Regulation of the cell cycle at the G1-S transition by proteolysis of cyclin E and p27Kip1

The transition from G1 phase to S phase of the mammalian cell cycle is controlled by many positive and negative regulators, among which cyclin E and p27Kip1, respectively, undergo the most marked changes in concentration at this transition. The abundance of both cyclin E and p27Kip1 is regulated predominantly by posttranslational mechanisms, in particular by proteolysis mediated by the ubiquitin-proteasome pathway. Cyclin E and p27Kip1 each bind to and undergo polyubiquitination by the same ubiquitin ligase, known as SCF(Skp2). The degradation of cyclin E and p27Kip1 is greatly impaired in Skp2-deficient mice, resulting in intracellular accumulation of these proteins. In this article, recent progress in characterization of the molecular mechanisms that control the proteolysis of cyclin E and p27Kip1 is reviewed.

[The genetics of Parkinson syndrome]

A genetic contribution to the etiology of Parkinson's disease was first suspected by Charcot and later confirmed by case control, family, and twin studies, as well as by the description of large parkinsonian families with Mendelian inheritance of the disease. Recent progress in the field of molecular neurogenetics has led to the identification of several Parkinson disease genes and gene loci. Mutations in the alpha-Synuclein gene (PARK1) and in the gene for the ubiquitin C-terminal hydrolase I (PARK5), along with two gene loci harboring currently unknown genes (PARK3 and PARK4), have been linked to very rare autosomal dominantly inherited parkinsonian syndromes. Mutations in the parkins gene (PARK2), causing autosomal recessive early-onset parkinsonism, are much more common and therefore of clinical relevance. A second gene locus for an autosomal dominantly inherited Parkinsonian syndrome was recently localized on chromosome 1 (PARK6). All three parkinson genes identified thus far imply the involvement of the ubiquitin pathway of protein degradation in the pathogenesis of Parkinson's disease.

EH, Ledbetter DH. The human aminophospholipid-transporting ATPase gene ATP10C maps adjacent to UBE3A and exhibits similar imprinted expression

Maternal duplications of the imprinted 15q11-13 domain result in an estimated 1%-2% of autism-spectrum disorders, and linkage to autism has been identified within 15q12-13. UBE3A, the Angelman syndrome gene, has, to date, been the only maternally expressed, imprinted gene identified within this region, but mutations have not been found in autistic patients. Here we describe the characterization of ATP10C, a new human imprinted gene, which encodes a putative protein homologous to the mouse aminophospholipid-transporting ATPase Atp10c. ATP10C maps within 200 kb distal to UBE3A and, like UBE3A, also demonstrates imprinted, preferential maternal expression in human brain. The location and imprinted expression of ATP10C thus make it a candidate for chromosome 15-associated autism and suggest that it may contribute to the Angelman syndrome phenotype.

Cell cycle control of septin ring dynamics in the budding yeast

Septins constitute a cytoskeletal structure that is conserved in eukaryotes. In Saccharomyces cerevisiae, the Cdc3, Cdc10, Cdc11, Cdc12 and Shs1/Sep7 septins assemble as a ring that marks the cytokinetic plane throughout the budding cycle. This structure participates in different aspects of morphogenesis, such as selection of cell polarity, localization of chitin synthesis, the switch from hyperpolar to isotropic bud growth after bud emergence and the spatial regulation of septation. The septin cytoskeleton assembles at the pre-bud site before bud emergence, remains there during bud growth and duplicates at late mitosis eventually disappearing after cell separation. Using a septin-GFP fusion and time-lapse confocal microscopy, we have determined that septin dynamics are maintained in budding zygotes and during unipolar synchronous growth in pseudohyphae. By means of specific cell cycle arrests and deregulation of cell cycle controls we show that septin assembly is dependent on G1 cyclin/Cdc28-mediated cell cycle signals and that the small GTPase Cdc42, but not Rho1, are essential for this event. However, during bud growth, the septin ring shapes a bud-neck-spanning structure that is unaffected by failures in the regulation of mitosis, such as activation of the DNA repair or spindle assembly checkpoints or inactivation of the anaphase-promoting complex (APC). At the end of the cell cycle, the splitting of the ring into two independent structures depends on the function of the mitotic exit network in which the protein phosphatase Cdc14 participates. Our data support a role of cell cycle control mechanisms in the regulation of septin dynamics to accurately coordinate morphogenesis throughout the budding process in yeast.

