Adenine phosphoribosyltransferase-deficient mice develop 2,8-dihydroxyadenine nephrolithiasis

Adenine phosphoribosyltransferase (APRT) deficiency in humans is an autosomal recessive syndrome characterized by the urinary excretion of adenine and the highly insoluble compound 2,8-dihydroxyadenine (DHA) that can produce kidney stones or renal failure. Targeted homologous recombination in embryonic stem cells was used to produce mice that lack APRT. Mice homozygous for a null Aprt allele excrete adenine and DHA crystals in the urine. Renal histopathology showed extensive tubular dilation, inflammation, necrosis, and fibrosis that varied in severity between different mouse backgrounds. Thus, biochemical and histological changes in these mice mimic the human disease and provide a suitable model of human hereditary nephrolithiasis.

Protein and messenger RNA expression of connexin43 in astrocytomas: implications in brain tumor gene therapy

The expression of connexin43, the primary gap-junction constituent of glial cells, was evaluated at the messenger RNA and protein levels in different grades of astrocytoma to investigate the relevance of gap junctions in herpes simplex virus-thymidine kinase (HSV-tk)-mediated gene therapy of brain tumors. Transduction of the retroviral-mediated HSV-tk gene into tumor cells with subsequent administration of ganciclovir has recently been used as an experimental therapeutic strategy for treatment of brain tumors. One aspect of this approach is the bystander effect, which augments the efficacy of this therapeutic approach. Glioblastoma cells with minimum levels of connexin43 protein were transfected with a connexin43 complementary DNA. These cells manifested a marked increase in the in vitro bystander effect, supporting the contention that the in vitro bystander effect is a consequence of metabolic cooperation between cells mediated by gap junctions. To assess relative levels of gap-junction protein expression in the relevant tumor type, we examined primary astrocytomas, primary astrocytoma cell cultures, and glioblastoma cell lines. Although most astrocytoma tumor samples expressed connexin43, they differed in the level of expression, with the greatest variation exhibited in high-grade astrocytomas. Primary glioblastoma cell cultures and established glioblastoma cell lines also displayed some variability in connexin43 levels. In aggregate, our results anticipate that glioblastomas will have a varied bystander effect during HSV-tk gene therapy depending on the level of connexin43 expression.

Stage of disease confounds apparent relationship between levels of N-ras and duration of survival in head and neck tumours

The objective of this study was to determine whether elevated levels of N-ras correlated with clinicopathological data. Complete clinical data were available on 133 of 481 patients surgically treated for squamous cell carcinoma of the head and neck (SCCHN) who had immunohistochemical data for N-ras. Advanced stages of disease were strongly related to the staining for N-ras in tumour cells (P = 0.0031). The stage of disease was inversely related to duration of survival (P = 0.0017). Initial statistical evaluation revealed an apparent correlation between survival and N-ras staining. However, duration was found to be independent of the level of N-ras. The illusory relationship initially was a result of the confounding effect of the stage of disease.

APRT: a versatile in vivo resident reporter of local mutation and loss of heterozygosity

We describe an in vivo mutagenesis model that utilizes reverse mutation and forward mutation at the endogenous Aprt locus. Reverse mutation provides an in situ method for detecting environments or agents that cause point mutations. Forward mutation detects large chromosomal events, including mitotic recombination, chromosome loss, and large multilocus deletion, all of which can lead to loss of heterozygosity. Detection of reverse mutation in vivo is based on the differential capacity of Aprt and Aprt cells to sequester radiolabeled adenine by catalyzing its conversion to adenosine monophosphate with subsequent incorporation into nucleic acids. Cells lacking APRT activity cannot accumulate exogenously administered, tagged adenine, whereas Aprt+ cells can and will thereby become marked. Thus, genetically modified mice with mutant but revertible Aprt alleles should be a useful vehicle for in situ detection of mutagenic activity in the whole animal. the feasibility of this model has been illustrated, first, by showing that APRT-deficient mice are viable and, second, by demonstrating that the minority of Aprt+ cells within a chimeric tumor growing in an Aprt+ mouse can be selectively labeled following IP injection of [14C]-adenine and can be identified by autoradiography. Forward mutation, detected by growth in selective medium of primary cells derived from Aprt+/- heterozygous mice, provides on independent estimate of in vivo mutation frequency. The frequency with which Aprt colonies arise provides a measure of the frequency of Aprt(-)-negative cells in the tissue at that point in time. Culture of skin fibroblasts in 2,6-diaminopurine (DAP) produced Aprt+ colonies with a frequency of about 10(-4). This frequency is similar to that found for human T lymphocytes from individuals heterozygous at the Aprt locus. In both cases, the majority of mutagenic events involved allele loss. Polymerase chain reaction with linked polymorphic microsatellites on mouse chromosome 8 demonstrated that allele loss was mediated mostly by mitotic recombination, as was the case for human T lymphocytes. The high frequency of mitotic recombination and allele loss at a neutral locus has significant implications for the process of tumorigenesis and argues that spontaneous or induced mitotic recombination may play a causal role in the progression to cancer.

