Life (and death) in a malignant tumour

Expression of apoptosis regulatory proteins of the Bcl-2 family and p53 in primary resected non-small-cell lung cancer

Proteins of the Bcl-2 family as well as p53 are important regulators of apoptosis. Alterations in the expression of these proteins can contribute to the formation of cancer, as well as influence tumour response to chemo- and radiotherapy. We used antibodies specific for the human Bcl-2, Mcl-1, Bax, Bak and p53 proteins to examine the expression of these apoptosis-regulating genes in 49 archival specimens of patients with radically resected non-small-cell lung cancer (NSCLC). Tumour cells containing immunostaining for the antiapoptotic proteins Bcl-2 and Mcl-1 were present in 31% and 58% of the cases evaluated, respectively, whereas immunopositivity for the proapoptotic proteins Bax and Bak was found in 47% and 58% of the samples. p53 immunopositivity was detected in 61% of the samples. The expression of Bcl-2 and p53 and the expression of Mcl-1 and Bax showed a positive association (P = 0.02 and P = 0.06 respectively), whereas the expression of Bax was inversely related to p53 (P = 0.008). The expression of Bcl-2 had a negative influence on relapse-free survival in this population of primary resected NSCLC patients (P = 0.02). The expression of p53 and Bcl-2 was significantly associated with metastasis-free survival (P < 0.01). Only patients with p53-positive tumours developed metastases during the follow-up period. Our results establish the frequent expression of the Bcl-2 family proteins Bcl-2, Mcl-1, Bax and Bak in NSCLC. It can be expected that Bcl-2 family members have no straightforward impact on clinical outcome in this disease because their interactions in the regulation of apoptosis are complex.

Evidence for a role of delayed death and genomic instability in radiation-induced neoplastic transformation of human hybrid cells

HeLa x skin fibroblast human hybrid cells have been developed into a model of radiation-induced neoplastic transformation. The authors' studies indicate that the loss of putative tumour suppressor loci on fibroblast chromosomes 11 and 14 is evident after radiation-induced neoplastic transformation. How these fibroblast chromosomes/putative tumour suppressor loci are lost after radiation exposure is currently being investigated. It has been shown that the appearance of transformed foci correlates with the onset of the delayed reduction in plating efficiency or delayed death. This delayed death appears to be the result of the onset of a novel delayed apoptosis in the irradiated progeny beginning around day 8 post-irradiation. It was proposed that the reduction in plating efficiency and subsequent neoplastic transformation are all the result of a radiation-induced genomic instability. The instability process has two relevant outcomes: (1) cell death due to the induction of a delayed apoptosis in cells; and (2) neoplastic transformation of a small subset of survivors that have lost fibroblast chromosomes 11 and 14 (tumour suppressor loci) but either have not acquired enough genetic damage to induce the apoptotic response or have undergone molecular changes allowing them to bypass apoptosis. Data from the genomic instability and delayed death literature will be reviewed in terms of relevance to radiation-induced neoplastic transformation. New data are presented which demonstrate that use of growth media supplemented with a specific lot of calf serum was found to increase the number of cells undergoing radiation-induced neoplastic transformation, compared with standard serum after a fixed dose of radiation. This correlates with an increase in delayed death in the irradiated progeny which the authors propose is the result of increased genomic instability post-irradiation of cells grown in this serum. Preliminary data are presented indicating that a delayed apoptosis is also seen after high-energy He- particle exposure in this system.

