The bmi-1 and mel-18 gene products define a new family of DNA-binding proteins involved in cell proliferation and tumorigenesis

From 1957 to Nowadays: A Brief History of Epigenetics

Due to the spectacular number of studies focusing on epigenetics in the last few decades, and particularly for the last few years, the availability of a chronology of epigenetics appears essential. Indeed, our review places epigenetic events and the identification of the main epigenetic writers, readers and erasers on a historic scale. This review helps to understand the increasing knowledge in molecular and cellular biology, the development of new biochemical techniques and advances in epigenetics and, more importantly, the roles played by epigenetics in many physiological and pathological situations.

Desethylamiodarone-A metabolite of amiodarone-Induces apoptosis on T24 human bladder cancer cells via multiple pathways

Bladder cancer (BC) is a common malignancy of the urinary tract that has a higher frequency in men than in women. Cytostatic resistance and metastasis formation are significant risk factors in BC therapy; therefore, there is great interest in overcoming drug resistance and in initiating research for novel chemotherapeutic approaches. Here, we suggest that desethylamiodarone (DEA)–a metabolite of amiodarone—may have cytostatic potential. DEA activates the collapse of mitochondrial membrane potential (detected by JC-1 fluorescence), and induces cell death in T24 human transitional-cell bladder carcinoma cell line at physiologically achievable concentrations. DEA induces cell cycle arrest in the G0/G1 phase, which may contribute to the inhibition of cell proliferation, and shifts the Bax/Bcl-2 ratio to initiate apoptosis, induce AIF nuclear translocation, and activate PARP-1 cleavage and caspase-3 activation. The major cytoprotective kinases—ERK and Akt—are inhibited by DEA, which may contribute to its cell death-inducing effects. DEA also inhibits the expression of B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1) and reduces colony formation of T24 bladder carcinoma cells, indicating its possible inhibitory effect on metastatic potential. These data show that DEA is a novel anti-cancer candidate of multiple cell death-inducing effects and metastatic potential. Our findings recommend further evaluation of its effects in clinical studies.

Polycomb group oncogene RING1 is over-expressed in non-small cell lung cancer

Ring finger protein 1 (RING1) have recently been reported to be related to aggressive tumor features in Prostate Cancer and urothelial carcinoma of the bladder. However, the role of RING1 in non-small-cell lung cancer (NSCLC) tumorigenesis has never been elucidated. So we aimed at investigating the potential role of RING1 in NSCLC. RING1 expression was evaluated by Immunoblot in 8 paired fresh lung cancer tissues and immunohistochemistry on 69 paraffin-embedded sections from 2006 to 2009. Furthermore, flow-cytometry and RNA interference were performed to analyse the role of RING1 in A549 cells. We showed that the expression level of RING1 was significant increased in lung cancer as compared with the adjacent normal tissue. High expression level of RING1 was associated with TNM stage (P = 0.013), and RING1 was positively related with proliferation marker Ki67 (P < 0.05). Moreover, RING1 knockdown induces growth suppression of human lung cancer cells through G1/S cell cycle phase arrest in vitro. Kaplan-Meier survival curves showed that high expression level of RING1 was associated with poor prognosis (P = 0.03). On the basis of these results, we suggested that RING1 protein expression may be a favorable independent prognostic parameter for non-small cell lung cancer.

Knockdown BMI1 expression inhibits proliferation and invasion in human bladder cancer T24 cells

B cell-specific moloney murine leukemia virus integration site 1 (BMI1) is a transcriptional repressor of polycomb repressive complex 1, which is involved in the proliferation, senescence, migration, and tumorigenesis of cancer. Experimental researchers have convincingly linked BMI1 to tumorigenesis. However, there is no study about the issue on the role of BMI1 in the proliferation, apoptosis, and migration of bladder cancer. To address this question, we examined the expression of BMI1 in bladder cancer tissues and used siRNA to knockdown BMI1 expression in bladder cancer T24 cells. Then we tested the cell proliferation by CCK8 assay and soft agar colony formation assay, apoptosis by flow cytometry assay, and cell invasiveness by transwell migration assay. Our results revealed that BMI1 promoted proliferation, migration, invasion, and progression in bladder cancer. Over-expression of BMI1 was correlated with tumor clinic-pathological features. BMI1 siRNA effectively inhibited bladder cancer cell proliferation and migration in vitro, and it promoted bladder cancer invasion, maybe by causing epithelial-to-mesenchymal transition. Our findings suggested that BMI1 may represent a novel diagnostic marker and a therapeutic target for bladder cancer, and deserves further investigation.

