Institutional guidelines on maternal care and investigations following antepartum stillbirth - a national survey

Background

Antepartum stillbirth, i.e., intrauterine fetal death (IUFD) above 24 weeks of gestation, occurs with a prevalence of 2.4–3.1 per 1000 live births in Central Europe. In order to ensure highest standards of treatment and identify causative and associated (risk) factors for fetal death, evidence-based guidelines on clinical practice in such events are recommended. Owing to a lack of a national guideline on maternal care and investigations following stillbirth, we, hereby, sought to assess the use of institutional guidelines and clinical practice after IUFD in Austrian maternity units.

Methods

A national survey with a paper-based 12-item questionnaire covering demographic variables, local facilities and practice, obstetrical care and routine post-mortem work-up following IUFD was performed among all Austrian secondary and tertiary referral hospitals with maternity units (n = 75) between January and July 2019. Statistical tests were conducted using Chi² and Fisher’s Exact test, respectively. Univariate logistic regression analyses were performed to calculate odds ratio (OR) with a 95% confidence interval (CI).

Results

46 (61.3%) obstetrical departments [37 (80.4%) secondary; 9 (19.6%) tertiary referral hospitals] participated in this survey, of which 17 (37.0%) have implemented an institutional guideline. The three most common investigations always conducted following stillbirth are placental histology (20.9%), fetal autopsy (13.1%) and maternal antibody screen (11.5%). Availability of an institutional guideline was not significantly associated with type of hospital, on-site pathology department, or institutional annual live and stillbirth rates. Post-mortem consultations only in cases of abnormal investigations following stillbirth were associated with lower odds for presence of such guideline [OR 0.133 (95% CI 0.018–0.978); p = 0.047]. 26 (56.5%) departments consider a national guideline necessary.

Conclusions

Less than half of the surveyed maternity units have implemented an institutional guideline on maternal care and investigations following antepartum stillbirth, independent of annual live and stillbirth rate or type of referral centre.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-03995-z.

The onset of p53 loss of heterozygosity is differentially induced in various stem cell types and may involve the loss of either allele

p53 loss of heterozygosity (p53LOH) is frequently observed in Li-Fraumeni syndrome (LFS) patients who carry a mutant (Mut) p53 germ-line mutation. Here, we focused on elucidating the link between p53LOH and tumor development in stem cells (SCs). Although adult mesenchymal stem cells (MSCs) robustly underwent p53LOH, p53LOH in induced embryonic pluripotent stem cells (iPSCs) was significantly attenuated. Only SCs that underwent p53LOH induced malignant tumors in mice. These results may explain why LFS patients develop normally, yet acquire tumors in adulthood. Surprisingly, an analysis of single-cell sub-clones of iPSCs, MSCs and ex vivo bone marrow (BM) progenitors revealed that p53LOH is a bi-directional process, which may result in either the loss of wild-type (WT) or Mut p53 allele. Interestingly, most BM progenitors underwent Mutp53LOH. Our results suggest that the bi-directional p53LOH process may function as a cell-fate checkpoint. The loss of Mutp53 may be regarded as a DNA repair event leading to genome stability. Indeed, gene expression analysis of the p53LOH process revealed upregulation of a specific chromatin remodeler and a burst of DNA repair genes. However, in the case of loss of WTp53, cells are endowed with uncontrolled growth that promotes cancer.

p53 counteracts reprogramming by inhibiting mesenchymal-to-epithelial transition

The process of somatic cell reprogramming is gaining increasing interest as reprogrammed cells are considered to hold a great therapeutic potential. However, with current technologies this process is relatively inefficient. Recent studies reported that inhibition of the p53 tumor suppressor profoundly facilitates reprogramming and attributed this effect to the ability of p53 to restrict proliferation and induce apoptosis. Given that mesenchymal-to-epithelial transition (MET) was recently shown to be necessary for reprogramming of fibroblasts, we investigated whether p53 counteracts reprogramming by affecting MET. We found that p53 restricts MET during the early phases of reprogramming and that this effect is primarily mediated by the ability of p53 to inhibit Klf4-dependent activation of epithelial genes. Moreover, transcriptome analysis revealed a large transcriptional signature enriched with epithelial genes, which is markedly induced by Klf4 exclusively in p53(-/-) cells. We also found that the expression of the epithelial marker E-Cadherin negatively correlates with p53 activity in a variety of mesenchymal cells even before the expression of reprogramming factors. Finally, we demonstrate that the inhibitory effect of p53 on MET is mediated by p21. We conclude that inhibition of the p53-p21 axis predisposes mesenchymal cells to the acquisition of epithelial characteristics and renders them more prone to reprogramming. Our study uncovers a novel mechanism by which p53 restrains reprogramming and highlights the role of p53 in regulating cell plasticity.

Understanding wild-type and mutant p53 activities in human cancer: new landmarks on the way to targeted therapies

Three decades of p53 research have led to many advances in understanding the basic biology of normal and cancer cells. Nonetheless, the detailed functions of p53 in normal cells, and even more so in cancer cells, remain obscure. A major breakthrough is the realization that mutant p53 has a life of its own: it contributes to cancer not only through loss of activity, but also through gain of specific 'mutant functions'. This new focus on mutant p53 is the rationale behind the meeting series dedicated to advances on mutant p53 biology. This review provides an overview of results presented at the Fourth International Workshop on Mutant p53, held in Akko, Israel in March 2009. New roles and functions of p53 relevant for tumor suppressions were presented, including the regulation of microRNAs networks, the modulation of cell-stroma interactions and the induction of senescence. A main focus of the meeting was the rapidly growing body of knowledge on autonomous properties of mutant p53 and on their oncogenic 'gain of function' impact. Importantly, the meeting highlighted that, 30 years after p53 discovery, research on mutant p53 is entering the clinical and translational era. Two major steps forward in this respect are a better understanding of the active mechanism of small drugs targeting mutant p53 in tumor cells and an improved definition of the prognostic and predictive value of mutant p53 in human cancer.

