title: Specific detection of OCT3/4 isoform A/B/B1 expression in solid (germ cell) tumours and cell lines: confirmation of OCT3/4 specificity for germ cell tumours.
abstract: BACKGROUND
  OCT3/4 (POU5F1) is an established diagnostic immunohistochemical marker for specific histological variants of human malignant germ cell tumours (GCTs), including the seminomatous types and the stem cell component of non-seminomas, known as embryonal carcinoma. OCT3/4 is crucial for the regulation of pluripotency and the self-renewal of normal embryonic stem- and germ cells. Detection of expression of this transcription factor is complicated by the existence of multiple pseudogenes and isoforms. Various claims have been made about OCT3/4 expression in non-GCTs, possibly related to using nonspecific detection methods. False-positive findings undermine the applicability of OCT3/4 as a specific diagnostic tool in a clinical setting. In addition, false-positive findings could result in misinterpretation of pluripotency regulation in solid somatic cancers and their stem cells. Of the three identified isoforms--OCT4A, OCT4B and OCT4B1--only OCT4A proved to regulate pluripotency. Up until now, no convincing nuclear OCT4A protein expression has been shown in somatic cancers or tissues.
  
  
  METHODS
  This study investigates expression of the various OCT3/4 isoforms in GCTs (both differentiated and undifferentiated) and somatic (non-germ cell) cancers, including representative cell lines and xenografts.
  
  
  RESULTS
  Using specific methods, OCT4A and OCT4B1 are shown to be preferentially expressed in undifferentiated GCTs. The OCT4B variant shows no difference in expression between GCTs (either differentiated or undifferentiated) and somatic cancers. In spite of the presence of OCT4A mRNA in somatic cancer-derived cell lines, no OCT3/4 protein is detected. Significant positive correlations between all isoforms of OCT3/4 were identified in both tumours with and without a known stem cell component, possibly indicating synergistic roles of these isoforms.
  
  
  CONCLUSIONS
  This study confirms that OCT4A protein only appears in seminomatous GCTs, embryonal carcinoma and representative cell lines. Furthermore, it emphasises that in order to correctly assess the presence of functional OCT3/4, both isoform specific mRNA and protein detection are required.
authors.affiliation: Department of Pathology, Josephine Nefkens Institute, Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: Rijlaarsdam
authors.forename: H A D M
authors.initials: HA
authors.lastname: van Herk
authors.forename: A J M
authors.initials: AJ
authors.lastname: Gillis
authors.forename: H
authors.initials: H
authors.lastname: Stoop
authors.forename: G
authors.initials: G
authors.lastname: Jenster
authors.forename: J
authors.initials: J
authors.lastname: Martens
authors.forename: G J L H
authors.initials: GJ
authors.lastname: van Leenders
authors.forename: W
authors.initials: W
authors.lastname: Dinjens
authors.forename: A M
authors.initials: AM
authors.lastname: Hoogland
authors.forename: M
authors.initials: M
authors.lastname: Timmermans
authors.forename: L H J
authors.initials: LH
authors.lastname: Looijenga
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism*; D018236:Carcinoma, Embryonal / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D008297:Male; D009373:Neoplasms, Germ Cell and Embryonal; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011544:Pseudogenes; D012333:RNA, Messenger / Q000378:metabolism; D018239:Seminoma / Q000378:metabolism; D012680:Sensitivity and Specificity
chemical_list: D014408:Biomarkers, Tumor; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; D020033:Protein Isoforms; D012333:RNA, Messenger