No abstract

Anthracycline drugs are widely used for the treatment of solid tumors and leukemia, but the molecular basis of their biological eect is still poorly understood. In the HCT 116 colon carcinoma cell line, which retains a wildtype inducible p53 gene, we show that the anthracycline daunomycin is a potent inducer of p53 and NF-kB transcription factors. Nuclear accumulation of p53 protein occurred because of increased protein stability and enhanced gene expression. In addition, daunomycin induced the p53 promoter through the binding of p50/p65 NF-kB heterodimers to the kB site in the p53 promoter. Under our conditions, the free radical scavengers NAC and PDTC were not able to block NF-kB activation or p53 induction, indicating that reactive oxygen intermediates were not involved in the cellular response to daunomycin stimulation. Overexpression of a stable unresponsive IkBa mutant in HCT116 cells resulted in a complete inhibition of the NF-kB activation but only a partial impairment of the p53 protein accumulation induced by daunomycin. We conclude that the p53-activating signal generated by daunomycin is partially regulated by NF-kB.

The tumor suppressor p53 plays a pivotal role in the cellular response to DNA damage as it controls DNA repair, cell cycle arrest and apoptosis. We studied the autoregulation of human p53 gene transcription in colon cancer cell lines. Wild-type p53 has been shown to autoregulate its own transcription either positively or negatively and probably in a cell-type-speci®c manner. Indeed, a p53 binding site has been described in the human and murine p53 promoters, but a direct binding of wild-type p53 protein to this site has never been reported.In this study, we demonstrated a transactivation of human p53 promoter by wild-type p53 in human colon cancer cells. We identi®ed in the human p53 promoter a novel potential p53-responsive element that binds wildtype p53. Moreover, wild-type p53 protein transactivated a reporter plasmid containing a luciferase gene driven by a minimal promoter harboring this p53 binding site. Finally, as the p53 promoter contains an NF-kB binding site, we demonstrated an additive e ect when NF-kB subunits and p53 protein combined to transactivate the human p53 promoter. Oncogene (2000) 19, 4787 ± 4794.

Mesenchymal stem cells (MSCs) are studied as a cellular source for the treatment of various diseases. In this work, we isolated and cultivated murine bone marrow-derived MSCs. After a first observation of a solid tumor in a mouse injected with these cells, we systematically explored their chromosomal stability. We observed in all the cytogenetically analyzed cases gross chromosomal alterations every time the MSCs went through the senescence crisis while the lymphocytes from the same animals showed a normal chromosome count. This observation was confirmed in different mouse strains, with different culture protocols, and even in short-term cultures after a hematopoietic cell negative immunodepletion performed in order to accelerate the isolation procedure. Therefore, we conclude that murine MSCs display high chromosomal instability and can generate tumors, and that care must be taken before using them for the evaluation of MSC therapeutic potential.

Aminopyropheophorbide (APP) is a second generation of photosensitizer for photodynamic therapy (PDT). We demonstrated that APP strongly absorbed red light and, after being taken up by colon cancer cells (HCT-116 cells), was localized in cytoplasmic and internal membranes but not in mitochondria. The APP-mediated photosensitization was cytotoxic for HCT-116 cells through an induction of apoptosis. Indeed, DNA fragmentation (DNA laddering and terminal deoxyuridine nick-end labeling) and chromatin condensation (4',6-diamidine-2'-phenylindole staining) could be visualized soon after photosensitization. Because nuclear factor (NF)-kappa B is involved in the response to many photosensitizers, we also demonstrated its nuclear translocation in two waves: a rapid and transient one, followed by a slow and sustained phase. The NF-kappa B turned out to be involved in an antiapoptotic response to APP-mediated photosensitization because the HCT-116 cell line expressing the dominant negative mutant of inhibitor-kappa B alpha was more sensitive to apoptosis as measured by DNA fragmentation and caspase activation. These data unambiguously show that a membrane-located photosensitizer can lead to effective apoptosis, reinforcing the idea that PDT can be an effective means to eradicate colon cancer cells.