title: BNIP3 is essential for mediating 6-thioguanine- and 5-fluorouracil-induced autophagy following DNA mismatch repair processing.
abstract: DNA mismatch repair (MMR) processes the chemically induced mispairs following treatment with clinically important nucleoside analogs such as 6-thioguanine (6-TG) and 5-fluorouracil (5-FU). MMR processing of these drugs has been implicated in activation of a prolonged G2/M cell cycle arrest for repair and later induction of apoptosis and/or autophagy for irreparable DNA damage. In this study, we investigated the role of Bcl2 and adenovirus E1B Nineteen-kilodalton Interacting Protein (BNIP3) in the activation of autophagy, and the temporal relationship between a G2/M cell cycle arrest and the activation of BNIP3-mediated autophagy following MMR processing of 6-TG and 5-FU. We found that BNIP3 protein levels are upregulated in a MLH1 (MMR(+))-dependent manner following 6-TG and 5-FU treatment. Subsequent small-interfering RNA (siRNA)-mediated BNIP3 knockdown abrogates 6-TG-induced autophagy. We also found that p53 knockdown or inhibition of mTOR activity by rapamycin cotreatment impairs 6-TG- and 5-FU-induced upregulation of BNIP3 protein levels and autophagy. Furthermore, suppression of Checkpoint kinase 1 (Chk1) expression with a subsequent reduction in 6-TG-induced G2/M cell cycle arrest by Chk1 siRNA promotes the extent of 6-TG-induced autophagy. These findings suggest that BNIP3 mediates 6-TG- and 5-FU-induced autophagy in a p53- and mTOR-dependent manner. Additionally, the duration of Chk1-activated G2/M cell cycle arrest determines the level of autophagy following MMR processing of these nucleoside analogs.
authors.affiliation: Department of Radiation Oncology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Xuehuo
authors.initials: X
authors.lastname: Zeng
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Kinsella
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001343:Autophagy / Q000187:drug effects / Q000235:genetics*; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics; D053843:DNA Mismatch Repair / Q000187:drug effects / Q000235:genetics*; D005472:Fluorouracil / Q000494:pharmacology*; D045325:HCT116 Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013866:Thioguanine / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; C090121:BNIP3 protein, human; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D051025:bcl-Associated Death Protein; D058570:TOR Serine-Threonine Kinases; D013866:Thioguanine; D005472:Fluorouracil