Genesis and evolution of high-ploidy tumour cells evaluated by means of the proliferation markers p34(cdc2), cyclin B1, PCNA and 3[H]-thymidine.
Although cell polyploidization is not an infrequent event in mammalian cells and is common in tumours, the mechanisms involved are not well understood. Using the murine B16 cell line as a model, we evaluated the role of some key proteins involved in cell cycle progression: p34(cdc2), cyclin B1 and PCNA. By means of flow cytometry, we showed that both in modal- and in high-ploidy subpopulations, almost all cells were p34(cdc2)-positive. In the modal-ploidy subpopulation only 17.1% cells were cyclin B1-positive and 85.6% PCNA-positive; in contrast, in the high-ploidy subpopulation up to 91.8% cells were cyclin B1-positive and 97.3% cells were PCNA-positive (P < 0.001). Immunofluorescence microscopy showed that PCNA was located in the nucleus; p34(cdc2), both in the nucleus and cytoplasm; and cyclin B1 yielded a cytoplasmic spotted pattern with a perinuclear reinforcement. After a 24-h incubation with 3[H]-thymidine followed by withdrawal of the isotope, high-ploidy cells remained labelled 8 days after thymidine withdrawal, in contrast to modal-ploidy cells. Taken together, our results suggest that polyploid cells are not quiescent, their cell cycle is longer than that of the modal-ploidy population, and they maintain cyclin B1 throughout the cycle, which may contribute to their genesis by impeding the exit from mitosis.
Baroja
A
A
Departmento de Fisiología, Facultad de Medicina y Odontología, Universidad del País Vasco, Leioa, Vizcaya, Spain.
de la Hoz
C
C
Alvarez
A
A
Ispizua
A
A
Bilbao
J
J
de Gandarias
J M
JM
D000818:Animals; D015415:Biomarkers; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002455:Cell Division; D019926:Cyclin B; D056744:Cyclin B1; D016213:Cyclins / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism; D005434:Flow Cytometry; D008545:Melanoma / Q000473:pathology; D051379:Mice; D011003:Ploidies; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D015415:Biomarkers; C534700:Ccnb1 protein, mouse; D019926:Cyclin B; D056744:Cyclin B1; D016213:Cyclins; D004273:DNA, Neoplasm; D018809:Proliferating Cell Nuclear Antigen; D016203:CDC2 Protein Kinase