Alterations in the p53 gene and the clonal evolution of the blast crisis of chronic myelocytic leukemia

Hemizygous expression of the wild-type p53 allele may confer a selective growth advantage before complete inactivation of the p53 gene in the progression of chronic myelogenous leukaemia

We analysed the expression of the p53 gene in various clinical phases of chronic myelogenous leukaemia (CML) by quantitative reverse transcriptase (RT) polymerase chain reaction (PCR). Hemizygous expression of the wild-type p53 allele was observed in two samples showing the loss of one p53 allele, and affected p53 expression was associated with p53 allelic loss rather than the clinical phase of CML. In four patients with CML showing p53 inactivation, we performed a detailed sequential analysis of p53 allelic loss, p53 mutation and expression from the onset of the disease to the patients' death. Consequently, we demonstrated that the loss of a wild-type p53 allele preceded mutation of the remaining allele, and that cells hemizygous for the wild-type p53 allele dominated those with both wild-type alleles, then were replaced by cells with complete p53 inactivation. These observations indicate that not only complete p53 inactivation but also hemizygous expression of the wild-type p53 allele may confer a selective growth advantage, and that the former is implicated in a more malignant phase than the latter. Alternatively, the inactivation of another undefined anti-oncogene on chromosome 17p may allow selective growth before the p53 mutation occurs.

Direct transplantation of chronic myelogenous leukemia cells into nude mice and establishment of a leukemic stem cell (Ph1+, CD34+) line dependent on mouse bone marrow stromal cells in vitro

Peripheral blood cells from a female patient with Ph1-positive chronic myelogenous leukemia (CML) in blast crisis were serially transplanted in BALB/c nude mice for 16 passages. This in vivo cell line, designated CML-N-1, had Ph1 chromosome abnormality and BCR gene rearrangement. The cells expressed CD11b, CD13, CD33, CD34, CD38, and HLA-DR antigens until the 11th passage and subcutaneous tumors produced by these passages were composed of admixtures of immature and maturing cells that differentiated to basophils when cultured in vitro. From the 12th passage on, the tumors became composed mainly of immature cells expressing CD13, CD34, and HLA-DR, and no longer differentiated to basophils even upon in vitro culture. In contrast to the vigorous proliferation in vivo, CML-N-1 cells from any passage failed to proliferate in vitro under standard liquid culture conditions with or without growth factors, such as granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, monocyte colony-stimulating factor, interleukin 3, interleukin 6 and stem cell factor. However, a continuously growing cell line, designated CML-C-1, was established by culturing CML-N-1 cells on feeder layers of mouse bone marrow stromal cells. This mouse bone marrow stromal cell-dependent cell line showed immature cell morphology and expressed early myeloid phenotype positive for CD13, CD34, and HLA-DR. These results indicate that mouse bone marrow stromal cells provide a certain growth factor(s) active on human leukemia cells.

The SKM-1 leukemic cell line established from a patient with progression to myelomonocytic leukemia in myelodysplastic syndrome (MDS)-contribution to better understanding of MDS

Although molecular and cytogenetic studies strongly point to the role of oncogenes, the mechanisms underlying the development of MDS and their progressive evolution to AML are still largely unknown. It has been postulated that AML has a preleukemic stage and a multi step pathogenesis, with the preleukemic stem cell able to undergo clonal evolution, with the acquisition of karyotypic abnormalities, leading to the development of acute leukemic subclones. The activations of the ras oncogenes or inactivation of the p53 anti-oncogene by point mutations have been described recently in several cases of MDS as well as AML, suggesting a critical role for these alterations in the development of these myelogenous leukemias. We reported previously establishment of a leukemic cell line, SKM-1, from the patient who initially possessed multiple point mutations of ras genes but lost these mutations during disease progression to myelomonocytic leukemia with acquisition of chromosomal abnormalities involving the p53 anti-oncogene. This process is characterized by genetic instabilities probably due to the failure of their DNA repairment leading to abnormal control of cell proliferation and differentiation. Studying this cell line, SKM-1, is a promising approach to understand the mechanisms of the initiation, disease progression, alterations of DNA repairment, and genetic instability in MDS and myelogenous malignancies.

Establishment and characterization of a new Ph1-positive chronic myeloid leukemia cell line MC3 with trilineage phenotype and an altered p53 gene

A new Ph1-positive leukemic cell line (MC3) expressing the P210bcr/abl oncoprotein was established from a patient with CML in blast crisis. The MC3 cells showed the trilineage phenotype of myeloid, lymphoid (CD19) and megakaryocytoid lineages, and had a proliferative response to rhIL-1 and rhIL-3 in the serum-free culture. These results and the expression of CD34 indicated that the MC3 cells have characteristics of hematopoietic progenitor cells. Recently, it has been documented that alterations of the p53 gene in leukemic cells are frequently detected during the blast crisis of CML. The MC3 cells contained the altered p53 gene. In addition, the original leukemic cells showed the point-mutational activation of the N-ras gene and an additional chromosomal abnormality inv(3q), but the MC3 cells contained no such abnormalities, indicating that not all of the original leukemic cells had these abnormalities. Thus, the MC3 cell line may provide several insights into investigations of the blast crisis in CML as well as hematopoietic progenitor cells.

