Growth inhibition of anaplastic glioma cells by nerve growth factor

Nerve growth factor (NGF) inhibited cellular DNA synthesis of rat T9 anaplastic glioma cells in a dose-dependent manner in the range of 0.5-5 micrograms/ml. Oxidation of 2 to 3 tryptophan residues of NGF, which had been known to destroy biological and immunological activity, greatly diminished its inhibitory effect on DNA synthesis. The inhibition was also abolished by anti-NGF IgG. Flow cytometric analyses and immunocytochemical assays of DNA synthesis using bromodeoxyuridine incorporation at various times during cell exposure to NGF revealed that the growth inhibition was attributable to gradual accumulation of growth-arrested cells at the G1 phase. Synthesis of nuclear regulatory proteins JUN and p53 was inhibited preferentially and progressively by NGF as inhibition of DNA synthesis increased.

Altered structure and expression of the p53 gene in human neuroepithelial tumors

The p53 gene, located on chromosome 17p13.1, may be important in the pathogenesis of human neuroepithelial tumors, because it is a tumor suppressor gene and genetic alteration is essential for certain human cells to acquire the neoplastic phenotype. The structure and expression of the p53 gene were investigated in cultured human glioma cells and biopsied specimens of neuroepithelial tumors. Immunocytochemical examination of p53 gene expression revealed positive nuclear staining in six of seven glioma cell lines tested. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis demonstrated unequivocal heterogeneity of migration rate in p53 bands. Pulse-chase analysis clearly showed an increased half-life of p53 in cultured human glioma cells. These abnormalities are presumably due to genetic alterations in the p53 gene. Nucleotide substitutions in exon 5, 7, or 8 of the p53 gene could be detected by polymerase chain reaction-single strand conformational polymorphic analysis in four of seven (57%) human glioma cell lines, and nine of 29 (31%) biopsied specimens of neuroepithelial tumors examined. The present results indicate that genetic alterations in the p53 gene are responsible for the tumorigenesis of at least some human neuroepithelial tumors.

Involvement of p53 mutation in the development of human salivary gland pleomorphic adenomas

We examined the status of the p53 mutation, a putative tumor suppressor gene, as well as the expressions of myc and mos oncogene products in human salivary gland pleomorphic adenoma cells in culture derived from four individuals using techniques which enabled selective and favourable growths of tumor cells. Culture techniques empolyed in this study consisted of type I collagen gel-coated dishes and serum-free medium as substrates and growth medium, respectively. Cells grown under above conditions were subjected to the analyses of p53, myc and mos expression. When analyzed by both immunocytochemical staining and immunoblot, mutant forms of p53 specifically detected by PAb240 were observed in three of 4 cases. However, none of the 4 cases expressed myc and mos oncogene products. These results may imply a role for p53 mutation in the development of human salivary gland pleomorphic adenomas.

Expression of wild-type and mutant p53 proteins by recombinant vaccinia viruses

To facilitate the purification of wild type p53 protein, we established a recombinant p53 vaccinia viral expression system. Using this efficient eukaryotic expression vector, we found that the expressed p53 proteins retained their specific structural characteristics. A comparison between wild type and mutant p53 proteins showed the conservation of the typical subcellular localization and the expression of specific antigenic determinants. Furthermore, wild type p53 exhibited a typical binding with large T antigen, whereas no binding was detected with mutant p53. Both wild type and mutant p53 proteins were highly stable and constituted 5-7% of total protein expressed in the infected cells. These expression recombinant viruses offer a simple, valuable system for the purification of wild type and mutant p53 proteins that are expressed abundantly in eukaryotic cells.

High frequency of p53 gene alterations associated with protein overexpression in human squamous cell carcinoma of the larynx

A series of 58 primary human squamous cell carcinomas of the larynx (LSCCs) was examined for the expression of the p53 tumor-suppressor gene by a combined immunohistochemical and molecular approach. About 60% of the cases displayed nuclear p53 overexpression as revealed by immunostaining with PAb1801, PAb122 and PAb240 monoclonal antibodies. This phenomenon was associated with the presence of structural and/or transcriptional alterations of the p53 gene. Our results provide evidence that p53 abnormalities constitute the most frequent genetic alteration identified so far in LSCC and indicate that the abnormal accumulation of the protein correlates with the presence of p53-mutated versions. These findings, taken together with the peculiar biochemical properties of p53, support the hypothesis of a possible pathogenetic relationship between smoke carcinogen exposure and p53 inactivation in the development of this tumor type.

