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M Havredaki

Publications and source records attributed to M Havredaki.

22 records · Page 2Linked to original sources
PubMedDate not supplied

Early 5-fluorouracil-induced changes of poly(A) polymerase in HeLa and WISH cells.

5-Fluorouracil (5-FU), a drug with numerous mechanisms of action which has a long-term suppressive effect on human cancer cell proliferation, mediates both partial dephosphorylation and inactivation of poly(A) polymerase (PAP) [EC. 2.7.7.19] as detected by immunoblotting analysis and non-specific enzyme assay, respectively, in human carcinoma HeLa and diploid WISH cells at a concentration of 100 microM. When the same experiment is done in the presence of phosphatase inhibitors, 5-FU-induced partial PAP dephosphorylation is abolished. Moreover, a cell type-modulated, differential response of HeLa cells (5-FU chemosensitive cells) versus WISH cells (drug-resistant diploid cells) is observed. These results suggest that 5-FU induces early direct or indirect changes in the structure and function of PAP and may regulate pre-mRNA cleavage-polyadenylation.

Alkaline Phosphatase↗
PubMedDate not supplied

K562 cell sensitization to 5-fluorouracil- or interferon-alpha-induced apoptosis via cordycepin (3'-deoxyadenosine): fine control of cell apoptosis via poly(A) polymerase upregulation.

K562 cells represent a classical model for the study of drug resistance. Induction of apoptosis is accompanied by concomitant distinct modulations of poly(A) polymerase (PAP) and other proteins involved in mRNA maturation. Recent data suggest the involvement of mRNA stability in the induction of specific apoptosis pathways. In this study we used a specific polyadenylation inhibitor, cordycepin (3-deoxyadenosine), to investigate the involvement of polyadenylation in K562 cell apoptosis and drug resistance. The combination of cordycepin with either 5-fluorouracil or interferon-alpha sensitized chemoresistant K562 cells to apoptosis. This sensitization was followed by distinct PAP modulations before and after the appearance of characteristic apoptosis pointers (DNA laddering, DAPI staining, mitochondrial transmembrane potential). PAP modulations appeared essential for K562 sensitization. mRNA polyadenylation therefore seemed to be involved not only in apoptosis but also in drug resistance. Polyadenylation inhibition by cordycepin under certain conditions sensitized chemoresistant K562 cells to apoptosis and thus polyadenylation could prove to be a fine target for overcoming drug resistance.

Apoptosis↗
PubMedDate not supplied

PAP modulations in Daudi cells and Molt-3 cells treated with etoposide are mutually associated with morphological evidence of apoptosis.

Daudi (B-cell line) and Molt-3 (T-cell line) cells provide a model for the study of apoptosis, the induction of which is often accompanied by concominant modulations of proteins involved in mRNA maturation. One of these proteins is poly(A) polymerase (PAP), which is responsible for mRNA cleavage and polyadenylation. A number of recent reports also suggest involvement of mRNA maturation and stability in the induction of specific pathways of cell apoptosis. In this study we identified PAP activity levels and isoform modulations in two different cell lines (Daudi and Molt-3) and related them to DNA fragmentation (a hallmark of apoptosis) and cell cycle phase specificity in terms of the temporal sequence of events and the time that elapsed between administration of the apoptosis inducer (the widely used anticancer drug etoposide) and the observed effects. Treatment of both cell lines with 20 microg/mL etoposide induced apoptosis after four hours in Molt-3 cells and only after 24 hours in Daudi cells, as revealed by two independent methods. In Daudi cells the PAP activity levels and isoforms were downregulated prior to deltapsim reduction, DNA fragmentation and the morphological changes of the nucleus, whereas in Molt-3 cells no PAP activity and isoform modulations were observed prior to the early hallmarks of apoptosis.

Apoptosis↗