Carcinogenesis, Vol. 20, No. 6, 1043-1048,
June 1999
© 1999 Oxford University Press
Carcinogenesis |
Okadaic acid mediates p53 hyperphosphorylation and growth arrest in cells with wild-type p53 but increases aberrant mitoses in cells with non-functional p53
1 Department of Molecular and Cellular Biology and
2 Department of Radiation Oncology, Arizona Cancer Center, The University of Arizona, 1501 North Cambell Avenue, Tucson, AZ 85724, USA
The protein phosphatase inhibitor and tumor promoting agent okadaic acid (OA), has been shown previously to induce hyperphosphorylation of p53 protein, which in turn correlated with increased transactivation or apoptotic function. However, how the tumor promotion effects of OA relate to p53 tumor supressor function (or dysfunction) remain unclear. Rat embryonic fibroblasts harboring a temperature-sensitive mouse p53 transgene were treated with 50 nM doses of OA. At the wild-type permissive temperature this treatment resulted in: (i) the hyperphosphorylation of sites within tryptic peptides of the transactivation domain of p53; (ii) an increase in p53 affinity for a p21waf1 promotor oligonucleotide; (iii) an increase in cellular steady state levels of p21waf1 message; (iv) a G2/M cell cycle blockage in addition to the G1/S arrest previously associated with p53; and (v) no increased incidence of apoptosis. On the other hand, OA treatment at the mutated p53 permissive temperature resulted in a relatively high incidence of aberrant mitosis with no upregulation of p21waf1 message. These results suggest that while wild-type p53 blocks the proliferative effects of OA through p21waf1-mediated growth arrest, cells with non-functional p53 cannot arrest and suffer relatively high levels of OA-mediated aberrant mitoses.
Abbreviations: DMSO, dimethyl sulfoxide; OA, okadaic acid.
3 To whom correspondence should be addressed Email: bowdenlab{at}azcc.arizona.edu
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