Mutant p53(R175H) upregulates Twist1 expression and promotes epithelial-mesenchymal transition in immortalized prostate cells

A mutation within one allele of the p53 tumor suppressor gene can inactivate the remaining wild-type allele in a dominant-negative manner and in some cases can exert an additional oncogenic activity, known as mutant p53 'gain of function' (GOF). To study the role of p53 mutations in prostate cancer and to discriminate between the dominant-negative effect and the GOF activity of mutant p53, we measured, using microarrays, the expression profiles of three immortalized prostate epithelial cultures expressing wild-type, inactivated p53 or mutated p53. Analysis of these gene expression profiles showed that both inactivated p53 and p53(R175H) mutant expression resulted in the upregulation of cell cycle progression genes. A second group, which was upregulated exclusively by mutant p53(R175H), was predominantly enriched in developmental genes. This group of genes included the Twist1, a regulator of metastasis and epithelial-mesenchymal transition (EMT). Twist1 levels were also elevated in metastatic prostate cancer-derived cell line DU145, in immortalized lung fibroblasts and in a subset of lung cancer samples, all in a mutant p53-dependent manner. p53(R175H) mutant bearing immortalized epithelial cells showed typical features of EMT, such as higher expression of mesenchymal markers, lower expression of epithelial markers and enhanced invasive properties in vitro. The mechanism by which p53(R175H) mutant induces Twist1 expression involves alleviation of the epigenetic repression. Our data suggest that Twist1 expression might be upregulated following p53 mutation in cancer cells.

Upregulation of survivin during immortalization of nontransformed human fibroblasts transduced with telomerase reverse transcriptase

These investigations demonstrate that expression of the inhibitor of apoptosis family member, survivin, is dramatically increased during immortalization of nontransformed human fibroblasts that were transduced with telomerase reverse transcriptase (hTERT). Expression of survivin in immortalized fibroblasts peaked during G(2)/M phase of the cell cycle. However, the upregulation of survivin was dissociated from the rate of proliferation and proportion of G(2)/M cells. Depletion of survivin from immortal fibroblasts increased sensitivity to stress-induced apoptosis and resulted in an accumulation of cells with 4N DNA content. Conversely, overexpression of survivin in mortal fibroblasts conferred resistance to apoptosis. In contrast, very low levels of survivin in proliferating parental fibroblasts had no bearing on sensitivity to apoptosis. The upregulation of survivin did not appear to be a direct consequence of hTERT transduction. However, repression of hTERT resulted in the rapid downregulation of survivin in telomerase-immortalized fibroblasts and tumor cell lines, but not in cells immortalized via an Alternative Lengthening of Telomeres mechanism. These results have important therapeutic implications, as telomerase and survivin are both broadly expressed in human cancers. Selection during the immortalization process for cells expressing high levels of survivin may account for the abundance of survivin in diverse tumor types.

The expression of the DeltaNp73beta isoform of p73 leads to tetraploidy

The p73 locus gene has a complex structure encoding a plethora of isoforms. The different DeltaN truncated isoforms of p73 may exert different activities depending on the cellular context. The beta isoform of DeltaNp73 seems to have a particular pattern of action even if its role in cell cycle and mitosis is still under investigation. To gain further knowledge of DeltaNp73beta's function, we investigated the effects of its over-expression in tumour cellular models, using the tetracycline-inducible expression system. In the human lung carcinoma cell line H1299, DeltaNp73beta over-expression resulted in suppression of cell growth and in cell death. Surprisingly stable over-expression of DeltaNp73beta impaired the genomic stability of tumour cells, leading to the formation of tetraploid cells. The cells become enlarged and multinucleate, with incorrect mitotic figures, and died by apoptotic-independent pathways. Our data suggest that DeltaNp73beta-induced aberrant mitosis evades the control of the mitotic spindle assay checkpoint, leading to tetraploidy and cell death through mitotic catastrophe rather than apoptosis. The various C-terminal regions of DeltaNp73 may influence the final cellular phenotype and we assume that the beta one in particular could be important in both cell growth control and regulation of mitosis.

Amyloid-beta precursor-like protein APLP1 is a novel p53 transcriptional target gene that augments neuroblastoma cell death upon genotoxic stress

The tumor suppressor p53 is a key modulator of the cellular stress response, inducing cell-cycle arrest, apoptosis, senescence and cell differentiation. To evaluate further the molecular mechanism underlying p53 function, the transcriptional profiles of proliferating and senescent WI-38 cells, both wild-type p53 expressers and counterparts with an inactivated p53, were compared by DNA microarray analysis. In particular, the amyloid-beta precursor-like protein 1 (APLP1) is induced in senescent cells in a p53-dependent manner. APLP1 was confirmed to be a novel transcriptional target of p53 by in vivo and in vitro characterization of a p53 responsive element found in the first intron of the APLP1 gene locus. APLP1 knockdown experiments demonstrate that APLP1 is required for the proliferation of fibroblastic and epithelial cells. Moreover, depletion of APLP1 expression diminishes stress-induced apoptosis of neural cells, whereas ectopic APLP1 expression augments apoptosis. Based on these data, a mechanism is proposed whereby p53-dependent induction of APLP1 is involved in neural cell death, and which may exacerbate neuronal cell loss in some acute or chronic neurodegenerative disorders.

Transcription regulation by mutant p53

In addition to the loss of wild-type p53 activity, a high percentage of tumor cells accumulate mutant p53 protein isoforms. Whereas the hallmark of the wild-type p53 is its tumor suppressor activities, tumor-associated mutant p53 proteins acquire novel functions enabling them to promote a large spectrum of cancer phenotypes. During the last years, it became clear that tumor-associated mutant p53 proteins are not only distinct from the wild-type p53, but they also represent a heterogeneous population of proteins with a variety of structure-function features. One of the major mechanisms underlying mutant p53 gain of function is the ability to regulate gene expression. Although a large number of specific target genes were identified, the molecular basis for this regulation is not fully elucidated. This review describes the present knowledge about the transcriptional activities of mutant p53 and the mechanisms that might underlie its target gene specificity.

