Induction of apoptosis by wild-type p53 in a human colon tumor-derived cell line

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

GADD45 induction of a G2/M cell cycle checkpoint

G1/S and G2/M cell cycle checkpoints maintain genomic stability in eukaryotes in response to genotoxic stress. We report here both genetic and functional evidence of a Gadd45-mediated G2/M checkpoint in human and murine cells. Increased expression of Gadd45 via microinjection of an expression vector into primary human fibroblasts arrests the cells at the G2/M boundary with a phenotype of MPM2 immunopositivity, 4n DNA content and, in 15% of the cells, centrosome separation. The Gadd45-mediated G2/M arrest depends on wild-type p53, because no arrest was observed either in p53-null Li-Fraumeni fibroblasts or in normal fibroblasts coexpressed with p53 mutants. Increased expression of cyclin B1 and Cdc25C inhibited the Gadd45-mediated G2/M arrest in human fibroblasts, indicating that the mechanism of Gadd45-mediated G2/M checkpoint is at least in part through modulation of the activity of the G2-specific kinase, cyclin B1/p34(cdc2). Genetic and physiological evidence of a Gadd45-mediated G2/M checkpoint was obtained by using GADD45-deficient human or murine cells. Human cells with endogenous Gadd45 expression reduced by antisense GADD45 expression have an impaired G2/M checkpoint after exposure to either ultraviolet radiation or methyl methanesulfonate but are still able to undergo G2 arrest after ionizing radiation. Lymphocytes from gadd45-knockout mice (gadd45 -/-) also retained a G2/M checkpoint initiated by ionizing radiation and failed to arrest at G2/M after exposure to ultraviolet radiation. Therefore, the mammalian genome is protected by a multiplicity of G2/M checkpoints in response to specific types of DNA damage.

Evaluation of apoptosis of tumor and of apparently normal cells in human renal carcinoma

Apoptosis of tumor cells and of apparently normal renal cells (ANRC) isolated from the same kidney in 42 untreated patients with renal carcinomas (RC) was evaluated. Thirty five of the investigated tumors were of Grawitz type in different grades of differentiation. The intensity of the apoptotic process was routinely assessed by propidium iodide staining and flow-cytometry analysis. Similar results were obtained in the same cases by using TUNEL assay, by staining with annexin V and by DNA electrophoresis. In 85% of Grawitz carcinomas the proportion of apoptotic tumor cells was quite high, with mean% +/- SD of 57.7+/-27.3, whereas in transitional cell carcinoma of the bladder (TCC), the mean percentage of cells in apoptosis was of 22.3+/-13.9. Unexpectedly, in ANRC displaying normal morphology and normal DNA content (diploidy), the mean% +/- SD of apoptotic cells were found to exceed that of apoptotic tumor cells, 79.2+/-21.6. The percentages of cells expressing Fas receptor and/or Fas ligand varied between large ranges in both tumor and ANRC, thus suggesting that other mechanisms are also involved in the activation of apoptosis. Immunohistochemical studies showed that the intensity of apoptosis correlated well with high p-53 and low bcl-2 expression. The intensity of apoptosis was generally not correlated with the cell proliferation index (S phase fraction), suggesting that in RC apoptosis can be activated in any stage of the cell cycle. Further investigations are necessary to understand the peculiar behaviour of tumor cells as well as of ANRC in renal carcinomas as compared to other types of malignancies.

Prognostic and predictive value of p53 and p21 in breast cancer

The prognostic and predictive value of p53 has been extensively studied in breast cancer. p53 serves a multifunctional role as a transcriptional regulator, genomic stabilizer, inhibitor of cell cycle progression, facilitator of apoptosis, and also perhaps an inhibitor of angiogenesis. Abrogation of its function should therefore lead to a more aggressive breast cancer phenotype and a worse clinical outcome, and indeed the preponderance of studies confirm this, with the risk of recurrence and death increasing by 50% or more if p53 is abnormal. Lack of unanimity of results may be due to differences in technique, study design, or population, as well as the subjectivity inherent in some approaches; however, the complexity and random nature of genomic change present in cancer cells may well also contribute to the lack of unanimity. Because many anticancer agents may exert a therapeutic effect through genomic damage and subsequent triggering of apoptosis, and because p53 can respond to genomic damage and facilitate apoptosis, it can be hypothesized that an intact p53 would predict sensitivity to therapy. Present data in breast cancer, however, does not clearly indicate that this is the case. There are several potential explanations. Study designs to accurately test the predictive value of a molecular marker are more exacting and difficult to achieve than prognostic studies. There may also be multiple alternative pathways, not involving p53, that play a part in determining the therapeutic effect of a treatment. The prognostic value of a downstream effector of p53 has also been assessed, though less extensively. p21 is transcriptionally upregulated by p53 and is an inhibitor of cyclin-dependent kinases and thus of cell cycle progression. Higher levels of p21 might indicate a more indolent type of breast cancer. However, data from a number of clinical studies is very conflicting, and at present p21 is not a promising prognostic factor in breast cancer.

Immunohistochemical and mutational analysis of p53 tumor suppressor gene in gestational trophoblastic disease: correlation with mdm2, proliferation index, and clinicopathologic parameters

The role of p53 in the pathogenesis of gestational trophoblastic disease (GTD) was investigated. Immunohistochemical studies for p53, its regulator mdm2, and proliferation marker Ki67 were performed on paraffin-embedded tissues of 28 partial moles (PM), 57 complete moles (CM), 14 choriocarcinomas (CCA), and 31 normal placentas. Three antibodies to p53 (DO-7, Ab-2, Ab-3) were used and demonstrated immunoreactivity for wild-type p53 protein predominantly in the nuclei of cytotrophoblasts. Direct DNA sequencing of 36 hydatidiform moles using frozen tissues confirmed an absence of mutational changes in exons 5-8. CCA was found to have the highest p53 protein expression, followed by CM, PM, and normal placenta (P < 0.001). In normal placentas (P = 0.0001), PM, and CM (P = 0.016), an inverse correlation between their gestational age and p53 expression was observed. p53 expression was found to correlate with proliferation index in normal placenta (P = 0.0001) and all three groups of GTD (P = 0.012). Significant correlation between p53 and mdm2 expression was also observed (P < 0.01). The distinctive expression of p53 wild-type protein in the cytotrophoblasts and its positive correlation with the proliferative index suggests that its overexpression in GTD may be related to its effect on cell proliferation. The parallel expression of mdm2 and p53 also supports the presence of an autoregulatory feedback loop in the control of this process. No correlation could be found between clinical progress of the patients with hydatidiform moles, and the p53 (P = 0.78) or mdm2 protein (P = 0.54) expression suggesting that neither of them carries any prognostic significance.

Multinucleated variant endothelial cells (MVECs) of human aorta: expression of tumor suppressor gene p53 and relationship to atherosclerosis and aging

Multinucleated variant endothelial cells (MVECs) generally exist in atherosclerotic human aorta and even in nonatherosclerotic aorta. Because the number of nuclei is increased in every MVEC, and because DNA instability was suspected, a series of oncogene expressions was conducted to clarify the nature of nuclear abnormality. The tumor suppressor gene p53 was found to be specifically expressed in the multinuclei of MVECs, while double nuclei were sometimes positive, and mononuclear typical endothelial cells were always negative for p53. Polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) revealed extra bands in exons 5 and 7 of the p53 gene, but no additional band in exons 6 and 8. In a BCL family, BCL-2 was coexpressed in one or two nuclei in the perinuclear space of the multinuclei of MVECs, whereas MCL-1, BCL-XS/L, and BAX were all negative, indicating that the BCL-2 coding gene is expressed only in the corresponding one or two nuclei of the multinuclei. Another oncogene, c-MET (hepatocyte growth factor receptor), was universally expressed in either type of endothelial cells, but other oncogenes, k-RAS and c-ERBB2, were not expressed in either type. MVECs were derived from human aorta and therefore non-tumorous somatic cells. No morphologic evidence of apoptosis was found. Although it is unclear that the extra bands came from the MVECs or just from ECs associated with atherosclerosis, combined immunocytological studies and PCR analysis suggest that MVECs express mutant type p53.

