DNA damage, oncogenesis and the p53 tumour-suppressor gene

The p53 tumour-suppressor gene encodes a transcription factor which plays a central role in controlling oncogenic development in mouse and humans. Mice which over-express mutant p53 transgenes or have a homozygous deletion of the p53 gene show a high frequency of spontaneous tumour development. This review will focus on recent developments using these transgenic and null mice which suggest that p53 is important in maintaining genomic stability, and is a critical component in the cellular response to ionizing radiation.

Assessing drug use prevalence in the workplace: a comparison of self-report methods and urinalysis

A random sample of 800 employees of a steel manufacturing company were randomly assigned to one of four self-report methods of assessing illicit drug use: 1) Individual interview in the workplace, 2) group-administered questionnaire in the workplace, 3) telephone interview, and 4) individual interview off the worksite. All 621 subjects participating in the research were also tested by urinalysis. Rates of drug use self-report were highest in the workplace interview condition and lowest in the overall group questionnaire condition. Although the overall prevalence rates produced by self-reports and urinalysis were similar, there was little concordance between urinalysis positives and self-report positives. The results indicated that self-reports and urinalysis are complementary methods of drug use assessment, and are best used in combination.

Forearm compartment syndrome following brachial arterial puncture in uremia

Although compartment syndromes of the forearm are infrequently encountered, they are well described in the literature. Forearm compartment syndrome uncommonly occurs after percutaneous arterial blood sampling and is usually associated with anticoagulant therapy. Our review of the English literature revealed no other cases of forearm compartment syndrome after arterial blood sampling in patients with bleeding diathesis due to chronic renal failure. This article discusses a 30-year-old woman with Good-pasture's syndrome who developed a compartment syndrome after a brachial artery blood gas. The cause, diagnosis, and treatment of compartment syndrome and uremic bleeding, as well as a review of the literature, are discussed.

Expression of the Kit and KitA receptor isoforms in human acute myelogenous leukemia

Genetic and biologic evidence suggests that the Kit receptor tyrosine kinase is important in early events in hematopoietic stem cell differentiation. Two naturally occurring isoforms of the Kit receptor, termed Kit and KitA, were originally described in mouse cells and, subsequently, in human cells. These isoforms differ by the presence (KitA) or absence (Kit) of four amino acids (Gly-Asn-Asn-Lys) that lie immediately outside the transmembrane domain. RNase protection was used to measure the levels of Kit and KitA mRNA in normal bone marrow and the blast cells from individuals with acute myelogenous leukemia (AML). Although both isoforms were present in all the AML samples tested, there was considerable heterogeneity in the relative levels of the two transcripts, with Kit to KitA RNA ratios varying from as low as 1.3 to as high as 12. In contrast, the ratio of Kit to KitA transcripts in normal bone marrow was tightly clustered between 4.4 and 5.5. Because alterations in the relative levels of expression of Kit and KitA may affect the ability of a cell to respond to the Kit ligand, Steel factor, we examined the Kit/KitA RNA ratio in AML patients that differed with respect to a number of diagnostic, prognostic, and biologic parameters. The relative levels of Kit to KitA RNA was independent of French-American-British subtype, response to therapy, and primary and secondary plating efficiencies in vitro. Thus, these data suggest that the relative levels of the two isoforms of the Kit receptor in AML are not associated with any obvious biologic or clinical parameters and, therefore, may reflect naturally occurring changes in splicing mechanisms as stem cells differentiate.

Temporal order and functional analysis of mutations within the Fli-1 and p53 genes during the erythroleukemias induced by F-MuLV

The erythroleukemias induced by Friend murine leukemia virus (F-MuLV) result from the accumulation of a number of genetic changes, including activation of the Fli-1 proto-oncogene and inactivation of the p53 tumor suppressor gene. We have determined the temporal order of mutation of the genes involved in this multistage malignancy, by serial in vivo transplantation of F-MuLV induced primary erythroleukemias into syngenic Balb/c mice. These primary tumors are capable of growing when transplanted into syngenic mice, but die after several days of in vitro culture. From the transplanted tumors grown in syngenic mice, erythropoietin-dependent cell lines were established in culture that are clonally related to cells in the primary tumors. We show that retroviral insertional activation of the Fli-1 ets family member is the first detectable genetic event in F-MuLV induced primary erythroleukemias. Mutations in the p53 gene were observed in the Epo-dependent cell lines but not in the transplanted erythroleukemias used to establish these cell lines in culture. These data suggest that activation of Fli-1 plays an important role in the early stages of F-MuLV-induced leukemia, perhaps by altering the self-renewal probabilities of erythroid progenitor cells and that p53 mutations immortalize these cells, enabling them to grow in vitro in the presence of Epo.