Fission yeast mfr1 activates APC and coordinates meiotic nuclear division with sporulation

Meiosis is the developmental program by which sexually reproducing diploid organisms generate haploid gametes. In yeast, meiosis is followed by spore morphogenesis. These two events are normally coordinated in such a way that spore formation is dependent upon completion of the meiotic nuclear divisions. Here we describe a meiosis-specific protein, mfr1, that is involved in this coordination. mfr1 is an activator of the anaphase-promoting complex (APC), which is necessary for the rapid degradation of the cdc13 cyclin at the end of meiosis II, prior to the formation of spores. An mfr1 null mutant completes meiosis II but remains with high levels of cdc13 and cdc2 kinase activity and has considerably delayed spore formation. By analogy with the mitotic cell cycle, where proteolysis and inactivation of cdc2 kinase are necessary to trigger mitotic exit and cytokinesis, we propose that at the end of meiosis rapid and timely proteolysis of cyclins is required to switch on the differentiation program that eventually leads to the formation of haploid gametes.

Functional analysis of relA and rshA, two relA/spoT homologues of Streptomyces coelicolor A3(2)

Deletion of the (p)ppGpp synthetase gene, relA, of Streptomyces coelicolor A3(2) results in loss of production of the antibiotics actinorhodin (Act) and undecylprodigiosin (Red) and delayed morphological differentiation when the mutant is grown under conditions of nitrogen limitation. To analyze the role of (p)ppGpp as an intracellular signaling molecule for the initiation of antibiotic production, several C-terminally deleted derivatives of S. coelicolor relA that could potentially function in the absence of ribosome activation were placed under the control of the thiostrepton-inducible tipA promoter. While 0.82- and 1.28-kb N-terminal segments failed to restore (p)ppGpp and antibiotic production upon induction in a relA null mutant, 1.46- and 2.07-kb segments did. Under conditions of phosphate limitation, deletion of relA had little or no effect on Act or Red synthesis, potentially reflecting an alternative mechanism for ppGpp synthesis. A second S. coelicolor RelA homologue (RshA, with 42% identity to S. coelicolor RelA) was identified in the genome sequence. However, deletion of rshA had no effect on the ability of the relA mutant to make Act and Red when grown under conditions of phosphate limitation. While high-level induction of tipAp::rshA in the relA mutant resulted in growth inhibition, low-level induction restored antibiotic production and sporulation. In neither case, nor in the relA mutant that was grown under phosphate limitation and producing Act and Red, could (p)ppGpp synthesis be detected. Thus, a ppGpp-independent mechanism exists to activate antibiotic production under conditions of phosphate limitation that can be mimicked by overexpression of rshA.

Developmental changes in the expression of parkin and UbcR7, a parkin-interacting and ubiquitin-conjugating enzyme, in rat brain

Parkin is a product of the Park2 gene the mutation of which causes autosomal recessive juvenile parkinsonism (AR-JP) characterized by selective dopaminergic neuronal death and absence of Lewy bodies. Recently we found that parkin is directly linked to the ubiquitin (Ub)-proteasome pathway as a Ub-protein ligase (E3) collaborating with a Ub-conjugating enzyme (E2) UbcH7. Here we analysed by in situ hybridization the expression of mRNAs for parkin and UbcR7 (rat orthologue of human UbcH7) in the developing rat brain. Parkin mRNA increased in parallel with neuronal maturation, but was unevenly distributed in various brain regions after four postnatal days. The expression pattern of the UbcR7 mRNA was almost identical to that of the parkin mRNA in all cases examined. Both parkin and UbcR7 mRNAs were distributed in neurones but not glial cells. Our findings indicate that parkin is expressed not only in the substantia nigra, but also uniformly in various brain regions in a development-dependent manner. Co-expression of UbcR7 with parkin suggests that UbcR7 may interact with parkin in vivo for ubiquitination of yet unidentified target protein(s).