The effects of combining ionizing radiation and adenoviral p53 therapy in nasopharyngeal carcinoma

PURPOSE

Nasopharyngeal carcinoma (NPC) is a malignant disease of the head/neck region, with a 5-year survival level of approximately 65%. To explore gene therapy as a novel approach which might improve outcome, we have shown previously that introduction of human recombinant wild-type p53 mediated by the adenoviral vector (Ad5CMV-p53) was cytotoxic in two human nasopharyngeal carcinoma (NPC) cell lines (CNE-1 and CNE-2Z). The current work was designed to determine whether this strategy, combined with ionizing radiation (XRT), was more effective than either treatment alone.

METHODS AND MATERIALS

CNE-1, CNE-2Z, and a normal human nasopharyngeal fibroblast strain, KS1, were infected with 2- and 6-plaque-forming units (pfu)/cell of Ad5CMV-p53, respectively. These doses were isoeffective for beta-galactosidase activity in the CNE-1 and CNE-2Z cells. XRT was administered 24 h post-infection, and Western blot analyses were conducted for p53, p21WAF1/CIP1, bax, and bcl-2 2 days after XRT. Cell survival was assessed using a clonogenic assay. Presence of DNA ladders reflecting apoptosis was detected using DNA agarose gel electrophoresis, and cell cycle was analyzed using flow cytometry.

RESULTS

The combination of Ad5CMV-p53 plus XRT (2, 4, and 6 Gy) resulted in an approximately 1-log greater level of cytotoxicity compared to that observed with XRT alone for both NPC cell lines. The two modalities appear to be interacting in a synergistic manner in cancer cells, but not in KS1 fibroblasts. XRT alone stimulated minimal p53 expression in control cells; Ad5CMV-p53 alone induced significant recombinant p53 expression, which was not further enhanced by the addition of XRT. Similar observations were made for p21WAF1/CIP1 expression. No changes were observed for bax or bcl-2 expression with any of these treatments. Apoptosis was induced following 4 Gy of XRT alone, but was observed after only 2 Gy when combined with Ad5CMV-p53. Cell cycle analysis indicated that Ad5CMV-p53 infection did not perturb the cell cycle beyond that observed with XRT alone.

CONCLUSION

p53 gene therapy and XRT appears to interact in a synergistic manner; underscoring the significant potential of this novel strategy in the treatment of NPC.

Alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia

We investigated the alterations of the p53, p21, p16, p15 and RAS genes in childhood T-cell acute lymphoblastic leukemia (T-ALL) and T-ALL cell lines by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and direct sequencing. Mutations of the p53 gene were found in three of 57 (5%) patients at diagnosis, one of 14 (7%) patients at relapse and in 12 of 18 (67%) cell lines. In these 12 cell lines, four had more than two mutations of the p53 gene. The p53 mutations were found in four of five cell lines whose original fresh leukemic cells were simultaneously examined original fresh leukemic cells. However, only one of the four fresh leukemic cells had the same mutation. All patients with p53 mutations in the course of disease died. Mutations of the p21 gene were not identified in 71 fresh samples and in 18 cell lines. N-RAS mutations were found in two of 57 (4%) fresh T-ALL patients at diagnosis, and four of 18 cell lines (22%), whereas no mutations were detected in any samples at relapse. Alterations of the p16 gene were found in 18 of 47 (38%) patients at diagnosis and in seven of 14 (50%) at relapse. These differences were not statistically significant. There were no differences in the frequency of alteration of the p16 and p15 genes between event-free patients and the remaining patients. Furthermore, we found the methylation of p16 gene in three of seven patients lacking homozygous deletions, suggesting higher frequency of p16 inactivation than previous reports in T-ALL. Interestingly, we found that one allele is inactivated by methylation and another allele had nonsense mutation in one cell line (KOPT-KI), resulting in loss of protein expression of p16. This type of p16 inactivation has not been so far reported in leukemia. We conclude that, (1) p53 mutations are infrequent at diagnosis but tend to be associated with poor clinical outcome; (2) RAS and p21 mutations may not be involved in the pathogenesis of T-ALL; (3) not only frequent alterations of p16 and p15 genes but also methylation of p16 gene are involved in initiating the leukemogenesis of T-ALLs, and (4) these 5 genes are independently involved in T-ALL.

p53 represses ribosomal gene transcription

Induction of the tumor suppressor protein p53 restricts cellular proliferation. Since actively growing cells require the ongoing synthesis of ribosomal RNA to sustain cellular biosynthesis, we studied the effect of p53 on ribosomal gene transcription by RNA polymerase I (Pol I). We have measured rDNA transcriptional activity in different cell lines which either lack or overexpress p53 and demonstrate that wild-type but not mutant p53 inhibits cellular pre-rRNA synthesis. Conversely, pre-rRNA levels are elevated both in cells which express mutant p53 and in fibroblasts from p53 knock-out mice. Transient transfection assays with a set of rDNA deletion mutants demonstrate that intergenic spacer sequences are dispensable and the minimal rDNA promoter is sufficient for p53-mediated repression of Pol I transcription. However, in a cell-free transcription system, recombinant p53 does not inhibit rDNA transcription, indicating that p53 does not directly interfere with the basal Pol I transcriptional machinery. Thus, repression of Pol I transcription by p53 may be a consequence of p53-induced growth arrest.

Apoptosis-prone phenotype of human colon carcinoma cells with a high level amplification of the c-myc gene

Although apoptosis can be induced by the enforced expression of exogenously introduced c-myc genes, it is not clear whether overexpression resulting from the amplification of the resident c-myc gene in tumor cells is sufficient to induce apoptosis. We have investigated the relationship between c-myc gene amplification and the propensity of tumor cells to undergo apoptosis, using the SW613-12A1 and SW613-B3 cell lines, which are representatives, respectively, of tumorigenic and non-tumorigenic clones isolated from the SW613-S human colon carcinoma cell line. Tumorigenic clones are characterized by a high level of amplification and expression of the c-myc gene, whereas cells of non-tumorigenic clones have a small number of copies and a lower level of expression of this gene. Analysis of c-myc mRNA level in cells cultured under low serum conditions indicated that the expression of the gene is tightly regulated by serum growth factors in non-tumorigenic B3 cells, whereas it is poorly regulated in tumorigenic 12A1 cells, the level of mRNAs remaining relatively high in serum-starved 12A1 cells. Under these conditions, 12A1 cells showed clear evidence of apoptosis, whereas B3 cells were completely refractory to the induction of apoptosis. Moreover, the study of cell lines derived from non-tumorigenic apoptosis-resistant clones following the introduction by transfection of exogenous c-myc gene copies showed that they have acquired an apoptosisprone phenotype. Altogether, our results strongly suggest that deregulated c-myc expression due to high-level amplification confers an apoptosis-prone phenotype to tumor cells. The possible consequences of these observations for cancer therapy are discussed.

