Induction of nitric oxide release by MRC OX-44 (anti-CD53) through a protein kinase C-dependent pathway in rat macrophages.

Many membrane proteins are implicated in the control of cell function by triggering specific signaling pathways. There is a new family of membrane proteins, defined by its structural motifs, which includes several lymphoid antigens, but lacks a function. To study its biological role, we determined which signaling pathways are affected by the CD53 antigen, a prototypic member of this family, in rat macrophages. Activation of CD53 by cross-linking results in an increase in inositol phosphates and diacylglycerol and in Ca2+ mobilization, which are insensitive to pertussis or cholera toxins. There is a translocation of protein kinase C to the membrane accompanied by nitric oxide (NO) release in macrophages. This effect is the result of the expression of the inducible nitric oxide synthase (iNOS), which is dependent on protein kinase C and protein synthesis. These results have linked a new receptor with a specific pathway of NO induction and thus have opened up a novel aspect of NO regulation in cell biology.

The rat leukocyte antigen MRC OX-44 is a member of a new family of cell surface proteins which appear to be involved in growth regulation.

Moloney murine leukemia virus (MoMuLV)-induced rat T-cell lymphomas express discrete 1.8-, 2.2-, and 4-kb mRNA transcripts hybridizing under conditions of reduced stringency to a probe derived from a region upstream of the first exon of the Tpl-1/Ets-1 gene. Screening a cDNA library from one rat T-cell lymphoma with this genomic probe yielded 15 cDNA clones which were derived from 10 different genes. One of these genes, defined by the cDNA clone pRcT7a, was expressed as a 1.8-kb mRNA transcript in spleen and thymus but not in other normal rat tissues. Expression of the gene defined by the pRcT7a cDNA clone in a series of MoMuLV-induced rat T-cell lymphomas showed a perfect correlation with the expression of the rat leukocyte antigen MRC OX-44. Because of this observation, the pRcT7a clone was sequenced and it was shown to identify a gene coding for a 219-amino-acid protein. The homology between pRcT7a and the Tpl-1 probe used for its detection mapped within the 3' untranslated region of the pRcT7a cDNA clone. The pRcT7a protein, which exhibits four putative transmembrane regions and three putative glycosylation sites, contains a region which is nearly identical in sequence to a peptide derived from the rat leukocyte antigen MRC OX-44. This finding suggested that the pRcT7a cDNA clone defines the gene coding for OX-44. To confirm this finding, a pRcT7a construct in the retrovirus vector pZipNeo was introduced into the OX-44- T-cell lymphoma line 2788. Immunostaining with the MRC OX-44 monoclonal antibody followed by flow cytometry revealed that following gene transfer, the 2788 cells became OX-44+. Sequence comparisons revealed that pRcT7a/MRC OX-44 is a member of a family of genes which includes the melanoma-specific antigen ME491; the human leukocyte antigen CD37; the protein TAPA-1, which is expressed on the surface of human T cells and appears to be involved in growth regulation; the human gastrointestinal tumor antigen CO-029; and the Schistosoma mansoni-associated antigen Sm23.

Aberrant expression of tetraspanin molecules in B-cell chronic lymphoproliferative disorders and its correlation with normal B-cell maturation.

Tetraspanin proteins form signaling complexes between them and with other membrane proteins and modulate cell adhesion and migration properties. The surface expression of several tetraspanin antigens (CD9, CD37, CD53, CD63, and CD81), and their interacting proteins (CD19, CD21, and HLA-DR) were analyzed during normal B-cell maturation and compared to a group of 67 B-cell neoplasias. Three patterns of tetraspanin expression were identified in normal B cells. The first corresponded to bone marrow CD10(+) B-cell precursors (BCP) which showed high expression of CD81 and CD9, low reactivity for CD53 and negativity for CD37. CD10(-) B-lymphocytes showed downregulation of CD9/CD81 and upregulation of CD53/CD37. Plasma cells showed re-expressed CD9 and downregulated CD37. Hierarchical clustering analysis of flow cytometry immunophenotypic data showed a good correlation between the tumor differentiation stage and the pattern of tetraspanin expression, with all analyzed individual samples classified into three major groups, independently of their normal or neoplastic origin. Despite this, neoplastic B-cells frequently showed aberrantly high/low expression of the different markers analyzed. Interestingly, in B-cell chronic lymphocytic leukemia, abnormal expression of CD53 and CD9 were associated with different patterns of disease infiltration, which would support the role of these molecules on modulating adhesion and migration of neoplastic B cells.