Polycomb group genes Psc and Su(z)2 maintain somatic stem cell identity and activity in Drosophila

Adult stem cells are essential for the proper function of many tissues, yet the mechanisms that maintain the proper identity and regulate proliferative capacity in stem cell lineages are not well understood. Polycomb group (PcG) proteins are transcriptional repressors that have recently emerged as important regulators of stem cell maintenance and differentiation. Here we describe the role of Polycomb Repressive Complex 1 (PRC1) genes Posterior sex combs (Psc) and Suppressor of zeste two (Su(z)2) in restricting the proliferation and maintaining the identity of the Cyst Stem Cell (CySC) lineage in the Drosophila testis. In contrast, Psc and Su(z)2 seem to be dispensable for both germline stem cell (GSC) maintenance and germ cell development. We show that loss of Psc and Su(z)2 function in the CySC lineage results in the formation of aggregates of mutant cells that proliferate abnormally, and display abnormal somatic identity correlated with derepression of the Hox gene Abdominal-B. Furthermore, we show that tumorigenesis in the CySC lineage interferes non-cell autonomously with maintenance of GSCs most likely by displacing them from their niche.

Identification and characterization of Bmi-1-responding element within the human p16 promoter

Bmi-1, the first functionally identified polycomb gene family member, plays critical roles in cell cycle regulation, cell immortalization, and cell senescence. Bmi-1 is involved in the development and progression of carcinomas and is a potent target for cancer therapy. One important pathway regulated by Bmi-1 is that involving two cyclin-dependent kinase inhibitors, p16(Ink4a) and p19(Arf), as Bmi-1 represses the INK4a locus on which they are encoded. A close correlation between the up-regulation of Bmi-1 and down-regulation of p16 has been demonstrated in various tumors; however, how Bmi-1 regulates p16 expression is not clear. In this study, we revealed that Bmi-1 regulates the expression of p16 by binding directly to the Bmi-1-responding element (BRE) within the p16 promoter. The BRE resided at bp -821 to -732 upstream of the p16 ATG codon. BRE alone was sufficient to allow Bmi-1-mediated regulation of the CMV promoter. Bmi-1 typically functions by forming a complex with Ring2; however, regulation of p16 was independent of Ring2. Chromatin immunoprecipitation sequencing of Bmi-1-precipitated chromatin DNA revealed that 1536 genes were targeted by Bmi-1, including genes involved in tissue-specific differentiation, cell cycle, and apoptosis. By analyzing the binding sequences of these genes, we found two highly conserved Bmi-1-binding motifs, which were required for Bmi-1-mediated p16 promoter regulation. Taken together, our results revealed the molecular mechanism of Bmi-1-mediated regulation of the p16 gene, thus providing further insights into the functions of Bmi-1 as well as a sensitive high-throughput platform with which to screen Bmi-1-targeted small molecules for cancer therapy.

Polycomb group protein gene silencing, non-coding RNA, stem cells, and cancer

Epigenetic programming is an important facet of biology, controlling gene expression patterns and the choice between developmental pathways. The Polycomb group proteins (PcGs) silence gene expression, allowing cells to both acquire and maintain identity. PcG silencing is important for stemness, X chromosome inactivation (XCI), genomic imprinting, and the abnormally silenced genes in cancers. Stem and cancer cells commonly share gene expression patterns, regulatory mechanisms, and signalling pathways. Many microRNA species have oncogenic or tumor suppressor activity, and disruptions in these networks are common in cancer; however, long non-coding (nc)RNA species are also important. Many of these directly guide PcG deposition and gene silencing at the HOX locus, during XCI, and in examples of genomic imprinting. Since inappropriate HOX expression and loss of genomic imprinting are hallmarks of cancer, disruption of long ncRNA-mediated PcG silencing likely has a role in oncogenesis. Aberrant silencing of coding and non-coding loci is critical for both the genesis and progression of cancers. In addition, PcGs are commonly abnormally overexpressed years prior to cancer pathology, making early PcG targeted therapy an option to reverse tumor formation, someday replacing the blunt instrument of eradication in the cancer therapy arsenal.