Wild-type murine p53 represses transcription from the murine c-myc promoter in a human glial cell line

Here we analyzed the effect of the suppressor proto-oncogene p53 on transcription from the P2 promoter of the murine c-myc gene. c-myc promoter constructs were coupled to the chloramphenicol acetyl-transferase (CAT) gene and were transiently transfected into a human glial cell along with plasmids overexpressing wild-type or mutant p53. It was found that significant repression of c-myc transcription took place following cotransfection with wild-type but not mutant p53. However wild-type p53 did not suppress transcription from the SV40 early promoter or from the MHC promoter. Promoter-CAT constructs containing only the ME1a2 or E2F elements, from the P2 promoter, were repressed by p53, indicating that p53 may exert its effect at these two sites within the P2 promoter. Finally, when the SV40 T antigen and wild-type p53 were expressed together in glial cells the repressive effect of p53 was abolished.

Detection of both mutant and wild-type p53 protein in normal skin fibroblasts and demonstration of a shared 'second hit' on p53 in diverse tumors from a cancer-prone family with Li-Fraumeni syndrome

Germline transmission of mutant p53 gene in cancer-prone families with Li-Fraumeni syndrome has revealed a new role for p53 in the genetic predisposition to cancer. The studies reported here focus on the analysis of the expression of normal and mutant p53 RNA and protein in germline configuration and demonstrate that normal skin fibroblasts derived from members of a family with Li-Fraumeni syndrome express mutant p53Gly----Asp(245) protein and RNA at levels similar to the wild-type p53. Thus, these fibroblasts represent a unique biological system in which endogenous promoters are utilized for the expression of both mutant and normal p53. We have further extended the earlier observations on the analysis of mutant p53 with a limited number of tumors derived from individuals with Li-Fraumeni syndrome. Tumors arising from two different germ layers in four individuals in a single family clearly exhibited the loss of the wild-type allele and the retention of the mutant allele observed in the normal skin fibroblasts derived from the same individuals. These observations further support the notion that germline p53 mutation plays a key role in the tumorigenesis of individuals with Li-Fraumeni syndrome.

Elevation of large-T antigen production by sodium butyrate treatment of SV40-transformed WI-38 fibroblasts

The effects of sodium butyrate on simian virus 40 early gene expression were determined in SV40-transformed human embryonic lung fibroblasts (SVWI-38). Northern blot analysis and nuclear run-off transcription studies revealed that treatment of cells with millimolar concentrations of sodium butyrate (2.5 to 10 mM) resulted in increased levels of SV40 early gene transcripts, with a concomitant increase in their corresponding proteins (large-T and small-t antigens). Although sodium butyrate treatment enhanced the expression of the early genes, it was associated with a reduction in cell growth and total protein synthesis, as measured by cell number and incorporation of 3H-leucine into macromolecules, respectively. Immunoprecipitation of 35S-labelled cellular proteins with anti-p53 and anti-T antibodies revealed that the level of the cellular protein, p53, declined markedly in the presence of sodium butyrate. Furthermore, in control cells only 30% of the p53 was complexed with large-T antigen, whereas in butyrate-treated cells all the p53 was complexed with large-T antigen. The increased early gene expression was not due to altered methylation patterns, gene amplification, or rearrangement of the integrated SV40 genome. Sodium butyrate treatment did, however, result in the appearance of a new nuclear protein which bound specifically to a SV40 promoter fragment containing large-T antigen binding sites I and II.

Constitutive expression of p53 protein in enriched normal human marrow blast cell populations

Previous studies by others using metabolic labeling, cell lysis, and immunoprecipitation have reported elevated levels of p53 protein in blast cells derived from patients with acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML), whereas p53 protein was not detected in normal light-density bone marrow cells. In this report, using the same detection methods, we confirm the negligible expression of p53 protein in normal light density marrow cells. However, we find clearly significant levels of p53 protein expression in enriched normal human marrow blast populations. Furthermore, using a panel of p53 specific monoclonal antibodies, we find the p53 protein constitutively synthesized by normal marrow blasts has the immunologic phenotype identified by PAb240 that reportedly recognizes a common conformational-dependent epitope on mutant p53. We have also found that the p53 immunologic subclass identified by PAb240 exists in normal human circulating lymphocytes either resting, serum starved, or PHA activated. In summary, it is clear that (1) normal marrow blast populations provide the appropriate control for assessing the levels of p53 protein expression in leukemic blast cells; and (2) PAb240 cannot be used to distinguish p53 mutated at the DNA level from normal p53 in fresh human hematopoietic cells.