Amplification of the integrated viral transforming genes of human papillomavirus 18 and its 5'-flanking cellular sequence located near the myc protooncogene in HeLa cells.

The human papillomavirus type 18 integrated in the HeLa cell genome is amplified on chromosome 8. E6, E7, and E1 open reading frames are amplified 5-fold, and the late viral DNA region, the viral long control region, and cellular flanking sequences are amplified 15-fold. The common 5'-flanking cellular DNA was localized by in situ hybridization of normal and HeLa cells only on chromosome 8 band q24. This flanking probe is included in the amplification unit of Colo320 cells, but in the case of HeLa the amplified region does not include the myc gene which is structurally conserved. Viral integration on chromosome 8 represents an independent event and not a rearrangement of viral DNA located on other chromosomes. The amplification of HPV-18 E6 and E7 open reading frames and the constitutive expression of the myc protooncogene may contribute to immortalization and/or proliferative capacity of HeLa cells.

Gene amplification-associated overexpression of the RNA editing enzyme ADAR1 enhances human lung tumorigenesis.

The introduction of new therapies against particular genetic mutations in non-small-cell lung cancer is a promising avenue for improving patient survival, but the target population is small. There is a need to discover new potential actionable genetic lesions, to which end, non-conventional cancer pathways, such as RNA editing, are worth exploring. Herein we show that the adenosine-to-inosine editing enzyme ADAR1 undergoes gene amplification in non-small cancer cell lines and primary tumors in association with higher levels of the corresponding mRNA and protein. From a growth and invasion standpoint, the depletion of ADAR1 expression in amplified cells reduces their tumorigenic potential in cell culture and mouse models, whereas its overexpression has the opposite effects. From a functional perspective, ADAR1 overexpression enhances the editing frequencies of target transcripts such as NEIL1 and miR-381. In the clinical setting, patients with early-stage lung cancer, but harboring ADAR1 gene amplification, have poor outcomes. Overall, our results indicate a role for ADAR1 as a lung cancer oncogene undergoing gene amplification-associated activation that affects downstream RNA editing patterns and patient prognosis.

The human vaccinia-related kinase 1 (VRK1) phosphorylates threonine-18 within the mdm-2 binding site of the p53 tumour suppressor protein.

The tumour suppressor p53 protein integrates multiple signals regulating cell cycle progression and apoptosis. This regulation is mediated by several kinases that phosphorylate specific residues in the different functional domains of the p53 molecule. The human VRK1 protein is a new kinase related to a poxvirus kinase, and more distantly to the casein kinase 1 family. We have characterized the biochemical properties of human VRK1 from HeLa cells. VRK1 has a strong autophosphorylating activity in several Ser and Thr residues. VRK-1 phosphorylates acidic proteins, such as phosvitin and casein, and basic proteins such as histone 2b and myelin basic protein. Because some transcription factors are regulated by phosphorylation, we tested as substrates the N-transactivation domains of p53 and c-Jun fused to GST. Human c-Jun is not phosphorylated by VRK1. VRK1 phosphorylates murine p53 in threonine 18. This threonine is within the p53 hydrophobic loop (residues 13-23) required for the interaction of p53 with the cleft of its inhibitor mdm-2. The VRK1 C-terminus domain (residues 268-396) that contains a nuclear localization signal targets the protein to the nucleus, as determined by using fusion proteins with the green fluorescent protein. We conclude that VRK1 is an upstream regulator of p53 that belongs to a new signalling pathway.

Expression of a new isoform of the tumor susceptibility TSG101 protein lacking a leucine zipper domain in Burkitt lymphoma cell lines.

The tumor susceptibility gene, TSG101, has been identified as a candidate tumor suppressor gene. We have examined the expression of TSG101 in Burkitt lymphoma cell lines. Several aberrant messages were detected in all cell lines. Aberrant splice donor sites are located within exon 1 at positions 132, 154, 172 and 284. Splice acceptors are located at positions 847 and 1054 within exon 5. The aberrant messages are coexpressed with a normal message and could be the result of additional splicing reactions of the mature message that behaves as an intermediate. The normal message codes for 46 kDa protein (TSG101A). One aberrant message joins in frame nucleotides 283-1055 and codes for a protein isoform of 17 kDa (TSG101B), as demonstrated by in vitro translation assays. The TSG101B isoform lacks the leucine zipper near the C-terminus, a transcriptional repressor domain, and retains most of the N-terminal region which has homology to E2 ubiquitin regulatory enzymes and the CROC-1 transcriptional regulator. The TSG101B isoform was detected in sixteen out of twenty-two (72%) BL cell lines, but not in normal lymphoid populations. The presence of two TSG101 isoforms with different dimerization potential opens up a new level of regulation of the TSG101 proteins possibly affecting cell cycle regulation.

