Nucleic Acids Research, 2000, Vol. 28, No. 11 2234-2241
© 2000 Oxford University Press
Loss-of-function genetics in mammalian cells: the p53 tumor suppressor model
Institute of Child Health, 30 Guilford Street, London WC1 1EH, UK and 1Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
Using an improved system for the functional identification of active antisense fragments, we have isolated antisense fragments which inactivate the p53 tumour suppressor gene. These antisense fragments map in two small regions between nt 350 and 700 and nt 800 and 950 of the coding sequence. These antisense fragments appear to act by inhibition of p53 mRNA translation both in vivo and in vitro. Expression of these antisense fragments overcame the p53-induced growth arrest in a cell line which expresses a thermolabile mutant of p53 and extended the in vitro lifespan of primary mouse embryonic fibroblasts. Continued expression of the p53 antisense fragment contributed to immortalisation of primary mouse fibroblasts. Subsequent elimination of the antisense fragment in these immortalised cells led to restoration of p53 expression and growth arrest, indicating that immortal cells continuously require inactivation of p53. Expression of MDM2 or SV40 large T antigen, but not E7 nor oncogenic ras, overcomes the arrest induced by restoration of p53 expression. Functional inactivation of both p21 and bax (by overexpression of Bcl2), but not either alone, allowed some bypass of p53-induced growth arrest, indicating that multiple transcriptional targets of p53 may mediate its antiproliferative action. The ability to conditionally inactivate and subsequently restore normal gene function may be extremely valuable for genetic analysis of genes for which loss-of-function is involved in specific phenotypes.
* To whom correspondence should be addressed at present address: Wolfson Institute for Biomedical Research, UCL, Cruciform Building, Gower Street, London WC1E 6BT, UK. Tel: +44 171 679 6771; Fax: +44 171 209 0470; Email: d.beach@ucl.ac.uk Present address: Amancio Carnero, Wolfson Institute for Biomedical Research, UCL, Cruciform Building, Gower Street, London WC1E 6BT, UK
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