Altered expression of wild-type p53 tumor suppressor gene during murine epithelial cell transformation

An epidermal cell model in which initiated, benign tumor-producing and carcinoma stages were derived from a cloned parental cell strain was used to examine p53 expression during multistage epithelial carcinogenesis. Increased steady-state levels of p53 RNA were detected in squamous cell carcinomas compared to papilloma and normal epidermal cells. Nontumorigenic initiated cell precursors of the carcinomas exhibited normal p53 expression, localizing altered p53 regulation to the malignant conversion stage. Immunoprecipitation and Western immunoblot analyses demonstrated elevated levels of p53 protein in the moderately differentiated carcinoma compared to normal cells, and negligible levels of p53 in the poorly differentiated carcinoma cells. Sequence analysis of p53 complementary DNA from normal and carcinoma cells revealed no mutations in the coding or 5'- and 3'-untranslated regions, suggesting a novel mechanism of p53 inactivation.

Selective alterations in the patterns of newly synthesized proteins by acetaminophen and its dimethylated analogues in primary cultures of mouse hepatocytes

Alterations in protein synthesis following exposure to and recovery from hepatotoxic doses of acetaminophen (APAP) and its analogues, 3,5-dimethyl acetaminophen (3,5-DMA) and 2,6-dimethyl acetaminophen (2,6-DMA), were investigated in primary cultures of mouse hepatocytes. The rates of protein synthesis decreased within 4 hr after administration of 10 mM APAP and occurred after significant depletion of intracellular glutathione and covalent binding of APAP to proteins, but preceded the leakage of lactate dehydrogenase into the media. The inhibition of protein synthesis was reversible only if APAP exposure did not exceed 8 hr. Electrophoretic analysis of 35S-labeled proteins by one-dimensional SDS-PAGE revealed two consistent alterations in the patterns of newly synthesized proteins. First was a progressive diminution in the de novo synthesis of a protein migrating at approximately 58 kDa (p58). This was observed with APAP (10 mM) and 3,5-DMA (5 mM) but not with 2,6-DMA (10 mM). If exposure to APAP exceeded 8 hr, the biosynthesis of this protein was not only further decreased but was also no longer detectable during the recovery period. The second major alteration was an increase in the relative rate of biosynthesis of a 32-kDa protein (p32) following exposure and recovery from APAP and 3,5-DMA but not 2,6-DMA. Exposure to heme or arsenite induced the synthesis of a protein of similar molecular weight but did not result in the inhibition of p58 biosynthesis. The fact that the reactive metabolites of both APAP and 3,5-DMA, but not 2,6-DMA, possess oxidative properties suggests that the alterations in the synthesis of p32 and p58 may be related to an oxidative component induced by these compounds.

Alterations in the structural gene and the expression ofp53 in rat liver tumors induced by aflatoxin B1

Rat hepatocellular carcinomas (HCCs) induced by aflatoxin B1 (AFB) treatment were examined for changes in the p53 tumor suppressor gene and in p53 suppressor gene expression. A high proportion of HCCs (nine of 11 tumors in six of eight animals) exhibited new p53 restriction fragments, indicating genomic alterations of one of the p53 alleles. Each tumor with an altered p53 restriction-fragment pattern exhibited a new fragment in one of two size classes (3 kb or 7 kb with EcoRI digestion) that were missing portions of the 3' end of the p53 gene. These findings indicate that apparently similar genomic rearrangements or deletions occurred independently in AFB-induced tumors. When compared with nontumor liver tissue from the same animal, the tumors with p53 gene alterations showed dramatically reduced levels of p53 mRNA and protein and greatly increased levels of histone H2B and retinoblastoma tumor suppressor (Rb) mRNA. In two HCCs showing no evidence of p53 restriction-fragment alterations, mutant p53 protein was detected. Mutant protein was also detected in two liver samples containing an adenoma and altered foci. These data suggest that alterations of the p53 tumor suppressor gene are involved in the induction of rat HCC by AFB.

