The old and the new in p53 functional regulation

Molecular basis of arsenite (As⁺³)-induced acute cytotoxicity in human cervical epithelial carcinoma cells

BACKGROUND

Rapid industrialization is discharging toxic heavy metals into the environment, disturbing human health in many ways and causing various neurologic, cardiovascular, and dermatologic abnormalities and certain types of cancer. The presence of arsenic in drinking water from different urban and rural areas of the major cities of Pakistan, for example, Lahore, Faisalabad, and Kasur, was found to be beyond the permissible limit of 10 parts per billion set by the World Health Organization. Therefore the present study was initiated to examine the effects of arsenite (As(+3)) on DNA biosynthesis and cell death.

METHODS

After performing cytotoxic assays on a human epithelial carcinoma cell line, expression analysis was done by quantitative polymerase chain reaction, western blotting, and flow cytometry.

RESULTS

We show that As(+3) ions have a dose- and time-dependent cytotoxic effect through the activation of the caspase-dependent apoptotic pathway. In contrast to previous research, the present study was designed to explore the early cytotoxic effects produced in human cells during exposure to heavy dosage of As(+3) (7.5 µg/ml). Even treatment for 1 h significantly increased the mRNA levels of p21 and p27 and caspases 3, 7, and 9. It was interesting that there was no change in the expression levels of p53, which plays an important role in G2/M phase cell cycle arrest.

CONCLUSION

Our results indicate that sudden exposure of cells to arsenite (As(+3)) resulted in cytotoxicity and mitochondrial-mediated apoptosis resulting from up-regulation of caspases.

Antisense makes sense in engineered regenerative medicine

The use of antisense strategies such as ribozymes, oligodeoxynucleotides (ODNs) and small interfering RNA (siRNA) in gene therapy, in conjunction with the use of stem cells and tissue engineering, has opened up possibilities in curing degenerative diseases and injuries to non-regenerating organs and tissues. With their unique ability to down-regulate or silence gene expression, antisense oligonucleotides are uniquely suited in turning down the production of pathogenic or undesirable proteins and cytokines. Here, we review the antisense strategies and their applications in regenerative medicine with a focus on their efficacies in promoting cell viability, regulating cell functionalities as well as shaping an optimal microenvironment for therapeutic purposes.

P53 autoantibodies in sera from Danish ovarian cancer patients and their correlation with clinical data and prognosis

The p53 gene, a tumour suppressor gene located on the short arm of chromosome 17 (17p13), is frequently mutated in various human tumours. Accumulation of p53 protein in neoplastic cells and its release following tumour necrosis can lead to development of circulating autoantibodies (AAb) against p53. Earlier studies of ovarian cancer (OC) patients reported different frequencies of p53 AAb and conclusions regarding the clinical and prognostic value of these AAb have not been in agreement. We therefore analysed for the presence of p53 AAb in a total of 227 preoperative serum samples from 193 OC patients and 34 patients with ovarian borderline tumours, and, in addition, serum samples from 86 healthy controls. An enzyme-linked immunosorbent assay (ELISA) was used to measure serum IgG antibodies against p53. The p53 protein used in the assay was produced as a hexahistidine-tagged fusion protein by baculovirus-infected Spodoptera frugiperda cells. Cut-off values for p53 AAb were evaluated, and correlations of p53 AAb with clinical-, biochemical data and survival were examined. We found a low sensitivity for p53 AAb alone, and no major additional effect of the detection rate of CA125 was found. No significant associations were found between p53 AAb and clinical stage, age, histological subtype and radicality after primary surgery. In contrast, we found significantly elevated CA125 levels in p53 AAb-positive patients compared to lower CA125 levels in p53 AAb-negative patients (p=0.003). No significant differences were found between p53 AAb-positive and p53 AAb-negative patients in the univariate and multivariate survival analyses. In conclusion, in a screening study for OC serum p53 AAb levels are of no diagnostic value, even if combined with the tumour marker CA125. The presence of increased serum p53 AAb in patients with diagnosed OC could not be correlated with any clinical data and preoperative serum p53 AAb status had no evident value.

p53 is associated with cellular microtubules and is transported to the nucleus by dynein

Here we show that p53 protein is physically associated with tubulin in vivo and in vitro, and that it localizes to cellular microtubules. Treatment with vincristine or paclitaxel before DNA-damage or before leptomycin B treatment reduces nuclear accumulation of p53 and expression of mdm2 and p21. Overexpression of dynamitin or microinjection of anti-dynein antibody before DNA damage abrogates nuclear accumulation of p53. Our results indicate that transport of p53 along microtubules is dynein-dependent. The first 25 amino acids of p53 contain the residues that are essential for binding to microtubules. We propose that functional microtubules and the dynein motor protein participate in transport of p53 and facilitate its accumulation in the nucleus after DNA damage.

Cell-cycle control in cell-biomaterial interactions: expression of p53 and Ki67 in human umbilical vein endothelial cells in direct contact and extract testing of biomaterials

Current biocompatibility testing involves the demonstration of cell proliferation, which is usually interpreted as a sign of positive biocompatibility when the materials sustain cell proliferation. As the field of biomaterials research is rapidly moving toward tissue-engineered devices and hybrid organs, control of cell function has become a main topic. Cell function, which involves specific differentiation pathways, cannot be separated from cell-cycle control. The study of cell-cycle control is an important extension of routine proliferation assays and has extensive roots in developmental and tumor biology. We studied the expression of the tumour suppressor gene p53 and the proliferation-associated antigen Ki67 of endothelial cells in response to biomaterial contact. Cells were seeded in six- or 24-well plates, in which one or three 12-mm-diameter biomaterial disks were laid down. After 48- and 72-h incubation periods, cells were processed for flow cytometry, immunofluorescence, or Western blotting. The following materials were used: titanium, NiCr alloy, and CoCr alloy. Cells were also exposed to 24-h (ISO-norm) extracts in 25-cm(2) culture flasks (600, 000 cells) for 24 and 48 h. For extract testing, serially diluted Ni-ion suspensions were also used. Human umbilical vein endothelial cells adhered to metal surfaces and started forming a monolayer within 3 days. Ki67 expression was positive in more than 60% after 2 days and decreased markedly after 3 days of adhesion. During this time cells developed focal contacts and produced a fibronectin matrix. p53 expression could be demonstrated with Western blotting and flow cytometry, but not with immunofluorescence. Differences due to both culturing time and material were found in expression patterns with both methods. Inverse correlations between Ki67 and p53 expression were detected, which are probably based on culture kinetics. The results indicate that expression of p53 and also Ki67 is clearly influenced by biomaterials in direct contact testing, despite the absence of obvious morphological differences. The p53 marker can be used for defining cell function in more detail, although the correlation with specific physiological function has still to be clarified.