Septin 9_i2 is downregulated in tumors, impairs cancer cell migration and alters subnuclear actin filaments.

Functions of septin cytoskeletal polymers in tumorigenesis are still poorly defined. Their role in the regulation of cytokinesis and cell migration were proposed to contribute to cancer associated aneuploidy and metastasis. Overexpression of Septin 9 (Sept9) promotes migration of cancer cell lines. SEPT9 mRNA and protein expression is increased in breast tumors compared to normal and peritumoral tissues and amplification of SEPT9 gene was positively correlated with breast tumor progression. However, the existence of multiple isoforms of Sept9 is a confounding factor in the analysis of Sept9 functions. In the present study, we analyze the protein expression of Sept9_i2, an uncharacterized isoform, in breast cancer cell lines and tumors and describe its specific impact on cancer cell migration and Sept9 cytoskeletal distribution. Collectively, our results showed that, contrary to Sept9_i1, Sept9_i2 did not support cancer cell migration, and induced a loss of subnuclear actin filaments. These effects were dependent on Sept9_i2 specific N-terminal sequence. Sept9_i2 was strongly down-regulated in breast tumors compared to normal mammary tissues. Thus our data indicate that Sept9_i2 is a negative regulator of breast tumorigenesis. We propose that Sept9 tumorigenic properties depend on the balance between Sept9_i1 and Sept9_i2 expression levels.

Gene expression profiling identifies sST2 as an effector of ErbB2-driven breast carcinoma cell motility, associated with metastasis.

Overexpression of the ErbB2 receptor tyrosine kinase in breast cancer contributes to tumor development and is associated with poor prognosis. However, the mechanism by which ErbB2 might contribute to metastasis is not well defined. To identify genes that mediate ErbB2-driven cell motility, we performed differential gene expression analysis of ErbB2-expressing migrating breast cancer cells vs mutant ErbB2-expressing non-migrating cells. Among the genes that were specifically induced in migrating cells were known transcriptional targets of ErbB2, such as matrix metalloproteinases, and novel ErbB2 targets. Contribution of selected candidate genes to ErbB2-driven cell motility was tested by small interfering RNA targeting. Knockdown of the soluble form of ST2 (sST2), also called interleukin-1 receptor-like 1, one of the most robustly induced genes, decreased ErbB2-induced cell motility in two different cell lines. In response to ErbB2 activation, sST2 protein expression and secretion were increased. Moreover, recombinant sST2 associated with the plasma membrane and sST2-blocking antibodies reduced ErbB2-induced motility. Interestingly, cells from metastatic breast tumors secreted higher levels of sST2 than primary tumor cells. Finally, sST2 was found at high levels in the serum of metastatic breast cancer patients. Our data suggest that sST2 contributes to breast cancer cell motility and that sST2 secretion is associated with metastasis.

Survival motor neuron (SMN) protein in rat is expressed as different molecular forms and is developmentally regulated.

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by a progressive degeneration of motoneurons in spinal cord and brainstem. The telomeric copy of a duplicated gene termed survival motor neuron (smn), which maps to chromosome 5q13, has been found to be deleted in most patients. The encoded gene product is a novel protein which recently has been shown to accumulate in specific nuclear organelles (gemini of coiled bodies, GEMS), and to play a part in the formation of the spliceosome complex. We have cloned and sequenced the rat smn cDNA. Antibodies generated against an N-terminus peptide recognized a main protein of 32 kDa in immunoblots of rat embryonic tissue extracts. Minor bands of 35 kDa, 45 kDa and, in perinatal muscle, of 24 kDa were also specifically detected, indicating that SMN is expressed as different molecular forms. Subcellular fractionation indicated that the 32 kDa form is mainly soluble, while the 35 kDa and 45 kDa products segregate to the microsomal-mitochondrial fraction. SMN protein is highly regulated during development: expression is high in embryonic tissues (central nervous system, muscle, lung and liver), and then progressively decreases to very low levels in most tissues of the adult. The demonstration of different molecular forms of SMN along with its developmental regulation may help to understand the contribution of this protein in the appearance of SMA phenotype.

Genetic control of infection of primary macrophages with T-cell-tropic strains of HIV-1.