PA26, a novel target of the p53 tumor suppressor and member of the GADD family of DNA damage and growth arrest inducible genes

Exposure of mammalian cells to hypoxia, radiation and certain chemotherapeutic agents promotes cell cycle arrest and/or apoptosis. Activation of p53 responsive genes is believed to play an important role in mediating such responses. In this study we identified a novel gene, PA26, which maps to chromosome 6q21 and encodes at least three transcript isoforms, of which two are differentially induced by genotoxic stress (UV, gamma-irradiation and cytotoxic drugs) in a p53-dependent manner. A functional p53-responsive element was identified in the second intron of the PA26 gene, in consistance with a mechanism of transcriptional induction of the PA26 gene by p53. No clues to its functions were revealed by sequence analysis, although pronounced negative regulation by serum factors argues for a potential role of PA26 in growth regulation. Immunological analysis suggests that PA26 protein(s) is localized to the cell nucleus. Our results suggest that the PA26 gene is a novel p53 target gene with properties common to the GADD family of growth arrest and DNA damage-inducible stress-response genes, and, thus, a potential novel regulator of cellular growth.

Interference of proteins involved in the cytoplasmic sequestration of p53 with human papillomavirus E6-mediated degradation

The oncogenic human papillomaviruses (HPVs) are able to efficiently target p53 for degradation by the ubiquitin pathway. We previously demonstrated inefficient HPV E6-mediated degradation and resulting high steady-state levels of p53 in cell hybrids between a peripheral neuroepithelioma cell line and a cervical carcinoma cell line (HeLa). We now show that the p53 protein in these cell hybrids was cytoplasmically sequestered and exhibited sporadic punctate staining, which is characteristic of the p53 expression pattern observed in neuroblastic neuroblastoma (NB) cell lines, in which p53 is also sequestered. We hypothesized that the cytoplasmic sequestration of p53 in the cell hybrids might correlate with its inability to be rapidly degraded by HPV E6. Using NB cell lines as a model system to test this hypothesis, we demonstrated that the introduction of HPV E6 into two NB cell lines resulted in p53 insensitivity to HPV E6-mediated degradation. This was assessed by both pulse-chase analysis of p53 in metabolically labeled NB cells and western blotting. The enhanced stability of p53 was not due to a lack of HPV E6 expression or to a mutant conformation of the p53 protein. Our results therefore suggest that proteins involved in the cytoplasmic sequestration of p53 may also interfere with the ability of HPV E6 to target p53 for degradation.

Failure of wild-type p53 gene therapy in human cancer cells expressing a mutant p53 protein

The introduction of exogenous wild-type p53 into human cancer cells bearing p53 mutation does not necessarily result in inhibition of tumor growth. We have demonstrated this in MDA-MB468 breast cancer cells which are hemizygous for p53 mutation and also in KM12SM colorectal carcinoma cells which are heterozygous for p53 mutation. The wtp53 transfectants decreased three- to four-fold the number of colonies compared with controls. Most wtp53-expressing cells died by apoptosis at early passages, but some cells were able to form colonies and their proliferation rate was similar to control transfectants. This reversion was observed in three of the six MDA-MB-468 clones selected. When MDA-wtp53 transfectants were implanted orthotopically in nude mice only one clone showed prolonged tumor latency. No differences were found in either tumor proliferation or apoptosis in tumors. Integration and expression of exogenous wtp53 was assessed in early and late passages in vitro, and in tumors growing in vivo. Consistently, we found mutations in the exogenous wtp53 gene of MDA-MB468 transfectants. Excision of the exogenous gene was an alternative to abrogate the wtp53 function that was extremely efficient in KM12 cells, although they maintained resistance to geneticin. These results were corroborated by the functional assay in yeast. In conclusion, wtp53 is inactivated in these cancer cells by different mechanisms. The presence of mutated p53 may confer genome instability and mutator ability, which allows cells to escape the effects of the exogenous wtp53 and contributes to the failure of wtp53 gene therapy.

Protein kinase CK2-dependent regulation of p53 function: evidence that the phosphorylation status of the serine 386 (CK2) site of p53 is constitutive and stable

The p53 tumour suppressor protein is regulated by several mechanisms including multisite phosphorylation. One of the protein kinases which has an established role in regulating p53 function is the protein kinase CK2. The regulation by CK2 occurs both through interaction of p53 with CK2 itself (the regulatory beta subunit) and phosphorylation at the penultimate residue of p53, serine 386 (murine p53). Strikingly, this phosphorylation event controls several independent functions of p53 including site-specific DNA binding, strand renaturation, transcriptional repression and the anti-proliferative function of p53. However, CK2 is a constitutively-active enzyme and therefore the mechanism by which the phosphorylation of p53 at serine 386 is itself regulated, or indeed the question as to whether phosphorylation of this site is regulated at all, remains unresolved. In this paper we provide evidence that serine 386 is highly resistant to dephosphorylation in cultured cells, even though this site can be dephosphorylated in vitro by recombinant protein phosphatase 1. These data suggest that, once phosphorylated at the CK2 site, a p53 molecule remains in this modified form throughout its lifespan. To address the issue of whether the level of serine 386 phosphorylation may be regulated through controlling the subcellular compartmentalisation of p53 and CK2, we examined the subcellular localisation of p53 and CK2alpha in C57MG cells and Rat-1 fibroblasts by immunofluorescence staining. Both proteins were present in the cytoplasm and enriched in the nucleus, with minor variations in the intensity of subcellular location over the course of the cell cycle. Similarly, activation of p53 by UV irradiation or DNA damage-inducing drugs had no effect on either the localisation or levels of CK2alpha, even although significant nuclear p53 accumulation was observed. A striking observation arising from these studies was the intense staining of CK2alpha with the centrosomes, suggesting a potentially important role for this kinase in microtubule formation and/or chromosomal segregation.

The C-terminal domain of p53 catalyzes DNA-renaturation and strand exchange toward annealing between intact ssDNAs and toward eliminating damaged ssDNA from duplex formation through preferential recognition of damaged DNA by a duocarmycin

The C-terminal domain of p53 may bind single-stranded (ss) DNA ends and catalyze renaturation of ss complementary DNA molecules, suggesting a possible direct role for p53 in DNA repair (Proc. Natl. Acad. Sci. USA, 92, 9455-9459, 1995). We found that DU-86, a duocarmycin derivative which alkylates DNA, bound ssDNA and enhanced the DNA binding activity of the p53 C-terminus. DU-86 weakened p53-mediated catalysis of complementary ssDNA renaturation. p53 C-terminus catalyzed DNA strand transfer toward annealing between intact ssDNAs and toward eliminating DU-86-damaged ssDNA from duplex formation. These results suggest that p53, via the C-terminal domain, may play a direct role in DNA repair by preferential recognization and elimination of damaged DNA.

New developments in the multi-site phosphorylation and integration of stress signalling at p53

PURPOSE

To summarize recent progress in the understanding of the role of multi-site phosphorylation in mediating the integration of stress signals at the p53 tumour suppressor protein.

RESULTS

The p53 protein plays a key role in the response to a range of cellular stresses including agents that can damage DNA; consequently the involvement of p53 in sensing these effects is central to the prevention of tumour development. p53 is a potent but latent transcription factor that can be activated by a range of cellular stresses leading to the induction of cellular growth arrest or controlled cell removal through apoptosis. Accordingly, p53 is under tight control and is subject to several levels of regulation including multi-site phosphorylation. Recent evidence has implicated individual phosphorylation events in the activation of p53 by different types of stress (e.g. ionizing radiation, UV and mitotic spindle damage).

CONCLUSIONS

A picture is now emerging of the p53 protein as an integration point for stress signals. Different signals impinge on different domains of the protein and may cooperate in modulating the type of p53 response, depending on the nature of the incoming signal.

Genomic organization and mutation analyses of the DR5/TRAIL receptor 2 gene in colorectal carcinomas

The DR5/TRAIL receptor 2 gene is a novel TNF receptor family member and induces apoptosis by overexpression of its product. DR5 is located on chromosome 8p21, where allelic deletions are often observed in advanced colorectal cancers. This evidence led us to examine whether or not mutations of the DR5 gene exist in these tumors. We determined the genomic structure of DR5, which consists of nine exons. DR5 has two alternatively spliced isoforms. All seven colorectal cancer (CRC) cell lines examined expressed the longer isoform predominantly. No somatic mutation was found in 41 CRC cases. Loss of heterozygosity of DR5 was found in nine (52.9%) of the 17 informative cases, which is similar to the previously reported frequencies observed for 8p21-22 in colorectal cancers. These findings suggest that inactivation of the DR5 gene may play only a small role, if any, in colorectal tumorigenesis.