The novel tumor-suppressor Mel-18 in prostate cancer: its functional polymorphism, expression and clinical significance

Mel-18 is a member of the polycomb group (PcG) proteins, which are chromatin regulatory factors and play important roles in development and oncogenesis. This study was designed to investigate the clinical and prognostic significance of Mel-18 in patients with prostate cancer. A total of 539 native Japanese subjects consisting of 393 prostate cancer patients and 146 controls were enrolled in this study. Mel-18 genotyping was analyzed using a PCR-RFLP method and an automated sequencer using the GENESCAN software. Immunohistochemistry revealed that Mel-18 expression was diminished in high grade and high stage prostate cancers. Moreover, patients with positive Mel-18 expression had significantly longer PSA recurrence-free survival than patients negative for Mel-18 expression (p=0.038). A Mel-18 1805A/G SNP was located in the 3' untranslated region and was predicted to alter the secondary structure of the mRNA. Mel-18 mRNA expression of the 1805A allele was clearly higher than expression of the 1805G allele by allele specific quantitative RT-PCR. In multivariate analysis, a homozygous G allele genotype and negative Mel-18 expression were independent risk factors predicting high PSA recurrence after radical prostatectomy, with HRs of 2.757 (p=0.022) and 2.271 (p=0.045), respectively. Moreover, the G allele was also an independent predictor of poor cancer-specific survival with an HR of 4.658 (p=0.019) for patients with stage D2 prostate cancer. This is the first study to provide important evidence demonstrating that Mel-18 is a tumor suppressor and possible therapeutic target, as well as a diagnostic marker for poor prognosis in prostate cancer patients.

Analysis of Mel-18 expression in prostate cancer tissues and correlation with clinicopathologic features

OBJECTIVE

Mel-18 is a member of the polycomb group (PcG) of proteins, which are chromatin regulatory factors that play an important role in development and oncogenesis. This study was designed to investigate the clinical and prognostic significance of Mel-18 in the patients with prostate cancer.

PATIENTS AND METHODS

Immunostaining with Mel-18 specific antibodies was performed on paraffin sections from 202 patients. Correlations between Mel-18 and the Gleason grading system, clinical stage, serum prostate-specific antigen (PSA) levels, and age were evaluated. PSA recurrence in 76 patients who underwent radical prostatectomy and survival in 59 patients with metastases at diagnosis were analyzed to evaluate the influence of Mel-18 expression in cancer progression using Kaplan-Meier analysis and multivariate Cox regression analysis.

RESULTS

Staining was seen in all prostatic tissues. Mel-18 expression was significantly reduced in the prostate cancer patients with PSA levels over 100 ng/ml (P=0.009), advanced clinical stage (>T4, N1, or M1 disease, P=0.029), higher Gleason grade or with a higher Gleason score (P=0.018) than in those with other clinicopathologic features. Negative expression of Mel-18 was associated with significantly higher rates of PSA recurrence after radical prostatectomy than with positive expression of Mel-18 (P = 0.029), and was an independent predictor of PSA recurrence (P=0.034, HR=2.143) in multivariate analysis. Similarly, metastatic prostate cancer patients with negative expression of Mel-18 showed significantly worse survival compared with the positive expression of Mel-18 (P=0.025). In multivariate analysis, negative expression of Mel-18 was an independent predictor of cancer-specific survival (P=0.024, HR=2.365).

CONCLUSION

Our study provides important evidence for the recognition of Mel-18 as a tumor suppressor. The expression of Mel-18 showed potential as a prognostic marker for human prostate cancer.