Intrachromosomal recombination after targeted monocopy integration in Penicillium chrysogenum: stabilization of the direct repeats to prevent loss of the inserted gene

Monocopy systems obtained by targeted integration at the pyrG locus of P. chrysogenum led to the formation of unstable direct repeats in the genome. A previously isolated pyrG mutant was sequenced and the mutation was found to be located at nucleotide position 665 of the pyrG gene. A different pyrG mutation was introduced in vitro at the BamHI site of this gene. Recombination products arising from monocopy systems using the bleomycin/phleomycin resistance gene (ble) as a model were studied to elucidate the intrachromosomal recombination mechanisms. Experimental results showed that both gene conversion and deletion events occurred spontaneously at the integration site. Gene conversion products were obtained at a frequency of one in 3.4x10(4) viable transformant spores. When gene conversion occurred, the inserted exogenous gene was retained and was flanked by rearranged direct repeats of the pyrG gene, each containing at least one pyrG mutation. Deletion events resulted in the loss at high frequency of the inserted exogenous gene. Genetic stabilization of a monocopy system was obtained when both pyrG repeats (formed at the targeted integration site) contained at least one identical mutation, since in this case further recombinations can be easily counter-selected.

A conserved cyclin-binding domain determines functional interplay between anaphase-promoting complex-Cdh1 and cyclin A-Cdk2 during cell cycle progression

Periodic activity of the anaphase-promoting complex (APC) ubiquitin ligase determines progression through multiple cell cycle transitions by targeting cell cycle regulators for destruction. At the G(1)/S transition, phosphorylation-dependent dissociation of the Cdh1-activating subunit inhibits the APC, allowing stabilization of proteins required for subsequent cell cycle progression. Cyclin-dependent kinases (CDKs) that initiate and maintain Cdh1 phosphorylation have been identified. However, the issue of which cyclin-CDK complexes are involved has been a matter of debate, and the mechanism of how cyclin-CDKs interact with APC subunits remains unresolved. Here we substantiate the evidence that mammalian cyclin A-Cdk2 prevents unscheduled APC reactivation during S phase by demonstrating its periodic interaction with Cdh1 at the level of endogenous proteins. Moreover, we identified a conserved cyclin-binding motif within the Cdh1 WD-40 domain and show that its disruption abolished the Cdh1-cyclin A-Cdk2 interaction, eliminated Cdh1-associated histone H1 kinase activity, and impaired Cdh1 phosphorylation by cyclin A-Cdk2 in vitro and in vivo. Overexpression of cyclin binding-deficient Cdh1 stabilized the APC-Cdh1 interaction and induced prolonged cell cycle arrest at the G(1)/S transition. Conversely, cyclin binding-deficient Cdh1 lost its capability to support APC-dependent proteolysis of cyclin A but not that of other APC substrates such as cyclin B and securin Pds1. Collectively, these data provide a mechanistic explanation for the mutual functional interplay between cyclin A-Cdk2 and APC-Cdh1 and the first evidence that Cdh1 may activate the APC by binding specific substrates.

Molecular cloning and functional characterization of two murine cDNAs which encode Ubc variants involved in DNA repair and mutagenesis

Ubiquitin-conjugating enzyme (Ubc) variants share structural similarity with Ubcs but lack the essential cysteine residue required to form a thioester bond with ubiquitin. Yeast Mms2 is a Ubc variant and plays an important role in error-free DNA postreplication repair to protect cells from killing by DNA damaging agents and mutagenesis. Ironically, one of two known Mms2 homologs, CROC1, has been linked to cell immortalization and tumorigenesis. To further investigate cellular roles played by mammalian Mms2 homologs, we report here the molecular cloning, tissue distribution and functional characterization of two mouse cDNAs encoding mMMS2 and mCROC1. Unlike human CROC1, the mCROC1 gene does not encode two alternative transcripts in most tissues. Instead, nonoverlapping sequences were found in two distinct cDNA clones that together would constitute a full-length open reading frame homologous to CROC1B. Both mMMS2 and the C-terminal mCROC1 core domain are able to complement the yeast mms2 mutant functionally and are able to interact with Ubc13 in a yeast two-hybrid assay, indicating that they are true yeast Mms2 homologs and may play a similar role in DNA postreplication repair. We propose several hypotheses to reconcile the seemingly contradictory observations regarding roles of the two mammalian Mms2 homologs in tumorigenesis and carcinogenesis.