EB1089, a synthetic analogue of vitamin D, induces apoptosis in breast cancer cells in vivo and in vitro

1. Effects of the synthetic vitamin D analogue EB1089 on indices of apoptosis in cultured human breast cancer cells and in nitrosomethylurea-induced rat mammary tumours in vivo were investigated. 2. At a dose of 0.5 microg kg(-1) body weight, EB1089 caused significant inhibition of tumour progression over the 28 day treatment period in the absence of a significant increase in serum calcium concentration. Higher doses of EB1089 (1 and 2.5 microg kg(-1)) produced substantial regression of the experimental tumours which was accompanied by a striking change in the histological appearance of tumours consistent with induction of tumour cell death. 3. Fragmentation of genomic DNA is a characteristic feature of apoptosis. With the terminal transferase (TdT) assay, 3' DNA breaks indicative of DNA fragmentation were detected histochemically in mammary tumour cells from animals treated with EB1089 (2.5 microg kg(-1)) for 14 days. 4. Effects of the vitamin D analogue on induction of apoptosis were examined in vitro using the MCF-7 human breast cancer cell line. Using the TUNEL method, positive nuclear staining indicative of DNA fragmentation was detected in cells treated for 4 days with 10 nM EB1089. Apoptosis was also quantitated using a cell death ELISA which revealed a time and dose dependent induction of apoptosis by EB1089. 5. The effects of EB1089 on the expression of two oncoproteins which may regulate apoptosis, bcl-2 and bax were examined by Western analysis. In MCF-7 cell cultures treated with 1,25(OH)2D3 or EB1089 (1 x 10(-8) M), bcl-2 protein levels were decreased in a time-dependent manner relative to control levels. In contrast bax protein was not markedly regulated by these compounds. Densitometric analyses indicate that the vitamin D compounds lower the bcl-2/bax ratio favouring increased susceptibility of MCF-7 cells to undergo apoptosis. 6. These results suggest that the synthetic vitamin D analogue EB1089 may promote tumour regression by inducing active cell death.

Angiogenesis during tumor progression in the oral cavity is related to reduced apoptosis and high tumor cell proliferation

Angiogenesis, the growth of new blood vessels, is believed to aid tumor progression and metastasis. Tumor progression is also influenced by the extent of proliferation and apoptosis. This study, therefore, analyzed in lesions of the oral cavity, the significance of angiogenesis in relation to apoptosis, expression of apoptosis regulatory p53, bax and bcl-2 proteins as well as tissue proliferation defined by cyclin D1 expression. Results from this study suggest that angiogenesis increases as histological abnormality increases in the oral mucosa. The expression of apoptosis regulatory proteins also appears to be altered in a histologically dependent manner. The correlation seen between CD34 expression, cyclin D1 and TUNEL reactive cells suggests that increased angiogenesis, decreased apoptosis and deregulated proliferation occur simultaneously during tumor progression in the oral mucosa. Presence of a mutant p53, increased bcl-2 expression and altered bax expression are also involved in this complex process.

Growth patterns in various macroscopic types of noninvasive intramucosal colorectal carcinoma with special reference to apoptosis and cell proliferation

PURPOSE

Apoptotic cell death and cell proliferation play important roles in the histogenesis and development of colorectal carcinoma. The aim of this study was to examine the relationship between apoptosis and cell proliferation in various macroscopic types of intramucosal colorectal carcinoma in relation to the expression of p53 and bcl-2.

METHODS

One hundred forty cases with endoscopically or surgically resected intramucosal colorectal carcinoma were studied. There were 57 cases of polypoid-type carcinomas, 55 cases of superficial-type carcinomas, and 28 cases of granular-type, laterally spreading tumors. Polypoid-type carcinomas were pedunculated, subpedunculated, or sessile polyps. Superficial-type carcinomas were flat lesions with a smooth, even surface. Granular-type, laterally spreading tumors were superficially spreading lesions with aggregates of nodules and a granular surface. Apoptotic cells were identified by the in situ DNA nick end labeling method. Ki-67, p53, and bcl-2 expression were examined immunohistochemically.

RESULTS

The superficial-type carcinoma apoptotic index (30.9 percent) was significantly lower than that of polypoid-type carcinoma (54.4 percent) and granular-type, laterally spreading tumor (60.7 percent). The superficial-type carcinoma proliferative index (67.3 percent) was significantly higher than that of polypoid-type carcinoma (42.1 percent) and granular-type, laterally spreading tumor (28.6 percent). In superficial-type carcinomas the proliferative index in p53-positive carcinomas was significantly higher, and the apoptotic index was higher in carcinomas with a lower proliferative index. There was no significant difference in apoptotic index, proliferative index, or p53 protein overexpression between de novo carcinomas and those that had arisen in precursor adenomas.

CONCLUSIONS

The pattern of cell death and proliferation may vary with different macroscopic types of intramucosal colorectal carcinoma. Superficial-type colorectal carcinomas especially demonstrate diminished apoptosis and increased cell proliferation. This may be useful in understanding their biologic behavior.

Stimulation of p53-mediated transcriptional activation by the p53-binding proteins, 53BP1 and 53BP2

p53 is a tumor suppressor protein that controls cell proliferation by regulating the expression of growth control genes. In a previous study, we identified two proteins, 53BP1 and 53BP2, that are able to bind to wild type but not to mutant p53 via the DNA-binding domain of p53. We isolated cDNAs expressing a full-length human 53BP1 clone, which predicts a protein of 1972 residues that can be detected in the H358 human lung carcinoma cell line. The 53BP1 and 53BP2 genes were mapped to chromosomes 15q15-21 and 1q41-42, respectively. Immunofluorescence studies showed three types of staining patterns for 53BP1 as follows: both cytoplasmic and nuclear, homogeneous nuclear, and a nuclear dot pattern. In contrast, 53BP2 localized exclusively to the cytoplasm, and this pattern did not change upon coexpression of wild type p53. Although our previous study revealed that p53 is not able to bind simultaneously to either 53BP1 or 53BP2 and to DNA carrying a consensus binding site, both 53BP1 and 53BP2 enhanced p53-mediated transcriptional activation and induced the expression of a p53-dependent protein, suggesting that these proteins might function in signal transduction pathways to promote p53 activity.

Apoptosis and expression of Bax, Bcl-x, and Bcl-2 apoptotic regulatory proteins in colorectal carcinomas, and association with p53 genotype/phenotype

AIMS

Spontaneous apoptosis and expression of the apoptotic regulatory proteins Bax, Bcl-x, and Bcl-2 were investigated in 50 colorectal carcinomas. The p53 genotypes/phenotypes and BAX genotypes were also determined, and possible associations of these with apoptosis and/or with expression of the different apoptotic regulatory proteins were studied.

METHODS

Terminal deoxynucleotidyl transferase (TdT) mediated dUTP labelling of DNA fragments was used to detect apoptotic tumour cells in sections and peroxidase immunohistochemistry was used to assess protein expression. p53 genotype/phenotype was determined using constant denaturant gel electrophoresis/immunoblotting and bax genotype was determined using polymerase chain reaction based methods.