The G1-phase growth-arresting action of interleukin-1 is independent of p53 and p21/WAF1 function

Interleukin-1 (IL-1) causes G1-phase growth arrest of A375-C6 human melanoma cells by hypophosphorylation of the retinoblastoma susceptibility gene product Rb. Because p53 and p21/WAF1 proteins are key components of growth arrest pathways involving Rb hypophosphorylation, we tested the functional role of these two proteins in IL-1 action. Exposure to IL-1 caused induction of both p53 and p21/WAF1 proteins. However, inhibition of p53 function by the K1 mutant of SV40-T antigen or by m175 (Arg to His) dominant-negative mutant of p53 did not result in abrogation of IL-1 action, suggesting that p53 function is not required for growth arrest by IL-1. Studies aimed at testing the role of p21/WAF1 in IL-1 action indicated that IL-1 induced p21/WAF1 expression independently of the p53 status of the cells. However, inhibition of p21/WAF1 expression resulted in only a marginal rescue from the growth-arresting action of IL-1. These findings imply that despite their induction, neither wild-type p53 nor p21 can fully account for the growth arrest by IL-1. Thus, a p53- and p21-independent pathway(s) mediates IL-1 action.

Comparison of bax, waf1, and IMP dehydrogenase regulation in response to wild-type p53 expression under normal growth conditions

Recently, we demonstrated that downregulation of inosine-5'-monophosphate dehydrogenase (IMPD; IMP:NAD oxidoreductase, EC 1.2.1.14), the rate-limiting enzyme for guanine nucleotide biosynthesis, is required for p53-dependent growth suppression. These studies were performed with cell lines derived from immortal, nontumorigenic fibroblasts that express wild-type p53 conditionally by virtue of a metal-responsive promoter. Here, the p53-dependent properties of the original "p53-inducible" fibroblasts are presented in detail and compared to related properties of epithelial cells that also express wild-type p53 conditionally, but by virtue of a temperature-responsive promoter. Both types of p53-inducible cells were designed to approximate normal physiologic relationships between the host cell and the regulated p53 protein. Together, they were used to investigate expression relationships between IMPD and other p53-responsive genes proposed as mediators of p53-dependent growth suppression. In both types of cells, IMPD activity, protein, and mRNA were consistently coordinately reduced in response to p53 expression. In contrast, mRNAs for waf1, bax, and mdm2 showed disparate patterns of expression, being induced in one conditional cell type, but not the other. This distinction in regulation pattern suggests that under normal growth conditions, unlike IMPD downregulation, bax and waf1 induction is not a rate-determining event for p53-dependent growth suppression.

Strand asymmetry of CpG transitions as indicator of G1 phase-dependent origin of multiple tumorigenic p53 mutations in stem cells

In dividing cells, expression of mutations is DNA strand symmetric. Of all mutations originating de novo in nondividing cells, only those in the transcribed (noncoding) strand are immediately expressed in mRNA and protein. In contrast, any new mutation in the nontranscribed (coding) strand remains unexpressed until the cells enter S phase and begin proliferation. This previously unrecognized difference enables us to examine the cell cycle-dependent origin of multiple tumorigenic mutations in stem cells. The human p53 gene, which acts as a gatekeeper in the control of G1 to S phase transition, was chosen for the analysis. Of all multiple mutations contained in p53 databases, we have tested in detail CpG transitions. Three features of CpG sites dictate this choice: C --> T transitions at methylated mCpG are the direct product of mC deamination and are replication-independent; it is easy to identify the strand bearing a primary mC --> T event because C --> T on the transcribed strand appears as G --> A on the nontranscribed strand; and CpG transitions are the most frequent (as both singular and multiple occurrences) tumor-related p53 mutations. The origin of double nonsilent CpG transitions in nondividing cells predicts a significant excess of the heterostrand (C --> T, G --> A) doublets over the homostrand (C --> T, C --> T and G --> A, G --> A) doublets. For p53, we found such an excess. Based on this result, along with the results of three other tests reported here, we conclude that the majority of multiple p53 mutations from human tumors occurred in quiescent stem cells.

A new role for hypoxia in tumor progression: induction of fragile site triggering genomic rearrangements and formation of complex DMs and HSRs

Genome rearrangements including gene amplification are frequent properties of tumor cells, but how they are related to the tumor microenvironment is unknown. Here, we report direct evidence for a causal relationship between hypoxia, induction of fragile sites, and gene amplification. Recently, we showed that breaks at fragile sites initiate intrachromosomal amplification. We demonstrate here that hypoxia is a potent fragile site inducer and that, like fragile sites inducing drugs, it drives fusion of double minutes (DMs) and their targeted reintegration into chromosomal fragile sites, generating homogeneously staining regions (HSRs). This pathway operates efficiently for DMs bearing different sequences, suggesting a model of hypoxia-driven formation of the HSRs containing nonsyntenic sequences frequently observed in solid tumors.

