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Cell Biology International (2000) 24, 621–633 (Printed in Great Britain)

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POLYPLOID GIANT CELLS PROVIDE A SURVIVAL MECHANISM FOR p53 MUTANT CELLS AFTER DNA DAMAGE

Timothy M. Illidge^ab,f1, Mark S. Cragg^b, Birgitta Fringes^c, Peggy Olive^d and Jekaterina A. Erenpreisa^e

^aCRC Department of Oncology, Southampton General Hospital, Southampton University, Southampton, SO16 6YD, U.K.
^bTenovus Cancer Research Laboratory, Southampton General Hospital, Southampton University, Southampton, SO16 6YD, U.K.
^cDepartment of Pathology, University of Giessen, Germany
^dTerry Fox Cancer Centre, British Columbia, Vancouver, Canada, V5Z 1L3
^eLaboratory Tumor Cell Biology, Latvian University Biomedicine Centre, Riga, LV-1067, Latvia

Abstract

The relationships between delayed apoptosis, polyploid ‘giant’ cells and reproductive survivors were studied in p53-mutated lymphoma cells after DNA damage. Following severe genotoxic insult with irradiation or chemotherapy, cells arrest at the G2-M cell cycle check-point for up to 5 days before undergoing a few rounds of aberrant mitoses. The cells then enter endoreduplication cycles resulting in the formation of polyploid giant cells. Subsequently the majority of the giant cells die, providing the main source of delayed apoptosis; however, a small proportion survives. Kinetic analyses show a reciprocal relationship between the polyploid cells and the diploid stem line, with the stem line suppressed during polyploid cell formation and restituted after giant cell disintegration. The restituted cell-line behaves with identical kinetics to the parent line, once re-irradiated. When giant cells are isolated and followed in labelling experiments, the clonogenic survivors appear to arise from these cells. These findings imply that an exchange exists between the endocyclic (polyploid) and mitotic (diploid or tetraploid) populations during the restitution period and that giant cells are not always reproductively dead as previously supposed. We propose that the formation of giant cells and their subsequent complex breakdown and subnuclear reorganization may represent an important response of p53-mutated tumours to DNA damaging agents and provide tumours with a mechanism of repair and resistance to such treatments.

Key words: apoptosis, endoreduplication, p53 mutation, giant cells, polyploidy, tumour.

^f1To whom correspondence should be addressed, at CRC Department of Oncology, Southampton General Hospital, Southampton University, SO16 6YD, U.K. E-mail:tmi@soton.ac.uk

Received 11 January 2000; accepted 3 May 2000