Molecular genetic approaches to the elucidation of hematopoietic stem cell function

The past few years have seen considerable advances in the development of the methodologies for discovering novel genes critical to hematopoietic stem cell function and for analyzing their biological role in hematopoiesis. This review briefly discusses some common themes that are emerging from the molecular genetic approaches to hematopoietic stem cell function.

p53 mutations increase resistance to ionizing radiation

Mouse and human tumors of diverse origin frequently have somatically acquired mutations or rearrangements of the p53 gene, or they have lost one or both copies of the gene. Although wild-type p53 protein is believed to function as a tumor-suppressor gene, it is as yet unclear how p53 mutations lead to neoplastic development. Wild-type p53 has been postulated to play a role in DNA repair, suggesting that expression of mutant forms of p53 might alter cellular resistance to the DNA damage caused by gamma radiation. Moreover, p53 is thought to function as a cell cycle checkpoint after irradiation, also suggesting that mutant p53 might change the cellular proliferative response to radiation. We have used transgenic mice expressing one of two mutant alleles of p53 to test this prediction. Our results show that expression of both mutant variants of the mouse p53 gene significantly increases the cellular resistance of a variety of hematopoietic cell lineages to gamma radiation. These observations provide direct evidence that p53 mutations affect the cellular response to DNA damage, either by increasing DNA repair processes or, possibly, by increasing cellular tolerance to DNA damage. The association of p53 mutations with increased radioresistance suggests possible mechanisms through which alterations in the p53 gene might lead to oncogenic transformation.

The Fli-1 proto-oncogene, involved in erythroleukemia and Ewing's sarcoma, encodes a transcriptional activator with DNA-binding specificities distinct from other Ets family members

The late stages of the erythroleukemias induced by either the replication-defective Friend spleen focus-forming virus (SFFV) or the Friend murine leukemia virus (F-MuLV) are associated with the insertional activation of one of two members (Spi-1 or Fli-1) of the Ets protooncogene family of transcriptional factors. Fli-1 is not rearranged or activated in the erythroleukemias induced by SFFV, and similarly Spi-1 is not rearranged or activated in the leukemic cell clones induced by F-MuLV. This strict specificity of integration sites suggests that Fli-1 and Spi-1 may be functionally distinct and transactivate different downstream genes during the progression of multistage Friend erythroleukemia. In this study, we show that the Fli-1 protein, like other Ets proteins, has DNA-binding activity and can act as a sequence-specific transcriptional activator. We also show that the Fli-1 and Spi-1 proteins are functionally distinct in that they recognize and transactivate through distinct DNA binding sites. Furthermore, we have identified an octanucleotide core sequence that is required in vitro for optimal binding of Fli-1 to the Drosophila E74 target and the promoter sequence of the human GPIIB gene.

Dynamic changes in ovarian c-kit and Steel expression during the estrous reproductive cycle

W and Steel mutant mice exhibit similar developmental defects in melanogenesis, haematopoiesis, and gametogenesis. Consistent with the cell autonomous and microenvironmental nature of W and Sl mutations, respectively, W encodes the c-kit receptor tyrosine kinase while Steel encodes the Kit ligand. Both c-kit and Steel are expressed in various cells in which no corresponding mutant phenotype has yet been demonstrated. In the adult ovary, certain stromal-derived cells (theca and interstitial), as well as oocytes, express c-kit, while granulosa cells express Steel. We show here that the cessation of oocyte growth, at the transition of the follicle to the antral stage, is associated with the cessation of Steel expression in the cumulus granulosa cells in the vicinity of the oocyte. These observations suggest a role for the Kit signaling pathway in oocyte growth or in meiotic arrest. In addition, the cyclic secretion of luteinizing hormone immediately and dramatically results in elevated Steel expression in mural granulosa cells and decreased levels of c-kit transcripts in stromal-derived cells. This influence of the estrous reproductive cycle on c-kit/Steel expression suggests that the Kit signaling pathway, in addition to its previously described role in primordial germ cell development, is involved in follicular development in the adult female.

What should a clinical director do?

