title: The NAD(+) salvage pathway modulates cancer cell viability via p73.
abstract: The involvement of the nicotinamide adenine dinucleotide (NAD(+)) salvage pathway in cancer cell survival is poorly understood. Here we show that the NAD(+) salvage pathway modulates cancer cell survival through the rarely mutated tumour suppressor p73. Our data show that pharmacological inhibition or knockdown of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in the NAD(+) salvage pathway, enhances autophagy and decreases survival of cancer cells in a p53-independent manner. Such NAMPT inhibition stabilizes p73 independently of p53 through increased acetylation and decreased ubiquitination, resulting in enhanced autophagy and cell death. These effects of NAMPT inhibition can be effectively reversed using nicotinamide mononucleotide (NMN), the enzymatic product of NAMPT. Similarly, knockdown of p73 also decreases NAMPT inhibition-induced autophagy and cell death, whereas overexpression of p73 alone enhances these effects. We show that the breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) harbour significantly higher levels of NAMPT and lower levels of p73 than does the normal cell line (MCF-10A), and that NAMPT inhibition is cytotoxic exclusively to the cancer cells. Furthermore, data from 176 breast cancer patients demonstrate that higher levels of NAMPT and lower levels of p73 correlate with poorer patient survival, and that high-grade tumours have significantly higher NAMPT/p73 mRNA ratios. Therefore, the inverse relationship between NAMPT and p73 demonstrable in vitro is also reflected from the clinical data. Taken together, our studies reveal a new NAMPT-p73 nexus that likely has important implications for cancer diagnosis, prognosis and treatment.
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: T
authors.initials: T
authors.lastname: Sharif
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: D-G
authors.initials: DG
authors.lastname: Ahn
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada.
authors.forename: R-Z
authors.initials: RZ
authors.lastname: Liu
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: E
authors.initials: E
authors.lastname: Pringle
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: E
authors.initials: E
authors.lastname: Martell
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: C
authors.initials: C
authors.lastname: Dai
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: A
authors.initials: A
authors.lastname: Nunokawa
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: M
authors.initials: M
authors.lastname: Kwak
authors.affiliation: Department of Pathology, Dalhousie University, Halifax, NS, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Clements
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: J P
authors.initials: JP
authors.lastname: Murphy
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: C
authors.initials: C
authors.lastname: Dean
authors.affiliation: Department of Pathology, Dalhousie University, Halifax, NS, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Marcato
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.
authors.forename: C
authors.initials: C
authors.lastname: McCormick
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Godbout
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.|Strategy and Organizational Performance, IWK Health Centre, Halifax, NS, Canada.
authors.forename: S A
authors.initials: SA
authors.lastname: Gujar
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4R2.|Department of Pathology, Dalhousie University, Halifax, NS, Canada.
authors.forename: P W K
authors.initials: PW
authors.lastname: Lee
mesh_terms: D001343:Autophagy; D002470:Cell Survival; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D061986:MCF-7 Cells; D009243:NAD / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D054409:Nicotinamide Phosphoribosyltransferase / Q000235:genetics / Q000378:metabolism*; D000072160:Tumor Protein p73 / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D016207:Cytokines; C495901:TP53 protein, human; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D009243:NAD; D054409:Nicotinamide Phosphoribosyltransferase; C085455:nicotinamide phosphoribosyltransferase, human