RESULTS

The distribution of tumour apoptotic indices was bimodal with a natural cut off at 1.0% (range, 0.0-5.4%); the median fraction of apoptotic tumour cells was 0.8%. Tumour apoptosis was not associated significantly with tumour DNA ploidy status. Normal mucosal tissue had less than 0.1% apoptotic cells. Staining intensities for Bax, Bcl-x, and Bcl-2 were strong; that is, equivalent to or greater than positive normal mucosal cells, in 11 of 50, 20 of 49, and 20 of 48 carcinomas. Frameshift mutations in the bax gene were detected in three of 42 tumours analysed, all of which were DNA diploid, and Bax protein expression in these tumours was absent or very low. Bax, Bcl-x, and Bcl-2 protein expression were not correlated with tumour apoptosis or tumour DNA ploidy status. p53 was expressed in 34 of 50 tumours and p53 gene mutations were detected in 22 of 29 p53 positive tumours analysed. Apoptosis was significantly lower in a greater number of p53 positive tumours than p53 negative tumours. In addition, Bcl-2 protein expression was significantly higher in a greater number of p53 positive tumours compared with p53 negative tumours. Bax and Bcl-x protein expression were not significantly associated with p53 phenotype/genotype.

CONCLUSIONS

The results indicate that acquisition of a p53 phenotype is associated with lower spontaneous apoptosis and higher expression of Bcl-2. The results also suggest that p53 is not a major determinant for Bax expression in colorectal carcinomas in vivo.

Tumor suppressor p53 as a component of the tumor necrosis factor-induced, protein kinase PKR-mediated apoptotic pathway in human promonocytic U937 cells

Despite what is known about the early signaling events in tumor necrosis factor (TNF) alpha-induced apoptosis, characterization of the downstream events remains largely undefined. It is now known that a cross-talk exists between the interferon and TNF-alpha pathways. This linkage allows recruitment of the cell proliferation suppressor PKR (dsRNA-dependent protein kinase) from the interferon pathway to play a pivotal role in TNF-alpha-induced apoptosis. In this study, we took advantage of the differential TNF-alpha susceptibilities of human promonocytic U937 subclones, deficient in or overexpressing PKR, to further characterize the role of PKR in apoptosis. By reverse transcription-polymerase chain reaction, we demonstrated that TNF-alpha transiently induces the tumor suppressor p53 in U937 cells. This p53 induction lags behind the TNF-alpha induction of PKR by 1 h. By cell viability determination, ultrastructural studies, apoptotic DNA laddering, and antisense techniques, it was shown that inhibition of p53 expression in PKR-overexpressing U937 cells abrogates the TNF-alpha-induced apoptosis in these cells. Conversely, overexpressing wild type p53 in PKR-deficient U937 cells confers the susceptibility of these cells to TNF-alpha-induced apoptosis. This latter result indicates that p53 induction is an event downstream of TNF-alpha-induced up-regulation of PKR, thereby further establishing the critical role of p53 in TNF-alpha-induced apoptosis in U937 cells. PKR-overexpressing U937 cells were found to possess a constitutively higher level of p53, which partly explains why these cells spontaneously undergo apoptosis even without TNF-alpha treatment. Finally, a model is presented on the interplay between PKR and p53 in effecting TNF-alpha-induced apoptosis in U937 cells.

Bcl-2 protein expression associated with resistance to apoptosis in clear cell adenocarcinomas of the vagina and cervix expressing wild-type p53

BACKGROUND

Clear cell adenocarcinomas (CCAs) of the vagina and cervix are rare tumors that often overexpress wild-type p53. In vitro, expression of protooncogene bcl-2 can block p53-mediated apoptosis. The objective of this study was to determine if bcl-2 is expressed in CCAs and whether this expression is associated with inhibition of apoptosis.

METHODS

Twenty-one paraffin-embedded clear cell adenocarcinomas were immunohistochemically stained for bcl-2 (antibody M 887, Dako, Carpinteria, CA) and DNA fragmentation (ApopTag, Oncor, Gaithersburg, MD), a marker for apoptosis. Fifteen tumors were associated with in utero exposure to diethylstilbestrol (DES). Prior p53 gene analysis had indicated the presence of wild-type p53 in each tumor. Human lymphoid tissue containing bcl-2-expressing lymphocytes and DNase I-exposed CCA tissue sections were used as positive controls for the bcl-2 and apoptosis assays, respectively. Expression of bcl-2 and DNA fragmentation was classified (0 to 3+) according to percentage of positive cells and intensity of staining.

RESULTS

Expression of bcl-2 was identified in each CCA examined, and was strongly positive (2+ to 3+) in 18 of 21 samples. Despite the presence of wild-type p53, only 4 of 21 tumors showed evidence of apoptosis as assessed through DNA fragmentation.

CONCLUSIONS

DNA damage leads to increased intracellular p53 levels. Overexpression of p53 induces apoptosis as a means of protecting organisms from the development of malignancy. CCAs of the vagina and cervix, which contain wild-type p53 genes and often overexpress p53 protein, presumably have evolved mechanisms to avoid p53-induced apoptosis. Our observations are consistent with the hypothesis that overexpression of bcl-2 can inhibit p53-mediated apoptosis and suggest a mechanism by which these rare tumors can arise without mutation of the p53 gene.

Expression of 15-lipoxygenase by human colorectal carcinoma Caco-2 cells during apoptosis and cell differentiation

We studied arachidonic acid metabolism and the expression of cyclooxygenase (Cox) and 15-lipoxygenase (15-LO) in the human colorectal carcinoma cell line, Caco-2, which undergo apoptosis and cell differentiation in the presence of sodium butyrate (NaBT). Caco-2 cells expressed very low levels of Cox-1 but highly expressed Cox-2. NaBT treatment shifted the arachidonic acid metabolites by cell lysates from prostaglandins to 15-hydroxyeicosatetraenoic acid, indicating the presence of a 15-LO. Linoleic acid, an excellent substrate for 15-LO, was metabolized poorly by the Caco-2 cells, but NaBT treatment shifted metabolism to 15-LO metabolite, 13(S)-hydroxyoctadecadienoic acid. Caco-2 cells expressed a 15-LO but only after treatment with NaBT, as determined by Northern blotting. Immunoblotting with anti-human 15-LO antibody detected a 72-kDa band in NaBT-treated Caco-2 cells. Expression of 15-LO mRNA was dependent on the duration of NaBT treatment, with the highest expression observed between 10 and 24 h. Results from expression and metabolism studies with arachidonic and linoleic acid cells indicated Cox-2 was responsible for the lipid metabolism in control cells, whereas 15-LO was the major enzyme responsible after NaBT induction of apoptosis and cell differentiation. The 15-LO in Caco-2 cells was characterized as human reticulocyte 15-LO by reverse transcription-polymerase chain reaction and restriction enzyme analysis. The expression of 15-LO and 15-hydroxyeicosatetraenoic acid or 13(S)-hydroxyoctadecadienoic acid formation correlates with cell differentiation or apoptosis in Caco-2 cells induced by NaBT. The addition of nordihydroguaiaretic acid, a lipoxygenase inhibitor, significantly increased NaBT-induced apoptosis, whereas the addition of indomethacin did not alter NaBT-induced apoptosis in the Caco-2 cells. However, indomethacin treatment decreased the expression of Cox-2 in NaBT-treated cells and significantly increased the expression of 15-LO during NaBT treatment. These studies suggest a role for 15-LO, in addition to Cox-2, in modulating NaBT-induced apoptosis and cell differentiation in human colorectal carcinoma cells.