Clinical directors play an important role in developing service strategy and in the introduction of systems needed to generate efficiency and improve quality in health care delivery in their provider units. This article emphasizes the range of abilities needed to succeed as a clinical director.

'W' mutant forms of the Fms receptor tyrosine kinase act in a dominant manner to suppress CSF-1 dependent cellular transformation

Point mutations in highly conserved amino acid residues in the catalytic domain of the Kit receptor tyrosine kinase (RTK) are responsible for the coat color, fertility and hematopoietic defects of mice bearing mutant alleles at the dominant white-spotting (W) locus. The dominant nature of structural Kit mutations suggests that expression of other kinase-defective RTKs might also specifically interfere with signal transduction by normal receptors. To test this possibility, we have investigated the functional consequences of introducing analogous mutations into the RTK encoded by the c-fms proto-oncogene. Both Fms37 (glu582-->lys) and Fms42 (asp776-->asn) mutant proteins, corresponding to the strongly dominant-negative W37 and W42 mutant c-kit alleles, had undetectable in vitro kinase activity and were unable to transform Rat-2 fibroblasts in the presence of exogenous CSF-1. Moreover, expression of Fms37 or Fms42 proteins in Rat-2 cells specifically inhibited anchorage-independent growth mediated by the normal Fms receptor in the presence of exogenous CSF-1 and conferred a dominant loss of Fms-associated PI3-kinase activity on CSF-1 stimulation. Mutant RTKs, bearing point substitutions identical to those present in mild or severe W mutants, may provide a generally applicable strategy for inducing dominant loss of function defects in RTK-mediated signalling pathways.

Oncogenes in head and neck cancer

Primary head and neck squamous cell carcinomas from 58 patients were analyzed for the presence of alterations in the K-ras, raf, and erb-B oncogenes. Analysis of 17 fresh tumor specimens using sequence analysis of target sequences amplified by the polymerase chain reaction showed no evidence of mutations in the K-ras oncogene. Thirty fresh tumor specimens were analyzed for the presence of raf gene activation using Southern blot analysis. Under these conditions, no mutations in the c-raf oncogene were detected. In this study, 6 (13%) of the 47 tumors studied displayed epidermal growth factor receptor (EGFR) gene amplification and/or gene rearrangement. Overexpression of the erb-B gene was observed in 18 (67%) of the 27 head and neck tumors studied. Those patients expressing high levels of EGFR or showing EGFR amplification had tumors that were clinically more advanced. These data suggest that amplification and over-expression of the EGFR gene may be a useful diagnostic and prognostic marker in head and neck squamous cell carcinomas.

Retroviral insertions downstream of the heterogeneous nuclear ribonucleoprotein A1 gene in erythroleukemia cells: evidence that A1 is not essential for cell growth

A large number of novel cellular proto-oncogenes have been identified and cloned by analysis of common integration sites in retrovirally induced malignancies. In the multistage erythroleukemias induced by the various strains of Friend leukemia virus, the analysis of proviral-integration events has led to the identification of two genes, Fli-1 and Spi-1, both novel members of the ets oncogene family of transcription factors. In this report, we describe the identification of another integration site, designated Fli-2 (Friend leukemia virus integration-2), in an erythroleukemia cell line induced by Friend murine leukemia virus (F-MuLV). Rearrangements at the Fli-2 locus were found in two erythroleukemia cell lines independently induced by F-MuLV and one leukemic cell line derived from the spleen of a mouse infected with the polycythemia strain of Friend leukemia virus. The deduced amino acid sequence of a cDNA corresponding to a transcript originating from genomic DNA adjacent to Fli-2 is identical to that of the human heterogeneous nuclear ribonucleoprotein A1 gene, a member of the gene family of RNA-binding proteins involved in RNA splicing. In one erythroleukemia cell line, A1 expression was undetectable as a result of F-MuLV integration in one allele and loss of the other allele. These results suggest that perturbations in RNA splicing mechanisms may contribute to malignant transformation and provide direct evidence that the A1 protein is not required for cell growth.