Double P53 point mutation in extramedullary blast crisis of chronic myelogenous leukemia

A patient with Philadelphia-positive chronic myelogenous leukemia (CML) evolved in extramedullary blast crisis, was studied for the presence of alterations of the P53 tumor suppressor gene in the different stages of disease progression. No P53 gene aberrations were detected during the chronic and accelerated phases. Two identical missense point mutations, involving codons 249 and 281 and leading to the amino acid substitutions Arg-Ser and Thy-Asp, were identified in cells of an extramedullary mass and then in peripheral blood blast crisis cells. The data indicate that the medullary and extramedullary blast cells belong to the same cellular clone. They also strongly suggest that in this case, the alteration of P53 gene is strictly related to the progression of the disease, although this mechanism is certainly neither the only nor the most frequent molecular event leading to the acute phase.

Expression of the DCC gene in human hematological malignancies

Inactivation of the deleted in colorectal carcinoma (DCC) tumor suppressor gene has been reported not only in colorectal carcinoma but also in other human malignancies. In order to evaluate the role of the DCC gene in leukemogenesis, we examined DCC expression using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Expression of the DCC gene was reduced or absent in 10 of 39 (26%) patients with acute myelogenous leukemia (AML), three of 14 (29%) patients with acute lymphocytic leukemia (ALL), seven of 33 (21%) patients with chronic myelogenous leukemia (CML), three of 39 (8%) patients with myelodysplastic syndromes (MDS), and five of nine (56%) patients with overt leukemia progressed from MDS. These findings suggest that inactivation of the DCC gene contributes to some instances of leukemogenesis.

Progressive de novo DNA methylation at the bcr-abl locus in the course of chronic myelogenous leukemia

De novo methylation of CpG islands is a rare event in mammalian cells. It has been observed in the course of developmental processes, such as X chromosome inactivation and genomic imprinting. The methylation of DNA, an important factor in the epigenetic control of gene expression, may also be involved in tumorigenesis. After the t(9;22) chromosomal translocation and generation of the Philadelphia chromosome, the initiating event in chronic myelogenous leukemia (CML), most of the abl coding sequence is fused to the 5' region of the bcr gene. Expression of the hybrid bcr-abl gene is, therefore, regulated by the bcr promoter. In most cases of CML, one of the two abl promoters (Pa) is nested within the bcr-abl transcriptional unit and should be able to transcribe the type Ia 6-kb normal abl mRNA from the Philadelphia chromosome. However, we have found that the 6-kb transcript is present only in CML cell lines containing a normal abl allele and that the apparent inactivation of the nested Pa promoter is associated with allele-specific methylation. Furthermore, we have noticed that the Pa promoter is contained within a CpG island and undergoes progressive de novo methylation in the course of the disease. This is attested to by the fact that DNA samples from CML patients that are methylation-free at the time of diagnosis invariably become methylated in advanced CML. Since tumor progression in CML cannot always be inferred from the clinical presentation, assessment of de novo CpG methylation may prove to be of critical value in management of the disease. It could herald blastic transformation at a stage when bone marrow transplantation, the only potentially curative therapeutic procedure in CML, is still effective.

Multiple aberrant splicing of the p53 transcript without genomic mutations around exon-intron junctions in a case of chronic myelogenous leukaemia in blast crisis: a possible novel mechanism of p53 inactivation

We found three truncated p53 transcripts in a patient with chronic myelogenous leukaemia in blast crisis carrying chromosome 17 abnormalities. Sequencing of these transcripts revealed complete absence of the entire exons 7, 8 and 9 in one, exons 8 and 9 in another, and exon 10 in the other. Sequencing analysis of genomic DNA, however, revealed no mutation in exons 6-10 and their flanking introns. These results suggest that the aberrant p53 transcripts in this case might not result from splicing mutations but from an unknown affected splicing process.

Sequential relapses of blastic crisis may involve different clones of cells with different molecular abnormalities

A patient with typical Ph1-positive CML was studied during sequential phases: (1) initial chronic phase, (2) first myeloid blast crisis, (3) second chronic phase, and (4) accelerated disease leading to a second blast crisis. A point mutation in codon 239 of the p53 gene and a novel chromosome 17 alteration appeared concomitantly with the first blast crisis and then disappeared with re-establishment of a second chronic phase. They did not reappear with the second acute phase, indicating that the clone responsible for the original blast crisis had been suppressed and supplanted by another clone of malignant cells. This observation suggests that in at least some CML patients drug therapy can suppress or eliminate an aggressive malignant cell clone, but that the underlying molecular defect in haemopoietic cells (in this case the c-ABL translocation) persists and other aggressive clones with different molecular lesions eventually arise. Our observations and inferences are consistent with the hypothesis advanced by Fialkow et al (1991) to explain clonal remissions in acute non-lymphocytic leukaemia.

