Alkaline ceramidase 2 and its bioactive product sphingosine are novel regulators of the DNA damage response
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Ruijuan Xu1,2, Kai Wang1,2, Izolda Mileva3, Yusuf A. Hannun1,2, Lina M. Obeid1,2,4, Cungui Mao1,2
1Department of Medicine, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
2Stony Brook Cancer Center, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
3Lipidomics Core Facility, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
4Ralph H. Johnson Veterans Administration Hospital, Stony Brook, NY 11794, USA
Cungui Mao, e-mail: email@example.com
Keywords: ceramide, Golgi, p53, programmed cell death, reactive oxygen species
Received: September 18, 2015 Accepted: January 29, 2016 Published: March 01, 2016
Human cells respond to DNA damage by elevating sphingosine, a bioactive sphingolipid that induces programmed cell death (PCD) in response to various forms of stress, but its regulation and role in the DNA damage response remain obscure. Herein we demonstrate that DNA damage increases sphingosine levels in tumor cells by upregulating alkaline ceramidase 2 (ACER2) and that the upregulation of the ACER2/sphingosine pathway induces PCD in response to DNA damage by increasing the production of reactive oxygen species (ROS). Treatment with the DNA damaging agent doxorubicin increased both ACER2 expression and sphingosine levels in HCT116 cells in a dose-dependent manner. ACER2 overexpression increased sphingosine in HeLa cells whereas knocking down ACER2 inhibited the doxorubicin-induced increase in sphingosine in HCT116 cells, suggesting that DNA damage elevates sphingosine by upregulating ACER2. Knocking down ACER2 inhibited an increase in the apoptotic and necrotic cell population and the cleavage of poly ADP ribose polymerase (PARP) in HCT116 cells in response to doxorubicin as well as doxorubicin-induced release of lactate dehydrogenase (LDH) from these cells. Similar to treatment with doxorubicin, ACER2 overexpression induced an increase in the apoptotic and necrotic cell population and PARP cleavage in HeLa cells and LDH release from cells, suggesting that ACER2 upregulation mediates PCD in response to DNA damage through sphingosine. Mechanistic studies demonstrated that the upregulation of the ACER2/sphingosine pathway induces PCD by increasing ROS levels. Taken together, these results suggest that the ACER2/sphingosine pathway mediates PCD in response to DNA damage through ROS production.
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