved apoptosis. 2. Human T cell leukemia Jurkat was exposed to FTY720. Dephosphorylation of Akt occurred in a time- and concentration-dependent manner. FTY720 also induced Bad (Ser(136)) and ribosomal p70S6 kinase (p70(S6k)) (Thr(389)) dephosphorylation. 3. FTY720-induced Akt dephosphorylation was not because of Akt upstream phosphatidylinositol 3'-kinase (PI 3-kinase) pathway inhibition. 4. FTY720 also induced Akt dephosphorylation in human B cell leukemia BALL-1. BALL-1 cells were resistant to FTY720-induced apoptosis. 5. Okadaic acid (OA) inhibited the FTY720-induced dephosphorylation of Akt and p70(S6k), suggesting that FTY720 promotes Ser/Thr protein phosphatase (PP) activity. 6. OA partially inhibited FTY720-induced caspase-3 activation. 7. PP2A or PP2A-like phosphatase was temporarily activated in cells exposed to FTY720. In addition, FTY720 activated purified PP2A (ABC). 8. Overall, the results suggest that FTY720 activated PP2A or PP2A-like phosphatase and dephosphorylated Akt pathway factors resulting in the enhancement of apoptosis via mitochondria.
Insights
FTY720 triggers cancer cell death by activating protein phosphatase 2A (PP2A), leading to dephosphorylation of Akt and enhancing mitochondria-involved apoptosis. This immunosuppressive agent also causes cell cycle arrest.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- FTY720 (fingolimod) is an immunosuppressive agent known to induce apoptosis in cancer cells, involving mitochondria and G0/G1 cell cycle arrest.
- Bcl-2 overexpression can confer resistance to FTY720-induced apoptosis, highlighting the complexity of its mechanism.
- The precise intracellular signaling pathways targeted by FTY720 in relation to apoptosis require further elucidation.
Purpose of the Study:
- To investigate the role of intracellular signaling kinases in FTY720-induced mitochondria-involved apoptosis.
- To determine the effect of FTY720 on the Akt signaling pathway and its upstream regulators.
- To identify the specific protein phosphatases involved in FTY720's apoptotic effects.
Main Methods:
- Exposure of human T cell leukemia Jurkat and B cell leukemia BALL-1 cells to FTY720.
- Analysis of protein dephosphorylation of Akt, Bad, and p70S6K.
- Assessment of the impact of okadaic acid (OA) on FTY720-induced signaling events and caspase-3 activation.
- Enzyme assays using purified PP2A (ABC).
Main Results:
- FTY720 induced time- and concentration-dependent dephosphorylation of Akt, Bad (Ser136), and p70S6K (Thr389) in Jurkat cells.
- FTY720-induced Akt dephosphorylation was independent of PI 3-kinase inhibition.
- Okadaic acid inhibited FTY720-induced dephosphorylation and partially reduced caspase-3 activation, suggesting FTY720 activates Ser/Thr protein phosphatase (PP) activity, specifically PP2A.
- FTY720 activated purified PP2A (ABC) and enhanced apoptosis via mitochondria.
Conclusions:
- FTY720 activates PP2A or a PP2A-like phosphatase.
- This phosphatase activity leads to the dephosphorylation of Akt pathway factors, enhancing mitochondria-involved apoptosis.
- The findings elucidate a key mechanism by which FTY720 induces apoptosis in cancer cells, involving the PP2A/Akt signaling axis.