Phosphorylation of the cohesin subunit Scc1 by Polo/Cdc5 kinase regulates sister chromatid separation in yeast

At the onset of anaphase, a caspase-related protease (separase) destroys the link between sister chromatids by cleaving the cohesin subunit Scc1. During most of the cell cycle, separase is kept inactive by binding to an inhibitory protein called securin. Separase activation requires proteolysis of securin, which is mediated by an ubiquitin protein ligase called the anaphase-promoting complex. Cells regulate anaphase entry by delaying securin ubiquitination until all chromosomes have attached to the mitotic spindle. Though no longer regulated by this mitotic surveillance mechanism, sister separation remains tightly cell cycle regulated in yeast mutants lacking securin. We show here that the Polo/Cdc5 kinase phosphorylates serine residues adjacent to Scc1 cleavage sites and strongly enhances their cleavage. Phosphorylation of separase recognition sites may be highly conserved and regulates sister chromatid separation independently of securin.

Interactions of the COP9 signalosome with the E3 ubiquitin ligase SCFTIRI in mediating auxin response

The COP9 signalosome is an evolutionary conserved multiprotein complex of unknown function that acts as a negative regulator of photomorphogenic seedling development in Arabidopsis. Here, we show that plants with reduced COP9 signalosome levels had decreased auxin response similar to loss-of-function mutants of the E3 ubiquitin ligase SCFTIR1. Furthermore, we found that the COP9 signalosome and SCFTIR1 interacted in vivo and that the COP9 signalosome was required for efficient degradation of PSIAA6, a candidate substrate of SCFTIR1. Thus, the COP9 signalosome may play an important role in mediating E3 ubiquitin ligase-mediated responses.

Rma1, a novel type of RING finger protein conserved from Arabidopsis to human, is a membrane-bound ubiquitin ligase

Rma1 is a protein with a RING finger motif and a C-terminal membrane-anchoring domain and is well conserved among higher eukaryotes. We show that fusion proteins between maltose binding protein (MBP) and human or Arabidopsis Rma1 are polyubiquitinated, when incubated with the rabbit reticulocyte or the wheat germ lysate, respectively. The polyubiquitination of MBP-Rma1 has been reconstituted by incubation with purified ubiquitin, the ubiquitin-activating enzyme E1, and one of the two ubiquitin-conjugating E2 enzymes (Ubc4 or UbcH5a). Other E2 enzymes tested, E2-20k, E2-25k, Ubc3 and Ubc8, are not able to confer this modification. Mutational analysis shows that the RING finger motif of Rma1 is necessary for the auto-ubiquitination of MBP-Rma1. Thus, Rma1 represents a novel, membrane-bound type of ubiquitin ligase E3, which probably functions with the Ubc4/5 subfamily of E2. The MBP moiety but not Rma1 itself is ubiquitinated in the auto-ubiquitination reaction of MBP-Rma1. Free MBP in solution is not a substrate of Rma1. These observations indicate that bringing the substrate into its physical vicinity is very important for the action of ubiquitin ligase.