Peripherin assembles into homopolymers in SW13 cells

The properties of full-length and mutant peripherins were studied in intermediate filament-less SW13 cells to define regions of peripherin that are essential for initiation of filament assembly. A full-length rat peripherin gene transfected into SW13 cells resulted in filament formation, consistent with the close structural relationship of peripherin to other type III intermediate filament proteins that readily form homopolymers. Translation of full-length rat peripherin is initiated predominantly at the second of two inframe AUGs. Deletions within the amino terminus of wild-type peripherin abolished its ability to form filaments in SW13 cells. In contrast, deletion of the entire carboxyl-terminal tail of peripherin did not affect its ability to form filamentous arrays in transfected SW13 cells. These results indicate that, of the intermediate filament proteins that are expressed in mature neurons, only peripherin and alpha-internexin are capable of making homopolymer intermediate filaments. In addition, mutations of the carboxyl tail of peripherin generally do not interfere with filament network formation.

nm23-H1 gene expression in ovarian tumors--a potential tumor marker

Ovarian carcinomas that have a distinctive natural history with early dissemination are particularly problematic. The aim of this immunohistochemical study was to assess whether the nm23-H1 gene product, which in some tumors shows inverse association with metastatic potential, could serve as a prognostic marker for ovarian carcinomas. The study, based on 73 benign and 54 malignant ovarian tumors, showed clear differences in the frequency of nm23-H1-positive samples, the intensity of staining and the histological localization of this protein. Differences were observed between normal ovary samples and benign lesions as well as between benign tumors and ovarian carcinomas and were highly significant. Furthermore, carcinomas that had detectable metastasis at the time of surgery were negative for nm23-H1 protein more frequently than those that did not. Although this is a prospective study in which collection of clinical data is ongoing, the results strongly suggest that nm23-H1 may serve as a potentially valuable marker for ovarian tumors.

Aflatoxin B1, 2-aminoanthracene, and 7,12-dimethylbenz[a]anthracene-induced frameshift mutations in human APRT

Aflatoxin B1, 2-aminoanthracene, and 7,12-dimethylbenz[a]anthracene have been implicated in the etiology of human cancers. In this study, we demonstrate that these three chemicals can be activated by rat liver homogenate S9 coupled with NADPH coenzymes to produce a dose-dependent increase in the frequency of APRT reversion in the APRT-deficient human cell line HTD114. HTD114 contains single nucleotide insertions at different positions in each APRT allele and the spontaneous reversion frequency is < 10(-8). However, the highest reversion frequency induced by these chemicals is 1.2-2.0 x 10(-5), at least a 10(3)-fold increase over the frequency of spontaneous reversion. Reversion of either mutant allele was observed to be a consequence of a frame-restoring loss of a single nucleotide, which indicates that these three chemicals can function as frameshift mutagens in human cells.

