Cell death in paclitaxel-dependent chinese hamster ovary cells is initiated by the loss of telomeric DNA repeats.

We have reported earlier that cell death in a metastatic murine melanoma cell line induced by paclitaxel and its water-soluble conjugates is mediated through the extensive erosion of telomeric repeats. The purpose of this study was to investigate if loss of telomeric repeats was also involved in cell death of Tax-18 and Tax-2-4, two paclitaxel-requiring mutant Chinese hamster ovary (CHO) cell lines. Tax-18 and Tax-2-4 cells were grown in paclitaxel-free culture medium for 24, 48, 72, and 96 h at 37 degrees C and then harvested for cytological preparations. Control cultures of both cell lines were grown in paclitaxel-supplemented medium and harvested simultaneously. We found that: 1) the frequency of telomeric associations in metaphase preparations was increased with the duration of paclitaxel-depleted culture; 2) Tax-18 cells showed a higher incidence (33.0%) of endoreduplicated metaphases at 24 h of paclitaxel-depleted culture than did Tax-2-4 cells, in which endoreduplicated metaphases were rare; 3) the frequency of polyploid cells was increased after 48, 72, and 96 h of paclitaxel-depleted culture for Tax-18 relative to that for Tax-2-4 cells; 4) both cell lines showed reductions in telomeric signals at chromosomal termini, but not in the interphase nuclei; and 5) both cell lines had shorter terminal telomeric restriction fragments after culture in paclitaxel-depleted medium. These results support our earlier observations and indicate that reduction of telomeric repeats is involved in G2/M cell arrest (endoreduplication) followed by severe DNA fragmentation, and then cell death of two CHO mutant cell lines that require paclitaxel for cell division.

The arcABDC gene cluster, encoding the arginine deiminase pathway of Bacillus licheniformis, and its activation by the arginine repressor argR.

The arginine deiminase pathway enables Bacillus licheniformis to grow anaerobically on arginine. Both the presence of arginine and anaerobiosis are needed to trigger induction of the pathway. In this study we have cloned and sequenced the arc genes encoding the pathway. They appear clustered in an operon-like structure in the order arcA (arginine deiminase), arcB (ornithine carbamoyltransferase), arcD (putative arginine-ornithine antiporter), arcC (carbamate kinase). It was found that B. licheniformis has an arginine repressor, ArgR, homologous to the B. subtilis arginine repressor AhrC. Mutants affected in argR were isolated. These mutants have lost both repression by arginine of the anabolic ornithine carbamoyltransferase and induction of the arginine deiminase pathway. Electrophoretic band shift experiments and DNase I footprinting revealed that in the presence of arginine, ArgR binds to a site upstream from the arc promoter. The binding site is centered 108 nucleotides upstream from the transcription start point and contains a single Arg box.