Endoplasmic reticulum (ER)-associated degradation of T cell receptor subunits. Involvement of ER-associated ubiquitin-conjugating enzymes (E2s)

Degradation of proteins from the endoplasmic reticulum is fundamental to quality control within the secretory pathway, serves as a way of regulating levels of crucial proteins, and is utilized by viruses to enhance pathogenesis. In yeast two ubiquitin-conjugating enzymes (E2s), UBC6p and UBC7p are implicated in this process. We now report the characterization of murine homologs of these E2s. MmUBC6 is an integral membrane protein that is anchored via its hydrophobic C-terminal tail to the endoplasmic reticulum. MmUBC7, which is not an integral membrane protein, shows significant endoplasmic reticulum colocalization with MmUBC6. Overexpression of catalytically inactive MmUBC7 significantly delayed degradation from the endoplasmic reticulum of two T cell antigen receptor subunits, alpha and CD3-delta, and suggests a role for the ubiquitin conjugating system at the initiation of retrograde movement from the endoplasmic reticulum. These findings also implicate, for the first time, a specific E2 in degradation from the endoplasmic reticulum in mammalian cells.

The Prader–Willi Syndrome Imprinting Center Activates the Paternally Expressed Murine Ube3a Antisense Transcript but Represses Paternal Ube3a

The imprinted UBE3A gene exhibits maternal-only expression in specific cell types in the brain, but exhibits biallelic expression in other cell types. UBE3A is located adjacent to a cluster of imprinted, paternally expressed genes that are known to be positively regulated by the Prader-Willi syndrome imprinting center (PWS-IC). Here, we examined the effect of the PWS-IC on the UBE3A locus. Using intersubspecific crosses, we found that deletion of the PWS-IC causes an upregulation of the paternal Ube3a allele. This indicates that unlike its positive effect on all the other paternally expressed transcripts in the region, the PWS-IC negatively regulates the levels of paternal UBE3A. Interestingly, we found that like the human UBE3A locus, the murine Ube3a locus includes an imprinted, paternally expressed antisense transcript. We show that this paternal antisense transcript is positively regulated by the PWS-IC. These results are consistent with a model in which the PWS-IC mediates activation and maintenance of paternal gene expression in the 15q11-q13 region, with repression of the paternal UBE3A gene occurring as an indirect result of expression of the antisense transcript.

N-Terminally extended human ubiquitin-conjugating enzymes (E2s) mediate the ubiquitination of RING-finger proteins, ARA54 and RNF8

We have previously cloned cDNAs encoding the N-terminally extended class III human ubiquitin-conjugating enzymes (E2s), UBE2E2 and UBE2E3, the biological functions of which are not known. In this study, we performed yeast two-hybrid screening for protein(s) interacting with UBE2E2, and two RING-finger proteins, ARA54 and RNF8, were identified. Both ARA54, a ligand-dependent androgen receptor coactivator, and RNF8 interacted with class III E2s (UBE2E2, UbcH6, and UBE2E3), but not with other E2s (UbcH5, UbcH7, UbcH10, hCdc34, and hBendless) in the yeast two-hybrid assay. The use of various deletion mutants of UBE2E2 and RING-finger proteins and two RING point mutants, ARA54 C(220)S and RNF8 C(403)S, in which the RING structure is disrupted, showed that the UBC domain of UBE2E2 and the RING domain of these RING-finger proteins were involved in this association. Wild-type ARA54 and RNF8, expressed in insect Sf9 cells, catalyzed E2-dependent autoubiquitination in vitro, whereas the point mutated proteins showed markedly reduced activity. Ubiquitination of wild-type ARA54 and RNF8, expressed in COS-7 cells, was also observed, and a proteasome inhibitor, MG132, prevented the degradation of these wild-type proteins, but was much less effective in protecting the RING mutants. Transfection of COS-7 cells with a green fluorescent protein chimera showed that RNF8 was localized in the nucleus, and ARA54 in both the cytoplasm and nucleus. Our results suggest that ARA54 and RNF8 possibly act as Ub-ligases (E3) in the ubiquitination of certain nuclear protein(s).