Two murine GSTpi genes are arranged in tandem and are differentially expressed

An 8-kilobase mouse genomic fragment containing two intact glutathione S-transferase (GST) genes has been isolated from a mouse lambda genomic library. Each of the genes (designated mGSTpiA and mGSTpiB) is less than 3 kilobases in size and is comprised of seven exons that give rise to a 630-base pair open reading frame encoding 209 amino acids. The deduced amino acid sequences of the gene products differ in only 6 amino acids at positions 10, 11, 89, 104, 106, and 109. These two genes are highly homologous to rat GST-P and to a lesser extent to human GST-pi. Northern blot analysis of mRNAs from a variety of mouse tissues demonstrated that mGSTpiB is ubiquitously expressed, whereas mGST-piA is more selectively expressed in gallbladder, colon, heart, and skeletal muscle. Primer extension analysis revealed four potential transcription start sites in mGST-piB and one in mGSTpiA. Although both genes were expressed in vitro and in vivo only mGSTpiB product metabolized 1-chloro-2,4-dinitrobenzene, a common GST substrate. Further in vitro expression studies of three chimeric mGSTpi genes suggested that one or both of the amino acids at positions 10 and 11 of mouse GSTpi enzymes are important for the enzyme's ability to metabolize 1-chloro-2,4-dinitrobenzene.

Prognostic significance of transforming growth factor alpha TGF-alpha) in human lung carcinoma: an immunohistochemical study

Despite emerging data relating oncogene expression, growth factors and/or their receptors to the etiology of lung cancer, standard clinicopathological evaluation is still used for the diagnostic and prognostic purposes. Recent studies have shown that expression of some oncogenes and growth factors/receptors may be useful as markers in routine diagnostic and prognostic processes. For example, EGF/erb-B family of peptides may play a role in lung carcinogenesis. Similarly, expression of TGF-alpha mRNA and peptide has been shown to occur in various human lung carcinomas in vivo and in vitro. However, results concerning the role of TGF-alpha in lung carcinoma are conflicting and therefore its clinical value still remains obscure. To better evaluate the potential value of TGF-alpha in clinical application we have investigated the relationship between TGF-alpha expression in 51 lung carcinomas and 26 different clinical and clinicopathological parameters. The only significant correlation noted was between TGF-alpha and venous blood erythrocytes and eosinophils. This study suggests a relationship between metastasis and aggressive behavior of lung cancer. This data shows that TGF-alpha expression can not serve as an independent tumor marker for lung cancer.

Retroviral mediated gene transfer in megakaryocytic cell lines

There have been no reports, to date, of successful introduction of foreign DNA into committed megakaryocyte precursor cells. We have successfully infected two megakaryocytic cell lines, one a committed cell line (CHRF-288-11) and the other a bipotential cell line (K562), with a retroviral vector containing the bacterial lacZ gene and a neomycin resistance marker. Modification of standard protocols was required for successful infection of the committed megakaryocyte cell line. Presence of the lacZ transgene was demonstrated at the molecular level by polymerase chain reaction (PCR), and its expression at the mRNA level by reverse transcriptase-PCR. Presence of the bacterial beta-galactosidase was demonstrated by both immunofluorescence and enzyme activity. Treatment of the CHRF-288-11 infected cells with phorbol esters, which induces megakaryocytic differentiation, increases expression of the lacZ transgene. The staining pattern of the lacZ reaction product was perinuclear and punctate in the CHRF-288-11 cells, whereas it was uniform throughout the cytoplasm of the K562 cells, suggesting different sorting mechanisms for bacterial beta-galactosidase in these two cell types. Overall, these results demonstrate the feasibility and provide a method for infecting cultured megakaryocytic cell lines with retroviral of vectors such that a molecular analysis of megakaryocyte differentiation can be accomplished.

Immunohistochemical detection of the H-ras, K-ras, and N-ras oncogenes in squamous cell carcinoma of the head and neck

The expression of H-ras, K-ras and N-ras oncogenes was analyzed on frozen sections of squamous cell carcinoma of the head and neck (SCCHN) by immunohistochemistry using anti-ras monoclonal antibodies. Of 22 primary SCCHN, 15 (68%) stained positive for H-ras, 10 (45%) for K-ras and seven (32%) for N-ras. Thirteen specimens (59%) stained positive for at least two anti-ras monoclonal antibodies. The presence of immunohistochemically detectable H-ras, K-ras and N-ras proteins was most frequently associated with an increase in tumor size and later stages of disease (T3 and T4), with no apparent correlation with lymph node involvement, site of occurrence, degree of differentiation, age, sex, or race. Thus, overexpression of members of the ras gene family occurs as a relatively common even in SCCHN and may be an important event in the later stages of tumorigenesis.