Physiological activation of human neutrophils down-regulates CD53 cell surface antigen.

Tetraspanin transmembrane proteins have a metastasis suppressor effect by acting as cell motility brakes in tumor cells. CD53 is a panleukocyte antigen that belongs to the tetra-span superfamily. Human neutrophils express high levels of CD53. We tested the hypothesis that this antigen level changes when cells are activated. Treatment of human neutrophils with their physiological activators, tumor necrosis factor alpha or platelet-activating factor, resulted in down-regulation of this antigen from the cell surface, as assessed by immunofluorescence flow cytometry. Similar responses were observed when neutrophils were stimulated with chemotactic N-formyl-methionyl-leucyl-phenylalanine, phorbol ester, or the calcium ionophore ionomycin. The CD53 antigen down-regulation upon neutrophil stimulation was further confirmed by immunoblotting analysis and was not correlated with a change in the level of CD53 transcripts. This CD53 antigen down-regulation paralleled that of CD43 and CD44 antigens in these cells, despite their different protein structure. The down-regulation of the three antigens CD53, CD43, and CD44 could be inhibited by phenylmethylsulfonyl fluoride, suggesting that CD53 antigen down-regulation is the result of the activation of a proteolytic mechanism. Down-regulation of CD53 antigen level, as a result of cellular stimulation, might play a role in the different aspects of neutrophil biology, by modulating its interactions on the cell surface.

Co-expression of several human syntaxin genes in neutrophils and differentiating HL-60 cells: variant isoforms and detection of syntaxin 1.

Syntaxins are major components of vesicle trafficking and their pattern of expression depends on the cell type. Using reverse transcriptase-polymerase chain reaction (RT-PCR), cloning, and sequencing techniques, we have found that human neutrophils and neutrophil-differentiated HL-60 cells co-express syntaxins 1A, 3, 4, 5, 6, 7, 9, 11, and 16. These genes are also expressed in human peripheral blood lymphocytes and SH-SY5Y neuroblastoma cells, which, unlike neutrophils, also expressed syntaxin 10. We have identified two isoforms of syntaxin 3. Syntaxin 3A, similar to the previously reported syntaxin 3, and the novel isoform syntaxin 3B, which is identical to syntaxin 3A but lacks 37 amino acid residues at the carboxy-terminal region. Syntaxin 1 was mainly located to neutrophil granule membranes by confocal microscopy and by immunoblotting of subcellular fractions. These data indicate that syntaxin 1 cannot be considered specific to neural tissues. The level of expression of syntaxins 3, 4, 6, and 11 was increased during neutrophil differentiation of HL-60 cells, whereas that of syntaxins 1A, 5, 9, and 16 was unchanged. Syntaxin 7 was not expressed in undifferentiated HL-60 cells, but its expression was induced on neutrophil differentiation. The expression of several syntaxin genes in human neutrophils could be related to the high secretory capacity of these cells as well as to the presence of different cytoplasmic granules with distinct exocytic capabilities.

Shuttle vectors to study somatic mutagenesis and regulation of gene expression in the immune system.

Somatic mutagenesis is one of the main mechanisms for generation of diversity in the immunoglobulin genes. A family of 16 shuttle vectors has been designed to identify the mutation mechanism. These vectors are based on bovine papilloma virus replicon and carry selective markers (NmR and ApR), a mutation marker (the Escherichia coli galK) as well as several segments from the immunoglobulin (Ig) heavy- and kappa light-chain genes in different orientations. They can also be used to study general mutagenesis and the relative contribution of different DNA sequences to the regulation of gene expression by competition with trans-acting factors. These vectors start replicating in mammalian cells two days after transfection. Stable transformants carry the plasmids in an extrachromosomal form for at least three months without evidence of structural alteration.

Tumour-host metabolic interaction and cachexia.

