title: Cisplatin hypersensitivity of testicular germ cell tumors is determined by high constitutive Noxa levels mediated by Oct-4.
abstract: Testicular germ cell tumors (TGCT) are considered a paradigm of chemosensitive tumors. Embryonal carcinoma cells represent the pluripotent entity of TGCTs and are characterized by expression of Oct-4, a key regulator of pluripotency and a determinant of their inherent hypersensitivity to cisplatin. However, the mechanisms underlying this Oct-4-mediated sensitivity are poorly understood. We previously showed that p53 is a major player in cisplatin hypersensitivity and therefore investigated whether Oct-4 may directly affect p53 activity. Despite a significant decrease in sensitivity, depletion of Oct-4 neither did alter cisplatin-induced transactivation of p53 target genes nor its subcellular localization. These data indicate that, rather than directly modulating p53 activity, Oct-4 provides a cellular context that augments the proapoptotic activity of p53. As mitochondrial priming by the Bcl-2 family is a known determinant of chemosensitivity, we compared the constitutive levels of these proteins in Oct-4-positive and -depleted cells. We identified Noxa as the only Bcl-2 family protein to be highly correlated with Oct-4 status and cisplatin sensitivity. Compared with differentiated cells, constitutive Noxa levels were significantly higher in Oct-4-positive cell lines and cancer patient samples. Furthermore, RNA interference-mediated knockdown of Oct-4 resulted in reduced Noxa transcript, in an almost complete loss of constitutive Noxa protein and decreased cisplatin hypersensitivity to a similar extent as did Noxa depletion. In conclusion, our study indicates that Noxa is a central determinant of hypersensitivity to cisplatin. Oct-4-dependent high constitutive levels of this BH3-only protein prime embryonal carcinoma cells to undergo rapid and massive apoptosis in response to p53 activation.
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology and University of Tuebingen, Auerbachstrasse 112, Stuttgart, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Gutekunst
authors.forename: Thomas
authors.initials: T
authors.lastname: Mueller
authors.forename: Andrea
authors.initials: A
authors.lastname: Weilbacher
authors.forename: Michael A
authors.initials: MA
authors.lastname: Dengler
authors.forename: Jens
authors.initials: J
authors.lastname: Bedke
authors.forename: Stephan
authors.initials: S
authors.lastname: Kruck
authors.forename: Moshe
authors.initials: M
authors.lastname: Oren
authors.forename: Walter E
authors.initials: WE
authors.lastname: Aulitzky
authors.forename: Heiko
authors.initials: H
authors.lastname: van der Kuip
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D009373:Neoplasms, Germ Cell and Embryonal / Q000188:drug therapy* / Q000235:genetics; D050814:Octamer Transcription Factor-3 / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D013736:Testicular Neoplasms / Q000188:drug therapy* / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D050814:Octamer Transcription Factor-3; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D002945:Cisplatin