Trypanosomes are parasites that cycle between the insect host (procyclic form) and mammalian host (bloodstream form). These parasites lack conventional transcription regulation, including factors that induce the unfolded protein response (UPR). However, they possess a stress response mechanism, the spliced leader RNA silencing (SLS) pathway. SLS elicits shut-off of spliced leader RNA (SL RNA) transcription by perturbing the binding of the transcription factor tSNAP42 to its cognate promoter, thus eliminating trans-splicing of all mRNAs. Induction of endoplasmic reticulum (ER) stress in procyclic trypanosomes elicits changes in the transcriptome similar to those induced by conventional UPR found in other eukaryotes. The mechanism of up-regulation under ER stress is dependent on differential stabilization of mRNAs. The transcriptome changes are accompanied by ER dilation and elevation in the ER chaperone, BiP. Prolonged ER stress induces SLS pathway. RNAi silencing of SEC63, a factor that participates in protein translocation across the ER membrane, or SEC61, the translocation channel, also induces SLS. Silencing of these genes or prolonged ER stress led to programmed cell death (PCD), evident by exposure of phosphatidyl serine, DNA laddering, increase in reactive oxygen species (ROS) production, increase in cytoplasmic Ca2+, and decrease in mitochondrial membrane potential, as well as typical morphological changes observed by transmission electron microscopy (TEM). ER stress response is also induced in the bloodstream form and if the stress persists it leads to SLS. We propose that prolonged ER stress induces SLS, which serves as a unique death pathway, replacing the conventional caspase-mediated PCD observed in higher eukaryotes.

Loss of normal p53 function was found frequently to interfere with response of cancer cells to conventional anticancer therapies. Since more than half of all human cancers possess p53 mutations, we decided to explore the involvement of mutant p53 in drug induced apoptosis. To further evaluate the relationship between the p53-dependent and p53-independent apoptotic pathways, and to elucidate the function of mutant p53 in modulating these processes, we investigated the role of a p53 temperature-sensitive (ts) mutant in a number of apoptotic pathways induced by chemotherapeutic drugs that are currently used in cancer therapy. To that end, we studied the M1/2, myeloid p53 non-producer cells, and M1/2-derived temperature-sensitive mutant p53 expressing clones. Apoptosis caused by DNA damage induced with g-irradiation, doxorubicin or cisplatin, was enhanced in cells expressing wild type p53 as compared to that seen in parental p53 non-producer cells; mutant p53 expressing clones were found to be more resistant to apoptosis induced by these factors. Actinomycin D, a potent inhibitor of transcription, as well as a DNA damaging agent, abrogated the restraint apoptosis mediated by mutant p53. These observations suggest that while loss of wild type p53 function clearly reduces the rate of apoptosis, p53 mutations may result in a gain of function which signi®cantly interferes with chemotherapy induced apoptosis. Therefore, to achieve a successful cancer therapy, it is critical to consider the speci®c relationship between a given mutation in p53 and the chemotherapy selected.

The p53 tumor suppressor that plays a central role in the cellular response to genotoxic stress was suggested to be associated with the DNA repair machinery which mostly involves nucleotide excision repair (NER). In the present study we show for the first time that p53 is also directly involved in base excision repair (BER). These experiments were performed with p53 temperature-sensitive (ts) mutants that were previously studied in in vivo experimental models. We report here that p53 ts mutants can also acquire wild-type activity under in vitro conditions. Using ts mutants of murine and human origin, it was observed that cell extracts overexpressing p53 exhibited an augmented BER activity measured in an in vitro assay. Depletion of p53 from the nuclear extracts abolished this enhanced activity. Together, this suggests that p53 is involved in more than one DNA repair pathway.z 1999 Federation of European Biochemical Societies.

The present study examined whether the ability of mutant p53 to block apoptosis depended on its transcriptional activity. A core domain mutant p53 (143 Val to Ala), in which two N‐terminal residues (22 and 23) essential for transactivation were also mutated (Leu to Glu and Trp to Ser, respectively), was examined. While p53 containing only the core mutation efficiently interfered with drug‐induced apoptosis, further modification at the N‐terminus abolished this blocking activity. Furthermore, expression of c‐myc, a suggested target for core mutant p53 transactivation, was elevated in the core mutant p53‐expressing cells, but was abolished in the presence of the transcription‐deficient p53 core mutant. In addition, wild‐type p53, mutated in the N‐terminus (residues 22 and 23), was unable to induce apoptosis by itself. Nevertheless, it synergized with drugs in the induction of apoptosis. This suggests that the integrity of the N‐terminus is essential for both the activity of wild‐type p53 in apoptosis and for mutant p53‐mediated block of drug‐induced apoptosis. This supports the notion that core p53 mutants act via a gain of function mechanism.

Behavioural variation at the individual level has been shown to play an important role in animal ecology and evolution. Whereas most studies have focused on subadult or adult subjects, neonates have been relatively neglected, despite studies showing that neonates can exhibit consistent inter‐individual differences during early developmental stages. Steroid hormones, including glucocorticoids (e.g. cortisol) and androgens (e.g. testosterone), play a crucial role in foetal development and maturation and could therefore drive neonate behaviour, although this relationship is poorly understood in wild animal populations. Our study addresses these knowledge gaps by investigating the association between neonate fallow deer Dama dama fawn inter‐individual variability in behavioural response to human handling and hair cortisol and testosterone levels. We found strong evidence that individual neonates display repeatable differences in the way they cope with a risky situation during their first days of life, and showed how these differences are linked to cortisol and testosterone levels accumulated in utero. We showed that, when both steroids are included in the same model, neonates with high cortisol and low testosterone levels coped in a more proactive way with human handling (higher heart rate during handling and shorter latency to leave when released) compared to those with low cortisol and high testosterone levels (lower heart rate and longer latency to leave). These results provide novel insights into the proximate mechanism leading to neonate inter‐individual variation in a wild population of large mammals. A free Plain Language Summary can be found within the Supporting Information of this article.