Regulation of AIF expression by p53

The tumor suppressor p53 plays a pivotal role in suppressing tumorigenesis by inducing genomic stability, cell cycle arrest or apoptosis. AIF is a mitochondrial protein, which, upon translocation to the nucleus, can participate in apoptosis, primarily in a caspase-independent contexts. We now report that AIF gene expression is subject to positive transcriptional regulation by p53. Interestingly, unlike most known p53 target genes, the AIF gene is regulated by basal levels of p53, and activation of p53 by genotoxic stress does not result in a substantial further increase in AIF expression. The AIF gene harbors a p53 responsive element, which is bound by p53 within cells. p53 drives efficient induction of large-scale DNA fragmentation, a hallmark of AIF activity. Importantly, caspase-independent death is compromised in cells lacking functional p53, in line with the known role of AIF in this process. Thus, in addition to its documented effects on caspase-dependent apoptosis, p53 may also sensitize cells to caspase-independent death through positive regulation of AIF expression. Moreover, in the absence of overt apoptotic signals, the constitutive induction of AIF by p53 may underpin a cytoprotective maintenance role, based on the role of AIF in ensuring proper mitochondrial function.

Repression of the MSP/MST-1 gene contributes to the antiapoptotic gain of function of mutant p53

Tumor-associated mutant forms of p53 can exert an antiapoptotic gain of function activity, which confers a selective advantage upon tumor cells harboring such mutations. We report that mutant p53 suppresses the expression of the MSP (MST-1/HGFL) gene, encoding the ligand of the receptor tyrosine kinase RON, implicated in a variety of cellular responses. Mutant p53 associates with the MSP gene promoter and represses its transcriptional activity, leading to a decrease in mRNA levels and a subsequent decrease in the levels of secreted MSP protein. Forced downregulation of MSP expression in H1299 cells, derived from a large-cell lung carcinoma, confers increased resistance against etoposide-induced cell death. These antiapoptotic consequences of MSP downregulation seemingly conflict with the well-documented ability of the RON receptor to promote cell survival and tumor progression when aberrantly hyperactive. Yet, they are consistent with the fact that reduced MSP expression was observed in many types of human cancer, including large-cell lung carcinoma. Thus, repression of MSP gene expression by mutant p53 may contribute to oncogenesis in a cell type-specific manner.

p53 is a regulator of macrophage differentiation

While it is well accepted that p53 plays a role in apoptosis, less is known as to its involvement in cell differentiation. Here we show that wild-type p53 facilitates IL-6-dependent macrophage differentiation. Treatment of M1/2 cells expressing the temperature-sensitive p53 143 (Val to Ala) mutant, at the wild-type conformation, facilitated the appearance of mature macrophages that exhibited phagocytic activity. Enhancement of differentiation by the p53 143 (Val to Ala) in the wild-type conformation was coupled with the inhibition of apoptosis induction by this protein. In agreement with previous studies, we found that p53 levels were reduced during p53-dependent macrophage differentiation. This occurred when p53 levels before IL-6 stimuli were high. Interestingly, the p53 143 (Val to Ala) protein, at the mutant conformation, enhanced macrophage differentiation, as did the wild-type conformation, whereas the p53 273 (Arg to His) core mutant exerted an inhibitory effect on this pathway. The transcription-deficient p53 molecules, p53 (22-23) and p53 22,23,143, could not induce p53-dependent differentiation. Moreover, the p53 (22-23) protein inhibited the p53-independent differentiation pathway. Interestingly, the p53 (22-23) protein not only blocked IL-6-mediated differentiation, but also induced significant apoptotic cell death, upon IL-6 stimulation. Taken together, our data show that wild-type p53 enhances macrophage differentiation, while various p53 mutant types exert different effects on this differentiation pathway.

In search of the functions of normal p53 protein

p53 is of major importance in protecting cells from neoplasia. Most human tumours have an abnormal or inactivated p53 protein. Furthermore, when expression of normal p53 is reinstated in cancer cell lines, they undergo growth suppression leading to either cell differentiation or programmed cell death. But is p53 involved in the regulation of normal cell growth and differentiation in vivo? Here, Varda Rotter and colleagues critically assess some recent conflicting data on this issue.

p53 mediates density-dependent growth arrest

While the stress-response-associated importance of the p53 tumor suppressor is well established, recent studies have also linked p53 with several basic parameters in the normal behavior of cells. Here, we present evidence that basal p53 expression in WI38 human embryonic lung fibroblasts restricts growth rate and mediates density-dependent inhibition of growth and the associated G1 phase arrest of the cell cycle by affecting the density-dependent regulation of p16/INK4a. Additionally, we show that prolonged culturing of hTert-immortalized WI38 cells leads to a loss of density-dependent growth inhibition that correlates with p27/KIP deregulation as well as the previously shown INK4a locus silencing, and to an onset of contact-induced, p53-dependent cell death.

Altered subcellular localization of p53 in estrogen-dependent and estrogen-independent breast cancer cells

LCC2, an estradiol-independent tamoxifen (Tax)-resistant subline of MCF-7 human breast cancer cell line, is resistant relatively towards Tax and methotrexate (Mtx). The purpose of the present study is to evaluate the role of p53 in determining this resistance. While MCF-7 is sensitive to and undergoes apoptosis, as determined by propidium iodide stain, by Tax and Mtx, LCC2 is resistant to apoptosis induction by these agents. Both cell lines undergo apoptosis and are sensitive equally to doxorubicin (Adr). p53 cDNA of both sublines was evaluated by polymerase chain reaction (PCR) amplification and sequencing and was found to be of wild-type. p53 mRNA, as well as protein, are elevated markedly in LCC2 as compared to MCF-7 cells. p53 expression was increased by estradiol and Adr, not changed by Mtx, and decreased by Tax and estradiol-deprivation in both sublines. p53 modulation by the various agents, in both sublines, was evaluated by cytochemical staining and subcellular fractionation. This analysis showed that p53 is localized mainly in the nuclear fraction in MCF-7 cells, and in the cytoplasmatic fraction in LCC2 cells. Doxorubicin induced apoptosis in MCF-7 cells along with increase in its nuclear fraction. In contrast, LCC2 underwent apoptosis by Adr despite its cytoplasmatic sequestration. These experiments demonstrate that p53 is sequestered to cytoplasm in the estrogen-independent, Tax-resistant LCC2 cells. However, the differences in apoptotic rate between MCF-7 and LCC2 cells do not seem to be dependent on p53. The LCC2 cell line may serve as a useful model for the study of the mechanism of cytoplasmatic sequestration of wild type (wt) p53, its physiologic consequences, and its relation to estrogen-independence or Tax resistance of breast cancer cells.

