title: Retroviral vectors for establishing tetracycline-regulated gene expression in an otherwise recalcitrant cell line.
abstract: BACKGROUND
  Tetracycline-regulated systems have been used to control the expression of heterologous genes in such diverse organisms as yeast, plants, flies and mice. Adaptation of this prokaryotic regulatory system avoids many of the problems inherent in other inducible systems. There have, however, been many reports of difficulties in establishing functioning stable cell lines due to the cytotoxic effects of expressing high levels of the tetracycline transactivator, tTA, from a strong viral promoter.
  
  
  RESULTS
  Here we report the successful incorporation of tetracycline-mediated gene expression in a mouse mammary epithelial cell line, HC11, in which conventional approaches failed. We generated retroviruses in which tTA expression was controlled by one of three promoters: a synthetic tetracycline responsive promoter (TRE), the elongation factor 1-alpha promoter (EF1alpha) or the phosphoglycerate kinase-1 promoter (PGK), and compared the resulting cell lines to one generated using a cytomegalovirus immediate early gene promoter (CMV). In contrast to cells produced using the CMV and PGK promoters, those produced using the EF1alpha and TRE promoters expressed high levels of beta-galactosidase in a tetracycline-dependent manner.
  
  
  CONCLUSIONS
  These novel retroviral vectors performed better than the commercially available system and may have a more general utility in similarly recalcitrant cell lines.
authors.affiliation: Section of Gene Function and Regulation, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, United Kingdom. pakenny@lbl.gov
authors.forename: Paraic A
authors.initials: PA
authors.lastname: Kenny
authors.forename: Tariq
authors.initials: T
authors.lastname: Enver
authors.forename: Alan
authors.initials: A
authors.lastname: Ashworth