title: c-Abl-independent p73 stabilization during gemcitabine- or 4'-thio-beta-D-arabinofuranosylcytosine-induced apoptosis in wild-type and p53-null colorectal cancer cells.
abstract: Nucleoside anticancer drugs like gemcitabine (2'-deoxy-2',2'-difluorocytidine) are potent inducers of p53, and ectopic expression of wild-type p53 sensitizes cells to these agents. However, it is also known that nucleosides are efficient activators of apoptosis in tumor cells that do not express a functional p53. To clarify this issue, we examined the effects of gemcitabine and 4'-thio-beta-d-arabinofuranosylcytosine (T-ara-C) on p73, a structural and functional homologue of p53, whose activation could also account for nucleoside-induced apoptosis because no functionally significant mutations of p73 have been reported in cancers. Acute treatment of HCT 116 colon carcinoma cells with gemcitabine or T-ara-C induced marked cytotoxicity and cleavage of caspase-3 and poly(ADP-ribose) polymerase. T-ara-C and gemcitabine markedly induced p53 accumulation as well as increased levels of phospho-p53 (Ser15/Ser20/Ser46) and induced its binding to a consensus p53 response element. Despite robust activation of p53 by T-ara-C and gemcitabine, we found that wild-type and p53-/- HCT 116 cells exhibited almost equivalent sensitivity towards these nucleosides. Examination of p73 revealed that T-ara-C and gemcitabine markedly increased p73 protein levels and p73 DNA-binding activities in both p53-/- and wild-type cells. Furthermore, T-ara-C- and gemcitabine-induced increases in p73 levels occur due to a decrease in p73 protein turnover. RNA interference studies show that nucleoside-induced p73 increases are independent of c-Abl, a nucleoside-activated kinase recently implicated in p73 stabilization. HCT 116 lines, wherein the downstream p53/p73 targets Bax and PUMA (p53 up-regulated modulator of apoptosis) were deleted, were less sensitive to T-ara-C and gemcitabine. Together, these studies indicate that c-Abl-independent p73 stabilization pathways could account for the p53-independent mechanisms in nucleoside-induced apoptosis.
authors.affiliation: Department of Biochemistry and Molecular Biology, Drug Discovery Division, Southern Research Institute, 2000 Ninth Avenue South, Birmingham, AL 35205, USA. Thottassery@sri.org
authors.forename: Jaideep V
authors.initials: JV
authors.lastname: Thottassery
authors.forename: Louise
authors.initials: L
authors.lastname: Westbrook
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Someya
authors.forename: William B
authors.initials: WB
authors.lastname: Parker
mesh_terms: D017209:Apoptosis; D001087:Arabinonucleosides / Q000627:therapeutic use*; D002277:Carcinoma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D017353:Gene Deletion; D016147:Genes, Tumor Suppressor; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D016315:Proto-Oncogene Proteins c-abl / Q000235:genetics / Q000378:metabolism*; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D015854:Up-Regulation; D000093542:Gemcitabine
chemical_list: D001087:Arabinonucleosides; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D003841:Deoxycytidine; D011065:Poly(ADP-ribose) Polymerases; D016315:Proto-Oncogene Proteins c-abl; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C411255:4'-thio-arabinofuranosylcytosine; D000093542:Gemcitabine