p53-independent functions of the p19(ARF) tumor suppressor

The p19(ARF) tumor suppressor antagonizes Mdm2 to induce p53-dependent cell cycle arrest. Individual TKO (triple knock out) mice nullizygous for ARF, p53, and Mdm2 develop multiple tumors at a frequency greater than those observed in animals lacking both p53 and Mdm2 or p53 alone, demonstrating that p19(ARF) can act independently of the Mdm2-p53 axis in tumor surveillance. Reintroduction of ARF into TKO mouse embryo fibroblasts (MEFs), but not into those lacking both p53 and ARF, arrested the cell division cycle in the G1 phase. Inhibition of the retinoblastoma protein had no effect on the ability of ARF to arrest TKO MEFs. Thus, in the absence of Mdm2, p19(ARF) interacts with other targets to inhibit cell proliferation.     

胰腺癌p53上下游基因mdm2、p21WAF/CIP1以及P14ARF蛋白的表达及相互关系

目的 探讨p14ARF、p53、mdm2及p21WAF/CIP1蛋白在胰腺癌组织中的表达、相互关系及意义。方法 选取167例胰腺癌、101例癌旁与13例良性病变组织构建组织芯片(又称组织微阵列),应用免疫组织化学EnVision二步法检测这4种蛋白在胰腺良恶性病变中的表达。结果 p14ARF、p53、mdm12及p21WAF/CIP1在胰腺癌中表达的阳性率分别为35.3％(59/167)、57.5％(96/167)、64.1％(107/167)和39.5％(66/167)。同癌旁组织相比,p53和mdm2表达明显升高(P<0.01),而p14ARF和p21WAF/CIP1的表达明显降低(P<0.05)。p21WAF/CIP1的阳性表达与年龄、神经受累显著相关(P<0.05);p53的阳性表达与肿瘤的分化、淋巴结转移和神经受累均显著相关(P<0.05);mdm2的阳性表达与肿瘤的分化显著相关(P<0.05);p14ARF与年龄和浸润转移显著相关(P<0.05)。四者阳性表达两两之间统计学上具有关联性(P<0.05)。结论 p53和mdm2的过表达以及p14ARF和p21WAF/CIP1的缺失表达可能会导致胰腺癌的形成和进展;4种蛋白主要以p14ARF-p53-mdm2-p21WAF/CIP1通路的方式作用于细胞的转化和肿瘤的形成;联合检测p53和mdm2的表达可用于评定胰腺癌的恶性程度。     

Frequent alteration of p16(INK4a)/p14(ARF) and p53 pathways in the round cell component of myxoid/round cell liposarcoma: p53 gene alterations and reduced p14(ARF) expression both correlate with poor prognosis

In myxoid/round cell liposarcoma (MLS/RCLS), the presence of a round cell (RC) component has been reported to correlate with a worse prognosis for the patients. However, little is known about the molecular genetic differences between conventional myxoid (MX) components and RC components in this tumour. The aim of this study was to investigate the possible implications of molecular alterations of G1 to S-phase check-point genes, especially in the RC component. We evaluated the immunohistochemical expression of p53, MDM2, p14 and p16 protein and assessed proliferative activities using MIB-1 in 29 RC components and 81 MX components from 90 cases. Mutation of the p53 gene, amplification of the MDM2 gene, homozygous deletion, methylation status and mutation of the p16(INK4a)/p14(ARF) genes were also investigated, using concordant paraffin-embedded and frozen material. The data were analysed together with clinicopathological factors to assess their prognostic implications in MLS/RCLS. Immunohistochemically, the over-expression of p53 protein (p = 0.01366) and the reduced expression of p14 (p < 0.0001) and p16 (p < 0.0001) proteins were significantly more frequently observed in RC components than in MX components. Reduced expression of p14 protein correlated significantly with hypermethylation of the p14(ARF) gene promoter (p = 0.0176) and over-expression of p53 protein (p = 0.00837). By univariate analysis, reduced expression of p14 and p53 missense mutation were found to reduce the rate of survival significantly (p < 0.05). Multivariate analysis, including clinicopathological factors, revealed that tumour site (p = 0.0251), the presence of an RC component (p = 0.0113), high MIB-1 labelling index (p = 0.0005) and p53 missense mutation (p = 0.0036) were adverse prognostic factors. In MLS/RCLS, reduction of p14 protein expression and p53 mutation were related to poor prognosis. Accordingly, the p14(ARF)/p53 pathway may contribute to the presence of an RC component and malignant progression in this tumour.     