Myelomonocytic crisis with t(5;17) and a p53 mutation in a patient with chronic myelogenous leukemia

We report a 64-year-old Japanese man with chronic myelogenous leukemia (CML) who expired with myelomonocytic crisis. Cytogenetic analyses of chronic phase (CP) and accelerated phase (AP) cells revealed a Philadelphia chromosome and an isochromosome for the long arm of chromosome 17, i(17q). This karyotype was replaced by another karyotype in blast crisis (BC), resulting in near triploidy with t(5;17) (p15;p11) and loss of chromosome 17 pter-->p11. Interphase fluorescent in situ hybridization studies with a chromosome 17 specific alpha satellite DNA probe confirmed the presence of a clonal change in BC. In addition, single-strand conformation polymorphism analysis and PCR-direct sequencing of BC cells revealed a point mutation at codon 203 of the p53 gene, GTG to GAG (Val to Glu), and loss of the normal allele. In contrast, no alterations of the p53 gene were found in CP and AP cells. Therefore, progression of CML in this patient appeared to be related to loss of 17p, as well as a mutation in the p53 gene.

P53 overexpression in human soft tissue sarcomas: relation to biological aggressiveness

BACKGROUND

The tumor suppressor protein p53 is overexpressed in a large fraction of human tumors. It has been supposed that p53 abnormalities may be an early event that contributes to the neoplastic transformation; alternatively, p53 overexpression might be related to progression toward more aggressive tumor phenotypes. The aim of the present work was to better clarify the role of p53 overexpression in human soft tissue sarcomas (IISTS).

DESIGN

p53 immunohistochemistry analysis using the Pab 1801 was performed in frozen samples of HSTS obtained from 61 patients. Tumors were classified according to the WHO criteria, histologic grading was based on the criteria of Enzinger and Weiss, and DNA ploidy and S-phase determination was performed by flow cytometrical analysis.

RESULTS

Of all the HSTS we analyzed, p53 protein over-expression occurred more frequently in G3 grade tumors (p < 0.01), HSTS of III A-B stage (p = 0.02) and in aneuploid tumors (p < 0.01).

CONCLUSIONS

The association of p53 overexpression with parameters of biological aggressiveness suggests an involvement of p53 in the neoplastic progression of HSTS. This assumption is supported by the findings that in tumors with a mixed diploid/aneuploid neoplastic cell population p53 protein expression was significantly (p < 0.01) higher in the aneuploid cell subpopulation. In conclusion, our study suggests that overexpression of p53 is present mainly in the most biologically aggressive forms of HSTS and may therefore represent a neoplastic progression index possibly useful for prognostic purposes.

Genetic analysis of p53 and RB1 tumor-suppressor genes in blast crisis of chronic myeloid leukemia

We have investigated the involvement of the p53 and RB1 tumor-suppressor genes in 26 cases of chronic myeloid leukemia (CML) blast crisis, including 17 myeloid, eight lymphoid, and one megakaryoblastic crisis. The presence of p53 mutations in exons 5 through 9 was tested by the PCR-single-strand conformation polymorphism (SSCP) assay, followed by PCR-direct sequencing; in addition, loss of heterozygosity (LOH) at 17p13, the site of the p53 gene, was assayed by Southern blot. Given the variability of the mechanisms of inactivation of the RB1 gene in human tumors, a combination of Southern blot and mutational analysis by PCR-SSCP was used. p53 mutations were restricted to one case of myeloid blast crisis, showing a CGC-->TGC (Arg-->Cys) mutation at codon 283; two additional cases displayed LOH at 17p13 in the absence of p53 mutations. No molecular lesions of the RB1 gene were detected in any of the cases analyzed. These data indicate that inactivation of p53 and RB1 is a rare event in the molecular pathogenesis of CML acute transformation.

Analysis of deletions of the long arm of chromosome 11 in hematologic malignancies with fluorescence in situ hybridization

We studied samples containing deletions of the long arm of chromosome 11 (11q) from patients with hematologic malignancies by using cytogenetic and fluorescence in situ hybridization (FISH) techniques. Cytogenetic analysis of 28 patients and of a cell line showed that all deletions included band 11q23. FISH analysis demonstrated that the proximal part of 11q23, including NCAM, was deleted in 13 of 15 patients and the cell line. Recurring chromosomal losses in human tumors have been regarded as evidence that the affected regions contain tumor-suppressor genes. These results suggest that the putative tumor-suppressor gene is proximal to the MLL gene which is also located in 11q23.

p53 associated with cathepsin D in primary breast cancer

The p53 protein was identified in primary breast carcinomas by specific binding of PAb1801 and PAb240 antibodies. Using sodium dodecyl sulfate electrophoresis followed by immunoblotting on nitrocellulose membrane, the p53 protein was identified in 36 nuclear fractions obtained from 60 primary breast cancers; semiquantitation of p53 was performed by densitometric scanning. The total cathepsin D content, the estrogen and progesterone receptor concentration values and the axillary lymph node involvement were also assessed. Tumors expressing p53 had significantly higher levels of cathepsin D than those in which p53 was undetectable. p53 expression was strongly associated with low or negative estrogen receptor values; progesterone receptor concentrations were also significantly higher in p53-negative tumors than in those tumors with detectable p53 levels. Finally, a significant relationship between p53 expression and lymph node metastasis was observed. It was concluded that a positive association between p53 and cathepsin D values exists which is of prognostic interest in that both cathepsin D and p53 are associated with a high tumor grade and metastatic activity.

p53 gene mutations and 17p allelic deletions in hepatocellular carcinoma from Japan

BACKGROUND

p53 gene mutations at codon 249 have been reported in hepatocellular carcinoma (HCC) from China and South Africa, a phenomenon shown to be closely associated with food contamination by aflatoxin. There have been few reports, however, in regard to p53 gene mutations in HCC from other geographic areas.

