No abstract

Doxorubicin and other anthracycline compounds exert their anti-cancer effects by causing DNA damage and initiating cell cycle arrest in cancer cells, followed by apoptosis. DNA damage generally activates a p53-mediated pathway to initiate apoptosis by increasing the level of the BH3-only protein, Puma. However, p53-mediated apoptosis in response to DNA damage has not yet been validated in prostate cancers. In the current study, we used LNCaP and PC3 prostate cancer cells, representing wild type p53 and a p53-null model, to determine if DNA damage activates p53-mediated apoptosis in prostate cancers. Our results revealed that PC3 cells were 4 to 8-fold less sensitive than LNCaP cells to doxorubicin-inuced apoptosis. We proved that the differential response of LNCaP and PC3 to doxorubicin was p53-independent by introducing wild-type or dominant negative p53 into PC3 or LNCaP cells, respectively. By comparing several apoptosis-related proteins in both cell lines, we found that Bcl-xl proteins were much more abundant in PC3 cells than in LNCaP cells. We further demonstrated that Bcl-xl protects LNCaP and PC3 cells from doxorubicin-induced apoptosis by using ABT-263, an inhibitor of Bcl-xl, as a single agent or in combination with doxorubicin to treat LNCaP or PC3 cells. Bcl-xl rather than p53, likely contributes to the differential response of LNCaP and PC3 to doxorubicin in apoptosis. Finally, co-immunoprecipitation and siRNA analysis revealed that a BH3-only protein, Bim, is involved in doxorubicin-induced apoptosis by directly counteracting Bcl-xl.

We previously demonstrated that Bim is the main BH3-only protein replacing Bak/Bax from Bcl-xl to activate apoptosis in a p53-independent manner in response to doxorubicin in prostate cancer. However, the comparison of doxorubicin treatment between LNCaP cells carrying p53-wild type and PC3 cells carrying p53-null suggested that p53 might be essential for maximizing apoptosis. Inhibition of ATM did not affect doxorubicin-induced apoptosis. Overexpression of p53 did not affect ABT-263-induced apoptosis and nevertheless, the combination of doxorubicin with ABT-263 induced higher apoptotic responses than did doxorubicin or ABT-263 alone. These results advocated that doxorubicin-induced DNA damage controls p53 function for intensifying apoptosis. Indeed, overexpression of p53 only enhanced apoptosis under conditions of severe DNA damage induced by high concentrations of doxorubicin in LNCaP cells. Immunofluorescence staining showed vague γH2AX foci and enlarged nuclei in LNCaP cells in response to high concentrations of doxorubicin, en route to apoptosis. In addition, our results revealed that the apoptosis in response to DNA replication stress induced by CFS-1686, a catalytic inhibitor of topoisomerase, is p53-independent. Interestingly, the combination of doxorubicin with CFS-1686 generated DNA damage and replication stress simultaneously, resulting in a synergistic apoptotic effect in prostate cancer cells. Thus, we concluded that p53 is a sensor for enhanced apoptosis in response to DNA damage stress, not DNA replication stress, at least in prostate cancer.

We previously reported that p53-mediated apoptosis is determined by severity of DNA damage, not by the level of p53, in doxorubicin-treated prostate cancer cells. In addition to doxorubicin, our results here indicated that camptothecin and bortezomib, which are a topoisomerase 1 poison and a 26 S proteasome inhibitor, respectively, could also induce apoptosis in a p53-dependent manner in prostate cancer. Then, we examined whether p53-mediated apoptosis induced by genotoxic and non-genotoxic stress occur in the same or a different way. By using dominant negative p53 to compete with wild-type p53 in transcription activity, we demonstrated that p53-mediated apoptosis in response to doxorubicin- or camptothecin-induced genotoxic stress is transcription-independent. In contrast, p53-mediated apoptosis from bortezomib-induced stress is transcription-dependent. Interestingly, we also found that doxorubicin-induced p21 expression is activated by p53 in transcription-dependent manner, while camptothecin-induced p21 expression is p53-independent. We then investigated the p53 ratio of nucleus to cytosol corresponding to low and high dose doxorubicin, camptothecin, or bortezomib treatment. The results suggested that p53 translocation from cytoplasm to nucleus actively drives cells toward apoptosis in either transcription-dependent or -independent manner for responding to non-genotoxic or genotoxic stress, respectively.

A Gram-stain-positive strain, BS-W1, was isolated from a traditional fermented ma bamboo shoots (Dendrocalamus latiflorus Munro) product of Taiwan. It was rod-shaped, non-motile, non-haemolytic, asporogenous, facultatively anaerobic, heterofermentative and did not exhibit catalase or oxidase activities. Comparative analysis of 16S rRNA, pheS, rpoA and gyrB gene sequences demonstrated that the novel strain BS-W1 was a member of the genus Lactobacillus. On the basis of 16S RNA gene sequence similarity, the type strains of Lactobacillus oryzae (94.4 % similarity), Lactobacillus acidifarinae (93.8 %), Lactobacillus namurensis (93.7 %) and Lactobacillus zymae (93.7 %) were the closest neighbours to strain BS-W1. The pheS, rpoA and gyrB gene sequence similarities of strain BS-W1 to closely related these species were less than 80.2 %. DNA-DNA reassociation values with these type strains were 21.0-33.8 %. The DNA G+C content was 46.6 mol%. The average nucleotide identity values between BS-W1 and the closest relatives were lower than 70 %. Phenotypic and genotypic features demonstrated that the strain represents a novel species of the genus Lactobacillus, for which the name Lactobacillus bambusae sp. nov. is proposed. The type strain is BS-W1 (=BCRC 80970=NBRC 112377).