Characteristic chromosomal aberrations in sporadic cerebellar hemangioblastomas revealed by comparative genomic hybridization

Hemangioblastomas (HBs) of the central nervous system are benign tumors and occur as sporadic (sp) tumors (75%) or as a manifestation of the von Hippel-Lindau (VHL) disease (25%). VHL-disease is an autosomal dominant disorder characterized by HBs of the central nervous system and retina, renal cell carcinoma (RCC), phaeochromocytoma (PHEO), islet tumors of the pancreas, and endolympatic sac tumors as well as cysts and cystadenoma in the kidney, pancreas and epididymis. In VHL patients a large spectrum of germline mutations in the VHL gene has been detected. In spHBs VHL alleles are reported to be inactivated in up to 50% of the tumors. To our knowledge the involvement of other genes in spHBs has not been investigated. To elucidate the oncogenesis of spHBs, we performed CGH on 10 spHBs to screen for chromosomal imbalances throughout the entire tumor genome. Aberrations most frequently detected are losses of chromosomes 3 (70%), 6 (50%), 9 (30%), and 18q (30%) and a gain of chromosome 19 (30%). Based on these frequencies and the co-occurrence of these aberrations in the analyzed tumors we hypothesize that loss of chromosome 3 (harboring the VHL gene) is an early event in the oncogenesis of spHBs, followed by loss of 6, and then losses of chromosomes 9, 18q and gain of chromosome 19. Comparison of the chromosomal imbalances in spHBs to those previously reported in RCCs and PHEOs reveals that the pathway of spHBs shows similarities to both the RCCs and PHEOs.

Enhanced expression of mRNAs of antisecretory factor-1, gp96, DAD1 and CDC34 in human hepatocellular carcinomas

To identify differentially expressed genes in hepatocarcinogenesis, we performed differential display analysis using surgically resected hepatocellular carcinoma (HCC) and adjacent non-tumorous liver tissues. We identified four cDNA fragments upregulated in HCC samples, encoding antisecretory factor-1 (AF), gp96, DAD1 and CDC34. Northern blot analysis demonstrated that these mRNAs were expressed preferentially in HCCs compared with adjacent non-tumorous liver tissues or normal liver tissues from non-HCC patients. The expression of these mRNAs was increased along with the histological grading of HCC tissues. These mRNA levels were also high in three human HCC cell lines (HuH-7, HepG2 and HLF), irrespective of the growth state. We also demonstrate that sodium butyrate, an inducer of differentiation, downregulated the expression of AF and gp96 mRNAs, supporting in part our pathological observation. Immunohistochemical analysis revealed that gp96 and CDC34 proteins were preferentially accumulated in cytoplasm and nuclei of HCC cells, respectively. Overexpression of these genes could be an important manifestation of HCC phenotypes and should provide clues to understand the molecular basis of hepatocellular carcinogenesis.

Cancer-predisposing mutations within the RING domain of BRCA1: loss of ubiquitin protein ligase activity and protection from radiation hypersensitivity

BRCA1 is a breast and ovarian cancer-specific tumor suppressor that seems to be involved in transcription and DNA repair. Here we report that BRCA1 exhibits a bona fide ubiquitin (Ub) protein ligase (E3) activity, and that cancer-predisposing mutations within the BRCA1 RING domain abolish its Ub ligase activity. Furthermore, these mutants are unable to reverse gamma-radiation hypersensitivity of BRCA1-null human breast cancer cells, HCC1937. Additionally, these mutations within the BRCA1 RING domain are not capable of restoring a G(2) + M checkpoint in HCC1937 cells. These results establish a link between Ub protein ligase activity and gamma-radiation protection function of BRCA1, and provide an explanation for why mutations within the BRCA1 RING domain predispose to cancer. Furthermore, we propose that the analysis of the Ub ligase activity of RING-domain mutations identified in patients may constitute an assay to predict predisposition to cancer.

In vitro ubiquitination of cyclin D1 by ROC1-CUL1 and ROC1-CUL3

Overexpression of cyclin D1 has been implicated in a variety of tumors, such as breast cancers, gastrointestinal cancers and lymphomas. Both gene amplification and protein degradation mediated by ubiquitin (Ub)-dependent proteolysis regulate the abundance of cyclin D1. Here we report that ROC1 interacted with all three D type cyclins in vivo but did not bind to other cyclins tested. The ROC1-CUL1 and ROC1-CUL3, but not ROC1-CUL2, -CUL3 and -CUL4, immunocomplexes promoted polyubiquitination of bacterially purified cyclin D1 in vitro. RING finger mutations of ROC1 eliminated the Ub ligase activity toward cyclin D1. In all cases the ubiquitination of cyclin D1 was accompanied by autoubiquitination of the cullins. The results suggest the involvement of ROC1-cullin ligases in cyclin D1 ubiquitination and a potential mechanism whereby the cullin subunit is ubiquitinated itself while ubiquitinating a substrate.

