Expression of cyclin D1 after treatment with doxorubicin in the HL-60 cell line.

Increased levels of cyclin D1 and amplification of CCND1 gene occur in many types of cancers. We have followed the expression of cyclin D1 after treatment with doxorubicin with reference to cell death and other possible therapeutic implications. The effect of the treatment on the cell cycle, survival, intracellular level (flow cytometry), and intracellular localization of cyclin D1 (fluorescence microscopy) and expression of CCND1 (real-time RT-PCR) was investigated in HL-60 cells. An increase in the fluorescence intensity of cyclin D1 occurred after treatment with 0.15 and 0.3 μM doxorubicin. This tendency was confirmed by real-time RT-PCR. Expression of CCND1 in relation to the reference gene PBGD was increased in cells exposed to 0.15 μM doxorubicin. Concomitantly, some alterations in the regulation of the G0/G1, S, and G2/M checkpoints occurred, accompanied by changes in the polyploid fraction of the population. This was particularly evident at 0.3 μM doxorubicin, at which concentration the rate of cell death was also clearly higher. In conclusion, depending on the concentration used, alterations in cell death and the number of S, G2/M, and polyploid cells may correspond with cyclin D1 levels. This, in turn, may reflect an important role of the protein as one of the possible survival/point-of-no-return regulators dependent on its concentration, which seems especially plausible in the context of more prominent cell death in the above-mentioned fractions of cells.