A genome-scale in vivo loss-of-function screen identifies Phf6 as a lineage-specific regulator of leukemia cell growth

We performed a genome-scale shRNA screen for modulators of B-cell leukemia progression in vivo. Results from this work revealed dramatic distinctions between the relative effects of shRNAs on the growth of tumor cells in culture versus in their native microenvironment. Specifically, we identified many “context-specific” regulators of leukemia development. These included the gene encoding the zinc finger protein Phf6. While inactivating mutations in PHF6 are commonly observed in human myeloid and T-cell malignancies, we found that Phf6 suppression in B-cell malignancies impairs tumor progression. Thus, Phf6 is a “lineage-specific” cancer gene that plays opposing roles in developmentally distinct hematopoietic malignancies.     

A screen of Crohn's disease-associated microbial metabolites identifies ascorbate as a novel metabolic inhibitor of activated human T cells

Microbial metabolites are an emerging class of mediators influencing CD4⁺ T-cell function. To advance the understanding of direct causal microbial factors contributing to Crohn's disease, we screened 139 predicted Crohn's disease-associated microbial metabolites for their bioactivity on human CD4⁺ T-cell functions induced by disease-associated T helper 17 (Th17) polarizing conditions. We observed 15 metabolites with CD4⁺ T-cell bioactivity, 3 previously reported, and 12 unprecedented. A deeper investigation of the microbe-derived metabolite, ascorbate, revealed its selective inhibition on activated human CD4⁺ effector T cells, including IL-17A-, IL-4-, and IFNγ-producing cells. Mechanistic assessment suggested the apoptosis of activated human CD4⁺ T cells associated with selective inhibition of energy metabolism. These findings suggest a substantial rate of relevant T-cell bioactivity among Crohn's disease-associated microbial metabolites, and evidence for novel modes of bioactivity, including targeting of T-cell energy metabolism.     

Methylation of p14(ARF) gene in meningiomas and its correlation to the p53 expression and mutation.

We have previously reported the statistically significant correlation of immunohistochemical expression of MIB-1 and p53 proteins among benign, atypical, and anaplastic meningiomas and p53 protein expression was high in atypical and anaplastic meningiomas. In the present study, we analyzed 22 cases of meningiomas for mutation of p53 gene in its spectrum of exon 5 to 8 using automated genetic analyzer. We did not find any mutation of p53 in any of these cases, thus suggesting the p53 protein expression is wild type. We analyzed 72 cases of meningiomas for determining the methylation status of p14(ARF) gene and the immunohistochemical expression of MDM2 protein to explain p53 protein expression in these meningiomas. We found methylation of p14(ARF) gene in five of 58 cases of benign meningiomas (8.6%), two of 10 cases of atypical meningiomas (20%), and two of four cases of anaplastic meningiomas (50%). In absence of p53 gene mutation, the high percentage of p14(ARF) gene methylation in high-grade meningioma may have been responsible for accumulation of wild-type p53 protein. In addition, we also found the loss of MDM2 protein in high-grade meningiomas. These deregulations of p14-MDM2-p53 pathway may contribute to the malignant progression of meningioma.     

Investigation of germline PTEN, p53, p16(INK4A)/p14(ARF), and CDK4 alterations in familial glioma

Epidemiological studies suggest that some familial aggregations of glioma may be due to inherited predisposition. Many genes involved in familial cancers are frequently altered in the corresponding sporadic forms. We have investigated several genes known to be altered in sporadic gliomas for their potential contribution to familial glioma. Fifteen glioma patients with a family history of brain tumors were identified through the Mayo Clinic Department of Neurology (nine diffuse astrocytomas, two oligodendrogliomas, two mixed oligoastrocytomas, one pilocytic astrocytoma, and one pineal glioma). Eleven of the propositi had one or more first degree relative with a glioma. Lymphocyte DNA was derived from each of the patients and analyzed by polymerase chain reaction (PCR) and direct sequencing of the PTEN, p53, p16(INK4A)/p14(ARF), and CDK4 genes. In addition, fluorescence in situ hybridization (FISH) was performed on EBV-transformed lymphocytes from each affected individual to detect germline copy number of the p16(INK4A)/p14(ARF) tumor suppressor region. A p53 germline point mutation was identified in one family with some findings of Li-Fraumeni syndrome, and a hemizygous germline deletion of the p16(INK4A)/p14(ARF) tumor suppressor region was demonstrated by FISH in a family with history of both astrocytoma and melanoma. Thus, whereas germ-line mutations of PTEN, p53, p16(INK4A)/p14(ARF), and CDK4 are not common events in familial glioma, outside of familial cancer syndromes, point mutations of p53 and hemizygous deletions and other rearrangements of the p16(INK4A)/p14(ARF) tumor suppressor region may account for a subset of familial glioma cases. Collectively, these data lend genetic support to the heritable nature of some cases of glioma.     