The prevention of cancer

1. The major causes of cancer are as follows: (a) Smoking: about a third of U.S. cancer (90% of lung cancer). (b) Dietary imbalances, e.g., lack of dietary fruits and vegetables: The quarter of the population eating the least fruits and vegetables has double the cancer rate for most types of cancer compared to the quarter eating the most; micronutrients may account for much of the protective effect of fruits and vegetables. Excess calories may also contribute to cancer. (c) Chronic infections: mostly in developing countries. (d) Hormonal factors influenced by life-style. 2. There is no epidemic of cancer, except for lung cancer due to smoking. Cancer mortality rates have declined 16% since 1950 (excluding lung cancer and adjusted for the increased life span of the population). 3. Regulatory policy that is focused on traces of synthetic chemicals is based on misconceptions about animal cancer tests. Recent research contradicts these ideas: (a) Rodent carcinogens are not rare. Half of all chemicals tested in standard high-dose animal cancer tests, whether occurring naturally or produced synthetically, are "carcinogens." (b) There are high-dose effects in these rodent cancer tests that are not relevant to low-dose human exposures and which can explain the high proportion of carcinogens. (c) Though 99.9% of the chemicals humans ingest are natural, the focus of regulatory policy is on synthetic chemicals. Over 1000 chemicals have been described in coffee: 27 have been tested and 19 are rodent carcinogens. Plants that we eat contain thousands of natural pesticides which protect plants from insects and other predators: 64 have been tested and 35 are rodent carcinogens. 4. There is no convincing evidence that synthetic chemical pollutants are important for human cancer. Regulations that try to eliminate minuscule levels of synthetic chemicals are enormously expensive: EPA estimates that total expenditures on environmental regulations cost $140 billion/year. It has been estimated by others that the United States spends 100 times more to prevent one hypothetical, highly uncertain death from a synthetic chemical than it spends to save a life by medical intervention. Attempting to reduce tiny hypothetical risks also has costs; for example, if reducing synthetic pesticides makes fruits and vegetables more expensive, thereby decreasing consumption, then cancer will be increased. 5. Improved health will come from knowledge due to biomedical research and from life-style changes by individuals. Little money is spent on biomedical research or on educating the public about lifestyle hazards, compared to the cost of regulations.

Mutations in residues of TP53 that directly contact DNA predict poor outcome in human primary breast cancer

The tumour-suppressor gene TP53 is frequently mutated in breast tumours, and the majority of the mutations are clustered within the core domain, the region involved in DNA binding. We searched for alterations in this central domain of the TP53gene in 222 human breast cancer specimens using polymerase chain reaction-single-strand conformation analysis (PCR-SSCA) followed by sequencing. TP53 gene mutations were observed in 66 tumours (31%), including three tumours that contain two mutations. Fifty-four (78%) of these mutations were missense point mutations, one was a nonsense mutation and four were deletions and/or insertions causing disruption of the protein reading frame, whereas four mutations were either silent or a polymorphism (at codon 213; n = 6). Interestingly, the majority of missense mutations were observed at codon 248. The outcome has been related with patient and tumour characteristics, and with prognosis in 177 patients who were eligible for analysis of both relapse-free and overall survival (median survival for patients alive was 115 months). There was no significant association between the frequency of TP53 mutations and menopausal or nodal status, or tumour size. In a Cox univariate analysis, TP53 gene mutation was significantly associated with poor relapse-free survival (RFS: P = 0.02) but not with overall survival (OS: P = 0.07). In a Cox multivariate analysis, including classical prognostic factors, TP53 gene mutation independently predicted poor RFS and OS (RHR = 1.8 and 1.6 respectively). Unexpectedly, the median relapse-free survival of patients with a polymorphism at codon 213 or with a silent mutation was shorter (median 11 months) than the median relapse-free survival of patients with or without a TP53 gene mutation (median 34 or 48 months respectively). In an exploratory subset analysis, mutations in codons that directly contact DNA were related with the poorest relapse-free (P < 0.05) and overall survival (P < 0.02). These data imply that in the analysis of the prognostic value of TP53, the type of mutation and its biological function should be considered.