METHODS

The authors analyzed 20 HCC from Japan for alteration of the p53 gene by restriction fragment length polymorphisms and for nucleic acid mutations by polymerase chain reaction with direct sequencing.

RESULTS

Alterations associated with the p53 gene were found in 6 of 20 HCC (30%). Allelic loss of chromosome 17p occurred in 5 of 14 informative (heterozygous) cases (36%). Mutations in the p53 gene were detected in three cases (15%), at codons 176 (exon 5), 236 (exon 7), and 294 (exon 8). These cases were different from the HCC cases from China and South Africa, where point mutations in the p53 gene were reported at the same codon 249 in half of the cases and where aflatoxin food contamination and hepatitis B virus infection are recognized risk factors of HCC. No p53 gene alterations were found in smaller HCC (< 3 cm) or at earlier stages.

CONCLUSIONS

In Japan, p53 gene alterations seem to be a late event in the progression of hepatocarcinogenesis, which is often associated with persistent infection by the hepatitis C or B virus, but not usually with exposure to aflatoxin.

Selecting DNA fragments for mutation detection by temperature gradient gel electrophoresis: application to the p53 gene cDNA

Temperature gradient gel electrophoresis (TGGE) and related methods are widely employed to detect mutations in DNA fragments. DNA melting map calculations and GC clamps have been used to enhance the detection of mutations. While generally successful, these methods have not always revealed base changes within a DNA fragment. Previous work suggested that mutations are detected if they are in a DNA's first melting domain, and the melting domain is well separated from final strand dissociation. Two criteria from the DNA melting theory were established to determine when both of these conditions are met. The criteria involve calculating the derivative melting curve as well as the melting map of a DNA sequence. The approach was applied to the cDNA sequence of the human p53 gene. Mutations in the p53 gene are common in human cancers and are generally located in four 'hot spot' regions. Calculations indicated that three DNA fragments are needed to detect base substitutions in the four hot-spot regions. Predicted melting behavior was experimentally tested with eight single base substitutions distributed among the four hot-spot regions. All mutations tested behaved as predicted and were detected by vertical TGGE. Heteroduplex DNAs formed by melting and reannealing various ratios of wild type and mutant DNA fragments were also examined. Results indicated that point mutations can be detected by ethidium bromide staining from samples containing 10% mutant and 90% wild-type sequences.

Simultaneous presentation of symptomatic subependymomas in siblings: case reports and review

Two young adult siblings independently developed similar neurological complaints that included headaches, photophobia, nausea, and intermittent lancinating facial pains. Magnetic resonance imaging revealed fourth ventricular lesions that required surgery in both patients. A pathological review revealed subependymomas with virtually identical histological features. The clinical features and common pathological findings of both patients suggest that familial subependymomas may have a maldevelopmental origin with genetic implications.

The expression of p53 antigen in primary malignant epithelial tumors of the liver: an immunohistochemical study

We examined the expression of mutant p53 gene products in primary malignant epithelial tumors of the liver. Fourteen of 68 hepatocellular carcinomas, one of seven hepatoblastomas and one of nine intrahepatic cholangiocarcinomas showed nuclear staining for p53 proteins. None of the surrounding non-tumorous tissues expressed nuclear staining. The detection of p53 proteins in tumor cells was significantly higher in hepatocellular carcinomas of Oriental patients (31.6%) compared to non-Orientals (6.7%, p < 0.015). No significant differences were seen in p53 antigen expression between hepatitis B and non-hepatitis B associated hepatocellular carcinomas in Oriental patients. These results suggest a role for other environmental factors, such as aflatoxin, in the etiology of p53 mutation in hepatocellular carcinoma in Oriental patients.

Comparison between p53 staining in tissue sections and p53 proteins levels measured by an ELISA technique

We studied 51 paired samples of tissue sections and cytosol extracts from patients with breast cancer. A very high affinity monoclonal antibody to human p53 protein, DO-1, and polyclonal serum CM-1 to p53 protein were used for two site ELISA assays and CM-1 was used for immunohistochemistry to detect p53 protein accumulation in breast cancer samples. Eighteen carcinomas were positive for p53 by tissue staining and ELISA assay. Nineteen tumours were negative by ELISA and immunohistochemistry, and 14 cases with low levels of positive staining by immunohistochemistry were negative by the ELISA assay. A statistically significant correlation has been found between the degree of staining and the amount of p53 protein measured by ELISA (Pearson's correlation coefficient r = 0.59, P < 0.00001). Our ELISA assay offers an alternative approach to evaluating the p53 status of breast biopsy material, using cytosol extracts routinely prepared for steroid hormone receptor assays. This assay should also be of general application to other situations where the level of p53 protein needs to be determined.