Activation of p53 protein by telomeric (TTAGGG)n repeats

Genome instability is a primary factor leading to the activation of the p53 tumor suppressor protein. Telomeric repeat (TR) sequences are also responsible for genome integrity. By capping the termini of the chromosomes, TRs prevent them undergoing nucleolytic degradation, ligation or chromosome fusion. Interestingly, telomere shortening was suggested to activate p53, which in turn may cause primary cells to senesce. In order to elucidate the nature of a possible cross talk between the two, we introduced into cells TRs of defined length and investigated their effect on p53 activation and subsequent cellular response. We found that the introduction of a TR into cells leads to stabilization of the p53 protein. This stabilization was specific to TRs and was not observed in response to exposure of cells to plasmids containing non-TR sequences. p53 stabilization requires the presence of an intact p53 oligomerization domain. TR-activated p53 exhibited enhanced transcriptional activity. Eventually, TRs induced p53-dependent growth suppression, measured as a reduction in colony formation.

p53 is dispensable for apoptosis but controls neurogenesis of mouse dentate gyrus cells following gamma-irradiation

Mammalian cells respond to DNA insults by activating cell-cycle checkpoints. This may result in a temporary cell growth arrest which allows DNA repair before proliferation or induces apoptosis. p53 is one of the main contributors in regulating these activities. To get a better insight on the molecular mechanism underlying these activities we studied the role of p53 in apoptosis and neurogenesis of brain cells from adult p53(+/+) or p53(-/-) mice exposed to gamma-irradiation. Apoptosis and neurogenesis were assessed up to 14 days following the injury. Five-ten hours following gamma-irradiation, cells with TUNEL positive nuclei were identified within the subgranular zone of dentate gyrus (DG) of both p53(+/+) and p53(-/-) mice. At the same time-points, pyknotic and shrinking nuclei were visualized by Hoechst 33258 staining. Furthermore, gamma-irradiation increased the number of proliferating cell nuclear antigen (PCNA) positive cells with a peak at 5-10 h in both animal groups. PCNA immunoreactivity was detected in cells exhibiting condensed nuclei as visualized by Hoechst 33258 staining. Neurogenesis, assessed by mitotic marker p34(cdc2) immunoreactivity, showed a biphasic response to gamma-irradiation both in p53(+/+) and p53(-/-) mice which was characterized by an early inhibition and a delayed stimulation. In p53(-/-) mice, the time required by DG granule cells to recover from the lesion and to stimulate proliferation was significantly shortened in comparison with wild-type mice thus resulting in an accelerated neurogenesis. Our data indicate that following gamma-radiation p53 plays a role in regulating cell-cycle progression rate but it is dispensable for promoting apoptosis of DG granule cells.

The C-terminus of mutant p53 is necessary for its ability to interfere with growth arrest or apoptosis

The ability to suppress wild type p53-independent apoptosis may play an important role in the oncogenicity of p53 mutant proteins. However, structural elements necessary for this activity are unknown. Furthermore, it is unclear whether this mutant p53 mediated inhibition is specific to the apoptotic pathway or a more general suppression of the cellular response to stress. We observed that an unmodified C-terminus was required for the suppression of apoptosis by the p53 135(Ala to Val) oncogenic p53 mutant. It was also required for the novel activity of G2 arrest suppression, the predominant response at low levels of genotoxic stress. These observations are consistent with a model whereby mutant p53 suppressive activity is not specific to the apoptotic pathway, but rather increases the threshold of genotoxic stress needed for a DNA damage response to occur. Furthermore, these observations indicate that it may be possible to selectively kill mutant p53 expressing cells based on the lower sensitivity of their growth arrest response.

Autoimmunity to the p53 protein is a feature of systemic lupus erythematosus (SLE) related to anti-DNA antibodies

The induction of anti-DNA autoantibodies in systemic lupus erythematosus (SLE) patients is problematic because mammalian DNA is poorly immunogenic at best. Here we demonstrate a chain of connected antibodies in SLE patient sera that could account for the induction of anti-DNA antibody, and possibly for some of the pathogenic features of SLE. We now report that SLE patients, in addition to anti-DNA, produce antibodies to the carboxy-terminal domain of the tumour suppressor molecule p53; this p53 domain recognizes damaged DNA. Hence, these anti-p53 antibodies could mimic damaged DNA immunologically. Indeed, SLE sera do contain anti-idiotypic antibodies to a prototypic anti-p53 antibody. Moreover, SLE anti-DNA antibodies also recognize this type of anti-p53 antibody. Indeed, binding of affinity-purified anti-DNA both to DNA and to the anti-p53 antibody could be blocked by a p53 peptide derived from the DNA-binding domain. This mimicry of the p53 DNA-binding domain by the SLE anti-DNA antibodies is functional: activation of the p53 molecule could be inhibited by such anti-DNA antibodies. Thus, anti-DNA antibodies may arise in SLE patients by a chain of idiotypic autoimmunity centered around p53 autoimmunity. The SLE anti-DNA and anti-p53 antibodies can functionally block p53 activation, and so could affect apoptosis.

The role of the C' terminus of murine p53 in the p53/mdm-2 regulatory loop

Mdm-2 plays a central role in the regulation of p53 protein level and activity. Although the interaction of mdm-2 and p53 occurs through the N-terminus of the p53 protein, our present data suggest that the C' terminus plays an important role in the regulation of the p53/mdm-2 loop. Comparative analysis of the murine regularly spliced form of p53 (RSp53) and a physiological C-terminally modified p53 protein, which results from alternative splicing of the p53 mRNA (ASp53), indicated that the two isoforms behave differently in the p53/mdm-2 loop. We found that ASp53 can preferentially induce higher levels of the mdm-2 protein, compared with RSp53. Although the transactivation capacity of both forms is inhibited by mdm-2, only RSp53 is directed to proteolytic degradation by mdm-2, while ASp53 is relatively resistant. We present evidence that suggests that ASp53 protein levels determine the biological activities mediated by RSp53, such as the induction of apoptosis, through the mdm-2/p53 regulatory loop. We suggest, therefore, a new mechanism for the regulation of p53, and show that alteration of the p53 extreme C' terminus can significantly change the transcription activity and the resistance to degradation properties of the p53 protein.