Cachexia is a terminal metabolic problem observed in a wide variety of tumours. In this article I propose that the syndrome is a direct consequence of the common feature to all malignant tumours: growth. I suggest that the requirement for essential amino acids can be used as the unifying principle that links the tumour to the two main components of cachexia: muscle wastage and anorexia. This underlying factor is usually clouded by the overlapping of individual tumour characteristics.

Genetic alterations by human papillomaviruses in oncogenesis.

The integration sites in the cellular genome of human papillomavirus are located in chromosomal regions always associated with oncogenes or other known tumor phenotypes. Two regions, 8q24 and 12q13, are common to several cases of cervical carcinoma and can have integrated more than one type of papillomavirus DNA. These two chromosomal regions contain several genes implicated in oncogenesis. These observations strongly imply that viral integration sites of DNA tumor viruses can be used as the access point to chromosomal regions where genes implicated in the tumor phenotype are located, a situation similar to that of non-transforming retroviruses.

Amplification of human genomic sequences by human papillomaviruses universal consensus primers.

Detection of human papillomaviruses DNA (HPV) in tumour samples is often determined by a PCR based approach with standard universal consensus oligonucleotides. It is shown that these primers under the same amplification conditions can amplify a human genomic sequence of 1361 nucleotides in oral carcinomas and normal DNA samples. This sequence is detected more easily as the copy number of HPV DNA decreases. Therefore, in tumour samples that have a low copy number of HPV or that are contaminated by normal tissue there is a potential risk of misidentification of the presence of HPV if this observation is not taken into account.

Human papillomavirus DNA in cervical lesions from Morocco and its implications for cancer control.

To determine the types of human papillomaviruses (HPV) in northern Morocco, information which is needed for the design and use of HPV vaccines, we have analysed 129 cervical biopsies from this region. In our study, 91 cases were HPV positive, 45 cases had HPV-16 DNA, and 20 cases had HPV-18 DNA. This distribution of virus type was similar in inflammatory cervical lesions and in invasive cervical carcinomas. In conclusion, the HPV type distribution in Morocco is similar to that in other African Mediterranean countries, where the proportion of HPV-18 cases is significantly higher than in Europe. Determination of virus-type distribution is essential for vaccination programs.

Gene amplification of the histone methyltransferase SETDB1 contributes to human lung tumorigenesis.

Disruption of the histone modification patterns is one of the most common features of human tumors. However, few genetic alterations in the histone modifier genes have been described in tumorigenesis. Herein we show that the histone methyltransferase SETDB1 undergoes gene amplification in non-small and small lung cancer cell lines and primary tumors. The existence of additional copies of the SETDB1 gene in these transformed cells is associated with higher levels of the corresponding mRNA and protein. From a functional standpoint, the depletion of SETDB1 expression in amplified cells reduces cancer growth in cell culture and nude mice models, whereas its overexpression increases the tumor invasiveness. The increased gene dosage of SETDB1 is also associated with enhanced sensitivity to the growth inhibitory effect mediated by the SETDB1-interfering drug mithramycin. Overall, the findings identify SETDB1 as a bona fide oncogene undergoing gene amplification-associated activation in lung cancer and suggest its potential for new therapeutic strategies.

Human VRK2 modulates apoptosis by interaction with Bcl-xL and regulation of BAX gene expression.

VRK2 is a novel Ser-Thr kinase whose VRK2A isoform is located in the endoplasmic reticulum and mitochondrial membranes. We have studied the potential role that VRK2A has in the regulation of mitochondrial-mediated apoptosis. VRK2A can regulate the intrinsic apoptotic pathway in two different ways. The VRK2A protein directly interacts with Bcl-xL, but not with Bcl-2, Bax, Bad, PUMA or Binp-3L. VRK2A does not compete with Bax for interaction with Bcl-xL, and these proteins can form a complex that reduces apoptosis. Thus, high VRK2 levels confer protection against apoptosis. In addition, VRK2 knockdown results in an increased expression of BAX gene expression that is mediated by its proximal promoter, thus VRK2A behaves as a negative regulator of BAX. Low levels of VRK2A causes an increase in mitochondrial Bax protein level, leading to an increase in the release of cytochrome C and caspase activation, detected by PARP processing. VRK2A loss results in an increase in cell death that can be detected by an increase in annexinV+ cells. Low levels of VRK2A increase cell sensitivity to induction of apoptosis by chemotherapeutic drugs like camptothecin or doxorubicin. We conclude that VRK2A protein is a novel modulator of apoptosis.