P53 mutation in acute T cell lymphoblastic leukemia is of somatic origin and is stable during establishment of T cell acute lymphoblastic leukemia cell lines

Samples donated by patients with T cell acute lymphoblastic leukemia (T-ALL) were screened for mutations of the p53 tumor suppressor gene. Peripheral blood cells of T-ALL relapse patient H.A. were found to possess a heterozygous point mutation at codon 175 of the p53 gene. To determine whether this was an inherited mutation, a B cell line (HABL) was established. Leukemic T cell lines (HATL) were concurrently established by growing peripheral blood leukemic T cells at low oxygen tension in medium supplemented with IGF-I. Previously we had shown that > 60% of leukemic T cell lines possessed mutations in the p53 gene (Cheng, J., and M. Hass. 1990. Mol. Cell. Biol. 10:5502), mutations that might have originated with the donor's leukemic cells, or might have been induced during establishment of the cell lines. To answer whether establishment of the HATL lines was associated with the induction of p53 mutations, cDNAs of the HATL and HABL lines were sequenced. The HATL lines retained the same heterozygous p53 mutation that was present in the patient's leukemic cells. The HABL line lacked p53 mutations. Immunoprecipitation with specific anti-p53 antibodies showed that HATL cells produced p53 proteins of mutant and wild type immunophenotype, while the HABL line synthesized only wild-type p53 protein. The HATL cells had an abnormal karyotype, while the HABL cells possessed a normal diploid karyotype. These experiments suggest that (a) p53 mutation occurred in the leukemic cells of relapse T-ALL patient HA; (b) the mutation was of somatic rather than hereditary origin; (c) the mutation was leukemia associated; and (d) establishment of human leukemia cell lines needs not be associated with in vitro induction of p53 mutations. It may be significant that patient HA belonged to a category of relapse T-ALL patients in whom a second remission could not be induced.

Isolation and characterization of DNA sequences that are specifically bound by wild-type p53 protein

Wild-type p53 was shown to function as a transcription factor. The N-terminal region of the protein contains the transcription activation domain, while the C terminus is responsible for DNA binding. Localization of the DNA-binding domain of the p53 protein to the highly conserved carboxy-terminal region suggests that the interaction of p53 with DNA is important for its function. We have developed a strategy for studying the DNA sequence specificity of p53-DNA binding that is based on random sequence selection. We report here on the isolation of murine genomic DNA clones that are specifically bound by the wild-type p53 protein but are not bound by mutant p53 protein forms. The isolated p53 target gene contains the unique DNA-binding sequence GACACTGGTCACACTTGGCTGCTTAGGAAT. This fragment exhibits promoter activity as measured by its capacity to activate transcription of the chloramphenicol acetyltransferase reporter gene. Our results suggest that p53 directly binds DNA and functions as a typical transcription factor.

Isolation and characterization of DNA sequences that are specifically bound by wild-type p53 protein

Wild-type p53 was shown to function as a transcription factor. The N-terminal region of the protein contains the transcription activation domain, while the C terminus is responsible for DNA binding. Localization of the DNA-binding domain of the p53 protein to the highly conserved carboxy-terminal region suggests that the interaction of p53 with DNA is important for its function. We have developed a strategy for studying the DNA sequence specificity of p53-DNA binding that is based on random sequence selection. We report here on the isolation of murine genomic DNA clones that are specifically bound by the wild-type p53 protein but are not bound by mutant p53 protein forms. The isolated p53 target gene contains the unique DNA-binding sequence GACACTGGTCACACTTGGCTGCTTAGGAAT. This fragment exhibits promoter activity as measured by its capacity to activate transcription of the chloramphenicol acetyltransferase reporter gene. Our results suggest that p53 directly binds DNA and functions as a typical transcription factor.

p53 gene rearrangements in chronic myelocytic leukemia

We performed Southern-blot analysis of the p53 gene in 41 consecutive patients with typical chronic myelocytic leukemia (CML). In two of them, we were able to study cells during both the chronic and the accelerated phases. Only one of the 29 chronic-phase samples had rearrangement of the p53 gene, whereas three of the nine accelerated-phase samples and one of the five patients in blast crisis exhibited rearrangements. Gene deletion was observed in two patients, one in accelerated phase and the other in blast crisis. One patient with a nonrearranged p53 gene in chronic phase showed rearrangement after progression to the accelerated phase. On the other hand, one patient in accelerated phase exhibited rearrangements which disappeared after reversion to chronic phase with successful treatment. Our findings support the opinion that alterations of the p53 gene may play an important role in CML evolution.