A mammalian dual specificity protein kinase, Nek1, is related to the NIMA cell cycle regulator and highly expressed in meiotic germ cells

Screening of mouse cDNA expression libraries with antibodies to phosphotyrosine resulted in repeated isolation of cDNAs that encode a novel mammalian protein kinase of 774 amino acids, termed Nek1. Nek1 contains an N-terminal protein kinase domain which is most similar (42% identity) to the catalytic domain of NIMA, a protein kinase which controls initiation of mitosis in Aspergillus nidulans. In addition, both Nek1 and NIMA have a long, basic C-terminal extension, and are therefore similar in overall structure. Despite its identification with anti-phosphotyrosine antibodies, Nek1 contains sequence motifs characteristic of protein serine/threonine kinases. The Nek1 kinase domain, when expressed in bacteria, phosphorylated exogenous substrates primarily on serine/threonine, but also on tyrosine, indicating that Nek1 is a dual specificity kinase with the capacity to phosphorylate all three hydroxyamino acids. Like NIMA, Nek1 preferentially phosphorylated beta-casein in vitro. In situ RNA analysis of nek1 expression in mouse gonads revealed a high level of expression in both male and female germ cells, with a distribution consistent with a role in meiosis. These results suggest that Nek1 is a mammalian relative of the fungal NIMA cell cycle regulator.

Embryology and morphology of microphthalmia in transgenic mice expressing a gamma F-crystallin/diphtheria toxin A hybrid gene

BACKGROUND

Transgenic mice in which elongating lens fiber cells were ablated resulting in microphthalmia have been reported, however, their embryology and detailed morphology have not.

EXPERIMENTAL DESIGN

The morphology of homozygous and hemizygous CDI, transgenic mice carrying the gamma FDT-A gene was studied by light microscopy on different days of gestation as well as postpartum. The findings were compared with normal CD-1 wild type controls.

RESULTS

The earliest changes in mouse embryos transgenic for the gamma F-crystallin/diphtheria toxin A transgene are seen on day 12, when apoptotic cells appear in the area of elongation. In hemizygous embryos, ocular development is relatively normal until day 17 when the lens and eye are slightly smaller than normal and the lens vesicle is filled with abnormal lens material. At this time, the posterior capsule of the lens may rupture, releasing abnormal lens material which disperses throughout the eye, perturbing growth and other ocular structures. Additional breaks may subsequently occur and the ultimate morphology of the hemizygotes correlates with when the posterior capsule ruptures, how much lens material is released, and where it disperses. In homozygous embryos, due to extensive ablation of lens fiber cells, the "lens" becomes a diminutive mass of abnormal lens material, posteriorly located within the eye, and otherwise unable to fulfill its mechanical or inductive role in the development of the cornea, anterior chamber, iris, ciliary epithelium, and zonules with the result that all of these structures are markedly abnormal or absent. In addition, the lens is necessary for the accumulation of vitreous which in turn is required for the growth of the eye as a whole. In homozygous animals, vitreous does not accumulate and severe microphthalmia results.

CONCLUSIONS

This study confirms and extends previous observations and conclusions on the central, orchestrating role of the lens in the development of the eye and illustrates the power of transgenic technology to elucidate the finer points of mammalian ocular development.

A long-term prospective assessment of home nebulizer treatment

Forty-nine patients (15 asthma, mean FEV1/FVC 1.3/2.1; 34 COPD, mean FEV1/FVC 0.7/1.8) were referred for consideration of home nebulizer treatment. All were monitored for 2 weeks while using their usual inhaled treatment followed by 2 weeks using a 'Nebuhaler' spacer to deliver 1 mg of terbutaline and 80 micrograms of ipratoropium bromide (IB) four times daily. They then borrowed a System 22 nebulizer to self-administer salbutamol nebulizer solution (5 mg), IB unit dose vials (0.5 mg) or a mixture of these drugs four times daily for 1 month each. Both asthmatic and bronchitic patients had a significant rise in their mean daily peak flow rate (PFR) during home nebulizer treatment (P < 0.03) and the COPD patients also had a significant PFR rise during Nebuhaler treatment (P = 0.0004). The mean daily peak flow rates (PFR 1 min-1 were: baseline 179, Nebuhaler 195, salbutamol nebulizer 200, IB nebulizer 198, mixed nebulizer 216). Four patients failed to respond subjectively or objectively to either Nebuhaler or nebulizer treatment. Five patients responded well to Nebuhaler treatment and did not proceed to a home nebulizer trial. Eight further patients preferred Nebuhaler to nebulizer treatment or could not tolerate nebulizer treatment (two cases). Thirty-two patients requested home nebulizer treatment for long-term use (nine salbutamol, five IB, 18 mixture). Twenty-seven of these patients had an increased mean daily PFR (compared to their usual therapy) while using their chosen nebulized treatment. The mean increase in PFR for all 32 patients was 191 min-1 (11%).(ABSTRACT TRUNCATED AT 250 WORDS)

