Jesus Perez-Losada

Fbxw7 / Cdc4 is a p53-dependent, haploinsufficient tumour suppressor gene

The FBXW7/hCDC4 gene encodes a ubiquitin ligase implicated in the control of chromosome stability. Here we identify the mouse Fbxw7 gene as a p53-dependent tumour suppressor gene by using a mammalian genetic screen for p53-dependent genes involved in tumorigenesis. Radiation-induced lymphomas from p53+/- mice, but not those from p53-/- mice, show frequent loss of heterozygosity and a 10% mutation rate of the Fbxw7 gene. Fbxw7+/- mice have greater susceptibility to radiation-induced tumorigenesis, but most tumours retain and express the wild-type allele, indicating that Fbxw7 is a haploinsufficient tumour suppressor gene. Loss of Fbxw7 alters the spectrum of tumours that develop in p53 deficient mice to include a range of tumours in epithelial tissues such as the lung, liver and ovary. Mouse embryo fibroblasts from Fbxw7-deficient mice, or wild-type mouse cells expressing Fbxw7 small interfering RNA, have higher levels of Aurora-A kinase, c-Jun and Notch4, but not of cyclin E. We propose that p53-dependent loss of Fbxw7 leads to genetic instability by mechanisms that might involve the activation of Aurora-A, providing a rationale for the early occurrence of these mutations in human cancers.

Stem-cell hierarchy in skin cancer.

Tumour architecture mimics many of the features of normal tissues, with a cellular hierarchy that regulates the balance between cell renewal and cell death. Although many tumours contain cells with the characteristics of stem cells, the identity of the normal cells that acquire the first genetic hits leading to initiation of carcinogenesis has remained elusive. Identification of the primary cell of origin of cancers and the mechanisms that influence cell-fate decisions will be crucial for the development of novel non-toxic therapies that influence tumour-cell behaviour.

Genetic architecture of mouse skin inflammation and tumour susceptibility

Germline polymorphisms in model organisms and humans influence susceptibility to complex trait diseases such as inflammation and cancer. Mice of the Mus spretus species are resistant to tumour development, and crosses between M. spretus and susceptible Mus musculus strains have been used to map locations of genetic variants that contribute to skin cancer susceptibility. We have integrated germline polymorphisms with gene expression in normal skin from a M. musculus × M. spretus backcross to generate a network view of the gene expression architecture of mouse skin. Here we demonstrate how this approach identifies expression motifs that contribute to tissue organization and biological functions related to inflammation, haematopoiesis, cell cycle control and tumour susceptibility. Motifs associated with inflammation, epidermal barrier function and proliferation are differentially regulated in backcross mice susceptible or resistant to tumour development. The intestinal stem cell marker Lgr5 is identified as a candidate master regulator of the hair follicle, and the vitamin D receptor (Vdr) is linked to coordinated control of epidermal barrier function, inflammation and tumour susceptibility.

Deletion of the SLUG (SNAI2) gene results in human piebaldism.

Slug is a zinc‐finger neural crest transcription factor, encoded by the SLUG gene, which is critical for development of hematopoietic stem cells, germ cells, and melanoblasts in the mouse. In mouse, heterozygous and homozygous slug mutations result in anemia, infertility, white forehead blaze, and depigmentation of the ventral body, tail, and feet. This phenotype is very similar to the heterozygous W (KIT)‐mutant mouse phenotype and to human piebaldism, which is characterized by a congenital depigmented patches and poliosis (white forelock). To investigate the possibility that some cases of human piebaldism might result from abnormalities of the human SLUG (SNAI2) gene, we carried out Southern blot analysis of the SLUG gene in 17 unrelated patients with piebaldism, who lack apparent KIT mutations. Three of these patients had evident heterozygous deletions of the SLUG gene encompassing the entire coding region. Real‐time PCR confirmed the deletion in all cases. Fluoresence in situ hybridization (FISH) of genomic SLUG probes to metaphase chromosomes independently confirmed the deletion in one of the cases. These findings indicate that some cases of human piebaldism result from mutation of the SLUG gene on chromosome 8, and provide further strong evidence for the role of SLUG in the development of human melanocytes.

Liposarcoma initiated by FUS/TLS-CHOP: the FUS/TLS domain plays a critical role in the pathogenesis of liposarcoma

The most common chromosomal translocation in liposarcomas, t(12;16)(q13;p11), creates the FUS/TLS-CHOP fusion gene. We previously developed a mouse model of liposarcoma by expressing FUS-CHOP in murine mesenchymal stem cells. In order to understand how FUS-CHOP can initiate liposarcoma, we have now generated transgenic mice expressing altered forms of the FUS-CHOP protein. Transgenic mice expressing high levels of CHOP, which lacks the FUS domain, do not develop any tumor despite its tumorigenicity in vitro and widespread activity of the EF1α promoter. These animals consistently show the accumulation of a glycoprotein material within the terminally differentiated adipocytes, a characteristic figure of liposarcomas associated with FUS-CHOP. On the contrary, transgenic mice expressing the altered form of FUS-CHOP created by the in frame fusion of the FUS domain to the carboxy end of CHOP (CHOP-FUS) developed liposarcomas. No tumors of other tissues were found in these transgenic mice despite widespread activity of the EF1α promoter. The characteristics of the liposarcomas arising in the CHOP-FUS mice were very similar to those previously observed in our FUS-CHOP transgenic mice indicating that the FUS domain is required not only for transformation but also influences the phenotype of the tumor cells. These results provide evidence that the FUS domain of FUS-CHOP plays a specific and critical role in the pathogenesis of liposarcoma.