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.

Inosine-5'-monophosphate dehydrogenase is a rate-determining factor for p53-dependent growth regulation

We have proposed that reduced activity of inosine-5'-monophosphate dehydrogenase (IMPD; IMP:NAD oxidoreductase, EC 1.2.1.14), the rate-limiting enzyme for guanine nucleotide biosynthesis, in response to wild-type p53 expression, is essential for p53-dependent growth suppression. A gene transfer strategy was used to demonstrate that under physiological conditions constitutive IMPD expression prevents p53-dependent growth suppression. In these studies, expression of bax and waf1, genes implicated in p53-dependent growth suppression in response to DNA damage, remains elevated in response to p53. These findings indicate that under physiological conditions IMPD is a rate-determining factor for p53-dependent growth regulation. In addition, they suggest that the impd gene may be epistatic to bax and waf1 in growth suppression. Because of the role of IMPD in the production and balance of GTP and ATP, essential nucleotides for signal transduction, these results suggest that p53 controls cell division signals by regulating purine ribonucleotide metabolism.

p53 protein expression in peripheral lymphocytes from atrazine chronically intoxicated rats

The p53 expression in peripheral lymphocytes of rats chronically exposed to atrazine was investigated. The experiment was performed in female Wistar rats. Atrazine was administrated in different doses (2.7 and 5.4 mg/kg body weight), each dose once a day, 5 days per week, for 6 and 12 months. The percentage of rats peripheral lymphocytes expressing p53 protein was evaluated by immunocytochemical technique, using a monoclonal antibody (clone PAb 122) against a common epitope, both for the wild type and the mutant p53 protein. The results indicate that in the atrazine long-term administration, the serum level of atrazine is associated with: (i) Significantly increased percentage of lymphocytes expressing p53 protein for all treated animals; (ii) different p53 intracellular compartmentalization (nucleus and cytoplasm), depending on dose and time of atrazine administration. The present study suggests that atrazine modifies the p53 expression, which could confirm the clastogenicity of this herbicide, and that the detection of the p53 protein may serve as a biomarker for the long-term exposure to atrazine.

P53 expression in altered limbal basal cells of pingueculae, pterygia, and limbal tumors

PURPOSE

We previously discovered that the pathogenesis of pterygia was due to a vimentin-expressing, altered limbal epithelial basal cell, the pterygium cell. Since UV radiation epidemiologically correlates as the etiologic agent for pterygia and limbal tumors and is mutagenic for the p53 gene, our goal was to search for p53 gene mutations immunohistochemically in the altered limbal basal cells of these growths and of pingueculae from which they seem to originate.

METHODS

Longitudinal serial sections through six pingueculae, 14 primary and five recurrent pterygia, and five limbal tumors were studied immunohistochemically with p53 monoclonal antibody DO-1 and, in some specimens, with antivimentin antibody.

RESULTS

P53 expression was found in the limbal cells of all pterygia, limbal tumors, and Stage II pingueculae, but not in normal limbal-corneal epithelial cells. However, when the same specimens were examined with a TUNEL assay, few if any apoptotic cells were found. A finding of increased nuclear p53 gene product with little or no apoptosis is consistent with an activating mutation of the p53 gene, resulting in increased steady-state levels of the protein.