[Abnormalities of tumor suppressor genes at chromosome 3p in lung cancer]

OBJECTIVE

To investigate the allelic loss of heterozygosity in three tumor suppressor genes, Fhit, hMLH1 and VHL, located at three corresponding regions 3p14-cen, 3p21.3-22 and 3p25-26 with a high fregnency in lung cancer and to evaluate the expression of Fhit protein in the tumor tissue of lung cancer.

METHODS

Microsatellite analysis was performed by using the primers that amplified polymorphic sequences inside or flanking to the three genes in the tumor tissues collected from 45 cases of primary lung cancer. Immunohistochemical staining was performed to detect the expression of Fhit protein in the tumor tissues from 17 out of the 45 cases.

RESULTS

For loci D3S1234, D3S1300 and D3S4103 that are located in the intron of Fhit gene, LOH was found in informative cases as 62.9%, 63.6% and 59.5%, respectively. In D3S1561 and D3S1612 that are linked with hMLH1 gene, LOH was detected in 54.5% and 63.2% of informative cases, respectively. LOH was found in 64.3% and 41.7% of informative cases, at D3S1038 and D3S1283, respectively, which are flanked to VHL gene. Expression of Fhit protein was down regulated in tumor tissues of 11 out of 17 cases (64.7%); among 10 of the 11 samples, LOH was detected at one or more of the microsatellite loci tested.

CONCLUSION

High frequency loss of one allele in tumor suppressor genes Fhit, hMLH1 and VHL was observed in the tumor tissues of lung cancer, indicating that it may play a role in carcinogenesis of human lung, and may provide some new approaches to early gene detection for lung cancer. Loss of one allele of Fhit gene may be one of the mechanisms for down regulation of Fhit protein expression in lung cancer.

Expression of anaphase-promoting complex 5 in balloon angioplasty-injured rat carotid arteries and mitogen-stimulated human vascular smooth muscle cells

We utilized differential display to identify differentially expressed mRNAs induced by balloon angioplasty injury. A recently described subunit of the anaphase-promoting complex, APC5, is not expressed in uninjured rat carotid arteries. Expression of APC5 mRNA is detectable as early as 1 day post-injury, reached maximal levels by 3-7 days, and declined by 14 days post-injury. APC5 is not expressed in serum-starved cultured human vascular smooth muscle cells (VSMC), but is strongly induced by mitogenic factors, and to a lesser extent by nonmitogenic cytokines. The kinetics of APC5 expression is associated with cell cycle progression, and corresponds with PCNA expression in PDGF-stimulated human VSMC. Interestingly, APC5 is expressed in most human tissues examined, regardless of their proliferative state. These data are the first description of the cytokine-inducible expression of APC5 and suggest that expression of this gene may represent an important event in the pathogenesis of vascular proliferative diseases.

Identification, tissue expression, and chromosomal position of a novel gene encoding human ubiquitin-conjugating enzyme E2-230k

Through large-scale human genome mapping and sequencing of a region at chromosome 17q25.1 that is of particular interest because genes associated with breast, ovarian, and esophageal cancer are likely to be located there, we isolated the cDNA of a novel member of the family of ubiquitin-conjugating enzymes. The predicated peptide showed 97% identity in amino-acid sequence to murine ubiquitin-conjugating enzyme E2-230k (Mus UBE2-230k). The human cDNA consisted of 4878 nucleotides with an open reading frame encoding 1138 amino acids; the approximately 5 kb transcript was expressed predominantly in skeletal muscle and heart. The predicted UBE2-230k peptide contained a motif typical of the UBC domain that has been implicated in the ubiquitin-dependent proteolytic system and related pathways.