SH2 domains of the p85 alpha subunit of phosphatidylinositol 3-kinase regulate binding to growth factor receptors

The binding of cytoplasmic signaling proteins such as phospholipase C-gamma 1 and Ras GTPase-activating protein to autophosphorylated growth factor receptors is directed by their noncatalytic Src homology region 2 (SH2) domains. The p85 alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase, which associates with several receptor protein-tyrosine kinases, also contains two SH2 domains. Both p85 alpha SH2 domains, when expressed individually as fusion proteins in bacteria, bound stably to the activated beta receptor for platelet-derived growth factor (PDGF). Complex formation required PDGF stimulation and was dependent on receptor tyrosine kinase activity. The bacterial p85 alpha SH2 domains recognized activated beta PDGF receptor which had been immobilized on a filter, indicating that SH2 domains contact autophosphorylated receptors directly. Several receptor tyrosine kinases within the PDGF receptor subfamily, including the colony-stimulating factor 1 receptor and the Steel factor receptor (Kit), also associate with PI 3-kinase in vivo. Bacterially expressed SH2 domains derived from the p85 alpha subunit of PI 3-kinase bound in vitro to the activated colony-stimulating factor 1 receptor and to Kit. We infer that the SH2 domains of p85 alpha bind to high-affinity sites on these receptors, whose creation is dependent on receptor autophosphorylation. The SH2 domains of p85 are therefore primarily responsible for the binding of PI 3-kinase to activated growth factor receptors.

Influence of steel factor on hemoglobin synthesis in sickle cell disease

A new hematopoietic growth factor (Steel factor) has been identified which stimulates erythroid proliferation both in vitro and in vivo. We evaluated the influence of recombinant Steel factor on hemoglobin synthesis in peripheral blood (PB) BFU-E-derived cells from normal donors by radioimmunoassay (RIA) and compared it with stimulation with GM-CSF and interleukin-3 (IL-3). Only Steel factor stimulated a significant increase in BFU-E-derived colony size and a significant increase in fetal hemoglobin (HbF) in BFU-E-derived erythroblasts from 0.49% +/- 0.27% to 6.33% +/- 1.11% in serum-deprived media and from 1.88% +/- 0.24% to 11.17% +/- 0.91% in serum. To determine whether this influence on hemoglobinization also occurred in sickle cell disease, we studied 13 patients with sickle cell disease. In serum-deprived conditions, there was a significant increase in the number and size of BFU-E-derived colonies with Steel factor that was dose-dependent. In addition, the proportion of HbF in progenitor-derived cells increased by 66% from 4.1% +/- 0.6% to 6.8% +/- 1.2% with Steel factor. In serum-containing conditions studied in 12 patients, the increase in percentage of HbF was even greater, from 10.7% +/- 0.9% in control cultures to 22.5% +/- 2.6% with Steel factor. These increases in percentage of HbF were significant and dose-dependent. An increase in percentage of HbF was observed in erythroblasts harvested on day 11, 14, and 18 of culture. A decrease in mean picograms of total Hb per cell after coculture with Steel factor was noted, suggesting that growth kinetics influenced complete hemoglobinization. In serum-deprived conditions, picograms of HbF per cell was not affected by Steel factor, and in serum-containing conditions that augment in vitro HbF production it was enhanced. Thus, Steel factor stimulated a significant increase in percentage of HbF in erythroid cells from normal donors and patients with SCA in vitro.

The c-kit receptor ligand functions as a mast cell chemoattractant

Mast cells accumulate at sites of neovascularization, solid tumors, and many immune reactions. Such accumulation requires directed migration of mature mast cells or their precursors. The nature of the chemoattractants that regulate mast cell motility and the identity of the receptors that mediate the chemotactic response are poorly understood. We have tested the ability of stem cell factor (SCF), a mast cell growth factor, to stimulate mast cell migration. Our results show that SCF is a potent mast cell attractant that stimulates directional motility of both mucosal and connective tissue-type mast cells. The activity is potentiated by costimulation with interleukin-3 (IL-3), another mast cell chemoattractant. SCF, a known ligand for the c-kit tyrosine kinase receptor, was unable to stimulate motility in W42 mutant mast cells, which have a defective c-kit tyrosine kinase. However, W42 mast cells were still able to migrate in response to IL-3. These results show that SCF is a chemotactic factor as well as a growth factor and that the c-kit receptor can transduce signals leading to both cell proliferation and increased directional cell motility.