Change of the death pathway in senescent human fibroblasts in response to DNA damage is caused by an inability to stabilize p53

The cellular function of p53 is complex. It is well known that p53 plays a key role in cellular response to DNA damage. Moreover, p53 was implicated in cellular senescence, and it was demonstrated that p53 undergoes modification in senescent cells. However, it is not known how these modifications affect the ability of senescent cells to respond to DNA damage. To address this question, we studied the responses of cultured young and old normal diploid human fibroblasts to a variety of genotoxic stresses. Young fibroblasts were able to undergo p53-dependent and p53-independent apoptosis. In contrast, senescent fibroblasts were unable to undergo p53-dependent apoptosis, whereas p53-independent apoptosis was only slightly reduced. Interestingly, instead of undergoing p53-dependent apoptosis, senescent fibroblasts underwent necrosis. Furthermore, we found that old cells were unable to stabilize p53 in response to DNA damage. Exogenous expression or stabilization of p53 with proteasome inhibitors in old fibroblasts restored their ability to undergo apoptosis. Our results suggest that stabilization of p53 in response to DNA damage is impaired in old fibroblasts, resulting in induction of necrosis. The role of this phenomenon in normal aging and anticancer therapy is discussed.

Structural and functional involvement of p53 in BER in vitro and in vivo

p53 is involved in several DNA repair pathways. Some of these require the specific transactivation of p53-dependent genes and others involve direct interactions between the p53 protein and DNA repair associated proteins. Previously, we have shown that p53 acts directly in Base Excision Repair (BER) when assayed under in vitro conditions. Our present data indicate that this involvement is independent of the transcriptional activity of the p53 molecule. We found that under both in vitro and in vivo conditions, a p53 transactivation-deficient molecule, p53-22-23 was more efficient in BER activity than was wild type p53. However, mutations in the core domain or C-terminal alterations strongly reduced p53-mediated BER activity. These results are consistent with the hypothesis that the involvement of p53 in BER activity, a housekeeping DNA repair pathway, is a prompt and immediate one that does not involve the activation of p53 transactivation-dependent mechanisms, but rather concerns with the p53 protein itself. In an endogenous DNA damage status p53 is active in BER pathways as a protein and not as a transcription factor.

Thiazolidinediones (PPARgamma agonists) but not PPARalpha agonists increase IRS-2 gene expression in 3T3-L1 and human adipocytes

Thiazolidinediones (TZD) improve insulin sensitivity in human as well as in different animal models of insulin resistance and Type 2 diabetes. However, no clear link to the insulin signaling events has been identified. Using differentiated 3T3-L1 adipocytes, we found that TZD rapidly and markedly increased IRS-2 gene expression. This effect was specific for PPARgamma agonists and was not seen with PPARalpha agonists. It was rapidly induced (within 4 h) and maintained throughout the observation period of 48 h. It was also concentration dependent (EC50 approximately 50 nM) and not inhibited by cycloheximide, suggesting a direct effect on the IRS-2 promoter. There was no evidence that TZD altered IRS-2 mRNA stability, supporting that the increased mRNA levels were due to an increased gene transcription. IRS-2 protein expression was increased approximately 30% after 48 h and approximately 50% after 96 h. No effects of TZD were seen on IRS-1, PKB/Akt, or GLUT4 gene expression. TZD also increased IRS-2 mRNA levels in cultured human adipose tissue. These data show the first direct link between TZD and a critical molecule in insulin's signaling cascade in both 3T3-L1 and human adipocytes, and indicate a novel mode of action of these compounds.

p53 modulates base excision repair activity in a cell cycle-specific manner after genotoxic stress

To elucidate the nature of the cross-talk between the p53 protein and the DNA repair machinery, we have investigated the relationship between the two throughout the cell cycle. Base excision repair (BER) was analyzed in cell cycle phase-enriched populations of lymphoid cells expressing wild-type p53. Our study yielded the following novel findings: (a) BER exhibited two distinct peaks of activity, one associated with the G0-G1 checkpoint and the second with the G2-M checkpoint; (b) although the overall BER activity was reduced after exposure of cells to 400R, there was an augmentation of the G0-G1-associated BER activity and a reduction in the G2-M-associated BER activity; and (c) modulations in these patterns of BER after genotoxic stress were found to be p53 regulated. p53 protein levels induced after gamma-irradiation were distributed evenly in the various cell cycle populations (analyzed by the PAb-248 anti-p53 monoclonal antibody). However, both the dephosphorylation of serine 376 of p53 (contained in the PAb-421 epitope) and the specific DNA binding activity, as well as apoptosis, were enhanced toward the G2-M populations. Furthermore, inactivation of wild-type p53, mediated by mutant p53 expression, abolished the alterations in the BER pattern and showed no induction of a G2-M-associated apoptosis after gamma-irradiation. These results suggest that after genotoxic stress, stabilized p53 enhances the G0-G1-associated BER activity, whereas it predominantly reduces BER activity at the G2-M-enriched populations and instead induces apoptosis. After genotoxic stress, p53 functions as a modulator that determines the pattern of BER activity and apoptosis in a cell cycle-specific manner.

Oncogenic mutations of the p53 tumor suppressor: the demons of the guardian of the genome

The p53 guardian of the genome is inactivated in the majority of cancers, mostly through missense mutations that cause single residue changes in the DNA binding core domain of the protein. Not only do such mutations result in the abrogation of wild-type p53 activity, but the expressed p53 mutant proteins also tend to gain oncogenic functions, such as interference with wild-type p53-independent apoptosis. Because p53 mutants are highly expressed in cancer cells and not in normal cells, their reactivation to wild-type p53 function may eliminate the cancer by apoptosis or another p53-dependent mechanism. Several studies that embarked on this quest for reactivation have succeeded in restoring wildtype p53 activity to several p53 mutants. However, mutants with more extensive structural changes in the DNA binding core domain may be refractory to reactivation to the wild-type p53 phenotype. Therefore, understanding the structure and functions of oncogenic p53 mutants may lead to more potent reactivation modalities or to the ability to eliminate mutant p53 gain of function.

Differential sensitivity of MCF-7 and LCC2 cells, to multiple growth inhibitory agents: possible relation to high bcl-2/bax ratio?

