Biomedical subjects

L Vanhamme

Publications and source records attributed to L Vanhamme.

46 records · Page 3Linked to original sources

PubMed1994

Genetic controls for the expression of surface antigens in African trypanosomes.

The major surface antigens of African trypanosomes, variant surface glycoprotein (VSG) and procyclin, are typical markers of their respective developmental stages, the bloodstream form and the insect-specific procyclic form. Although the role of procyclin is still unclear, variation of the VSG in the blood allows the parasite to escape the immune response of the host and develop a chronic infection. In this review, we discuss the available information concerning the genetic mechanisms that control the expression of VSG and procyclin during the life-cycle of the trypanosome. Unlike other eukaryotes, trypanosomes do not appear to primarily control the expression of their genes through a specific modulation of promoter activity. Antigenic variation in the bloodstream results either from DNA rearrangements or from a change in telomeric chromatin structure, and stage-specific regulation of antigen synthesis is linked to differential control of RNA elongation, processing, stability, and/or translation. Trypanosomes' apparent lack of transcription-initiation control probably relates to the general organization of genes in long polycistronic transcription units. Only two promoters for protein-encoding genes, those of VSG and procyclin, are known in trypanosomes, and these share properties with the ribosomal gene promoter.

Africa↗

PubMed1993

Tumor necrosis factor alpha and interleukin 1 alpha induce anchorage independence in v-jun transgenic murine cells.

The oncogene jun encodes a transcription factor of the AP-1 family. In mice carrying viral jun (v-jun) as a transgene, wounding is a prerequisite for tumorigenesis, suggesting collaboration between the transgene and a wound-related event. To define possible candidates for this collaborative process, we examined the effect of several wound-related polypeptide growth factors on cells from transgenic mice. Tumor necrosis factor alpha and interleukin 1 alpha induce anchorage independence in embryo fibroblasts and tumor cell revertants from these mice. This effect was specific for the two cytokines and was restricted to cells from v-jun transgenic mice. Anchorage independence required the continued presence of the cytokines. Transfection of transgenic cells with a v-jun expression plasmid also induced anchorage independence and a tumorigenic phenotype in transgenic tumor cell revertants. However, there was no correlation between anchorage independence, expression of Jun, and AP-1 activity. These results suggest that while increased transgene expression can enhance the growth properties of v-jun transgenic cells, there exist other cytokine-dependent mechanisms that have a similar effect. Retinoic acid, dexamethasone, or forskolin inhibits induction of anchorage independence by tumor necrosis factor alpha, interleukin 1 alpha, and transfected v-jun. Although these agents affect both AP-1 transactivation potential and DNA binding in the transgenic cells, the changes are not correlated with the inhibition of growth.

Animals↗

PubMed1993

Characterization of sarcoma cell lines from v-jun transgenic mice.

Wounding is a prerequisite for tumor formation in v-jun transgenic mice. The progression from wound to dermal sarcoma is a multistep process which, at some stage, results in an increase in transgene mRNA expression in tumor tissue. However, transgene expression in individual sarcoma cells stained for Jun protein cultures is heterogeneous. We cloned several cell lines from wound-related v-jun transgenic tumors to determine whether a relationship existed between the cellular growth properties and structure, expression, or function of the transgene. Cell lines with very high v-jun expression had a high cloning efficiency in soft agar and tumorigenicity in nude mice. However, for cell lines with an intermediate or low level of transgene expression there was no correlation between transgene expression and the transformed phenotype. There was also no correlation between transgene expression and individual cell line morphologies, growth rates, transgene genomic DNA copy number, or mRNA expression of jun-related genes. The tumor cell subclones (1-20.2, 3-24.3) with very low transgene expression, very poor cloning efficiency, and low tumorigenicity also showed reduced activator protein 1 DNA binding activity and had an increased expression of endogenous c-jun when compared to other tumor cell lines. Transfection of a v-jun expression vector into cell lines with poor cloning efficiency and low tumorigenicity enhanced both in vitro cloning and in vivo tumor formation. However, such overexpressed v-jun had no effect on NIH3T3 cells. Our studies show that expression of the v-jun transgene contributes to the transformed phenotype of tumor cell lines but that there are additional factors that determine growth properties in culture and in the animal.

Animals↗

PubMed1992

Immunocytochemistry and immunoblotting of avian prolactins using polyclonal and monoclonal antibodies toward a synthetic fragment of chicken prolactin.

A major obstacle in the production of specific antibodies toward chicken prolactin (PRL) has been overcome by mimicking a putative epitope of the molecule using the synthetic decapeptide Lys-chPRL 59-67. This peptide represents the highest hydrophilicity peak of the amino acid sequence of chPRL that was recently derived from the nucleotide sequence. Polyclonal mouse antisera against the fragment specifically recognized the lactotropes in the cephalic lobe of the chicken pars distalis as illustrated by immunocytochemical double staining experiments. Monoclonal antibody production yielded antibodies that specifically labeled purified turkey PRL upon SDS-PAGE separation and immunoblotting. Turkey and chicken PRL showed a very similar polymorphism with respect to their apparent molecular weights, including the occurrence of a glycosylated variant of chicken PRL. The monoclonal antibodies were finally used to demonstrate the presence of PRL-like immunoreactivity both in the pituitary gland and in the brain of the quail. In the brain, immunoreactive neurons were in the nucleus accumbens and in the lateral parts of the ventro-medial hypothalamus, partly similar to those described in the rat.

Amino Acid Sequence↗

PubMed1992

Wounding acts as a tumor promoter in chickens inoculated with avian sarcoma virus 17.