Stepwise transformation of primary thyroid epithelial cells by a mutant Ha-ras oncogene: an in vitro model of tumor progression

Activating mutations of the ras oncogene family occur at high frequency in all stages of thyroid tumorigenesis, both human and experimental. To test the causal nature of this association, and to investigate the biological role of ras mutation, we introduced a mutant c-Ha-ras gene into normal rat thyroid follicular cells using an ecotropic retroviral vector. The major immediate effect was to greatly extend the proliferative lifespan of these cells in culture from less than 3 to more than 15 doublings, without any observable loss of growth-factor dependence or differentiated functions. This in vitro phenotype strongly supports an initiating role for ras mutation in the genesis of benign thyroid tumors (adenomas) in vivo. Spontaneous transformation was observed at low frequency on continuous culture of mutant ras-expressing cells, giving rise to fully immortalized, growth factor-independent, highly tumorigenic lines. Transformation was associated with (i) loss of responsiveness to the growth inhibitor TGF-beta 1, and (ii) greatly increased nuclear levels of p53 protein, which unexpectedly was not due to point mutation in the conserved regions of the p53-coding sequence. We postulate that these two phenomena are causally related to each other and to the transformed phenotype.

The p53 gene expression and its developmental regulation in schistosomes

We have studied the gene expression, especially of the oncoproteins, and its regulation in schistosomes. Schistosomes have a complex life cycle with a defined dimorphic lifestyle. The parasite are so far unique in biology in expressing oncogene products in their adult stage. In order to characterize the expression and developmental regulation, a lambda gt 11 cDNA library and lambda EMBL4 genomic DNA library of each growth stage of Schistosoma mansoni and S. japonicum was constructed, and was screened with various monoclonal antibodies against oncogene products. One positive plaque reacted to anti-p53 antibody (Ab-2, Oncogene Science, Inc.) was further analyzed. This fusion protein was about 120 KDa in molecular weights, and expressed as 1.4 Kb RNA in the adult stage. P53 gene is well-known as the negative regulator of the cell cycle, and the mutations in the gene are turning out to be the most common genetic alterations in human cancers. The comparison of the gene structure among species and stages were being conducted. Chromosome structures, C-band formation, and the results of in situ hybridization using the phage probe would be discussed.

A DNA binding domain is contained in the C-terminus of wild type p53 protein

In the present study we evaluated the DNA binding activity of wild type and mutant p53 proteins that were isolated from bacterial expression vectors. A comparison of the binding activities of the various purified p53 proteins, assessed by their ability to bind DNA cellulose columns, indicated that wild type p53 has a higher affinity to DNA than have mutant p53 forms. Furthermore, only wild type p53 was able to bind genomic DNA upon electrophoretic protein blotting. As specific deletion of the C-terminal region of wild type p53 totally abolished binding to genomic DNA, it was concluded that the 47 C-terminal amino acids contain the DNA binding region. The fact that the N-terminus contains a transcription activation region whereas the C-terminus contains a DNA binding domain places p53 in the family of typical transcription factors. Our experiments show that the topographical positioning of these domains plays an important role in the activity of wild type p53.

Comparative study of the expression of Rb and p53 genes in human colorectal cancers, colon carcinoma cell lines and synchronized human fibroblasts

We have compared the expression of the retinoblastoma (Rb) and p53 genes in normal human fibroblasts, colon carcinoma cell lines, matched pairs of colorectal tumor tissues and adjacent normal mucosa and in synchronized human diploid fibroblast cell line WI38. The increased expression of Rb and p53 RNA was observed in a majority of colorectal cancers in comparison to adjacent normal mucosa and is accompanied by proportional increase in the expression of histone H3 gene. The Rb and p53 RNA levels varied significantly between the various colon carcinoma cell lines. However, we found that the expression of Rb and p53 RNA is regulated differently in cell cycle synchronized normal human fibroblasts. The Rb mRNA level did not change with the position in the cell cycle and did not differ significantly whether the cells were serum deprived or in 10% serum. But p53 mRNA expression follows the same pattern as histone H3 mRNA.

Mutation of the p53 gene in human acute myelogenous leukemia

Heterogeneity of p53 protein expression is seen in blast cells of patients with acute myelogenous leukemia (AML). p53 protein is detected in the blasts of certain AML patients but not in others. We have identified p53 protein variants with abnormal mobility on gel electrophoresis and/or prolonged half-life (t 1/2). We have sequenced the p53 coding sequence from primary blast cells of five AML patients and from the AML cell line (OCIM2). In OCIM2, a point mutation in codon 274 was identified that changes a valine residue to aspartic acid. A wild type p53 allele was not detected in these cells. Two point mutations (codon 135, cysteine to serine; codon 246, methionine to valine) were identified in cDNA from blasts of one AML patient. Both mutations were present in blast colonies grown from single blast progenitor cells, indicating that individual leukemia cells had sustained mutation of both p53 alleles. The cDNAs sequenced from blast samples of four other patients, including one with prolonged p53 protein t 1/2 and one with no detectable p53 protein, were fully wild type. Thus, the heterogeneity of p53 expression cannot be explained in all cases by genetic change in the p53 coding sequence. The prolonged t 1/2 of p53 protein seen in some AML blasts may therefore reflect changes not inherent to p53. A model is proposed in which mutational inactivation of p53, although not required for the evolution of neoplasia, would confer a selective advantage, favoring clonal outgrowth during disease progression.