Comparison of LCC2, the E(2)-independent, tamoxifen-resistant subline of the MCF-7 human breast cancer cell line with its parent line, disclosed that it is more resistant to growth inhibition and apoptosis induction by a variety of agents acting by diverse mechanisms. Thus, LCC2 cells can serve as a useful in-vitro model for the study of the molecular mechanisms of this resistance. It was found that bcl-2 protein and mRNA were elevated and that bax protein and mRNA were reduced in LCC2 compared with MCF-7 cells. Incubation of both lines in the presence of bcl-2 antisense caused growth inhibition and reduced bcl-2 protein levels only in MCF-7 cells, suggesting the involvement of bcl-2 in the regulation of normal growth of breast cancer cells. Increased bcl-2 expression in breast cancer cells may correlate with their resistance to growth inhibitory agents. Bcl-2 is a useful target for enhancing the effects of growth inhibitory agents.

A fast signal-induced activation of Poly(ADP-ribose) polymerase: a novel downstream target of phospholipase c

We present the first evidence for a fast activation of the nuclear protein poly(ADP-ribose) polymerase (PARP) by signals evoked in the cell membrane, constituting a novel mode of signaling to the cell nucleus. PARP, an abundant, highly conserved, chromatin-bound protein found only in eukaryotes, exclusively catalyzes polyADP-ribosylation of DNA-binding proteins, thereby modulating their activity. Activation of PARP, reportedly induced by formation of DNA breaks, is involved in DNA transcription, replication, and repair. Our findings demonstrate an alternative mechanism: a fast activation of PARP, evoked by inositol 1,4,5,-trisphosphate-Ca(2+) mobilization, that does not involve DNA breaks. These findings identify PARP as a novel downstream target of phospholipase C, and unveil a novel fast signal-induced modification of DNA-binding proteins by polyADP-ribosylation.

p53-dependent apoptosis is regulated by a C-terminally alternatively spliced form of murine p53

It is now well accepted that the p53 C-terminus plays a central role in controlling the activity of the wild-type molecule. In our previous studies, we observed that a C-terminally altered p53 protein (p53AS), generated by an alternative spliced p53 mRNA, induces an attenuated p53-dependent apoptosis, compared to that induced by the regularly spliced form (p53RS). In the present study we analysed the interrelationships between these two physiological variants of wild-type p53, and found that in cells co-expressing both forms, in contrast to the expected additive effect on the induction of apoptosis, p53AS inhibits apoptosis induced by p53RS. This inhibitory effect is specific for p53-dependent apoptosis and was not evident in a p53-independent apoptotic pathway induced by growth factor deprivation. Furthermore, the expression of p53AS in transiently transfected cells caused both inhibition of apoptosis and inhibition of the p53RS-dependent transactivation of a number of p53 target genes. These results suggest that expression of an alternatively spliced p53 form may serve as an additional level in controlling the complexity of p53 function by the C-terminal domain.

Pooled analysis of p53 mutations in hematological malignancies

A computerized database is described that contains information about 507 mutations in the p53 gene of hematologic tumors and corresponding cell lines. Analysis of these mutations indicated the following findings: First, mutational spectrum analysis in these tumors was found to be similar to the pattern found for other solid tumors. However, when the patterns of base substitutions were examined separately according to the types of hematologic malignancies, followed by subgroup analysis, notable differences (in some cases of statistical significance) emerged. Second, mutational pattern analysis indicates that about 48% of base substitutions in hematologic tumors are suspected to be associated with carcinogen exposure. Third, deletions and insertions are localized mainly to exons 5-8 and repeated DNA sequences. However, the unusual profile of variations in frequency within each type of tumor suggests that, in addition to endogenous damage to template DNA, there is the factor of exposure to environmental physical and chemical carcinogens/mutagens. Fourth, p53 protein alterations analysis indicate that most of the changes in the amino acids are "semiconservative," presumably in order to avoid disrupting the structure of the p53 monomer. Consistent with this notion, structural mutations are more conservative than the binding mutations. Finally, molecular mechanisms that lead to p53 mutations, etiological factors that play a role in their formation, and the pathophysiological significance of consequent p53 protein alterations are discussed.

Systemic lupus erythematosus in mice, spontaneous and induced, is associated with autoimmunity to the C-terminal domain of p53 that recognizes damaged DNA

The tumor suppressor molecule p53 features a regulatory domain at the C terminus that recognizes damaged DNA. Since damaged DNA might be involved in activating anti-DNA autoantibodies, we tested whether autoimmunity to the C terminus of p53 might mark murine systemic lupus erythematosus (SLE). We now report that MRL / MpJ-Fas(lpr) mice, which spontaneously develop SLE, produce antibodies both to the C terminus of p53 and to a monoclonal antibody (PAb-421) that binds the p53 C terminus. Anti-idiotypic antibodies to PAb-421 (sampled as monoclonal antibodies) could also bind DNA. Thus, the PAb-421 antibody mimics DNA, and the anti-idiotypic antibody to PAb-421 mimics the p53 DNA-binding site. This mimicry was functional; immunization of BALB / c mice to PAb-421 induced anti-DNA antibodies and antibodies to the C terminus of p53, and most of the mice developed an SLE-like disease. Immunization of C57BL / 6 mice to PAb-421 induced antibodies to p53, but not to its C-terminal domain. The C57BL / 6 mice also did not develop anti-DNA antibodies or the SLE-like disease. Thus, network autoimmunity to the domain of p53 that recognizes damaged DNA can be a pathogenic feature in SLE in genetically susceptible strains of mice.

An intragenic deletion of nuclear localization signal-1 of p53 tumor suppressor gene results in loss of apoptosis in murine fibroblasts

We established mouse lines containing either full-length wild-type p53 or nuclear localization signal-I (NLS-I) deleted p53 to study the role of NLS-I in p53 translocation and function. Induction of apoptosis in response to DNA damage, a primary function of p53, was tested in these cell lines. After exposure to gamma-ionizing radiation or hydrogen peroxide, DNA ladders and labeling of nucelosomal fragments were detected in cells with wild-type p53 gene, but not in p53 null cells or NLS-I deleted cells, suggesting that the NLS-I of p53 protein is necessary for apoptosis. Analysis of p53 protein from subcellular fractions indicated that NLS-I deprived p53 remained in the cytoplasmic fraction, which may explain why NLS-I deleted p53 failed to induce apoptosis.

