Biomedical subjects

R Versteeg

Publications and source records attributed to R Versteeg.

44 records · Page 3Linked to original sources

PubMed1991

Sensitivity of melanoma cell lines to natural killer cells: a role for oncogene-modulated HLA class I expression?

N-ras and c-myc oncogenes were found to be activated in melanoma. High c-myc expression renders melanoma cell lines sensitive to lysis by natural killer (NK) cells. This effect is mediated by locus-specific downmodulation of HLA-B expression by c-myc. Cell lines with a mutation in the N-ras gene were relatively sensitive to NK cells irrespective of HLA class I expression. These findings indicate that NK cells can kill tumor cells with activated myc or ras oncogenes in various ways, thus providing potential mechanisms to eliminate cancer cells with an activation of these oncogenes.

Blotting, Northern↗

PubMed1990

N-myc expression switched off and class I human leukocyte antigen expression switched on after somatic cell fusion of neuroblastoma cells.

Neuroblastomas often show amplification and high expression of the N-myc oncogene. N-myc expression could be explained as a consequence of gene amplification, but an alternative possibility is that expression primarily results from the inactivation or loss of some factor that normally represses the N-myc gene. To test this idea, we fused N-myc-overexpressing neuroblastoma cell lines with lines that do not express N-myc. In the resulting hybrids, N-myc expression turned out to be switched off, although amplified N-myc copies were still present. This suggests that N-myc overexpression in neuroblastomas results, at least in part, from the inactivation of a suppressor gene that is present in normal cells. In rat neuroblastomas, it has been found that N-myc can switch off class I major histocompatibility complex (MHC) expression. Therefore, we analyzed in our hybrid cells whether suppression of N-myc results in reexpression of human class I MHC genes. Because this was found to be the case, the picture emerges of a hierarchic pathway that connects a putative tumor-suppressor gene with the expression of N-myc and consequently of class I MHC, thus affecting the potential immunogenic properties of neuroblastomas.

Animals↗

PubMed1989

High expression of the c-myc oncogene renders melanoma cells prone to lysis by natural killer cells.

NK cells kill a wide variety of tumor cells, but usually leave normal cells intact. It was earlier reported that low class I HLA expression can be one of the factors that render target cells relatively susceptible to NK lysis. In this contribution, we show that in human melanomas the class I HLA expression is down-modulated by high expression of transfected c-myc oncogenes. The extent of down-modulation depended on the level of c-myc expression in a dose-dependent way. Taken together, these data suggested to us that one of the results of high c-myc expression could be the induction of a NK susceptible phenotype in melanoma cells. Therefore, we analyzed the effect of c-myc on NK susceptibility. We have found that high expression of transfected c-myc genes indeed converts the melanoma cell lines from poor into good targets for NK cells. IFN-gamma was used to restore the class I HLA expression of the c-myc transfectants, and the resulting cells showed a decreased NK susceptibility. These results suggest the possibility that the c-myc-induced NK susceptibility is mediated by the reduction of class I HLA expression.

Cell Line↗

PubMed1989

Suppression of class I human histocompatibility leukocyte antigen by c-myc is locus specific.

The c-myc oncogene downregulates class I HLA expression in human melanoma. The major class I HLA antigens are encoded by three loci, A, B, and C, and we investigated whether these loci are suppressed equally by c-myc. In three melanoma cell lines with high c-myc expression, we analyzed mRNA, protein, and cell surface expression of the class I HLA antigens. Whereas the HLA-B locus expression was found to be strongly reduced, the HLA-A locus was expressed normally. Analysis of c-myc-transfected clones of two melanoma cell lines confirmed that c-myc preferentially suppresses the class I HLA-B locus. Immunohistochemical analysis of fresh melanoma lesions also showed that in the tumors the HLA-A loci are expressed normally, while on the majority of tumor cells no HLA-B antigen expression was found. This downregulation may have consequences for the recognition of malignant cells by tumor-infiltrating lymphocytes. Our results predict that HLA-B-restricted cytotoxic T cells will be unable to kill high c-myc-expressing melanoma cells.