USP22, an hSAGA subunit and potential cancer stem cell marker, reverses the polycomb-catalyzed ubiquitylation of histone H2A

Initial studies of the mammalian hSAGA transcriptional coactivator complex identified the acetyltransferase hGCN5/PCAF as the only known enzymatic subunit. Recently we demonstrated that the ubiquitin hydrolase USP22 comprises a second enzymatic subunit of hSAGA, and that is required for activator-driven transcription. USP22 is expressed with polycomb ubiquitin ligases in an 11 gene signature that defines therapy-resistant tumors. At the biochemical level, these Polycomb proteins function as global transcriptional repressors by catalyzing the ubiquitylation of histone H2A. In yeast, the USP22 homolog functions as a transcriptional coactivator by removing ubiquitin from a distinct core histones, H2B. Given that USP22 is expressed in cancer as part of an 11 gene signature that includes transcriptional repressors which ubiquitylate H2A, it seemed possible that USP22 might activate transcription in part via the deubiquitylation of this same substrate. As reported here, biochemical analysis of the substrate specificity of USP22 reveals that it deubiquitylates histone H2A in addition to H2B. This finding supports a model in which the H2A ubiquitin hydrolase USP22 is coordinately expressed with Polycomb H2A ubiquitin ligases in order that the transcription of certain critical transforming genes be maintained in the face of the global repression mediated by Polycomb.

Proteomic analysis of EZH2 downstream target proteins in hepatocellular carcinoma

Enhancer of zeste homolog 2 (EZH2) is suggested to be a potential therapeutic target and a diagnostic marker for cancer. Our previous study also showed the critical role of EZH2 in hepatocellular carcinoma (HCC) tumorigenesis. The present study is aimed at revealing the comprehensive downstream pathways of EZH2 by functional proteomic profiling. Lentivirus mediated RNA interference (RNAi) was employed to knockdown EZH2 in HCC cells. The 2-DE was employed to compare the expression profile difference between parental and EZH2-knockdown HCC cells. In total, 28 spots were differentially expressed during EZH2 inhibition. Among all, 18 proteins were identified by PMF with MALDI-TOF MS. Western blotting further validated upregulation of 60S acidic ribosomal protein P0 (L10E), and downregulation of two proteins with EZH2 inhibition: stathmin1 and probable protein disulfide isomerase (PDI) ER-60 precursor (ERp57). Moreover, L10E was downregulated with overexpression of EZH2 in hepatocytes, and L10E reversed the effect of EZH2 on cell proliferation, suggesting it a downstream target of EZH2. The comprehensive and comparative analyses of proteins associated with EZH2 could further our understanding on the downstream signal cascade of EZH2 leading to tumorigenesis.

Poorly differentiated breast carcinoma is associated with increased expression of the human polycomb group EZH2 gene

Polycomb group (PcG) genes contribute to the maintenance of cell identity, cell cycle regulation, and oncogenesis. We describe the expression of five PcG genes (BMI-1, RING1, HPC1, HPC2, and EZH2) innormal breast tissues, invasive breast carcinomas, and their precursors. Members of the HPC-HPH/PRC1 PcG complex, including BMI-1, RING1, HPC1, and HPC2, were detected in normal resting and cycling breast cells. The EED-EZH/PRC2 PcG complex protein EZH2 was only found in rare cycling cells, whereas normal resting breast cells were negative for EZH2. PcG gene expression patterns in ductal hyperplasia (DH), well-differentiated ductal carcinoma in situ (DCIS), and well-differentiated invasive carcinomas closely resembled the pattern in healthy cells. However, poorly differentiated DCIS and invasive carcinomas frequently expressed EZH2 in combination with HPC-HPH/PRC1 proteins. Most BMI-1/EZH2 double-positive cells in poorly differentiated DCIS were resting. Poorly differentiated invasive carcinoma displayed an enhanced rate of cell division within BMI-1/EZH2 double-positive cells. We propose that the enhanced expression of EZH2 in BMI-1(+) cells contributes to the loss of cell identity in poorly differentiated breast carcinomas, and that increased EZH2 expression precedes high frequencies of proliferation. These observations suggest that deregulated expression of EZH2 is associated with loss of differentiation and development of poorly differentiated breast cancer in humans.