Avian sarcoma virus 17 (ASV17) is an acutely transforming retrovirus which carries the oncogene v-jun. The virus induces fibrosarcomas in chickens at the site of inoculation. Here we describe wound-related tumor formation in 77% of chickens inoculated with ASV17 in one wing and wounded by metal clip insertion in the opposite wing. Tumors from both wound-related and inoculation-related sites were histologically diagnosed as fibrosarcomas. Tissues cultured from both tumor sites produced infectious virus in culture and expressed high levels of the v-Jun oncoprotein detectable by immunofluorescent staining. By varying the time of wounding relative to virus inoculation we defined the early stages of wound healing (2-7 days postinoculation) as favoring wound-related tumor formation. Three other acutely transforming retroviruses containing oncogenes coding for nonreceptor protein tyrosine kinases (v-src, v-yes, and v-fps), inoculated in the same manner, induced wound-related tumors in all cases. We conclude that in chickens, ASV17 collaborates with wound healing to promote tumorigenesis by a process which may relate either to a biochemical function of Jun or to a more general, shared characteristic of transforming retroviruses.

Animals↗

PubMed1991

A binding site for the cyclic adenosine 3',5'-monophosphate-response element-binding protein as a regulatory element in the grp78 promoter.

The 78-kDa glucose-regulated protein (GRP78) is ubiquitously expressed in many cell types. Its promoter contains multiple protein-binding sites and functional elements. In this study we examined a high affinity protein-binding site spanning bp -198 to -180 of the rat grp78 promoter, using nuclear extracts from both B-lymphoid and HeLa cells. This region contains a sequence TGACGTGA which, with the exception of one base, is identical to the cAMP-response element (CRE). Site-directed mutagenesis reveals that this sequence functions as a major basal level regulatory element in hamster fibroblast cells and is also necessary to maintain high promoter activity under stress-induced conditions. By gel mobility shift analysis, we detect two specific protein complexes. The major specific complex I, while immunologically distinct from the 42-kDa CRE-binding protein (CREB), binds most strongly to the grp site, but also exhibits affinity for the CRE consensus sequence. As such, complex I may consist of other members of the CREB/activating transcription factor protein family. The minor specific complex II consists of CREB or a protein antigenically related to it. A nonspecific complex III consists of the Ku autoantigen, an abundant 70- to 80-kDa protein complex in HeLa nuclear extracts. By cotransfection experiments, we demonstrate that in F9 teratocarcinoma cells, the grp78 promoter can be transactivated by the phosphorylated CREB or when the CREB-transfected cells are treated with the calcium ionophore A23187. The differential regulation of the grp78 gene by cAMP in specific cell types and tissues is discussed.

B-Lymphocytes↗

PubMed1989

Spontaneous and 5-azacytidine-induced revertants of methionine-dependent tumor-derived and H-ras-1-transformed cells.

Methionine dependence is a metabolic defect affecting several tumor-derived and transformed cell lines; it is defined as the inability of cells to grow in a medium where methionine has been depleted and replaced by its immediate metabolic precursor, homocysteine. This defect is acquired by normal epithelial Clone 9-3 cells upon transformation by the activated H ras-1 oncogene. We report that these H-ras-1-transformed cells (as well as some other tumor or transformed cells) spontaneously revert to methionine dependence at a high frequency. These revertants still express the H-ras-1 oncogene and retain their anchorage-independent growth: this reversion is thus not associated with a complete reversion to the normal phenotype. Furthermore, the reversion frequency is dramatically increased (up to 400-fold) by treatment of the cells with 5-azacytidine, a strong demethylating agent. Methionine dependence might thus be a consequence of hypermethylation of a critical gene involved in methionine metabolism and possibly in the methylation processes themselves.

Animals↗

PubMed1989

Inhibition of gap-junctional intercellular communication between epithelial cells transformed by the activated H-ras-1 oncogene.

In order to study the effects of an activated H-ras-1 oncogene on gap-junctional intercellular communication, we introduced the EJ/T24 H-ras-1 oncogene into cells of the epithelial Clone 9-3 cell line. Gap-junctional intercellular communication was significantly reduced in H-ras-1-transformed Clone 9-3 derivatives; this result shows that transformation by the activated H-ras-1 oncogene can inhibit gap-junctional intercellular communication. We postulate that the activated H-ras-1 oncogene product could mediate this effect through a change in the phosphorylation of the major gap-junction protein.

Animals↗

PubMed1988

Transforming activity of the human mammary line HBL100 DNA is associated with SV40 large T antigen genetic information integrated in its genome.

The HBL100 cell line, established in vitro from milk of an apparently healthy woman, expresses SV40 large T antigen defective in some of its functions. Here we demonstrate that the HBL100 genomic DNA possesses transforming activity in NIH3T3 cells and that this activity is associated with the viral information.

Antigens, Polyomavirus Transforming↗

PubMed1987

Methionine metabolism defect in cells transfected with an activated HRAS1 oncogene.

Methionine dependence is a metabolic defect characterized by the inability of eukaryotic cells in culture to proliferate in a medium where methionine has been replaced by its immediate metabolic precursor, homocysteine. This defect has been reported to be a specific property of diverse tumour-derived and transformed cell lines; normal cell strains grow well under the above culture conditions. The basis of methionine requirement in such cells is not known. We asked whether this defect might be controlled by activated oncogenes and in particular by the mutated (activated) HRAS1 oncogene derived from the EJ/T24 human carcinoma line. We report that this oncogene induces methionine requirement after transfection in non-transformed immortalized rat cells.

Animals↗