Overexpression of p53 protein is common in premalignant head and neck lesions

In order to determine whether or not the p53 gene is involved in the malignant transformation of the head and neck carcinoma HNSCC, we have analyzed archival specimens from 527 primary head and neck lesions and 27 corresponding lymph node metastases. Nuclear p53 protein was present in 107 of 190 (56%) dysplasias, 61 of 102 (60%) carcinoma in situ (CIS), and 262 of 493 (53%) carcinomas. The p53 score did not increase significantly with progression of these lesions from dysplasia to CIS and to carcinoma. All 357 normal samples of head and neck tissues were negative. The majority of the 172 sets of premalignant and malignant lesions displayed concordant p53 staining patterns. The staining was incongruous in only six cases. The p53 staining results were congruent in all 27 pairs of primary and metastatic (lymph nodes) tumors. These data strongly suggest that p53 protein could be altered in a very early phase of the head and neck tumorigenesis and is maintained during tumor progression and metastatic spread. Mutations in p53 were examined in 11 cases that exhibited high levels of p53 protein as detected by immunohistochemistry using PAb 1801 MAb. Mutation analysis was performed by direct sequencing of the PCR amplification products of exons 5 through 8, which contain greater than 90% of p53 mutations found in tumors. Three of 11 HNSCC had mutations at codon 130 (C to A), 193 (A to T), 283 (G to C), respectively. No mutations were found in the other 8 samples within the regions examined. However, they may have mutations in unsequenced regions of p53 or may have wild type protein that accumulates for other reasons.

The role of the p53 gene in the malignant transformation of pleomorphic adenomas of the parotid gland

Pleomorphic adenoma (PA), the most common neoplasm of the parotid gland in adults, undergoes malignant transformation in only two to six percent of cases. In order to determine whether or not the p53 gene is involved in the malignant transformation of PA of the parotid gland, we have analyzed archival specimens from four patients with carcinoma ex-pleomorphic adenoma (CEPA) by immunohistochemistry and sequencing of the amplified DNA. Tissue specimens from each patient contained both the CEPA and the precursor PA. Immunostaining revealed that while all CEPA were p53 positive, only one of the four precursor PA was positive for p53. In this case, DNA was isolated from both the PA and CEPA and exons five through eight were amplified using the polymerase chain reaction. The same p53 mutation (single base substitution) was found in both the PA and the CEPA at codon 248. Adjacent normal tissue contained the wild-type p53 sequence. To our knowledge, this is the first report of the same p53 point mutation in both a PA and the associated CEPA of the parotid. These results strongly suggest a role for p53 gene mutation in the malignant transformation of some PA of the parotid gland.

The human Ha-ras oncogene induces genomic instability in murine fibroblasts within one cell cycle

Many human tumors contain an activating mutation in one of the ras protooncogenes. Additionally, these tumor cells are often heteroploid and characterized by chromosome breaks and rearrangements that are consequences of the genomic instability that is thought to contribute to tumor progression. The concurrence of ras mutations and genomic instability in tumors prompted us to ask whether selective induction of an activated Ha-ras gene could render a genome unstable. The NIH 3T3 cells used in this study contained mutant p53 genes and carried a selectively inducible activated (EJ) Ha-ras transgene under the control of bacterial lactose regulatory elements. When stably transfected cells were induced to express activated Ha-ras by isopropyl beta-D-thiogalactoside administration, there was a marked increase in the number of gross chromosomal aberrations including acentric fragments, multicentric chromosomes, and double minutes, which occurred within the time frame of a single cell cycle from the time of induction. To confirm that these aberrations occurred within the first cell cycle after mutant Ha-ras induction, the cells were arrested in G1 phase by serum depletion and, subsequently, released by administration of isopropyl beta-D-thiogalactoside or serum. The mitoses from cells released with isopropyl beta-D-thiogalactoside contained a 3-fold elevation in the fraction of chromosomes containing aberrations compared to mitoses from parallel cell cultures that were released with serum. Thus, the induction of activated Ha-ras gene expression in these cells results in genomic instability that can be detected as aberrant chromosomes at the next mitosis.

