Reorganization of actin in the nucleus of HL-60 and K-562 cell lines treated with cytostatic drugs.

A Grzanka PhD^a,b, D Grzanka MD^b, D Smoliński PhD^c, M Orlikowska MSc^b

^aInstitute of Biology and Environment Protection, Kazimierz Wielki University, Bydgoszcz, Poland, ^bDepartment of Clinical Pathomorphology, The Ludwik Rydygier Medical University in Bydgoszcz, The Ludwik Rydygier Medical, Poland, ^cDepartment of Cell Biology, Nicolaus Copernicus University, Toruń, Poland

AIM: For last decades the presence of nuclear actin has been heavily debated, but recent data have clearly showed that actin is present in the nucleus. The problem is no longer the presence of actin in the nucleus but intranuclear localization and its function. Here we identify the distribution pattern of actin in the nucleus of HL-60 and K-562 cell lines treated with etoposide, doxorubicin and taxol especially with chromatin reorganization. METHODS: The distribution of F-actin was analysed by fluorescence microscopy. Actin was also studied by confocal microscopy and at the ultrastructural level. F-actin was labeled with phalloidin conjugated to rhodamine (TRITC). To demonstrate actin at the ultrastructural level, a postembedding streptavidin-gold method was used. The distribution of F-actin has been studied also in isolated nuclei. RESULTS: We detected F-actin in the nucleus of cells in both studied lines independently of the cytostatic drugs used. F-actin was seen in the center of the nucleus what can be labeling of the nucleoli by phalloidin. Using confocal microscopy distinct tracts of F-actin was observed from nucleoli to the nuclear envelope. Actin at the ultrastructural level was observed not only in treated cells but also in control ones. In control cells and with lower doses of cytostatic actin was observed in the nucleolus or around and scattered throughout the nucleus often resembling tracts observed by confocal microscope and very close to nuclear envelope. HL-60 cell line more than K-562 treated with 200 μM etoposide; 5, 10 μM doxorubicin and 2-10 μM taxol showed cells with characteristic features of apoptosis at the ultrastructural level. Intense immunogold labeling for actin was often seen in nucleus of HL-60 cells with compaction and margination of chromatin. In K-562 cells more intense labeling was often found in the cytoplasm of the cells. In an isolated nuclei the intense labeling was more often also observed in HL-60 cells. Positive labeling for actin was not found after control incubations. CONCLUSIONS: Actin is present in the nucleus of studied cells. Our results suggest that actin is necessary for chromatin reorganization during the process of apoptosis.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 895 (Chemotherapy response).