Mapping of an autoimmunity susceptibility locus (AIS1) to chromosome 1p31.3-p32.2

Generalized vitiligo is a common autoimmune disorder in which patchy loss of skin and hair pigmentation results from loss of pigment-forming melanocytes from the involved regions. Vitiligo occurs with a frequency of about 1% in most populations, and is highly associated with other autoimmune disorders, particularly Hashimoto thyroiditis. Most cases of vitiligo are sporadic, although some cases cluster in families, and the disorder is thought to be oligogenic in origin. We have studied a large family cluster in which vitiligo and Hashimoto thyroiditis occur in numerous individuals. A whole-genome scan of 24 family members, including 14 affected with autoimmune disease, showed significant linkage of an oligogenic autoimmune susceptibility locus, termed AIS1, to a 14.4 cM interval in 1p31.3-p32.2. A two-locus analysis of Hashimoto thyroiditis in family members segregating an AIS1 susceptibility allele showed suggestive linkage to markers in chromosome 6p22.3-q14.1, in a region spanning both the major histocompatibility complex and AITD1, a susceptibility locus for autoimmune thyroid disease. Our results indicate that the 1p AIS1 locus is associated with susceptibility to autoimmunity, particularly vitiligo, in this family, and that a chromosome 6 locus, most likely AITD1, may mediate the occurrence of Hashimoto's thyroiditis in AIS1-susceptible family members.     

A role for IL-27p28 as an antagonist of gp130-mediated signaling

The heterodimeric cytokine interleukin 27 (IL-27) signals through the IL-27Rα subunit of its receptor, combined with gp130, a common receptor chain used by several cytokines, including IL-6. Notably, the IL-27 subunits p28 (IL-27p28) and EBI3 are not always expressed together, which suggests that they may have unique functions. Here we show that IL-27p28, independently of EBI3, antagonized cytokine signaling through gp130 and IL-6-mediated production of IL-17 and IL-10. Similarly, the ability to generate antibody responses was dependent on the activity of gp130-signaling cytokines. Mice transgenic for expression of IL-27p28 showed a substantial defect in the formation of germinal centers and antibody production. Thus, IL-27p28, as a natural antagonist of gp130-mediated signaling, may be useful as a therapeutic for managing inflammation mediated by cytokines that signal through gp130.     

Duplication 19q13-qter and deletion 19p13-pter arising from an inversion (19)(p13.3q13.3) of maternal origin

Pericentric inversion of chromosome 19 appears to be a rare abnormality with only a few families reported. As far as we are aware, none of them were ascertained because of a recombinant individual. We describe the first identified case due to an affected patient, with duplication deficiency for chromosome 19 arising from a maternal inversion confirmed by FISH and CGH. His features included prenatal growth retardation, microcephaly, dysmorphic facies, congenital heart defect, hypoplasia of corpus callosum and psychomotor delay. The identification of recombinant individuals contribute to calculate a precise risk for inv (19) carriers and to provide a more accurate genetic counselling.     