Epithelial cells of different organs exhibit distinct patterns of p53-dependent and p53-independent apoptosis following DNA insult

The present study shows that DNA damage induces different patterns of p53-dependent and p53-independent apoptosis in epithelial cells of various organs of adult mice. Genotoxic stress induced a biphasic apoptotic response in the small intestine and tongue. While the first immediate apoptotic wave was p53-dependent, the second was slower in rate and was p53-independent. Under the same experimental conditions a single rapid, but a more extended, p53-independent response was evident in the skin of the tail. Indeed, exposure of p53+/+ mice to 400 R induced in epithelium of the small intestine and tongue an immediate rapid response that was followed by a second delayed p53-independent apoptotic wave. p53-/- mice exhibited in these organs the second wave only. However, epithelium of the tail derived from the same mice showed a single rapid apoptotic response that lasted much longer than the p53-dependent response and was similar in the p53-/- and the p53+/+ mice. Variations in apoptotic patterns observed in epithelial cells derived of the different tissues may point to differences in the physiological pathways expressed.

p53 controls low DNA damage-dependent premeiotic checkpoint and facilitates DNA repair during spermatogenesis

Previously, it was implicated that p53 plays a role in spermatogenesis. Here we report that p53 knockout mice exhibit significantly less mature motile spermatozoa than their p53(+/+) counterparts. To better understand the role of p53 in spermatogenesis, we analyzed the response of spermatogenic cells to DNA insult during prophase. It was found that although low-level gamma-irradiation activated a p53-dependent premeiotic delay, higher levels of gamma-irradiation induced a p53-independent apoptosis during meiosis. Furthermore, p53 knockout mice exhibited reduced in vivo levels of unscheduled DNA synthesis, indicative of compromised DNA repair. Thus, p53 provides another level of stringency in addition to other spermatogenic "quality control" mechanisms.

Cellular events and the pattern of p53 protein expression following cyclophosphamide-initiated cell death in various organs of developing embryo

This study was aimed at characterizing the temporal patterns of cell responses and p53 protein expression in the limbs, head, and liver of embryos responding to cyclophosphamide (CP)-induced teratogenic insult. ICR murine embryos were examined 24, 48, or 72 h after injection of 40 mg/kg CP on day 12 of pregnancy. The cellular events and temporal pattern of p53 protein expression were determined by FACS analysis and by TUNEL (apoptosis) in the head, limbs, and liver of the embryos. All tested organs showed apoptosis and a significantly decreased proportion of live cells after 24 h. Subsequent events were organ-dependent. In the liver, there were no dysmorphic events at any time and excessive cell death had been almost compensated for by 48 h. Compensation was preceded by G(1) arrest and accompanied by an increased level of p53 protein in surviving cells. Excessive cell death in the head and the limbs resulted in structural anomalies. In the head, there was an increased level of p53 protein and G(1) arrest after 24 h and the number of live cells at 48 h was equal to that seen in earlier samples, despite apoptosis. In the limbs, however, only isolated viable cells were seen by 48 h, but there was no increased level of p53 protein or G(1) arrest. Results of this study suggest that the differential sensitivity of tested organ systems to CP may be associated with differences in cellular events following CP-initiated cell death. They also suggest that the input of p53 in determining the response of these organ systems to CP-induced teratogenic insult may be different. Teratogenesis Carcinog. Mutagen. 19:353-367, 1999.

Tissue-specific p53 expression in the nervous system

P53 is a transcription factor that has been found to be expressed in association with cell proliferation and apoptosis. Previously, bacterial chloramphenicol acetyl transferase (CAT) enzymatic expression was predominantly found in the testes of p53 promoter driven-CAT transgenic mice. In the current study, we extended this study to survey p53 expression across both the central and peripheral nervous systems of the same strain of transgenic mice as well as their parental strain. High levels of p53 promoter driven-CAT activity was observed in the cerebellum, hippocampus, hypothalamus, pons, thalamus and upper cerebral spine. Furthermore, we consistently found unexpectedly high levels of p53 promoter-driven CAT expression in the eyes. These observations were reinforced by p53 protein analysis using a p53 pan ELISA assay. Immunohistochemical studies confirmed and further defined p53 expression in several regions of the nervous system. Significantly, p53 promoter-driven CAT expression was visualized in the Ammon horn of the hippocampus, in the Purkinje cells of the cerebellum and in the cornea as well as in the retina of the eye. Furthermore, strong p53 protein expression was found in the cornea of the parental mouse strain. p53 ELISA demonstrated a profile of p53 protein concentration, which correlate well with the high p53 promoter-driven CAT activities observed in the cerebellum, hindbrain, hypothalamus, thalamus, hippocampus, whole eyes as well as with the low CAT activities observed in the cortex and spinal cord. In both of these assays considerable p53 promoter activity and p53 protein levels were found in post-mitotic non-dividing cells.

Direct involvement of p53 in the base excision repair pathway of the DNA repair machinery

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.

Accentuated apoptosis in normally developing p53 knockout mouse embryos following genotoxic stress

In order to identify the alternative pathways which may substitute for the p53 function during embryogenesis, we have focused our studies on p53 -/- normally developing mouse embryos that survived a genotoxic stress. We assumed that under these conditions p53-independent pathways, which physiologically control genomic stability, are enhanced. We found that while p53 +/+ mouse embryos elicited, as expected, a p53-dependent apoptosis, p53-/- normally developing mice exhibited an accentuated p53-independent apoptotic response. The p53-dependent apoptosis detected in p53+/+ embryos, was an immediate reaction mostly detected in the brain, whereas the p53-independent apoptosis was a delayed reaction with a prominent pattern observed in epithelial cells of most organs in the p53-deficient mice only. These results suggest that in the absence of p53-dependent apoptosis, which is a fast response to damaged DNA, p53-independent apoptotic pathways, with slower kinetics, are turned on to secure genome stability.

p53-dependent cell cycle control: response to genotoxic stress

p53 protein is involved in key responses to genotoxic stress. These functions underlie the role of p53 as the 'guardian of the genome'. In a simplified manner, upon low or repairable levels of DNA damage, p53 mediates the delay or arrest at checkpoints preceding cell replication (the G1/S checkpoint), and is involved in delaying damaged cells prior premitotic chromosome condensation (the G2 and pre-meiotic check-points) and actual chromosome partition (the spindle check-point). During these delays, an opportunity is given to repair the DNA damage, before its fixation and propagation, that may lead to carcinogenesis. Upon high or irreparable DNA damage, p53 promotes the cells towards apoptosis. Here we review the known molecular pathways by which p53 controls the cell cycle, with a specific focus on the significance of p53-mediated checkpoint response for its 'tumor suppressor' function. The data reviewed is concerned with the in vivo mouse models including p53 knockout mice, transgenic mice harboring various mutant forms of p53 and mice knocked out for cell-cycle- and apoptosis-associated genes situated upstream or downstream from p53, that have been elaborated upon over the last few years.