Molecular analysis of the p53 alleles in primary hepatocellular carcinomas and cell lines

We have examined p53 oncogene/anti-oncogene alleles in 10 different human hepatoma cell lines and 18 primary hepatocellular carcinomas. The p53 allele in these hepatoma cell lines appears to be a frequent target of mutation as demonstrated by Southern and Northern blotting, immunoprecipitation and Western blot analysis. In general, the steady state level of p53 specific RNA or protein in these hepatoma cell lines is higher than in normal liver. However, in three out of ten cell lines, normal-sized p53 mRNA cannot be detected. In contrast, the involvement of the p53 allele in primary hepatocellular carcinoma appears to be an exceedingly rare event. Steady state levels of p53 specific RNA in primary hepatomas are practically indistinguishable from those in normal adult liver. Using the polymerase chain reaction technique, we have amplified and subcloned exons 5, 6, 7 and 8 of p53 from 10 different hepatoma samples. DNA sequence analysis of these exon subclones reveals no apparent structural alterations. Finally, synthesis of p53 specific mRNA or protein in a HepG2 human hepatoblastoma cell line does not appear to be affected by gene expression and replication of human hepatitus B virus. Surprisingly, unlike many other kinds of human solid tumors, point mutations in p53 do not appear to be important in primary tumors of hepatocellular carcinomas.

Expression of RB and p53 proteins in HPV-positive and HPV-negative cervical carcinoma cell lines

Mutations within the tumor suppressor genes Rb-1 and p53 are commonly found in many human malignancies, and loss of wild-type function of both p53 and RB appear to be important events in the development of these malignancies. Interference with normal RB and p53 function in the cell has apparently also been exploited by the oncogenic genital human papillomaviruses (HPVs), which encode transforming proteins capable of binding cellular RB and p53 proteins. We have investigated the expression of RB and p53 in a series of eight cervical carcinoma cell lines, six of which contain HPV sequences and two of which have arisen apparently independently of HPV infection. In the six HPV-positive lines, no evidence of abnormal RB or p53 protein could be detected. However, there was evidence for abnormal RB and p53 in the two HPV-negative lines. These data are consistent with the hypothesis that loss of wild-type RB and p53 function is necessary for tumor development and that such loss can occur either by mutation within the cellular gene or by expression of viral proteins capable of complexing wild-type cellular proteins.

Nuclear accumulation of p53 protein is mediated by several nuclear localization signals and plays a role in tumorigenesis

The basic carboxy terminus of p53 plays an important role in directing the protein into the nuclear compartment. The C terminus of the p53 molecule contains a cluster of several nuclear localization signals (NLSs) that mediate the migration of the protein into the cell nucleus. NLSI, the most active domain, is highly conserved in genetically diverged species and shares perfect homology with consensus NLS sequences found in other nuclear proteins. The other two NLSs, II and III, appear to be less effective and less conserved. Although nuclear localization is dictated primarily by the NLSs inherent in the primary amino acid sequence, the actual nuclear homing can be modified by interactions with other proteins expressed in the cell. Comparison between wild-type p53 and naturally occurring mutant p53 showed that both protein categories could migrate into the nucleus of rat primary embryonic fibroblasts by essentially similar mechanisms. Nuclear localization of both proteins was totally dependent on the existence of functional NLS domains. In COS cells, however, we found that NLS-deprived wild-type p53 molecules could migrate into the nucleus by complexing with another nuclear protein, simian virus 40 large-T antigen. Wild-type and mutant p53 proteins differentially complexed with viral or cellular proteins, which may significantly affect the ultimate compartmentalization of p53 in the cell; this finding suggests that the actual subcellular compartmentalization of proteins may differ in various cell type milieux and may largely be affected by the ability of these proteins to complex with other proteins expressed in the cell. Experiments designed to test the physiological significance of p53 subcellular localization indicated that nuclear localization of mutant p53 is essential for this protein to enhance the process of malignant transformation of partially transformed cells, suggesting that p53 functions within the cell nucleus.