Combination of p53(ser15) and p21/p21(thr145) in peripheral blood lymphocytes as potential Alzheimer's disease biomarkers

Alzheimer's disease (AD) is still difficult to be precisely diagnosed in its early stage to date. Establishing of reliable and manageable disease-specific biological markers is required to improve diagnostic accuracy. Based on the hypothesis of cell cycle regulatory failure at the early stage of AD, we tested whether cell cycle regulating proteins p53, p21 and their phosphorylated forms p53(ser15), p21(thr145) were changed in AD patients and whether these proteins could be used as diagnostic biomarkers. Western bolt, Enzyme-linked immunosorbent assay (ELISA), immunofluorescent staining and flow cytometry (FCM) analysis were employed to analyze levels of these proteins in peripheral blood lymphocytes (PBLs) from 95 controls, 94 AD, 12 Parkinson's disease (PD) and 15 vascular dementia (VaD) patients. Compared with controls, p53(ser15) and p21(thr145) levels were significantly increased and p21 level was significantly decreased in PBLs of AD patients but not in PD or VaD, while p53 was increased in both AD and VaD patients. The receiver operating characteristic (ROC) curve analysis showed that the specificity and sensitivity were 76% and 84% for p53, 88% and 82% for p53(ser15), 80% and 75% for p21 and 84% and 68% for p21(thr145) in identifying AD patients. The relatively high diagnostic accuracy support these proteins, especially p53(ser15) and p21 in PBLs may become potential biomarkers for diagnosis of AD.     

Quantitative multigene FISH on breast carcinomas identifies der(1;16)(q10;p10) as an early event in luminal A tumors

In situ detection of genomic alterations in cancer provides information at the single cell level, making it possible to investigate genomic changes in cells in a tissue context. Such topological information is important when studying intratumor heterogeneity as well as alterations related to different steps in tumor progression. We developed a quantitative multigene fluorescence in situ hybridization (QM FISH) method to detect multiple genomic regions in single cells in complex tissues. As a “proof of principle” we applied the method to breast cancer samples to identify partners in whole arm (WA) translocations. WA gain of chromosome arm 1q and loss of chromosome arm 16q are among the most frequent genomic events in breast cancer. By designing five specific FISH probes based on breakpoint information from comparative genomic hybridization array (aCGH) profiles, we visualized chromosomal translocations in clinical samples at the single cell level. By analyzing aCGH data from 295 patients with breast carcinoma with known molecular subtype, we found concurrent WA gain of 1q and loss of 16q to be more frequent in luminal A tumors compared to other molecular subtypes. QM FISH applied to a subset of samples (n = 26) identified a derivative chromosome der(1;16)(q10;p10), a result of a centromere‐close translocation between chromosome arms 1q and 16p. In addition, we observed that the distribution of cells with the translocation varied from sample to sample, some had a homogenous cell population while others displayed intratumor heterogeneity with cell‐to‐cell variation. Finally, for one tumor with both preinvasive and invasive components, the fraction of cells with translocation was lower and more heterogeneous in the preinvasive tumor cells compared to the cells in the invasive component. © 2014 The Authors Genes, Chromosomes & Cancer Published by Wiley Periodicals, Inc.     

A proteomic screen reveals the mitochondrial outer membrane protein Mdm34p as an essential target of the F-box protein Mdm30p

Ubiquitination plays various critical roles in eukaryotic cellular regulation and is mediated by a cascade of enzymes including ubiquitin protein ligase (E3). The Skp1-Cullin-F-box protein complex comprises the largest E3 family, in each member of which a unique F-box protein binds its targets to define substrate specificity. Although genome sequencing uncovers a growing number of F-box proteins, most of them have remained as "orphans" because of the difficulties in identification of their substrates. To address this issue, we tested a quantitative proteomic approach by combining the stable isotope labeling by amino acids in cell culture (SILAC), parallel affinity purification (PAP) that we had developed for efficient enrichment of ubiquitinated proteins, and mass spectrometry (MS). We applied this SILAC-PAP-MS approach to compare ubiquitinated proteins between yeast cells with and without over-expressed Mdm30p, an F-box protein implicated in mitochondrial morphology. Consequently, we identified the mitochondrial outer membrane protein Mdm34p as a target of Mdm30p. Furthermore, we found that mitochondrial defects induced by deletion of MDM30 are not only recapitulated by a mutant Mdm34p defective in interaction with Mdm30p but alleviated by ubiquitination-mimicking forms of Mdm34p. These results indicate that Mdm34p is a physiologically important target of Mdm30p.     