Reporter genes in transgenic mice

Although in vivo models utilizing endogenous reporter genes have been exploited for many years, the use of reporter transgenes to dissect biological issues in transgenic animals has been a relatively recent development. These transgenes are often, but not always, of prokaryotic origin and encode products not normally associated with eukaryotic cells and tissues. Some encode enzymes whose activities are detected in cell and tissue homogenates, whereas others encode products that can be detected in situ at the single cell level. Reporter genes have been used to identify regulatory elements that are important for tissue-specific gene expression or for development; they have been used to produce in vivo models of cancer; they have been employed for the study of in vivo mutagenesis; and they have been used as a tool in lineage analysis and for marking cells in transplantation experiments. The most commonly used in situ reporter gene is lacZ, which encodes a bacterial beta-galactosidase, a sensitive histochemical marker. Although it has been used with striking success in cultured cells and in transgenic mouse embryos, its postnatal in vivo expression has been unreliable and disappointing. Nevertheless, the ability to express reporter genes in transgenic mice has been an invaluable resource, providing insights into in vivo biological mechanisms. The development of new in vivo models, such as those in which expression of transgenes can be activated or repressed, should produce transgenic animal systems that extend our capacity to address heretofore unresolved biological questions.

Increased methotrexate resistance and dhfr gene amplification as a consequence of induced Ha-ras expression in NIH 3T3 cells

Oncogene activation and loss of tumor suppressor genes are known to play a role in tumor initiation as well as its progression. The potential roles of these genes in perturbation of genome stability has become a major interest. To better understand the relationship between expression of an oncogene and genetic instability, we have studied a cell line expressing an activated human Ha-ras under the control of bacterial lactose operon regulatory elements for changes in methotrexate resistance and dihydrofolate reductase (dhfr) gene amplification following mutant Ha-ras induction. In these cells mutant Ha-ras is directed by an inducible SV40 promoter containing a bacterial lac operator sequence which is repressed due to constitutive expression of bacterial lac repressor gene. The expression of this Ha-ras is specifically induced by the addition of isopropyl-1-thio-beta-D-galactopyranoside (IPTG), a lactose analogue, to the culture medium. During single-step methotrexate selection, these cells showed an increased frequency of methotrexate resistance in the presence of IPTG. More than 60% of the methotrexate-resistant colonies showed a 2-6-fold amplification of the dhfr gene. One clone with rearranged dhfr had about 100-fold amplification of the gene. The increased capacity to amplify DNA in response to mutant Ha-ras induction was not locus specific since cells also displayed an increased frequency of resistance to N-(phosphonacetyl)-L-aspartic acid in the presence of ITPG. Four of the methotrexate-resistant clones with amplified dhfr gene were cultured further in the presence or absence of IPTG and subsequently compared for their ability to grow in soft agar as a measure of transformation. In medium containing methotrexate but no IPTG, the clones were unable to grow in soft agar, indicating that methotrexate resistance due to gene amplification is separable from transformation.

Single-base deletion induced by benzo[a]pyrene diol epoxide at the adenine phosphoribosyltransferase locus in human fibrosarcoma cell lines

Benzo[a]pyrene diol epoxide (BPDE), a metabolic product of benzo[a]pyrene, is one of the most widely distributed environmental carcinogens. In this study, we demonstrate that BPDE produces a dose-dependent increase in the frequency of APRT gene reversion in the APRT-deficient cell line, HTD114, which contains single nucleotide insertions at different positions in each APRT allele. The highest reversion frequency observed after BPDE exposure was 3.3 +/- 0.9 x 10(-5), at least 10(3)-fold greater than the spontaneous frequency. Reversion of either mutant allele was observed to be a consequence of a frame-restoring loss of a single nucleotide. A similar frequency of BPDE-induced reversion at APRT also was observed in a cell line containing only one type of the mutant alleles of HTD114, thus eliminating the possibility that gene conversion plays a major role in APRT gene reversion in HTD114 cells. Therefore, the data demonstrate that BPDE can function as an effective frameshift mutagen in human cells.