CONCLUSIONS

The finding of increased nuclear p53 in the limbal epithelium of pterygia, limbal tumors, and most pingueculae indicates the probable existence of p53 mutations in these cells as an early event in their development, which is consistent with their causation by UV radiation causation. In addition, due to a damaged p53-dependent programmed cell death mechanism, mutations in other genes are progressively acquired which allows the multi-step development of pterygia and limbal tumor cells from p53 positive cells overlying a Stage II pinguecula. Similarly, a pterygium dysplasia could arise from a pterygium cell. A classification for limbal basal cell tumors is proposed, and the different stromal changes in pingueculae, pterygia, and limbal tumors are identified. Two cell types were also identified: a p53-positive pinguecula limbal epithelial cell (a pinguecula II cell) and a p53-positive pterygium dysplasia cell (pterygium dysplasia cell).

Molecular heterogeneity in prostate cancer: can TP53 mutation unravel tumorigenesis?

While prostate cancer is the most common malignant visceral neoplasm of men, its etiology remains largely unknown and its clinical course unpredictable. Molecular genetics of prostate cancer has become a fruitful area of investigation and might provide clues to understanding these phenomena. Mutation of the TP53 tumor suppressor gene (encoding the p53 protein) has been commonly reported as a critical event in human carcinogenesis, but recent findings in prostate cancer research call into question the correlation between TP53 mutation and prognosis for patients with this tumor. Whole-mount analysis has begun to address the histologic significance of the focal evolution of TP53 mutation in a pre-existing cancer and to reveal its role throughout the process of tumor progression. This model might also apply to other tumors.

Monoallelically expressed gene related to p53 at 1p36, a region frequently deleted in neuroblastoma and other human cancers

We describe a gene encoding p73, a protein that shares considerable homology with the tumor suppressor p53. p73 maps to 1p36, a region frequently deleted in neuroblastoma and other tumors and thought to contain multiple tumor suppressor genes. Our analysis of neuroblastoma cell lines with 1p and p73 loss of heterozygosity failed to detect coding sequence mutations in remaining p73 alleles. However, the demonstration that p73 is monoallelically expressed supports the notion that it is a candidate gene in neuroblastoma. p73 also has the potential to activate p53 target genes and to interact with p53. We propose that the disregulation of p73 contributes to tumorigenesis and that p53-related proteins operate in a network of developmental and cell cycle controls.

P53 mutations in tumours induced by intraperitoneal injection of crocidolite asbestos and benzo[a]pyrene in rats

Mutation analysis of the tumour suppressor gene p53 in tumours induced in the peritoneal cavity of rats revealed differences in the mutational pattern with regard to the carcinogenic substances applied. In tumours induced by benzo[a]pyrene a considerable amount of p53 mutations resulting in an altered protein structure could be detected. For the development of these tumours an escape from the p53 mediated cell cycle control can be assumed. However, in tumours of the same tumour type induced by crocidolite asbestos no mutations could be observed. Since there were even no spontaneous p53 mutations detectable in this tumour group, it is obvious that in these tumours the escape from cell cycle control does not take place via inactivation of p53. Therefore, it is concluded that the molecular mechanisms of carcinogenesis and tumour development in this tumour type depend on the type of carcinogen applied.

Proteolysis by calpains: a possible contribution to degradation of p53

p53 is a short-lived transcription factor that is frequently mutated in tumor cells. Work by several laboratories has already shown that the ubiquitin-proteasome pathway can largely account for p53 destruction, at least under specific experimental conditions. We report here that, in vitro, wild-type p53 is a sensitive substrate for milli- and microcalpain, which are abundant and ubiquitous cytoplasmic proteases. Degradation was dependent on p53 protein conformation. Mutants of p53 with altered tertiary structure displayed a wide range of susceptibility to calpains, some of them being largely resistant to degradation and others being more sensitive. This result suggests that the different mutants tested here adopt slightly different conformations to which calpains are sensitive but that cannot be discriminated by using monoclonal antibodies such as PAb1620 and PAb240. Inhibition of calpains by using the physiological inhibitor calpastatin leads to an elevation of p53 steady-state levels in cells expressing wild-type p53. Conversely, activation of calpains by calcium ionophore led to a reduction of p53 in mammalian cells, and the effect was blocked by cell-permeant calpain inhibitors. Cotransfection of p53-null cell lines with p53 and calpastatin expression vectors resulted in an increase in p53-dependent transcription activity. Taken together, these data support the idea that calpains may also contribute to the regulation of wild-type p53 protein levels in vivo.

