title: Alkaline ceramidase 2 (ACER2) and its product dihydrosphingosine mediate the cytotoxicity of N-(4-hydroxyphenyl)retinamide in tumor cells.
abstract: Increased generation of dihydrosphingosine (DHS), a bioactive sphingolipid, has been implicated in the cytotoxicity of the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) in tumor cells. However, how 4-HPR increases DHS remains unclear. Here we demonstrate that 4-HPR increases the expression of ACER2, which catalyzes the hydrolysis of dihydroceramides to generate DHS, and that ACER2 up-regulation plays a key role in mediating the 4-HPR-induced generation of DHS as well as the cytotoxicity of 4-HPR in tumor cells. Treatment with 4-HPR induced the accumulation of dihydroceramides (DHCs) in tumor cells by inhibiting dihydroceramide desaturase (DES) activity, which catalyzes the conversion of DHCs to ceramides. Treatment with 4-HPR also increased ACER2 expression through a retinoic acid receptor-independent and caspase-dependent manner. Overexpression of ACER2 augmented the 4-HPR-induced generation of DHS as well as 4-HPR cytotoxicity, and 4-HPR-induced death in tumor cells, whereas knocking down ACER2 had the opposite effects. ACER2 overexpression, along with treatment with GT11, another DES inhibitor, markedly increased cellular DHS, leading to tumor cell death, whereas ACER2 overexpression or GT11 treatment alone failed to do so, suggesting that both ACER2 up-regulation and DES inhibition are necessary and sufficient to mediate 4-HPR-induced DHS accumulation, cytotoxicity, and death in tumor cells. Taken together, these results suggest that up-regulation of the ACER2/DHS pathway mediates the cytotoxicity of 4-HPR in tumor cells and that up-regulating or activating ACER2 may improve the anti-cancer activity of 4-HRR and other DHC-inducing agents.
authors.affiliation: Department of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Zhehao
authors.initials: Z
authors.lastname: Mao
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Ruijuan
authors.initials: R
authors.lastname: Xu
authors.forename: Sergei
authors.initials: S
authors.lastname: Novgorodov
authors.forename: Zdzislaw M
authors.initials: ZM
authors.lastname: Szulc
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.forename: Lina M
authors.initials: LM
authors.lastname: Obeid
authors.forename: Cungui
authors.initials: C
authors.lastname: Mao
mesh_terms: D055574:Alkaline Ceramidase / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D017313:Fenretinide / Q000627:therapeutic use*; D005434:Flow Cytometry; D006367:HeLa Cells; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D000970:Antineoplastic Agents; D002518:Ceramides; D034741:RNA, Small Interfering; C109343:dihydroceramide; D017313:Fenretinide; C526750:ACER1 protein, human; D055574:Alkaline Ceramidase