Human immunodeficiency virus type 1 (HIV-1) NDK, a Zairian subtype D virus highly cytopathic for CD4-positive lymphocytes, and the prototype subtype B virus HIV-1 LAV are about 10(4) and 10(5) times more infectious, respectively, for T lymphocytes than for blood-derived macrophages (BDM). Recombinant viruses derived from HIV-1 LAV and HIV-1 NDK were used to determine the genetic control and the step of the virus/cell cycle responsible for infection of BDM with T-cell-tropic viruses. We found that recombinants bearing the envelope glycoprotein of HIV-1 NDK are able to enter more efficiently into BDM than recombinants with HIV-1 LAV envelope glycoprotein. We also found that a genetic region outside of the env gene is responsible for production of HIV-1 NDK infectious progeny from BDM. This region consists of the vif gene and the C- and N-terminal portions of pol and vpr genes, respectively. Our results suggest that productive infection of primary macrophages with T-cell-tropic strains of HIV-1 is determined by two different genetic mechanisms: one effective at the virus/cell entry, controlled by the env gene, and the second after entry, controlled by genes vif and vpr. In comparison with HIV-1 LAV, HIV-1 NDK has been able to more easily overcome both restriction mechanisms.

Fusogenic determinants of highly cytopathic subtype D Zairian isolate HIV-1 NDK.

Phenotypic characterization of subtype B strains of human immunodeficiency virus type 1 (HIV-1) indicates that the major determinants of their cytopathogenicity and tropism are contained in the gene coding for the envelope glycoprotein gp120, namely in its variable regions V1, V2, and V3. Recombinant viruses derived from HIV-1 LAV, the subtype B prototype virus, and HIV-1 NDK, the Zairian subtype D virus highly cytopathic for CD4-positive lymphocytes, were used to elucidate genetic control of fusogenic functions in subtype D viruses. Our data demonstrate that multigenic determination of fusogenic properties is more complex in the subtype D than in clade B viruses. Variability in three regions of HIV-1 NDK genome correlated with formation of large syncytia. These regions consisted of the matrix protein, the C-terminal portion of vpr up to the C1 region of gp120, and the V1-V3 regions of gp120. Variability in the envelope glycoprotein but not in other regions of the HIV-1 genome was related to enhanced resistance of HIV-1 NDK to treatment of target cells with OKT4-A anti-CD4 MAb. Therefore, a different genetic control affects two aspects of HIV-1 fusogenicity: (i) variability in the envelope glycoprotein itself is sufficient to influence a virus-to-cell fusion at the virus/cell entry, and (ii) a more complex genetic function including genes of matrix protein and envelope glycoprotein is related to variability of cell-to-cell fusion during formation of syncytium.

Neutralizing antibodies against highly cytopathic Zairian human immunodeficiency type-1 virus (HIV-1) NDK are present in sera outside Africa.

The prototype virus HIV-1 LAV and highly cytopathic Zairian virus HIV-1 NDK belong to the genetic subtypes B and D and represent low and highly cytopathic phenotypes, respectively. Their neutralization pattern and serotype were studied with respect to differences in their genotypes and phenotypes. Sera from HIV-1-infected persons living in four geographically distant areas, Philadelphia (USA), Ribeirao Preto (Brazil), Marseille (France) and Kinshasa (Zaire), were tested for the presence of type-specific and group-specific cross-reacting neutralizing antibodies against HIV-1 LAV and HIV-1 NDK in a continuous cell line MT4. The majority of type-specific antibodies were directed against HIV-1 LAV in Philadelphia, Ribeirao Preto and Marseille, and against HIV-1 NDK in Kinshasa. However, some sera with an HIV-1 NDK type-specific neutralization pattern were also found in Philadelphia, Ribeirao Preto and Marseille. These results indicate that strains with an HIV-1 NDK-like serotype could be found outside Africa. The presence of type-specific neutralizing antibodies against HIV-1 NDK in sera from North and South America and Europe should be taken into account during attempts to serotype HIV as well as in the course of selection of HIV-1 candidate strains for an AIDS vaccine.

Restriction of HIV-1 replication in intestinal cells is genetically controlled by the gag-pol region of the HIV-1 genome.

The human colon epithelial line HT29 represents a semipermisive cellular system for human immunodeficiency virus type 1 (HIV-1). It could be productively infected with HIV-1 NDK, a Zairian virus isolate highly cytopathic for CD4 positive lymphocytes, whereas infection with the prototype virus HIV-1 LAV was nonproductive. Recombinant viruses derived from HIV-1 LAV and HIV-1 NDK were used to determine the genetic control, step of virus/cell cycle, and molecular mechanism responsible for productive versus nonproductive infection of intestinal cells. Both parental viruses and all recombinants retrotranscribed their genomes with a similar kinetics and were able to complete HIV-1 DNA synthesis, HIV-1 LAV provirus present in preintegration complexes could be rescued by cocultivation with T-lymphocytes. However, it was aborted during prolonged cultivation of HT29 cells. Our results suggest that (i) gag/pol region of HIV-1 genome (fragment BssHII255-EcoRI4183) genetically controlled productive infection of intestinal cells and that (ii) the difference between productive and abortive infection occurred before synthesis of HIV-1 mRNA, at the integration level.