A molecular genetic model of astrocytoma histopathology

As the molecular events responsible for astrocytoma formation and progression are being clarified, it is becoming possible to correlate these alterations with the specific histopathological and biological features of astrocytoma, anaplastic astrocytoma and glioblastoma multiforme. In WHO grade II astrocytomas, autocrine stimulation by the plateletderived growth factor system coupled with inactivation of the p53 gene may lead to a growth stimulus in the face of decreased cell death with slow net growth ensuing. Such cells would also have defective responses to DNA damage and impaired DNA repair, setting the stage for future malignant change. Such biological scenarios recapitulate many of the clinicopathological features of WHO grade II astrocytomas. Anaplastic astrocytomas further display release of a critical cell cycle brake that involves the CDKN2/p16, RB and CDK4 genes. This results in mitoses seen histologically; clinically, there is more conspicuous, rapid growth. Finally, glioblastomas may emerge from the microenvironmental outgrowth of more malignant clones in a complex vicious cycle that involves necrosis, hypoxia, growth factor release, angiogenesis and clonal selection; growth signals mediated by activation of epidermal growth factor receptors may precipitate glioblastomas. It is clear as well that glioblastoma multiforme can arise via a number of independent genetic pathways, although the clinical significance of these distinctions remains unclear.

Role of ribonucleotide reductase and deoxynucleotide pools in the oxygen-dependent control of DNA replication in Ehrlich ascites cells

Cultured Ehrlich ascites cells were exposed to different oxygen tensions (ranging from nearly complete anoxia to 95% O2 at 10(5) Pa) and to transient (5-10 h) hypoxia (0.02% O2 at 10(5) Pa). Treated cells were examined with respect to the intracellular concentration of the M2-specific tyrosyl free radical of ribonucleotide reductase by EPR spectroscopy, and with respect to the pool sizes of all four deoxynucleoside triphosphates by an enzymatic assay employing DNA polymerase I of Escherichia coli. From 2% to 0.02% O2, the free radical level decreased continually from a normal value to just above detectability by the EPR measurement employed, and quickly recovered when hypoxic cells were resupplied with atmospheric O2. Concurrently, analogous changes of the size of the dCTP pool occurred, whereas the pool sizes dATP and dGTP underwent no changes, and the size of the dTTP pool only moderate changes. The changes of the free radical concentration and of the dCTP pool correlated well with the suppression or reactivation of DNA replication under the respective O2 conditions. The results consistently support the hypothesis of a fast-acting regulatory pathway that controls the rate of DNA replication in proliferating cells according to sufficient availability of O2. Therefore, ribonucleotide reductase may serve, in addition to providing DNA building blocks, as a pO2 sensor, which transmits the signal in the form of an altered intracellular dCTP concentration, directly or indirectly, to the nuclear-replication machinery.

p53: functions, mutations and sarcomas

The p53 gene is the most commonly altered gene in a multitude of human cancers. The alterations can be acquired somatically or transmitted through the germ-line. Bone and soft tissue sarcomas are frequently found to have acquired abnormalities in the p53 and mdm-2 genes. In soft tissue sarcoma, the amplification of the mdm-2 gene and the binding of its oncogene product to wild-type p53 protein functionally inactivates normal p53-regulated growth. Inherited mutations of the p53 gene are associated with the rare Li-Fraumeni familial cancer syndrome. Various tumor types arise in these families, with sarcomas of the bone and soft tissues and carcinoma of the breast being the most frequently observed. Transgenic mice with highly expressed mutated p53 have a higher incidence of tumors, including predominantly osteosarcomas and soft tissue sarcomas. In close similarity with the Li-Fraumeni syndrome, homozygously p53-null mice (transgenic mice carrying two non-functional p53 allele) are developmentally normal however they are susceptible to spontaneous tumor formation. This article reviews briefly the structure, function, and dysfunction of the p53 tumor-suppressor gene with particular focus on its role in the development of bone and soft tissue sarcoma.

