title: Involvement of sphingosine kinase 2 in p53-independent induction of p21 by the chemotherapeutic drug doxorubicin.
abstract: Sphingosine-1-phosphate is a potent lipid mediator formed by phosphorylation of sphingosine, a metabolite of sphingolipids, catalyzed by two sphingosine kinase (SphK) isoenzymes, SphK1 and SphK2. Expression of SphK2, which is enriched in the nucleus of MCF7 human breast cancer cells, increased expression of the cyclin-dependent kinase inhibitor p21 but had no effect on p53 or its phosphorylation. The anticancer drug doxorubicin is known to increase p21 via p53-dependent and p53-independent mechanisms. Down-regulation of endogenous SphK2 with small interfering RNA targeted to unique mRNA sequences decreased basal and doxorubicin-induced expression of p21 without affecting increased expression of p53. Down-regulation of SphK2 also decreased G(2)-M arrest and markedly enhanced apoptosis induced by doxorubicin. Moreover, siSphK2 reduced doxorubicin-induced p21 expression in p53-inactivated MCF7 cells. Likewise, in human wild-type p53- and p21-expressing HCT116 colon carcinoma cells, as well as in p53-null counterparts, down-regulation of SphK2 markedly reduced p21 induction by doxorubicin. Knockdown of SphK2 sensitized HCT116 cells to apoptosis induced by doxorubicin with concomitant cleavage of poly(ADP-ribose) polymerase. Collectively, our results show that endogenous SphK2 is important for p53-independent induction of p21 expression by doxorubicin and suggest that SphK2 may influence the balance between cytostasis and apoptosis of human cancer cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, VA 23298-0614, USA.
authors.forename: Heidi M
authors.initials: HM
authors.lastname: Sankala
authors.forename: Nitai C
authors.initials: NC
authors.lastname: Hait
authors.forename: Steven W
authors.initials: SW
authors.lastname: Paugh
authors.forename: Dai
authors.initials: D
authors.lastname: Shida
authors.forename: Sandrine
authors.initials: S
authors.lastname: Lépine
authors.forename: Lynne W
authors.initials: LW
authors.lastname: Elmore
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Sheldon
authors.initials: S
authors.lastname: Milstien
authors.forename: Sarah
authors.initials: S
authors.lastname: Spiegel
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis*; D004317:Doxorubicin / Q000494:pharmacology*; D045325:HCT116 Cells; D006801:Humans; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000032:analysis / Q000502:physiology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D000099157:Sphingosine Kinase
chemical_list: D000903:Antibiotics, Antineoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004317:Doxorubicin; D017853:Phosphotransferases (Alcohol Group Acceptor); D011065:Poly(ADP-ribose) Polymerases; D016159:Tumor Suppressor Protein p53; D000099157:Sphingosine Kinase; C493956:CDKN1A protein, human