Wild-type p53 is not a negative regulator of simian virus 40 DNA replication in infected monkey cells

To analyze the proposed growth-inhibitory function of wild-type p53, we compared simian virus 40 (SV40) DNA replication in primary rhesus monkey kidney (PRK) cells, which express wild-type p53, and in the established rhesus monkey kidney cell line LLC-MK2, which expresses a mutated p53 that does not complex with large T antigen. SV40 DNA replication proceeded identically in both cell types during the course of infection. Endogenously expressed wild-type p53 thus does not negatively modulate SV40 DNA replication in vivo. We suggest that inhibition of SV40 DNA replication by wild-type p53 in in vitro replication assays is due to grossly elevated ratios of p53 to large T antigen, thus depleting the replication-competent free large T antigen in the assay mixtures by complex formation. In contrast, the ratio of p53 to large T antigen in in vivo replication is low, leaving the majority of large T antigen in a free, replication-competent state.

CML: mechanisms of disease initiation and progression

Chronic myelogenous leukemia (CML) is a hematological stem cell disorder characterized by excessive proliferation of the myeloid lineage. It has a progressive course typified by the transition from the chronic phase to the accelerated phase and on to blast crisis. The hallmark of CML is the translocation between chromosomes 9 and 22 that results in the chimeric BCR-ABL gene encoding p210BCR-ABL. The oncogenic potential of this protein has been validated, and it is believed that it contributes in a critical way to the initiation of CML. However, the secondary genetic forces responsible for the transition from the chronic state to the fully blastic stage are not clear. Evidence for chromosomal instability includes the clonal evolution which characterizes advanced CML. In regard to specific genetic aberrations, sporadic reports have shown alterations in H-RAS, c-MYC, retinoblastoma, and P53 genes, as well as production of p190BCR-ABL during the progression of CML. In addition, we have recently found evidence for excessive interleukin-1 beta production, acting in an autocrine and/or paracrine manner, in the more advanced stages of the disease. Taken together, current data suggest that multiple molecular pathways lead to disease progression, and that distinct subsets of genetic alterations exist in blast crisis patients.

Screening for TP53 mutations in osteosarcomas using constant denaturant gel electrophoresis (CDGE)

We have previously developed conditions to screen for TP53 point mutations inside the conserved domains II-V of the gene by using constant denaturant gel electrophoresis (CDGE). The present study reports conditions for screening more of the codons in the frequently mutated region exon 5-8 and for detecting mutations in sequences encoding functional domains in the N- and C-terminal part of the protein. The ability of the CDGE technique to detect mutations was studied using controls with known sequence deviations. The resolution power of the technique to separate different types of mutations was tested by using seven different single base pair mutants all residing in a stretch of four base pairs. All mutants were separated from the wild type. The established CDGE screening strategy was then used to look for mutations in DNA from 28 osteosarcomas. Six (21.5%) of the samples were shown to have a TP53 mutation, and the exact characterization was performed by direct sequencing. All of these were within the frequently reported mutated region exon 5-8.

Molecular defects associated with the acute phase CML

Parts of the Bcr/Abl hybrid transcript supposed to be important for its transforming ability were sequenced in a series of CML blast crises, in order to evaluate the possible presence of alterations responsible for the disease transition from the chronic to the acute phase. In addition, the N- and Ki-ras as well as the p53 involvement was investigated by exploring their structure and expression in the same patients. We used traditional types of molecular analysis including Southern and Northern blot, together with methods that allow a rapid detection of point mutations and microdeletions, such as SSCP, single strand conformation polymorphism and direct sequencing. The results obtained may be summarized as follows: no alterations were found in the parts of the Bcr/Abl transcripts investigated in the present study (SH2, SH3 and the region surrounding codon 832); p53 alterations were observed in 5% and N- and Ki-RAS mutations in 5% of the cases examined. These molecular defects are therefore responsible for the clinical progression of the Ph1-positive CML only in a minority of cases.

Recurring chromosome abnormalities in Hodgkin's disease

Cytogenetic analysis was performed on lymph nodes or other tumor masses from 33 patients with Hodgkin's disease. Metaphase cells were obtained in 25 of the 33 cases. Analyzable abnormal clones were found in nine cases. Characteristic abnormalities included polyploidy and complex structural rearrangements nonrandomly involving certain chromosomal regions. Chromosomes most commonly gained were 2, 9, 11, 19, and 20, and those most often lost were 10, 13, 15, 16, 21, and Y. Translocation breakpoints clustered in bands 1p11-1p13, 1p36, 4q35, 14q11, and 15p11. In five patients, breakpoints were in bands to which T-cell receptor genes have been mapped. No specific, recurring translocation was identified. There was, however, recurring loss of chromosomal material from 1q, 4q, 6q, and 17p. Loss or deletions of chromosomes 4 and 6 were found in five and six patients, respectively. Deletions overlapped; the smallest overlapping segments included bands 4q25-4q27 and 6q21-6q23. The data suggest that loss of specific chromosomal regions may be important in the pathogenesis of Hodgkin's disease. With respect to tumor specificity, deletions of 4q are of particular interest because these have not been previously reported to occur nonrandomly in other human malignancies.

p53 over-expression is an early event in the development of human squamous-cell carcinoma of the larynx: genetic and prognostic implications