Hydrogen peroxide induces nuclear translocation of p53 and apoptosis in cells of oligodendroglia origin

The observation that apoptosis is an inherent pathway in oligodendrocytes development coupled with the notion that wild-type p53 is expressed in these cells, prompted us to investigate the interrelationship between the two phenomena. Using a permanent oligodendroglia-like cell line (OLN 93), we examined the role of p53 protein in apoptosis following a DNA insult induced by a brief exposure to H2O2. A marked translocation of p53 from the cytosolic to the nuclear compartment was notable by 20 min, following a 5 min treatment with 1 mM H2O2 as identified by cell immunostaining. By 48 h following H2O2 addition, nearly 60% of the cells exhibited p53 in the nuclei. At this time, a large proportion of the cells underwent apoptosis as identified by DAPI nuclear staining. The genotoxic-induced p53 relocalization appeared to be cell cycle phase specific; thus OLN 93 cultures enriched for cells in the G0/G1 stage by serum starvation, and abundant in nuclear-associated p53, were more susceptible to H2O2-induced apoptosis than their untreated counterparts and than double thymidine block, G1/S enriched, cultures. Analysis of the expression of p53 downstream genes indicated that p21 and mdm2 were upregulated following p53 nuclear translocation. From the kinetics of protein accumulation, it appears that mdm2 enhancement accelerated the exit of p53 from the nucleus to the cytosol. Our results suggest that following stress, oligodendroglia-like cells are induced to undergo p53-dependent apoptosis, an event that coincides with p53 nuclear translocation and is cell-cycle related.

COOH-terminal domain of p53 modulates p53-mediated transcriptional transactivation, cell growth, and apoptosis

The tumor suppressor protein p53 contributes to the control of cell cycle checkpoints and stress-induced apoptosis and is frequently mutated in many different types of human cancers. The COOH terminus of p53 modulates the transcriptional and apoptotic activities of the protein. Although COOH-terminal mutants of p53 are uncommon, we proposed that these p53 mutants nevertheless contributed to the selective clonal expansion of the cancer cells. Therefore, we analyzed the tumor-derived p53 COOH-terminal domain (CTD) mutants (352D/H, 356G/W, 342-stop, 360-del, and 387-del) functionally. The results have revealed that all mutants have impaired apoptotic activity when compared with wild-type p53. However, some of these mutants still transcriptionally transactivate p21Waf/Cip1 and inhibit cell growth. Interestingly, of the tumor-derived CTD mutants, oligomerization-defective mutant 342-stop was the only one that did not exhibit sequence-specific DNA binding or failed to transactivate p21Waf1/Cip1, Bax, and IGF-BP3 transcriptionally. The failure to inhibit cell growth by this tumor-derived CTD mutant supports the hypothesis that p53 sequence-specific transcriptional transactivity to p21Waf1/Cip1 is correlated with induction of cell cycle arrest and that the p53 transcriptional transactivity requires oligomerization of the p53 protein. These and other data indicate that the CTD of p53 is an important component of p53-mediated apoptosis and cell growth arrest and that inactivation of the apoptotic function, but not the inhibition of growth, is an important step during human tumorigenesis.

p53 tumor suppressor gene expression in the mouse ovary during an artificially induced ovulatory cycle

OBJECTIVE

To evaluate the expression of p53 in the mouse ovary during an artificially induced ovulatory cycle.

STUDY DESIGN

Ovulation induction was performed using pregnant mares' serum gonadotropin/human chorionic gonadotropin (PMSG/hCG). First, a p53 promoter-chloramphenicol acetyl transferase (CAT) transgenic mouse model was used. Protein samples from ovaries of transgenic mice were assayed for CAT activity as evidence of p53 promoter activation. Next, RNA extracted from CD-1 mouse ovaries was used for reverse transcription/polymerase chain reaction (PCR) and northern blot analysis using a p53-specific probe.

RESULTS

Increased CAT activity was noted in transgenic mice treated with PMSG/hCG as compared with controls. PCR studies on transgenic mice using primers for CAT and on CD-1 mice using primers for wild type p53 substantiated this observation. Furthermore, CAT assay and northern analysis, performed on samples obtained at serial time intervals from induction, indicated that maximal p53 expression occurs around the time of ovulation, beginning 48 hours after PMSG and peaking 6-12 hours after hCG administration.

CONCLUSION

The temporal expression of p53 in the ovary during a PMSG/hCG artificially induced ovulatory cycle may indicate a role for p53 in processes of differentiation of granulosa cells into luteal cells.

Introduction: p53--the first twenty years

The p53 protein was discovered 20 years ago, as a cellular protein tightly bound to the large T oncoprotein of the SV40 DNA tumour virus. Since then, research on p53 has developed in many exciting and sometimes unexpected directions. p53 is now known to be the product of a major tumour suppressor gene that is the most common target for genetic alterations in human cancer. The nonmutated wild-type p53 protein (wtp53) is often found within cells in a latent state and is activated in response to various intracellular and extracellular signals. Activation involves an increase in overall p53 protein levels, as well as qualitative changes in the protein. Upon activation, wtp53 can induce a variety of cellular responses, most notable among which are cell cycle arrest and apoptosis. To a great extent, these effects are mediated by the ability of p53 to activate specific target genes. In addition, the p53 protein itself possesses biochemical functions which may facilitate DNA repair as well as apoptosis. The role of p53 in normal development and particularly in carcinogenesis has been elucidated in depth through the use of mouse model systems. The insights provided by p53 research over the years are now beginning to be utilized towards better diagnosis, prognosis and treatment of cancer.