Potential of microsensor-based feedback bioactuators for biophysical cancer treatment

Solid tumors usually exhibit a poorly organized vascularization and a deviant energy metabolism which result in an acidic pH and large hypoxic areas in the tumor microenvironment. A lot of cell biological data support the hypothesis that such physico-chemical conditions are promoters of the microevolution of malignant cells, inhibitors of the immune response, and co-factors for tumor cell invasion. Our experimental in vitro analyses and computer simulations indicate that the efficiency of immunotherapies and classical methods for cancer treatment might be improved if a physico-chemical microenvironment could be restored which reflects that found in normal tissue. In order to monitor and manipulate the tumor microenvironment, we suggest utilizing silicon-based feedback bioactuators which are controlled by on-line microsensors. These miniaturized bioactuators play the role of 'pH clamps' and can be implanted directly at the sites of inoperable tumors and metastases where they can reconstitute normal physico-chemical conditions. The drug application scheme can be precisely controlled by an integrated microprocessor. The paper summarizes the current state of development of such microsensor-based feedback bioactuators and outlines their potential for biophysical cancer treatment.

p202, an interferon-inducible modulator of transcription, inhibits transcriptional activation by the p53 tumor suppressor protein, and a segment from the p53-binding protein 1 that binds to p202 overcomes this inhibition

p202, an interferon-inducible murine protein, is a member of the "200 family" of proteins and is primarily nuclear. p202 is a modulator of transcription; it binds several transcription factors, including NF-kappaB p50 and p65, AP-1 c-Fos and c-Jun, and E2F1, and inhibits their transcriptional activity. p202 also binds pRb, the retinoblastoma protein, and if overexpressed it retards cell proliferation. Here we report that using the yeast two-hybrid assay we found that p202 bound the murine homolog of the human p53-binding protein 1 (53BP1), a protein shown to interact with the DNA binding domain of the p53 tumor suppressor protein. p202 bound a 98amino acid segment from 53BP1. This binding was inhibited by the replacement in p202 of a histidine (from the M(F/L)HATVA(T/S) sequence that is conserved among all of the 200 family proteins) by phenylalanine. We also report that overexpression of p202 inhibited the p53-dependent expression of reporter genes containing p53-activable segments from the mdm2 and p21 genes, whereas a decrease in the p202 level (in consequence of the expression of 202 antisense RNA) resulted in an increase in the p53-dependent expression of these reporters. Expression of the 53BP1 segment binding to p202 overcame the inhibition by overexpressed p202 of the transcription of reporters mediated by the p53 or the AP-1 transcription factors and of the proliferation of yeast.

The role of nitric oxide (NO.) in the carcinogenic process

The inflammatory process has long been known to be a risk factor for human cancers, particularly of the lung, bladder, colon, stomach, and female breast. Earlier hypothesis cited production of oxygen radicals, release of cytokines, and synthesis of prostaglandins and leukotrienes as biochemical modulators of the carcinogenic process. The discovery of NO. as a product of cells in the immune system has implicated this chemical in the mechanism of carcinogenesis, particularly when NO. is overproduced over a long period of time. After briefly reviewing the important chemical reactions of NO. under physiological conditions, we examine how the chemistry of its key reactants toward biologically important molecules relate to DNA damage and cytotoxicity. In these two processes, NO may play an important role in currently accepted models of multistage carcinogenesis.

Tumor angiogenesis: a physiological process or genetically determined?

Continued tumor growth is dependent upon the growth of new blood vessels. This commentary reviews the mechanisms whereby tumors become vascularized and examines whether tumor angiogenesis is solely an example of a normal physiologic process or is part of the genetic program of the tumor. The likelihood that neovascularization of tumors combines both of these components, that is, utilizing tumor-specific elements as well as capacities common to all cells, is discussed.

p53: puzzle and paradigm

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