The tumor suppressor p53 is critical in preventing cancer due to its ability to trigger proliferation arrest and cell death upon the occurrence of a variety of stresses, most notably, DNA damage and oncogenic stress. Here, we report the generation and characterization of mice carrying supernumerary copies of the p53 gene in the form of large genomic transgenes. Prior to this, we demonstrate that the p53 transgenic allele (p53‐tg), when present in a p53‐null genetic background, behaves as a functional replica of the endogenous gene. 'Super p53' mice, carrying p53‐tg alleles in addition to the two endogenous alleles, exhibit an enhanced response to DNA damage. Importantly, 'super p53' mice are significantly protected from cancer when compared with normal mice. Finally, in contrast to previously reported mice with constitutively active p53, 'super p53' mice do not show any indication of premature aging, probably reflecting the fact that p53 is under normal regulatory control. Together, our results prove that cancer resistance can be enhanced by a simple genetic modification and in the absence of undesirable effects.

Alterations in the cell division:cell death ratio induce multiple autoimmune and transformation processes. Phosphoinositide 3-kinase (PI3K) controls cell division and cell death in vitro, but its effect on the function of the cellular immune system and on tumor formation in mammals is poorly characterized. Here we show that transgenic mice expressing in T lymphocytes an active form of PI3K derived from a thymic lymphoma, p65(PI3K), developed an infiltrating lymphoproliferative disorder and autoimmune renal disease with an increased number of T lymphocytes exhibiting a memory phenotype and reduced apoptosis. This pathology was strikingly similar to that described in mice exhibiting heterozygous loss of the tumor suppressor PTEN, a lipid and protein phosphatase. We show that overexpression of PTEN selectively blocks p65(PI3K)-induced 3T3 fibroblast transformation. Moreover, the early development of T cell lymphomas in p65(PI3K) Tg p53(-/-) mice indicated that PI3K contributes to tumor development. These observations demonstrate that constitutive activation of PI3K extends T cell survival in vivo, affects T cell homeostasis, and contributes to tumor generation, supporting a model in which selective increases in one type of PTEN substrate, the PI3K-derived lipid products, induce tumorigenesis. PI3K thus emerges as a potential target in autoimmune disease and cancer therapy.

Mammalian genes frequently present allelic variants that differ in their expression levels and that, in the case of tumor suppressor genes, can be of relevance for cancer susceptibility and aging. We report here the characterization of a novel mouse model with increased activity for the Ink4a and Arf tumor suppressors. We have generated a "super Ink4a/Arf" mouse strain carrying a transgenic copy of the entire Ink4a/Arf locus. Cells derived from super Ink4a/Arf mice have increased resistance to in vitro immortalization and oncogenic transformation. Importantly, super Ink4a/Arf mice manifest higher resistance to cancer compared to normal, nontransgenic, mice. Finally, super Ink4a/Arf mice have normal aging and lifespan. Together, these results indicate that modest increases in the activity of the Ink4a/Arf tumor suppressor result in a beneficial cancer-resistant phenotype without affecting normal viability or aging.[Keywords: Ink4a; Arf; tumor suppression; stress; cancer resistance; aging; senescence] Supplemental material is available at http://www.genesdev.org.

The myelodysplastic/myeloproliferative diseases (MDS/MPDs) are a heterogeneous group of myeloid neoplasms that share characteristics with chronic myeloproliferative diseases and myelodysplastic syndromes. The broad spectrum of clinical manifestations makes MDS/MPDs extremely difficult to diagnose and treat, with a median survival time of 1-5 years. No single gene defect has been firmly associated with MDS/MPDs, and no animal models have been developed for these diseases. The association of deletions on chromosome 20q with myeloid malignancies suggests the presence of unidentified tumor suppressor genes in this region. Here we show that the recently identified death inducer-obliterator (Dido) gene gives rise to at least 3 polypeptides (Dido1, Dido2, and Dido3) through alternative splicing, and we map the human gene to the long arm of chromosome 20. We found that targeting of murine Dido caused a transplantable disease whose symptoms and signs suggested MDS/MPDs. Furthermore, 100% of human MDS/MPD patients analyzed showed Dido expression abnormalities, which we also found in other myeloid but not lymphoid neoplasms or in healthy donors. Our findings suggest that Dido might be one of the tumor suppressor genes at chromosome 20q and that the Dido-targeted mouse may be a suitable model for studying MDS/MPD diseases and testing new approaches to their diagnosis and treatment.

The Par4 gene was first identified in prostate cells undergoing apoptosis after androgen withdrawal. PAR4 was subsequently shown to interact with, and inhibit, atypical protein kinase C isoforms, functioning as a negative regulator of the NF-κB pathway. This may explain its pro-apoptotic function in overexpression experiments. To determine the physiological role of PAR4, we have derived primary embryonic fibroblasts (EFs) from Par4 -/-mice. We show here that loss of PAR4 leads to a reduction in the ability of tumour necrosis factor-α (TNF-α) to induce apoptosis by increased activation of NF-κB. Consistent with recent reports demonstrating the antagonistic actions of NF-κB and c-Jun aminoterminal kinase (JNK) signalling, we have found that Par4 -/-cells show a reduced activation of the sustained phase of JNK and p38 stimulation by TNF-α and interleukin 1. Higher levels of an antiapoptotic JNK-inhibitor protein, X-chromosome-linked inhibitor of apoptosis, in Par4 -/-EFs might explain the inhibition of JNK activation in these cells.