Bcl-2 family expression in salivary glands from patients with primary Sjögren's syndrome: involvement of Bax in salivary gland destruction

To investigate the molecular mechanism of glandular parenchyma destruction in Sjögren's syndrome (SS), Bcl-2, Bax, Bcl-X, and Bak expression were studied. SS (n = 18) and control salivary glands (n = 6) were examined by immunohistochemistry. Apoptosis was assessed by in situ DNA nick end labeling. Infiltrating mononuclear cells in the SS salivary gland showed elevated Bcl-2. These mononuclear cells expressed increased Bax but did not undergo apoptosis. Both SS and control salivary gland ductal epithelial cells expressed Bcl-2, Bax, and Bcl-X. SS, but not normal, salivary gland acinar cells expressed Bax and underwent apoptosis. These results suggest that elevated Bax expression in SS salivary gland acinar cells may play an important role in the apoptotic pathway. In contrast, Bcl-2 expression in SS infiltrating mononuclear cells and ductal cells may contribute to their survival.

BAG-1 and Bcl-2 in IL-2 signaling

Some cytokines can prolong cell survival in hematolymphoid cells and thus may be crucial for regulation of hematolymphoid cell numbers. It has been shown that mitogenic cytokines can induce not only cellular proliferation but also cellular survival by inhibiting apoptosis in hematolymphoid cells. The signals transduced by these cytokines eventually go to the nucleus and induce expression of their specific target genes. In this context, the induction of anti-apoptotic molecules such as Bcl-2 oncoprotein and BAG-1 protein seems to be a key event for the anti-apoptotic function of cytokines. In T lymphocytes, the interaction of interleukin-2 (IL-2) with its receptor (IL-2R) induces both cellular proliferation and cellular survival. The IL-2R consists of three subunits, i.e., IL-2Ralpha, IL-2R(beta)c, and IL-2R(gamma)c chains. Structure-function analysis of the IL-2R(beta)c chain has revealed that there are at least two functional domains within the subunit. The serine-rich (S) region but not the acidic (A) region within the (beta)c chain is responsible for the mitogenic signaling of IL-2R. The S region is also crucial for the cellular survival signaling, which include the induction of anti-apoptotic gene expressions bcl-2 and bag-l. However, the cellular survival signaling is segregated from the mitogenic signaling in independence from the Jak-family protein kinase activation and rapamycin sensitivity. Segregation of the two signaling pathways of a cytokine receptor has also been shown in receptors of the other mitogenic cytokines. Current topics regarding signal transductions of cytokine receptors responsible for the suppression of apoptosis are discussed in this review.

Alterations in the growth factor signal transduction pathways and modulators of the cell cycle in endocervical cells from macaques exposed to TCDD

After more than a year had elapsed since a single oral exposure to 2 and 4 microgram 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg, there was an apparent dose-related increased incidence of significant endocervical squamous metaplasia in a group of cynomolgus macaques (Scott et al., 1998). In the present experiments we investigated the mechanisms by which chemicals like TCDD could induce epithelial cell transdifferentiation in the primate endocervix. One focus of investigation was epidermal growth factor receptor (EGFR) and the key cytosolic signaling kinases, c-Src and protein tyrosine kinase (PTK), whose responses to TCDD are well characterized. A second focus was the distal kinase Erk2 that transduces the cytosolic signal into a nuclear signal, and which in combination with nuclear casein kinase II (CKII), can lead to activation of p53. Finally, we studied three key target proteins of activated p53 (wafl/p21, Cdc2 p34, and Cdk4), whose modulation could produce cell cycle effects. The studies were carried out using primary cell cultures prepared from endocervical epithelium recovered at necropsy from TCDD-treated (2 and 4 microgram TCDD/kg) and untreated macaques. There was a significant decrease in EGFR binding activity in cells from TCDD-treated animals as compared to controls. A marked increase in the protein amount of H-Ras and a significant increase in the activity of c-Src kinase, PTK, and Erk2 were found in cells from TCDD-treated animals. A significant decrease in the activity of CKII and in the protein amount of p53, wafl/p21, and Cdc2 p34 was found. On the other hand, a substantial increase in the protein amount of Cdk4 and DNA binding activity of AP-1 was found in cells from TCDD-treated animals. In vitro experiments using primary cultures of endocervical cells from untreated macaques revealed that these cells have AhR, and that c-Src protein is functionally attached to the AhR and is specifically activated upon ligand binding as judged by the following criteria. (1) A structure-activity relationship study with TCDD and three dioxin congeners revealed a rank order for their potency in activation of AhR-associated c-Src kinase from cervical cells which was identical to that of previously determined toxicity indices. (2) TCDD-induced, AhR-associated c-Src kinase activity was abolished when an AhR immunoprecipitate from cervical cells was preincubated with alpha-naphthoflavone (AhR blocker) or geldanamycin (Src kinase inhibitor) prior to the addition of TCDD. (3) The analysis of the AhR complex showed three proteins of molecular weights of 100 (AhR), 90, and 60 kDa. (4) The same protein with molecular weight 60 kDa was found when the immunoprecipitate with anti AhR-antibody was analyzed by SDS-PAGE, then transferred into nitrocellulose membrane followed by immunobloting the membrane with anti c-Src-antibody. Our data suggest that TCDD induced pathology in endocervical cells through changes in growth factor receptor signaling, other cytosolic signaling proteins, tumor suppressor proteins, and cell cycle proteins.

Coexpression of p53 and tissue transglutaminase genes in human normal and pathologic adrenal tissues

The presence of p53 and tissue transglutaminase (tTG) gene expressions was investigated in human normal and pathologic adrenal tissues with two aims (1) to determine the tissue content of p53 protein, its messenger ribonucleic acid (mRNA) and, especially, tTG mRNA which has not been previously reported and (2) to study possible differences in the coexpression of p53 and tTG in various adrenal disorders. Using Northern blot analysis, p53 and tTG mRNAs were detected in each adrenal tissue examined including 5 normal human adrenals, 6 aldosterone-producing adenomas, 3 Cushing's adenomas, 1 primary nodular adrenocortical hyperplasia causing Cushing's syndrome in an infant, 12 non-hyperfunctioning adrenocortical adenomas, and 4 adrenocortical carcinomas. The results showed a significant positive correlation between these two mRNAs in all adrenal tissues except adrenocortical carcinomas. Compared to normal adrenals, high p53 mRNA levels were observed in aldosterone-producing and Cushing's adenomas and, most markedly, in a tissue from a primary nodular adrenocortical hyperplasia. Also, Cushing's adenomas had significantly higher tTG mRNA contents. Immunohistochemistry for wild-type and mutant p53 protein showed numerous p53 positive cells with a strong nuclear staining in a tissue from a primary nodular adrenocortical hyperplasia, whereas the p53 positive cells were absent, except those with a faint nuclear staining, in all other adrenal tissues. However, all adrenal tissues showed detectable p53 contents by the more sensitive method of luminometric immunoassay (LIA). Using this method, aldosterone-producing adenomas exhibited significantly higher p53 contents than normal adrenal tissues. These observations may support potentially important roles for p53 and tTG in adrenal pathophysiology, especially in mechanisms which influence the evolution and/or progression of aldosterone-producing and Cushing's adenomas and, most probably, hyperplasias.

New isolation technique to study apoptosis in human intestinal epithelial cells

Intestinal epithelial cells derive from stem cells at the base of the crypt and migrate along the crypt-lumen axis. Their life is terminated as they reach the luminal surface where they detach and are shed. Intestinal epithelial cells show evidence of apoptosis in the region of shedding, and cell death is thought to resemble a form of apoptosis called detachment-induced cell death, or anoikis. Human intestinal epithelial cells die rapidly in vitro due to loss of anchorage during isolation, making primary culture of these cells a goal that has not yet been reached. However, the molecular mechanisms underlying this process of anoikis are largely unknown. In this study, a novel protocol for the rapid, temperature-controlled isolation of highly purified human colonic epithelial cells from surgical specimens is described. Using this method, early molecular events of anoikis in nontransformed epithelial cells were studied. Intestinal epithelial cells were isolated at the beginning of the apoptotic cascade, before the activation of caspase 3 family members and cleavage of poly(ADP-ribose) polymerase and DNA fragmentation. Elucidating the molecular mechanisms of detachment-induced cell death may facilitate the establishment of long-term primary cultures of human intestinal epithelial cells and enhance our understanding of homeostasis in the intestinal epithelium.