The radioresistance biological function of the SCF/kit signaling pathway is mediated by the zinc-finger transcription factor Slug

Radiation-induced destruction of the hematopoietic system is the primary cause of death based on the findings that transfer of normal bone marrow cells prevents death from lethal irradiation. The stem cell factor-c-kit signaling pathway (SCF/c-kit) has been previously implicated in the hematopoietic recovery which prevents death from lethal irradiation, but the molecular mechanisms that mediate this biological effect are unknown. Since mutations on SCF, c-kit and Slug genes have a similar phenotype in mice, we examined if Slug could complement the radiosensitivity of kit-deficient mice. In this report, we show that Slug acts as a radioprotection agent as lack of Slug results in increased radiosensitivity. This effect cannot be recovered by activating SCF/c-kit in lethally irradiated Slug-deficient mice, as SCF-treated mice did not demonstrate stimulation of hematopoietic recovery leading to survival of the Slug-deficient mice. We found that we could complement the hematopoietic failure in lethally irradiated c-kit-deficient mice by transducing them with a TAT-Slug protein. We conclude that the zinc-finger transcription factor Slug is absolutely necessary for survival from lethal irradiation and identify Slug as the molecular target that mediates the radioprotection through SCF/c-kit. These results indicate that Slug may be a molecular component conferring radioresistance to cancer cells.

A functional switch from lung cancer resistance to susceptibility at the Pas1 locus in Kras2LA2 mice.

Pulmonary adenoma susceptibility 1 (Pas1) is the major mouse lung cancer susceptibility locus on chromosome 6 (ref. 1). Kras2 is a common target of somatic mutation in chemically induced mouse lung tumors and is a candidate Pas1 gene. M. spretus mice (SPRET/Ei) carry a Pas1 resistance haplotype for chemically induced lung tumors. We demonstrate that the SPRET/Ei Pas1 allele is switched from resistance to susceptibility by fixation of the parental origin of the mutant Kras2 allele. This switch correlates with low expression of endogenous Kras2 in SPRET/Ei. We propose that the Pas1 modifier effect is due to Kras2, and that a sensitive balance between the expression levels of wild-type and mutant alleles determines lung tumor susceptibility. These data demonstrate that cancer predisposition should also be considered in the context of somatic events and could have major implications for the design of human association studies to identify cancer susceptibility genes.

Cancer as a reprogramming-like disease: implications in tumor development and treatment.

Cancer is a clonal malignant disease originated in a single cell and characterized by the accumulation of partially differentiated cells that are phenotypically reminiscent of normal stages of differentiation. Given the fact that human cancer is diagnosed at later stages and cannot be monitored during its natural evolution, the origin of tumors has been a subject of continuing discussion. Animal models provide a means to determine the identity of the cell-of-origin leading to malignancy and to develop new treatments. Recent findings in mice have shown that cancer stem cells could arise through a reprogramming-like mechanism, suggesting that genetic lesions that initiate the cancer process might be dispensable for tumor progression and maintenance. This review addresses the impact of these results toward a better understanding of carcinogenesis and proposes research avenues for tackling these issues in the future.

Deletion of the PER3 Gene on Chromosome 1p36 in Recurrent ER-Positive Breast Cancer

PURPOSE To investigate the role of the PER3 circadian rhythm gene, located within the commonly deleted region of chromosome 1p36, in human breast cancer development. PATIENTS AND METHODS The frequency of genetic alterations at 1p36 and PER3 gene copy number status were analyzed in 180 lymph node-negative breast cancers from patients who had received treatment with chemotherapy and/or tamoxifen. The expression levels of PER3 were also analyzed using published microarray profiles from > 400 breast cancer samples. Finally, the effect of loss of Per3 on tumor susceptibility was tested using two mouse models of breast cancer. RESULTS Deletion of PER3 is directly related to tumor recurrence in patients with estrogen receptor (ER) - positive breast cancers treated with tamoxifen. Low expression of PER3 mRNA is associated with poor prognosis, particularly in a subset of tumors that are ER positive, and either luminal A or ERBB2-positive tumors. Mice deficient in Per3 showed increased susceptibility to breast cancer induced by carcinogen treatment or by overexpression of Erbb2. CONCLUSION Disruption of PER3 function may serve as an indicator of probability of tumor recurrence in patients with ER-positive tumors. Further investigations of this pathway may reveal links between deregulation of sleep homeostasis and breast tumorigenesis.

Genetic interactions between Pten and p53 in radiation-induced lymphoma development

Genetic analysis of radiation-induced lymphomas from p53 heterozygous or null mice has revealed a high frequency of genetic alterations on mouse chromosome 19. Detailed microsatellite analysis of chromosome 19 deletions identified three independent regions of loss of heterozygosity, one of which was refined to a 0.3 Mb interval that contained the Pten tumor suppressor gene. More than 50% of radiation-induced tumors from p53+/− and p53−/− mice showed heterozygous loss of one Pten allele. In most cases, the remaining allele was wild type and expressed, suggesting that Pten is a haploinsufficient tumor suppressor gene for mouse lymphoma development. This conclusion was supported by the detection of specific intragenic deletions in Pten in tumors that retained one wild-type allele. Pten heterozygous mice were just as sensitive as p53+/− mice to induction of tumors by radiation, and surprisingly, the double p53+/−Pten+/−mice were equivalent to p53 null mice in radiation sensitivity. Despite the fact that Pten appears to be a haploinsufficient tumor suppressor gene, most tumors from both the single and double heterozygous mice had lost the remaining wild-type allele. The mechanism of loss in all cases involved the complete chromosome, suggesting that it is driven by other tumor suppressor genes on this chromosome. This sensitized screen therefore identified complementary roles for Pten and p53 pathways in suppression of tumor development induced by radiation exposure.