Immunohistochemical detection of c-myc protein in head and neck tumors

OBJECTIVES

To evaluate the correlation between the levels of immunohistochemically detectable c-myc protein in squamous cell carcinoma of the head and neck and clinicopathologic prognostic variables utilized in clinical practice.

DESIGN

Cohort study.

SETTING

University and Veterans Administration medical centers, Cincinnati, Ohio.

PATIENTS OR OTHER PARTICIPANTS

Consecutive samples.

INTERVENTION

Surgery for squamous cell carcinoma of the head and neck.

MAIN OUTCOME MEASURE

Correlation between c-myc expression and tumor size, nodal involvement, clinical disease stage, and degree of differentiation. Hypothesis formulated after data collection.

RESULTS

Significant negative correlation between the c-myc levels and the number of metastatic nodes (P = .0001) and clinical stage of disease (P = .05). No correlation with tumor size or degree of differentiation.

CONCLUSIONS

Reduction or loss of c-myc oncoprotein might be associated with metastatic lymph node involvement and advanced stages of squamous cell carcinoma of the head and neck. Further studies are needed to substantiate preliminary findings.

In vitro evidence that metabolic cooperation is responsible for the bystander effect observed with HSV tk retroviral gene therapy

Tumor cells transduced with a retroviral vector expressing a herpes virus thymidine kinase (HSV tk) gene are rendered sensitive to the antiherpetic drug, ganciclovir. The bystander effect refers to the observation that not all cells need be transduced to eradicate the cell population by treatment with ganciclovir. We demonstrate that metabolic cooperation can account for this bystander effect. When HT1080 human fibrosarcoma cells marked with a lacZ gene (LZ+5) were cocultured with HT1080 cells transduced with a retrovirus expressing HSVtk (HT1080tk11), at a density at which the majority of cells were in contact, both HT1080tk11 and LZ+5 cells were killed by ganciclovir. When cells were cocultured at a low density where the majority of cells are not in contact with one another, however, only the HT1080tk11 cells were killed. This result suggests that cell contact with HT1080tk11 cells is necessary to render the HSVtk- LZ+5 cells sensitive to ganciclovir. Because involvement of metabolic cooperation in the killing of the LZ+5 cells would require not only contact between HT1080tk11 and LZ+5 cells but also the capacity to transfer small cytotoxic molecules from the former cell to the latter, transfer of radioactive molecules between the two cell lines was assessed by autoradiography after treatment of a coculture with [3H]ganciclovir. Isolated HT1080tk11 cells incorporated the labeled ganciclovir into their nuclei, whereas isolated LZ+5 cells did not. LZ+5 cells incorporated [3H]ganciclovir, only when in contact with HT1080tk11 cells. These findings indicate that a ganciclovir metabolic product, presumably a phosphorylated form, can pass from HSV tk+ to HSV tk- cells and mediate cytotoxicity as a consequence of direct contact.

Retrieval of p53 protein in paraffin-embedded head and neck tumor tissues

OBJECTIVES

To improve the detection of p53 protein in formalin-fixed, paraffin-embedded head and neck tumor tissues.

DESIGN

Cohort.

SETTING

University and Veterans Administration medical centers.

PATIENTS OR OTHER PARTICIPANTS

Retrospective samples.

INTERVENTION

Surgery for head and neck carcinoma.

MAIN OUTCOME MEASURES

Retrieval of p53 antigen. Hypothesis formulated after data collection.

RESULTS

An antigen retrieval method facilitated the unmasking of previously inaccessible p53 antigenic determinants in formalin-fixed, paraffin-embedded tissues. This approach has made possible a much more reliable and sensitive immunohistochemical detection of p53 antigen. The procedure is simple, requiring only microwave heating of tissue sections to 100 degrees C in the presence of a zinc sulfate solution.

CONCLUSIONS

Antigen retrieval method in formalin-fixed, paraffin-embedded tissue demonstrated a significant increase in p53 immunostaining.