Mutation analysis of the mel-18 gene that shows decreased expression in human breast cancer cell lines

BACKGROUND

Mammalian mel-18 is a member of the polycomb group, and it acts as a transcriptional repressor with DNA binding activity. Murine mel-18 negatively regulates the cell cycle through the c-myc/cdc25 cascade, and mice haploinsufficient for mel-18 develop mammary gland tumors. In addition, the human homolog of mel-18 is located at 17q, on which candidate tumor suppressor genes for breast cancer have been suggested for a long time. These observations indicate that the mel-18 gene may be a tumor suppressor gene for breast cancer. To investigate this possibility, we examined the expression of mel-18 mRNA in human breast cancer cell lines and searched for mel-18 gene mutations in sporadic and familial breast cancers.

METHODS

The expression of mel-18 mRNA was examined in five breast cancer cell lines by RT-PCR, and somatic and germline mutations of the mel-18 gene were analyzed by the PCR-SSCP and sequence methods in 48 sporadic breast cancers, including 16 cases with loss of heterozygosity (LOH) at the mel-18 locus, and in 23 cases from 18 breast cancer families, respectively.

RESULTS

We found that most cell lines examined here showed decreased expression of mel-18 mRNA, however, no alteration other than a single nucleotide change that did not lead to amino acid alteration in one patient was identified.

CONCLUSION

Our results reveal that mel-18 gene mutations are exceedingly rare in human breast cancers, and a reduction of mel-18 expression in human breast cancer cell lines would support a role for mel-18 haploinsufficiency in breast carcinogenesis.

Functions of mammalian Polycomb group and trithorax group related genes

Genes of the Polycomb and trithorax groups (PcG and trxG) are part of a cellular memory system that maintains inactive and active states of homeotic gene expression in Drosophila. Recent genetic evidence indicates that several related loci in mammals are also involved in the regulation of Hox genes. Like their Drosophila counterparts, the vertebrate gene products are components of multiprotein complexes that regulate transcriptional activation, repression and aspects of chromatin structure. Initial indications suggest the existence of a large mammalian PcG and trxG family, with a potential to encode multiple specialised functions in cell fate and cell-cycle control.

Suppression of tumor growth by the 3' untranslated region of mel-18 in 3Y1 cells transformed by the E6 and E7 genes of human papillomavirus type 18

By introducing a cDNA library derived from rat embryonic fibroblast cells, we isolated several morphologically flat revertants of rat 3Y1 cells transformed by the E6 and E7 genes of human papillomavirus type 18 (HPV18). From one of the revertants, we recovered a 0.2-kb cDNA, N56, that suppresses the tumor growth of the transformed 3Y1 cells irrespective of the expression of the E6 and E7 genes. The nucleotide sequence of the cDNA was shown to be identical to that of the 3' untranslated region of a putative mammalian polycomb group gene, mel-18.

The Polycomb-group homolog Bmi-1 is a regulator of murine Hox gene expression

Drosophila homeotic genes and vertebrate Hox genes are involved in the anteroposterior organization of the developing embryo. In Drosophila, the Polycomb- and trithorax-group genes are required to maintain the homeotic genes throughout development in the repressed or activated state, respectively. The murine Bmi-1 proto-oncogene was shown to exhibit homology to the Polycomb-group gene Posteior sex combs. Mice lacking the Bmi-1 gene revealed posterior transformations along the axial skeleton, whereas transgenic mice overexpressing Bmi-1 display anterior transformations. We have analysed the expression patterns of several Hox genes by RNA in situ hybridization on serial sections of 11.5- and 12.5-day Bmi-1 null mutant embryos. Furthermore, we have analysed the expression of a Hoxc-8/LacZ fusion gene in younger embryos. Our analyses show that Bmi-1 is involved in the repression of a subset of Hox genes from different clusters from at least day 9.5 onwards. We discuss the possibility that members of the murine Polycomb-group can form multimeric protein complexes of different compositions with varying affinity or specificity for different subsets of Hox genes.