Enhancement of radiosensitivity of wild-type p53 human glioma cells by adenovirus-mediated delivery of the p53 gene

OBJECT

The authors sought to determine whether combining p53 gene transfer with radiation therapy would enhance the therapeutic killing of p53 wild-type glioma cells. It has been shown in several reports that adenovirus-mediated delivery of the p53 gene into p53 mutant gliomas results in dramatic apoptosis, but has little effect on gliomas containing wild-type p53 alleles. Therefore, p53 gene therapy alone may not be a clinically effective treatment for gliomas because most gliomas are composed of both p53 mutant and wild-type cell populations. One potential approach to overcome this problem is to exploit the role p53 plays as an important determinant in the cellular response to ionizing radiation.

METHODS

In vitro experiments were performed using the glioma cell line U87MG, which contains wild-type p53. Comparisons were made to the glioma cell line U251MG, which contains a mutant p53 allele. Monolayer cultures were infected with an adenovirus containing wild-type p53 (Ad5CMV-p53), a control vector (dl312), or Dulbecco's modified Eagle's medium (DMEM). Two days later, cultures were irradiated and colony-forming efficiency was determined. Transfection with p53 had only a minor effect on the plating efficiency of nonirradiated U87MG cells, reducing the plating efficiency from 0.23 +/- 0.01 in DMEM to 0.22 +/- 0.04 after addition of Ad5CMV-p53. However, p53 transfection significantly enhanced the radiosensitivity of these cells. The dose enhancement factor at a surviving fraction of 0.10 was 1.5, and the surviving fraction at 2 Gy was reduced from 0.61 in untransfected controls to 0.38 in p53-transfected cells. Transfection of the viral vector control (dl312) had no effect on U87MG radiosensitivity. In comparison, transfection of Ad5CMV-p53 into the p53 mutant cell line U251 MG resulted in a significant decrease in the surviving fraction of these cells compared with controls, and no radiosensitization was detected. To determine whether Ad5CMV-p53-mediated radiosensitization of U87MG cells involved an increase in the propensity of these cells to undergo apoptosis, flow cytometric analysis of terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridinetriphosphate nick-end labeling-stained cells was performed. Whereas the amount of radiation-induced apoptosis in uninfected and dl312-infected control cells was relatively small (2.1 +/- 0.05% and 3.7 +/- 0.5%, respectively), the combination of Ad5CMV-p53 infection and radiation treatment significantly increased the apoptotic frequency (18.6 +/- 1.4%). To determine whether infection with Ad5CMV-p53 resulted in increased expression of functional exogenous p53 protein, Western blot analysis of p53 was performed on U87MG cells that were exposed to 9 Gy of radiation 2 days after exposure to Ad5CMV-p53, dl312, or DMEM. Infection with Ad5CMV-p53 alone increased p53 levels compared with DMEM- or dl312-treated cells. Irradiation of AdSCMV-p53-infected cells resulted in a further increase in p53 that reached a maximum at 2 hours postirradiation. To determine whether exogenous p53 provided by Ad5CMV-p53 had transactivating activity, U87MG cells were treated as described earlier and p21 messenger RNA levels were determined. Infection of U87MG cells with Ad5CMV-p53 only resulted in an increase in p21 compared with DMEM- and dl312-treated cells. Irradiation of AdSCMV-p53-infected cells resulted in an additional time-dependent increase in p21 expression.

CONCLUSIONS

These data indicate that adenovirus-mediated delivery of p53 may enhance the radioresponse of brain tumor cells containing wild-type p53 and that this radiosensitization may involve converting from a clonogenic to the more sensitive apoptotic form of cell death. Although the mechanism underlying this enhanced apoptotic susceptibility is unknown, the AdSCMV-p53-infected cells have a higher level of p53 protein, which increases further after irradiation, and this exogenous p53 is transcriptionally active. (ABSTRACT TRUNCATE

Moderate amplifications of the c-myc gene correlate with molecular and clinicopathological parameters in colorectal cancer

C-myc gene activation is a common event in multiple types of neoplasia and has been associated with different cellular processes relevant to the malignant transformation of cancer cells. C-myc gene amplification has been analysed in colorectal carcinomas by means of an innovative DNA fingerprinting method based on the arbitrarily primed PCR. This method requires a low amount of DNA, uses multiple internal controls and appears sensitive and reproducible. Clinicopathological and molecular correlates have been investigated in a series of 70 colorectal carcinomas. The incidence of c-myc amplification was 26%, ranging from two- to fivefold increase in copy number. C-myc amplification occurrence was more frequent in more advanced stages of tumour invasion (P < 0.001) and was associated with mutations in the p53 tumour-suppressor gene (P = 0.048). The presence of c-myc amplification was indicative of a shorter disease-free survival period but, because of its strong association with Dukes' stage, its prognostic value is questionable.

Bcl-2 protein expression: association with p53 and prognosis in colorectal cancer

Bcl-2 expression in colorectal carcinomas was studied in a series of 224 patients and the relation to p53 expression, stage and survival assessed. Bcl-2 expression was down-regulated compared with normal mucosa in 67% (151) of the cases. In 144 cases staining was positive for p53 (MAB DO7), and 41 of these 144 p53-positive cases were also bcl-2 positive (28%) compared with 32 of the remaining 80 p53-negative cases (40%). Survival was significantly worse (P = 0.01) in the p53-positive cases. Bcl-2-positive cases, including patients in all Dukes' stages, had a slightly better prognosis which was not statistically significant. However, cases at an early stage (Dukes' stages A and B) and with negative p53 status, had a much better prognosis if they showed bcl-2 protein expression, suggesting that the bcl-2 status itself has an effect on prognosis (P = 0.01). Neither bcl-2 nor p53 alone was correlated with stage, but when examined by both p53 and bcl-2 status a group [bcl-2(+)/p53(-)] with better prognosis was defined. The last group was significantly lower Dukes' stage, with 26 out of 32 cases (81%) being A or B compared with 22 (11%) of the 202 remaining cases (P = 0.004). Thus, either loss of bcl-2 expression or gain of abnormal p53 expression is associated with high stage and poor prognosis. The bcl-2(+)/p53(-) phenotype is similar to that of normal mucosa, and these results suggest that such cases represent an indolent group at an early stage in the progression of colorectal cancer.

Apoptosis in the pathogenesis of cutaneous lupus erythematosus

Defective regulation of apoptosis may play a role in the development of autoimmune diseases such as systemic lupus erythematosus, in which the skin is a prominent target. To our knowledge, however, the nature of epidermal changes in cutaneous lupus erythematosus (LE) has not previously been investigated. We investigated the involvement of apoptosis in cutaneous LE. A total of 44 lesional skin samples from patients with cutaneous LE, 44 skin samples from patients with scleroderma, five skin specimens from patients suffering from dermatomyositis, and 13 normal skin samples were stained immunohistochemically with monoclonal antibodies to Ki-67, p53 (DO-7), and bcl-2. The lesional skin from cutaneous LE, except LE profundus, showed a marked increase in Ki-67- and p53-positive keratinocytes, which were predominantly located in the basal layer of the epidermis and follicle, and a drastic reduction in the number of bcl-2-positive cells localized in the basal cell compartment. With TdT-mediated dUTP-biotin nick end-labeling staining, we demonstrated that extensive apoptosis occurred in almost the whole epidermis of cutaneous LE, except in cases of LE profundus. This abnormal expression of Ki-67, p53, and bcl-2 and the occurrence of apoptosis in the epidermis was also observed in epidermis from patients with dermatomyositis, but not in that from patients with scleroderma.