The tumor-suppressor protein p53 is over-expressed in a large fraction of squamous-cell carcinomas of the larynx (LSCCs). p53 overexpression is dependent upon the synthesis of mutated versions of the protein and has been associated with the malignant progression of certain tumor types. In order to examine the prognostic value of p53 immunodetection in LSCCs, we performed a retrospective analysis on a selected series of tumors, using the PAb 1801 and CM1 antibodies. No significant difference in the frequency of p53 over-expression was observed between tumors from patients with early relapse (67%) and those who had been disease-free for more than 5 years (84%). The lack of correlation of p53 immunoreactivity with clinical stage and differentiation grade of LSCCs, together with the coordinated expression of p53 in primary tumors and the corresponding lymph-node metastases, indicate that p53 over-expression is probably unrelated to the biological aggressiveness of these tumors. In addition, the detection of p53 immunostaining in pre-invasive areas as well as in preneoplastic lesions suggests that p53 abnormalities probably constitute a very early event in LSCC development.

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.

Molecular mechanisms in the evolution of chronic myelocytic leukemia

Chronic myelocytic or Ph1-positive acute lymphoblastic leukemias have been analyzed for alterations in a variety of proto-oncogenes and anti-oncogenes implicated in the progression of chronic myeloid leukemia (CML) from its chronic phase to blast crisis. The most frequent genetic change found in disease evolution is an alteration of the p53 gene involving a point mutation, a rearrangement or a deletion. These gene changes are common in myeloid and undifferentiated variants of blast crisis but are usually undetectable in lymphoid leukemic transformants. Other molecular changes also occur in the clonal evolution of CML. The retinoblastoma-susceptibility (Rb) gene is an anti-oncogene. Structural abnormalities of Rb are frequent in all types of human acute leukemia, but are particularly common in Ph1-positive leukemia of lymphoid phenotype including both Ph1-positive ALL and lymphoid blast crisis of CML. Changes in Rb occur early in the transition to blast crisis with loss of Rb protein being the common factor. Mutations in the N-RAS gene also occur, but are rare in typical blast crisis. They are sometimes seen in Ph1-negative myeloid blast crisis. Since changes in the p53 gene are generally associated with progression of disease of a myeloid phenotype and changes in the Rb gene occur more often with a lymphoid phenotype, a particular molecular alteration may influence the character of disease evolution in CML.

Mutations of the p53 tumour suppressor gene in haematologic neoplasms

Mutations of the p53 tumour suppressor gene have frequently been observed in several types of solid tumours and are believed to be implicated in the development of these tumours. To determine the relevance of p53 mutations in haematologic neoplasms, we performed polymerase chain reaction-single strand conformation polymorphism analysis on the p53 gene in 45 patients with various types of haematologic neoplasms. In exons 5-8 containing highly conserved regions, mobility shifts indicating sequence alterations were detected in four of the 45 patients, and subsequent sequencing was performed. A point mutation resulting in a novel stop codon was detected at codon 213 in one of 23 cases of chronic myelogenous leukaemia (one of five cases of blast crisis). Point mutations causing amino acid substitutions were detected in one of four cases of myelodysplastic syndrome at codon 195, one of three cases of adult T-cell leukaemia at codon 281, and one of eight cases of acute lymphoblastic leukaemia at codon 281, and these missense mutations were accompanied by loss of the wild type allele. Patients harbouring these nonsense and missense mutations were in advanced disease stages. These findings suggest that mutational inactivation of the p53 gene is infrequent but is involved in the tumorigenesis of several types of haematologic neoplasms at least in some cases.

Prevalence and spectrum of germline mutations of the p53 gene among patients with sarcoma

BACKGROUND

Recent studies have identified germline mutations of the p53 tumor-suppressor gene in families with the Li-Fraumeni syndrome, a rare inherited disorder characterized by a high risk of sarcomas of bone and soft tissue, breast cancer, and other tumors. In this report, we address the possibility that some sporadic sarcomas may be associated with new germline mutations of the p53 gene, which would not be manifested as familial cancer unless the patient survived to reproduce.

METHODS

We studied DNA from peripheral leukocytes of 196 patients with sarcoma and from 200 controls. Of the 196 patients with sarcoma, 15 were selected because they had had multiple primary cancers or had a family history of cancer. The entire coding sequence and splice junctions of the p53 gene were analyzed for mutations.

RESULTS

Eight germline mutations were found, three in patients with no known family history of cancer and five in patients with an unusual personal or family history of cancer. Four mutations caused amino acid substitutions, and four caused stop codons. These mutations were not present in any of the 200 controls.

CONCLUSIONS

New germline mutations of the p53 gene are rare among patients with "sporadic" sarcoma but may be common in patients with sarcoma whose background includes either multiple primary cancers or a family history of cancer. Diverse mutations of this gene were associated with an increased likelihood of cancer; hence, the entire gene should be considered a target for heritable mutation. It appears that the group of patients with cancer who carry germline mutations of the p53 gene is more diverse than is suggested by the clinical definition of the Li-Fraumeni syndrome. The identification of carriers could be of substantial clinical importance.

