title: Chemotherapeutic sensitivity of testicular germ cell tumors under hypoxic conditions is negatively regulated by SENP1-controlled sumoylation of OCT4.
abstract: Testicular germ cell tumors (TGCT) generally respond well to chemotherapy, but tumors that express low levels of the transcription factor OCT4 are associated with chemoresistance and poor prognosis. Hypoxia is known to induce drug resistance in TGCTs; however, the mechanistic basis for reduced expression of OCT4 and drug resistance is unclear. Here we show that hypoxia reduces OCT4 levels and increases the resistance of embryonal carcinoma (EC) cells to cisplatin and bleomycin. Furthermore, we show that the loss of OCT4 expression under hypoxia can be triggered by sumoylation, which was regulated by SUMO1 and the SUMO1 peptidase SENP1. Under hypoxic conditions, overexpression of SUMO1gg (the active form of SUMO1) not only increased the level of sumoylated OCT4 (Su-OCT4), but also decreased the stability of OCT4 protein. In addition, overexpression of SENP1 reduced the Su-OCT4 level induced by SUMO1gg overexpression, thereby maintaining OCT4 levels and enhancing chemosensitivity. Mechanistic investigations revealed that OCT4 sumoylation occurred at K123, as overexpression of an OCT4-K123R mutant effectively reduced the level of Su-OCT4 under hypoxic conditions. Taken together, our results showed that hypoxia reduces OCT4 expression levels in ECs to increase drug resistance and that these effects could be countered to ablate the suppressive effects of hypoxia on chemosensitivity. Our findings also highlight SENP1 as a potential therapeutic target for drug resistant TGCTs.
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Nankang Taipei, Taiwan.
authors.forename: Yu-Chih
authors.initials: YC
authors.lastname: Wu
authors.forename: Thai-Yen
authors.initials: TY
authors.lastname: Ling
authors.forename: Shing-Hwa
authors.initials: SH
authors.lastname: Lu
authors.forename: Hung-Chih
authors.initials: HC
authors.lastname: Kuo
authors.forename: Hong-Nerng
authors.initials: HN
authors.lastname: Ho
authors.forename: Shauh-Der
authors.initials: SD
authors.lastname: Yeh
authors.forename: Chia-Ning
authors.initials: CN
authors.lastname: Shen
authors.forename: Yen-Hua
authors.initials: YH
authors.lastname: Huang
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001761:Bleomycin / Q000494:pharmacology; D015153:Blotting, Western; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D003546:Cysteine Endopeptidases; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D000860:Hypoxia; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D008819:Mice, Nude; D016513:Mice, SCID; D009154:Mutation; D009373:Neoplasms, Germ Cell and Embryonal / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism*; D058207:Sumoylation; D013736:Testicular Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D050814:Octamer Transcription Factor-3; D001761:Bleomycin; D010450:Endopeptidases; C404512:SENP1 protein, human; D003546:Cysteine Endopeptidases; D002945:Cisplatin