The PITSLRE protein kinase family

A family of p34Cdc2 related protein kinases, the PITSLRE kinases, is generated by alternative splicing and promoter utilization from three duplicated and tandemly linked genes on human chromosome 1p36.3, which is frequently deleted during the late stages of tumorigenesis. PITSLRE mRNA, protein, and enzyme activity are induced during Fas receptor- and glucocorticoid-mediated apoptosis of human T cells. Several PITSLRE isoforms are specific targets of proteolysis during apoptosis, generating an enzymatically active 50 kDa isoform. Inhibition of this protease activity blocks PITSLRE processing and enzyme activation, as well as apoptosis. Thus, PITSLRE kinases may be integral downstream components of apoptotic signal transduction pathway(s). Furthermore, PITSLRE genes, and their products, are physically altered in human neuroblastoma tumors, suggesting that they may be tumor suppressors.

Cooperative interactions between RB and p53 regulate cell proliferation, cell senescence, and apoptosis in human vascular smooth muscle cells from atherosclerotic plaques

Compared with vascular smooth muscle cells (VSMCs) from normal vessels, VSMCs from human atherosclerotic plaques proliferate more slowly, undergo earlier senescence, and demonstrate higher levels of apoptosis in culture. The tumor suppressor genes p105RB (retinoblastoma, acting through the E2F transcription factor family) and p53 regulate cell proliferation, cell senescence, and apoptosis in many cell types. We have therefore determined whether these stable growth properties of plaque VSMCs reflect altered activity of RB and/or p53. VSMCs were derived from coronary atherectomies or from normal coronary arteries from transplant recipients. Compared with normal VSMCs, plaque VSMCs showed a higher ratio of the active (hypophosphorylated) to the inactive (phosphorylated) form of RB and a lower level of E2F transcriptional activity. Cells were stably transfected with retrovirus constructs that inhibited RB or p53 alone or in combination. Suppression of RB alone increased rates of cell proliferation and apoptosis and inhibited cell senescence in normal VSMCs. Suppression of p53 and RB together had similar effects but, additionally, resulted in immortalization of normal VSMC cultures. In contrast, inhibition of RB binding to E2F or ectopic expression of E2F-1 in plaque VSMCs induced massive apoptosis, which required suppression of p53 to rescue cells. Suppression of RB and p53 together increased cell proliferation and delayed senescence but failed to immortalize plaque VSMCs. Inhibition of p53 alone had minimal effects on plaque VSMCs but increased the lifespan of normal VSMCs. We conclude that human plaque VSMCs have slower rates of cell proliferation and earlier senescence than do cells from normal vessels because of a defect in phosphorylation of RB. Furthermore, both disruption of RB/E2F and inhibition of p53 are required for plaque VSMCs to proliferate without apoptosis. This observation may explain the relatively low level of cell proliferation and high level of apoptosis seen in VSMCs in human atherosclerotic plaques.

Nucleotide sequence of a highly conserved region of the canine p53 tumour suppressor gene

An evolutionary conserved region of the canine tumour suppressor gene, p53, was PCR amplified and its DNA sequence determined. The 1003 bp fragment consisted of exons 5 to 8 and the intervening introns. A high level of sequence homology was demonstrated with human sequences, with the evolutionary conserved domains II, III, IV and V being identical.

Multisite phosphorylation and the integration of stress signals at p53

The p53 tumour suppressor protein is a potent transcription factor that plays a major role in the defence against tumour development. p53 exists in a latent form that can be activated by a range of stresses including DNA damage, hypoxia, cytokines, metabolic changes, viral infection, and activated oncogenes. Activation of p53 can lead to cellular growth arrest prior to entry into either S phase or mitosis or can trigger cell death through apoptosis. The modification of p53 by multisite phosphorylation provides a potential link between stress signalling and the regulation of p53 activity, and there is now striking evidence that agents that activate p53 can lead to selective changes in its phosphorylation status. Topologically, the phosphorylation sites in p53 fall into two discrete functional domains. Four phosphorylation events take place within the N-terminal 83 amino acids containing the transactivation domain and a region involved in transcription-independent growth suppression. At least three of these modifications occur in response to agents that cause cellular stress such as DNA damage. At the C-terminus, there are three phosphorylation events, each of which can independently regulate the specific DNA-binding function of p53, suggesting convergent control by different signalling pathways. The multiplicity of these covalent modifications and their responsiveness to a wide range of signals suggest that p53 activity is tightly and coordinately controlled in response to stresses and changes in the cellular environment.

Apoptosis and cellular proliferation in human epidermal squamous cell neoplasia

We examined cell loss (apoptosis) and proliferation in a histopathological spectrum of epidermal squamous cell neoplasia, including 11 cases of solar keratosis (SK), 18 Bowen's diseases (BD) and 19 invasive squamous cell carcinomas (SCC). Apoptotic and proliferative cells were determined by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) and by the detection of nuclear antigen Ki-67, respectively. Few apoptotic cells were observed in normal epidermis, while TUNEL index (TI; percentage of TUNEL-positive cells) was highest for SCCs, followed by BDs and SKs, in the order given. Although the mean Ki-67 index did not differ between SCCs and BDs, both disease types showed a significantly higher index than the SKs. Of SCCs, both TI and Ki-67 index values were significantly higher in poorly than in well differentiated carcinomas. TI was significantly higher in SCCs without P53 immunohistochemical expression than in SCCs with P53 expression, while TI and Ki-67 indices did not correlate with P53 expression in the SKs and BDs. These results suggest that apoptosis reflects not only cell loss, but also proliferative activity in the epidermal neoplastic lesions.

A novel 52 kDa protein induces apoptosis and concurrently activates c-Jun N-terminal kinase 1 (JNK1) in mouse C3H10T1/2 fibroblasts

A 52 kDa protein (p52) was purified from chicken embryos and its corresponding cDNA was cloned. The p52 cDNA is 1768 bp long and has an open reading frame of 465 amino acids. The sequence of the p52 cDNA shows significant homology with mouse and human cDNAs from the EST database, so do the deduced amino acid sequences, indicating the existence of human and mouse homologues of p52. Northern blot hybridization showed that the p52 mRNA was expressed in a wide range of embryonic and adult tissues. There was more p52 mRNA in embryonic heart and liver than in the brain or muscle. The adult testis had the highest level of p52 mRNA, whereas adult liver had the lowest. Expression of p52 in mouse C3H10T1/2 fibroblasts caused apoptotic cell death, upregulation of transcription factor c-Jun and activation of c-Jun N-terminal kinase 1 (JNK1). In addition, expression of Bcl-2, but not of the dominant negative mutant JNK1, can block the p52-mediated apoptosis. These results indicate that p52 may represent a new cell-death protein inducing apoptosis and activating JNK1 through different pathways.

DNA-binding activity of wild-type p53 protein is mediated by the central part of the molecule and controlled by its C terminus

The DNA binding activity of wild type p53 is central to its activity. The "central" part of the molecule, where most mutations appear in primary human tumors, is the actual DNA binding domain. The C-terminal part was shown to exert a negative effect on the DNA binding activity. In the present study we show that while anti-p53 antibodies recognizing the C terminus of the wild type p53 facilitate DNA binding activity, blocking of the wild type specific epitope by specific anti-p53 antibodies, inhibited the DNA binding activity of the wild type p53 protein. An alternatively spliced p53 protein exhibits an augmented DNA binding activity. The fact that most p53 mutants have lost the wild type p53 conformation specific epitope, coupled with the observation that blocking of this site by binding specific antibodies, prevents the interaction of wild type p53 with DNA, suggests that maintaining the correct structural conformation of this site is central for DNA binding activity. Still, the internal structure of the p53 target and particularly the length of the sequence between the two tandem inverted repeats, is critical for protein-DNA interaction behavior.