Proto-oncogenes in mammalian development

The phenotypic analysis of mice carrying germline mutations in protooncogenes is beginning to provide convincing genetic evidence for the important role that these genes play in mammalian development and differentiation. Two approaches are being taken to elucidate the biological function of proto-oncogenes in vivo. The first involves the molecular analysis of existing mouse developmental mutants, while the second approach involves the generation of specific germline mutations by gene targeting using homologous recombination in embryonic stem cells. Several key points have already emerged from these genetic approaches. First, many proto-oncogenes are important to more than one cell lineage and function both during embryogenesis and in the adult. Second, the patterns of expression of these genes provide only a guide to their biological function. Third, mutant phenotypes are generally less severe than would be expected from their expression patterns, suggesting that there may be functional overlap between two or more members of a gene family.

Contiguous patterns of c-kit and steel expression: analysis of mutations at the W and Sl loci

Mutations in either the dominant white-spotting (W) or Steel (Sl) loci of the mouse lead to coat color, primordial germ cell and hematopoietic defects. Consistent with the cell autonomous and microenvironmental nature of W and Sl mutations, respectively, it has recently been shown that W encodes the c-kit receptor tyrosine kinase while Sl encodes a ligand for this receptor. Previous in situ hybridization analysis has shown that both c-kit and steel are expressed in the embryo in anatomical sites known to be affected by W and Sl mutations and in various tissues in which no corresponding phenotype has been described. To investigate the possible involvement of the Kit transduction pathway in developmental processes, we compared the patterns of expression of c-kit and steel in wild-type embryos and in embryos homozygous for severe (lethal) and mild (viable) alleles at the W and Sl loci. In addition, we analyzed the patterns of expression of both genes in adult wild-type and mutant gonads and brain. Both c-kit and steel are contiguously expressed in a wide variety of anatomical locations in both the developing embryo and in the adult. In adult gonads, steel is expressed in the follicular cells of the ovary and in Sertoli cells of the testis, the layers that immediately surround the c-kit expressing germ cells. In adult brain, the complementary patterns are particularly striking in the olfactory bulb, cerebral cortex, hippocampus region and cerebellum. steel expression in brain is probably restricted to neurons in certain areas, while c-kit is expressed in neurons and in some glial cells. Severe mutations in the W or Sl loci result in dramatic reduction or absence of c-kit positive cells in lineages known to be affected by these mutations. In contrast, these mutations do not affect the number or histological organization of c-kit positive cells in the embryonic peripheral or central nervous systems, nor is the number or organization of c-kit positive cells detectably altered in Wv/Wv or Sld/Sld adult brain. Taken together, these results suggest that the Kit signaling pathway is not obligatory for the viability and/or migration of most c-kit expressing cells either because of functional redundancy with another signaling pathway or because the Kit pathway is involved in post-developmental processes of mature cells.

p53 transgenic mice: accelerated erythroleukemia induction by Friend virus

Mutations in the p53 tumor-suppressor gene have been implicated in the pathogenesis of a significant proportion of human cancers and in a dominantly inherited familial cancer syndrome (Li-Fraumeni syndrome). Frequent rearrangements and point mutations have also been detected in the p53 gene in the murine erythroleukemias induced by Friend leukemia virus. We have previously reported that transgenic mice overproducing a mutated p53 protein are predisposed to the development of lung carcinomas, bone and soft-tissue sarcomas, as well as lymphoid malignancies. Here we report that p53 transgenic mice infected with the polycythemia-inducing strain of Friend virus (FV-P) progress to the late stage of erythroleukemia more rapidly than do normal mice. In addition, Friend leukemic cell lines derived from p53 transgenic mice overproduce mutant p53 protein and show a high frequency of rearrangement of the ets-related Spi-1 oncogene, as previously reported in Friend cell lines derived from non-transgenic animals. These results suggest that the same genetic changes involved in the evolution of Friend leukemia in normal mice are also required in mice with an inherited predisposition to cancer. The data also indicate that p53 transgenic mice provide an animal model in which to analyse the role that genetic and environmental factors play in influencing cancer predisposition.