The human immunodeficiency virus (HIV) gag gene product p18 is responsible for enhanced fusogenicity and host range tropism of the highly cytopathic HIV-1-NDK strain.

Formation of large syncytia and rapid cell killing are characteristics of the Zairian human immunodeficiency virus type 1 isolate HIV-1-NDK, which is highly cytopathic for CD4+ lymphocytes in comparison with the HIV-1-LAV prototype. Chimeric viruses containing different combinations of HIV-1-NDK genetic determinants corresponding to the splice donor, the packaging signal, and the coding sequence of the p18gag protein together with the HIV-1-NDK EcoRI5278-XhoI8401 fragment were obtained by polymerase chain reaction-directed recombination. Phenotypic analysis of recombinant viruses indicated that 75 amino acids from the N-terminal part of HIV-1-NDK p18gag protein together with the HIV-1-NDK envelope glycoprotein are responsible for enhanced fusogenicity of HIV-1-NDK in CD4+ lymphocytes as well as for enhanced infectivity of HIV-1-NDK in some CD4- cells lines. The HIV-1-NDK splice donor/packaging sequence and the sequence encoding the gag protein p25 were not important for the variation observed in HIV-1 fusogenicity.

HIV1 cytopathogenicity-genetic difference between direct cytotoxic and fusogenic effect.

Formation of large syncytia, rapid cell killing, and early onset of replication are characteristics of the highly cytopathic Zairian virus strain HIV1 NDK compared with the HIV1 LAV prototype. Recombinant provirus molecules derived from cloned infectious DNAs of HIV1 LAV and NDK were constructed by reciprocal exchange of genetic material using conserved restriction sites. Different regions of the HIV1 genome were responsible for variability of the direct single-cell cytotoxic and fusogenic effects. A minimal, provisionally defined portion of genetic information responsible for the higher cytotoxicity of HIV1 NDK compared to the HIV1 LAV prototype was localized in the fragment Spel1042/EcoRl4183, containing the 3'-terminal half of gag and a majority of the pol gene. This region also determined the rapid replication properties of HIV1 NDK. The increased fusogenic potential of HIV1 NDK was associated with the simultaneous presence of HIV1 NDK fragments BssHll255/Spel1042 and EcoRl5278/Xhol8401 which contained the splicing donor, packaging sequence, p18 gag protein, and the HIV env gene. The increase in the direct killing effect but not in the syncytium forming ability of HIV1 NDK correlated with the early onset of replication and rapid spread of HIV1 NDK in cell cultures. The HIV1 NDK fragments BssHll/Spel and EcoRl/Xhol were by themselves necessary but not sufficient to induce formation of large syncytia.

Induction of NF-KB during monocyte differentiation by HIV type 1 infection.

The production of human immunodeficiency virus type 1 (HIV-1) progeny was followed in the U937 promonocytic cell line after stimulation either with retinoic acid or PMA, and in purified human monocytes and macrophages. Electrophoretic mobility shift assays and Southwestern blotting experiments were used to detect the binding of cellular transactivation factor NF-KB to the double repeat-KB enhancer sequence located in the long terminal repeat. PMA treatment, and not retinoic acid treatment of the U937 cells acts in inducing NF-KB expression in the nuclei. In nuclear extracts from monocytes or macrophages, induction of NF-KB occurred only if the cells were previously infected with HIV-1. When U937 cells were infected with HIV-1, no induction of NF-KB factor was detected, whereas high level of progeny virions was produced, suggesting that this factor was not required for viral replication. These results indicate that in monocytic cell lineage, HIV-1 could mimic some differentiation/activation stimuli allowing nuclear NF-KB expression.

Human immunodeficiency virus type 1 infection of U937 cells promotes cell differentiation and a new pathway of viral assembly.

The differentiation of U937 monoblastoid cells after human immunodeficiency virus type 1 (HIV-1) infection was studied using the following approaches: reverse transcriptase activity measurement, immunofluorescence labeling, and electron microscopy. For comparison, uninfected U937 cells were induced to differentiate from monocyte to macrophage by phorbol 12-myristate 13-acetate (PMA) or retinoic acid (RA) treatment. Both infected and drug-treated cells showed important and similar ultrastructural cell modifications, with a phenotype that decreased in monocyte specificity and increased in that of macrophages. When U937 cells were induced to differentiate upon HIV-1 infection, a very different pathway of viral production was observed. Production and accumulation of the virus in a vacuolar compartment of intracytoplasmic origin and escape to the antiviral lysosomal activity could explain virus persistence. This makes the cell system a good model with which to study the relationship between HIV-1 production and cell differentiation.