Hereditary and acquired p53 gene mutations in childhood acute lymphoblastic leukemia

The p53 gene was examined in primary lymphoblasts of 25 pediatric patients with acute lymphoblastic leukemia by the RNase protection assay and by single strand conformation polymorphism analysis in 23 of 25 cases. p53 mutations were found to occur, but at a low frequency (4 of 25). While all four mutations were identified by single strand conformation polymorphism, the comparative sensitivity of RNase protection was 50% (2 of 4). Heterozygosity was retained at mutated codons in 3 of 4 cases. One pedigree was consistent with the Li-Fraumeni syndrome, and bone marrow from both diagnosis and remission indicated a germline G to T transversion at codon 272 (valine to leucine). Although members of another family were affected with leukemia, a 2-bp deletion in exon 6 was nonhereditary. The other two nonhereditary p53 mutations included a T to G transversion at codon 270 (phenylalanine to cysteine) and a G to C transversion at codon 248 (arginine to proline). These data support the role of both hereditary and acquired p53 mutations in the pathogenesis and/or progression of some cases of childhood acute lymphoblastic leukemia.

Association of induction of a fully tumorigenic phenotype in murine radiation-induced T-lymphoma cells with loss of differentiation antigens, gain of CD44, and alterations in p53 protein levels

We investigated the mechanism of radiation induction of murine thymic lymphomas by studying the characteristics of primary x-ray-induced thymic lymphoma (PXTL) cell lines and of their oncogene-induced, progressed progeny. It is widely thought that proto-oncogene alterations are associated with the induction of murine lymphomas; however, few, if any primary murine radiation-induced lymphomas possess (proto-)oncogene alterations. Independently derived cell lines grown directly (i.e., without in vivo transplantation) from thymic lymphomas of irradiated C57BL/6 mice possess the properties of immortalized pre-T cells and lack many of the characteristics of "tumor cells". PXTL cells are poorly tumorigenic upon transplantation, do not clone in methylcellulose cultures, are growth factor dependent and autocrine, and lack consistent chromosome and oncogene abnormalities. However, the thymic lymphomas are malignant and cause the death of each afflicted mouse. PXTL cells expressed two immunologically distinct forms of the tumor suppressor protein p53 that have moderately increased stability (t1/2 = 1 h) when compared with p53 of normal splenic T lymphocytes. Early PXTL cells could progress in vitro to a fully tumorigenic phenotype after infection with retroviruses encoding the c-myc and v-ras oncogenes. Progressed T-lymphoma cells acquired growth factor independence, a highly transplantable and tumorigenic phenotype, and the ability to quantitatively clone in methylcellulose cultures. Progressed lymphoma cells coordinately downregulated the expression of five T-cell differentiation markers, upregulated the expression of CD44 (Pgp-1), and harbored vastly elevated levels of two immunologically distinct forms of p53. Our results suggest that the early thymic lymphomas consist of differentiation-inhibited, immortal pre-T cells that are precursors to progressed, fully tumorigenic T-lymphoma cells.

Analysis of p53 mutants for transcriptional activity

The wild-type p53 protein functions to suppress transformation, but numerous mutant p53 proteins are transformation competent. To examine the role of p53 as a transcription factor, we made fusion proteins containing human or mouse p53 sequences fused to the DNA binding domain of a known transcription factor, GAL4. Human and mouse wild-type p53/GAL4 specifically transactivated expression of a chloramphenicol acetyltransferase reporter in HeLa, CHO, and NIH 3T3 cells. Several mutant p53 proteins, including a mouse p53 mutant which is temperature sensitive for suppression, were also analyzed. A p53/GAL4 fusion protein with this mutation was also transcriptionally active only at the permissive temperature. Another mutant p53/GAL4 fusion protein analyzed mimics the mutation inherited in Li-Fraumeni patients. This fusion protein was as active as wild-type p53/GAL4 in our assay. Two human p53 mutants that arose from alterations of the p53 gene in colorectal carcinomas were 30- to 40-fold less effective at activating transcription than wild-type p53/GAL4 fusion proteins. Thus, functional wild-type p53/GAL4 fusion proteins activate transcription, while several transformation competent mutants do so poorly or not at all. Only one mutant p53/GAL4 fusion protein remained transcriptionally active.

Adult T-cell leukemia: structures and expression of the p53 gene

Experiments were undertaken to investigate a genetic event involved in leukemogenesis in adult T-cell leukemia (ATL). For this purpose, the p53 gene was chosen for study, since alteration of the gene has been found in a wide variety of human cancers. Structures and expression of the p53 gene in ATL cells were investigated by Southern and Northern blot analyses and a polymerase-chain-reaction single-strand conformation-polymorphism (PCR-SSCP) analysis. Either subtle alterations of the p53 gene or the absence of detectable level of p53 mRNA were found in 2 of 3 acute ATL cell lines and 2 of 12 acute ATL fresh samples. In contrast, no mutation was detected in 4 cases with less aggressive types of ATL (3 chronic and 1 smoldering ATL cases). Mutations found in acute ATL cells occurred in regions highly conserved in evolution and all the cells carrying p53 mutation showed loss of the other p53 allele. These results suggests that alteration of the p53 gene may contribute to progression of the disease in some cases of ATL.