Alleles↗

PubMed1989

N-ras mutations in human cutaneous melanoma from sun-exposed body sites.

In 7 of 37 patients with cutaneous melanoma, mutations in the N-ras gene were found. The primary tumors of these seven patients were exclusively localized on body sites continuously exposed to sunlight. Moreover, the ras mutations were all at or near dipyrimidine sites known to be targets of UV damage. Two primary tumors were biclonal with respect to ras mutation. An active role for UV irradiation in induction of the mutations is suggested.

DNA, Neoplasm↗

PubMed1988

c-myc down-regulates class I HLA expression in human melanomas.

Expression of class I HLA antigen has been shown to be reduced in a number of human tumours. Here we show that in a panel of 11 melanoma cell lines with variable class I HLA expression an inverse correlation exists between the mRNA levels of c-myc and class I HLA. This suggests that high expression of the c-myc oncogene might inhibit the class I HLA expression. To test this hypothesis a melanoma cell line with a low c-myc and high class I HLA mRNA expression was transfected with a c-myc expression vector. All clones expressing the transfected c-myc gene show reduced class I HLA mRNA and beta 2-microglobulin mRNA expression. Reduced class I HLA mRNA levels result in a lowered class I protein expression on the cell surface. Treatment with gamma-interferon fully restores the class I HLA and beta 2-microglobulin expression in these cells. This effect is preceded by a transient decrease of the c-myc mRNA level. These results show that the class I HLA expression is modulated by the level of c-myc expression, thus opening up the possibility that high expression of this oncogene influences the interaction of melanoma cells with the immune system.

Gene Expression Regulation↗

PubMed1984

Cloning a cDNA for the lysosomal alpha-glucosidase.

Messenger RNA was isolated from monkey testes and size-fractionated on sucrose gradients. In vitro translation of these mRNA fractions resulted in nascent, labeled alpha-glucosidase that could be precipitated with anti human alpha-glucosidase antiserum. A cDNA library was constructed from the most enriched fraction. The library was screened with cDNA made from mRNA obtained from immunoselected polysomes. Five cross-hybridizing clones were isolated and identified by their selection of alpha-glucosidase mRNA, as shown by hybrid released translation and further by their ability to hybridize with DNA from human chromosome 17, on which the gene coding for acid alpha-glucosidase is located.

Animals↗

PubMed1983

Genes and regulatory sequences of bacteriophage phi X174.

Fragments of the DNA of bacteriophage phi X174 were inserted in the plasmids pACYC177 and pBR322, in order to test the in vivo effects of separate phage genes and regulatory sequences. The phi X174 inserts were identified by recombination and complementation with phage mutants, followed by restriction enzyme analysis. The genes B, C, F and G can be maintained stably in the cell even when there is efficient expression of these viral genes. Recombinant plasmids with the complete genes D and E can only be maintained when the expression of these genes is completely blocked. Expression of complete H and J genes could not yet be demonstrated. The intact gene A was apparently lethal for the host cell, as it was never found in the recombinants. The genes F and G are expressed, even when they are not preceded by one of the well characterized viral or plasmid promoter sequences. Screening of the nucleotide sequence of phi X174 gives two promoter-like sequences just in front of the two genes. Viral sequences with replication signals (the phi X174 (+) origin of replication, the initiation site for complementary strand synthesis and the incompatibility sequence) appeared to be functional also when inserted in recombinant plasmids. A plasmid with the phi X (+) origin can be forced to a rolling circle mode of replication. The A protein produced by infecting phages works in trans on the cloned viral origin. The (-) origin can function as initiation signal for complementary strand synthesis during transduction of single-stranded plasmid DNA. The intracellular presence of the incompatibility sequence on a plasmid prevents propagation of infecting phages.

Bacteriophage phi X 174↗