Presence of a new conserved domain in CART1, a novel member of the tumor necrosis factor receptor-associated protein family, which is expressed in breast carcinoma

CART1, a novel human gene, encodes a putative protein exhibiting three main structural domains: first, a cysteine-rich domain located at the amino-terminal part of the protein, which corresponds to an unusual RING finger motif; second, an original cysteine-rich domain located at the core of the protein and constituted by three repeats of an HC3HC3 consensus motif that we designated the CART motif, and which might interact with nucleic acid; third, the carboxyl-terminal part of the CART1 protein corresponds to a TRAF domain known to be involved in protein-protein interactions. Similar association of RING, CART, and TRAF domain was observed in the human CD40-binding protein and in the mouse tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2), both involved in signal transduction mediated by the TNF receptor family and in the developmentally regulated Dictyostelium discoideum DG17 protein. CART1 is specifically expressed by epithelial cells in breast carcinomas and metastases. Moreover, in these malignant cells, the CART1 protein is localized in the nucleus. Altogether, these observations indicate that CART1 may be involved in TNF-related cytokine signal transduction in breast carcinoma.

The Drosophila melanogaster gene lethal(3)73Ah encodes a ring finger protein homologous to the oncoproteins MEL-18 and BMI-1

The Drosophila melanogaster (Dm) gene lethal(3)73Ah, essential at the late pupal stage, encodes a protein with a novel Cys-rich sequence motif, typical for ring-finger proteins. Amino-acid sequence comparison revealed a striking homology of the entire lethal(3)73Ah sequence to the gene products of the mammalian oncogenes, mel-18 and bmi-1, and to the zinc-finger-containing N-terminal region of the Dm proteins encoded by the Posterior sex combs and Suppressor two of zeste genes. The lethal(3)73Ah gene is located in a densely transcribed region sharing 3'-untranslated sequences with the adjacent sex-determining gene, transformer. Its transcription is temporally and spatially regulated with maximal expression in adult females. In all stages the mRNA can be localized to the fat body and, in addition, to the ovaries of adult females.

Characterization of a region of the X chromosome of Drosophila including multi sex combs (mxc), a Polycomb group gene which also functions as a tumour suppressor

Genetic analysis of the 8D3;8D8-9 segment of the Drosophila melanogaster X chromosome has assigned seven complementation groups to this region, three of which are new. A Polycomb group (Pc-G) gene, multi sex combs (mxc), is characterized and mutant alleles are described. Besides common homeotic transformations characteristic of Pc-G mutants that mimic the ectopic gain of function of BX-C and ANT-C genes, mxc mutants show other phenotypes: they zygotically mimic, in males and females, the characteristic lack of germ line seen in progeny of some maternal effect mutants of the so-called posterior group (the grandchildless phenotype). Loss of normal mxc function can promote uncontrolled malignant growth which indicates a possible relationship between Pc-G genes and tumour suppressor genes. We propose that gain-of-function of genes normally repressed by the wild-type mxc product could, in mxc mutants, give rise to an incoherent signal which would be devoid of meaning in normal development. Such a signal could divert somatic and germ line development pathways, provoke the loss of cell affinities, but allow or promote growth.

Posterior transformation, neurological abnormalities, and severe hematopoietic defects in mice with a targeted deletion of the bmi-1 proto-oncogene

The bmi-1 proto-oncogene has been implicated in B-cell lymphomagenesis in E mu-myc transgenic mice. Distinct domains of the Bmi-1 protein are highly conserved within the Drosophila protein Posterior Sex Combs, a member of the Polycomb group involved in maintaining stable repression of homeotic genes during development. We have inactivated the bmi-1 gene in the germ line of mice by homologous recombination in ES cells. Null mutant mice display three phenotypic alterations: (1) a progressive decrease in the number of hematopoietic cells and an impaired proliferative response of these cells to mitogens; (2) neurological abnormalities manifested by an ataxic gait and sporadic seizures; and (3) posterior transformation, in most cases along the complete anteroposterior axis of the skeleton. The observations indicate that Mbi-1 plays an important role in morphogenesis during embryonic development and in hematopoiesis throughout pre- and postnatal life. Furthermore, these data provide the first evidence of functional conservation of a mammalian Polycomb group homolog.