A germline deletion of p14(ARF) but not CDKN2A in a melanoma-neural system tumour syndrome family

The melanoma-astrocytoma syndrome is characterized by a dual predisposition to melanoma and neural system tumours, commonly astrocytoma. Germline deletions of the region on 9p21 containing the CDKN2A and CDKN2B genes and CDKN2A exon 1beta have been reported in kindreds, implicating contiguous tumour suppressor gene deletion as a cause of this syndrome. We describe a family characterized by multiple melanoma and neural cell tumours segregating with a germline deletion of the p14(ARF)-specific exon 1beta of the CDKN2A gene. This deletion does not affect the coding or minimal promoter sequences of either the CDKN2A or CDKN2B genes. Our results are consistent with either: (i) loss of p14(ARF) function being the critical abnormality associated with this syndrome, rather than contiguous loss of both the CDKN2A and CDKN2B genes as suggested previously; or (ii) disruption of expression of p16 by mechanisms as yet unknown.     

A screen of yeast respiratory mutants for sensitivity against the mycotoxin citrinin identifies the vacuolar ATPase as an essential factor for the toxicity mechanism

In countries with a hot climate the mycotoxin citrinin represents a serious problem in fungal food-poisoning. In humans the renal system is affected the most and the mitochondrial respiratory chain was identified as a possible sensitive target for this toxin. In addition, citrinin has an antifungal activity that also inhibits the growth of the yeast Saccharomyces cerevisiae. So far the precise mode of action and the subcellular targets for citrinin have not been identified. Therefore, we decided to use the model organism yeast for a genetic approach to identify genes that play a role in the sensitivity against this mycotoxin. A large collection of conditional respiratory deficient yeast mutants was screened for sensitivity against citrinin. One special pet-ts mutant was identified that exhibited a higher sensitivity against citrinin. The genetic system of yeast allowed the isolation of the respective wild-type gene. This yeast gene encodes the Vph2p subunit that is essential for the correct assembly of the vacuolar ATPase. Isolation of the mutated gene and gene-disruption experiments of VPH2 and the partially overlapping small YKL118W gene verified this finding. The wild-type VPH2 gene restores all defects of the mutants. In contrast to this, YKL118W gave no complementation and the null mutant showed no phenotype. Thereby the yeast vacuolar ATPase was found to be important for the toxic effect of citrinin in yeast cells. The consequences of this finding for the molecular mechanism of citrinin action and its relation to the mitochondrial respiratory chain are discussed. Received: 18 November / 27 December 1999     

Interaction of alphaPIX (ARHGEF6) with beta-parvin (PARVB) suggests an involvement of alphaPIX in integrin-mediated signaling

Members of the Rho GTPase family are key regulatory molecules that link surface receptors to the organization of the actin cytoskeleton. It is now well established that these small GTPases are also crucial for neuronal morphogenesis and connectivity. Moreover, mutations in ARHGEF6 (also known as alphaPIX or Cool-2 ), encoding a Rac1/Cdc42-specific guanine nucleotide exchange factor, have been implicated in X-linked mental retardation. In an attempt to get insight into the biological function of ARHGEF6 and the upstream signaling cascades leading to its activation, we used the full-length coding region of ARHGEF6 as bait in yeast-two hybrid screens and identified PARVB (beta-parvin or affixin) as a novel binding partner. The interaction was confirmed by co-immunoprecipitation and GST pull-down. We showed by immunofluorescence that ARHGEF6 and PARVB co-localize at the cell periphery to lamellipodia and ruffles in well-spread and actively spreading cells adhered to fibronectin. In addition, interaction of ARHGEF6 to ARHGEF7 (betaPIX or Cool-1), a close homolog of ARHGEF6, was confirmed. In in vivo assays, two ARHGEF6 mutations identified previously in patients with X-linked non-specific mental retardation, ARHGEF6 deltaaa56-83 and deltaaa396-776, abolished interaction of ARHGEF6 to PARVB. Binding between ARHGEF6 and ARHGEF7 was not affected by ARHGEF6 deltaaa56-83 but did not occur with ARHGEF6 deltaaa396-776. These data suggest that both the N-terminal calponin homology (CH) and C-terminal coiled-coil domains are necessary for the ARHGEF6-PARVB binding. In contrast, it seems that only the coiled-coil domain is required for the interaction and heterodimerization of ARHGEF6 and ARHGEF7. PARVB is known to interact with integrin-linked kinase (ILK) and is involved in the early stage of cell-substrate interaction through integrins. The identification of PARVB as an ARHGEF6 interacting partner together with the co-localization of ARHGEF6 and ILK in spreading cells suggest that ARHGEF6 is involved in integrin-mediated signaling leading to activation of the GTPases Rac1 and/or Cdc42.