Cloning and chromosome mapping of the human Mel-18 gene which encodes a DNA-binding protein with a new 'RING-finger' motif

It has recently been reported that there exists a new 'RING-finger' protein family among the zinc-finger (Zf) proteins. Previously, we had isolated the mouse Mel-18 cDNA (mMel-18) encoding the nuclear RING-finger protein that exhibits an ability to bind to a nonspecific DNA column. Here, we have isolated and characterized the human Mel-18 cDNA (hMel-18) using the mMel-18 cDNA as a probe. The deduced hMel-18 protein contains 344 amino acids (38 kDa) with a RING-finger motif, a helix-loop-helix (HLH)-like structure and a Pro/Ser-rich region. The hMel-18 gene is conserved among vertebrates. Its mRNA is highly expressed in placenta, lung and kidney, but the level is low in liver, pancreas and skeletal muscle. Using in situ hybridization, we mapped hMel-18 to band q22 of chromosome 12. It is possible that the Mel-18/bmi-1 gene family represents a mammalian homologue of the Drosophila polycomb gene group.

LYAR, a novel nucleolar protein with zinc finger DNA-binding motifs, is involved in cell growth regulation

A cDNA encoding a novel zinc finger protein has been isolated from a mouse T-cell leukemia line on the basis of its expression of a Ly-1 epitope in a lambda gt11 library. The putative gene was mapped on mouse chromosome 1, closely linked to Idh-1, but not linked to the Ly-1 (CD5) gene. The cDNA is therefore named Ly-1 antibody reactive clone (LYAR). The putative polypeptide encoded by the cDNA consists of 388 amino acids with a zinc finger motif and three copies of nuclear localization signals. Antibodies raised against a LYAR fusion protein reacted with a protein of 45 kD on Western blots and by immunoprecipitation. Immunolocalization indicated that LYAR was present predominantly in the nucleoli. The LYAR mRNA was not detected in brain, thymus, bone marrow, liver, heart, and muscle. Low levels of LYAR mRNA were detected in kidney and spleen. However, the LYAR gene was expressed at very high levels in immature spermatocytes in testis. The LYAR mRNA is present at high levels in early embryos and preferentially in fetal liver and fetal thymus. A number of B- and T-cell leukemic lines expressed LYAR at high levels, although it was not detectable in bone marrow and thymus. During radiation-induced T-cell leukemogenesis, high levels of LYAR were expressed in preleukemic thymocytes and in acute T leukemia cells. Fibroblast cells overexpressing the LYAR cDNA from a retrovirus vector, though not phenotypically transformed in vitro, had increased ability to form tumors in nu/nu mice. Therefore, LYAR may function as a novel nucleolar oncoprotein to regulate cell growth.

Identification and preliminary characterization of a protein motif related to the zinc finger

We have identified a protein motif, related to the zinc finger, which defines a newly discovered family of proteins. The motif was found in the sequence of the human RING1 gene, which is proximal to the major histocompatibility complex region on chromosome six. We propose naming this motif the "RING finger" and it is found in 27 proteins, all of which have putative DNA binding functions. We have synthesized a peptide corresponding to the RING1 motif and examined a number of properties, including metal and DNA binding. We provide evidence to support the suggestion that the RING finger motif is the DNA binding domain of this newly defined family of proteins.

Nucleotide sequence of bup, an upstream gene in the bmi-1 proviral insertion locus

The ability of Moloney murine leukemia virus to accelerate lymphomagenesis in E mu-myc transgenic mice is frequently associated with proviral integration within a locus denoted bmi-1. This locus contains not only the bmi-1 gene implicated as a collaborator with myc in lymphomagenesis but also just upstream an unknown gene denoted bup. The nucleotide sequence reported here for bup cDNA and flanking genomic sequences reveals that this widely expressed gene comprises at least 7 exons and potentially encodes a polypeptide of 195 amino acid residues. Computer searches with this polypeptide sequence revealed no close homolog in the databases, nor any conserved motifs, and it is unrelated to the product of the mel-13 gene, which lies just upstream from the bmi-1 homolog mel-18.

Transgenic approaches to modifying cell and tissue function

As our knowledge of cell regulation pathways becomes increasingly sophisticated, the tools and techniques that have emerged from in vitro studies are being applied to the whole organism through transgenesis. With the development of new ways of modifying cellular signalling in intact animals comes the ability to analyse physiological systems and their pathologies with greater spatial and temporal precision.