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L van der Voorn

Publications and source records attributed to L van der Voorn.

9 recordsLinked to original sources
PubMed1994

Platelet-derived growth factor-induced p21ras-mediated signaling is independent of platelet-derived growth factor receptor interaction with GTPase-activating protein or phosphatidylinositol-3-kinase.

Stimulation with platelet-derived growth factor (PDGF) results in the association of several SH2 domain-containing proteins with the activated PDGF receptor, including GAP, a GTPase-activating protein of p21ras, and phosphatidylinositol-3-kinase (PI-3K). To investigate the role of GAP-PI-3K receptor interaction in p21ras signaling, we have used cell lines expressing mutant PDGF receptors that either are impaired in GAP binding or fail to bind both GAP and PI-3K. In these cell lines, PDGF treatment resulted in activation of extracellular signal-regulated kinase 2 (ERK2), which could be blocked by the expression of a dominant-negative mutant of p21ras (p21ras(asn17)), indicating that these mutations in the PDGF receptor do not abolish p21ras-mediated activation of ERK2. In addition, the PDGF-induced increase in levels of p21rasGTP, as measured either in intact cells or in permeabilized cells, appears to be normal in the cell lines expressing the mutant PDGF receptors. These results indicate that binding of GAP and/or PI-3K to the PDGF receptor is not necessary for PDGF-induced p21ras activation and p21ras-mediated signaling to ERK2. We also show that, in contrast to the activation of ERK2, PDGF-induced GAP and PI-3K interaction with the PDGF receptor are not inhibited by p21ras(asn17) expression, indicating that these interactions do not require p21ras activation.

Animals↗
PubMed1993

Structural and functional studies on the G(o) protein.

Monoclonal antibodies were raised against purified bovine and human brain G-proteins. The epitopes recognized by three monoclonal antibodies (MONO, 3C2, and 3E7) were mapped by expressing defined parts of the bovine G(o) alpha-cDNA in bacteria, followed by immunoblotting. All three antibodies recognize the recombinant bovine alpha o-protein, but at distinct sites. The epitopes of MONO and 3C2 were mapped between alpha o amino acids 80 and 145, and both antibodies recognize alpha o exclusively. Heterotrimeric G(o)-proteins as well as guanosine 5'-3-O-(thio)triphosphate-liganded free alpha o-subunits are readily immunoprecipitated by these monoclonal antibodies. Binding of MONO or 3C2 does not affect ADP-ribosylation of the alpha o-subunit by pertussis toxin. Apparently, the antibodies do not bind to or induce large conformational changes in regions of the alpha o-subunit that are involved in association with beta gamma-subunits or ADP-ribosylation. 3E7 behaves as an anti common alpha-subunit antibody when used in immunoblots. However, under nondenaturing conditions, 3E7 recognizes alpha o exclusively. After binding of 3E7, the pertussis toxin-dependent ADP-ribosylation of alpha o is effectively blocked, while the ADP-ribosylation of the various alpha i-subunits is not affected. The epitope of 3E7 was mapped between alpha o amino acids 13-88, a region which has been implicated in the interaction between alpha- and beta gamma-subunits. Possibly, the inhibitory effect of 3E7 on ADP-ribosylation of G(o) is secondary to the loss of beta gamma-subunits that is observed upon binding of 3E7.

Adenosine Diphosphate Ribose↗
PubMed1992

Subunit interactions of the Go protein.

The monoclonal antibody, MONO, recognizes an epitope on the G protein alpha o-subunit [van der Voorn et al., submitted] and readily immunoprecipitates heterotrimeric Go proteins from solubilized, crude bovine brain membranes, as well as from a purified bovine brain G protein preparation. Upon incubation of the immunoprecipitates with GTP gamma S, all beta gamma-subunits are released from the alpha o-subunit. Thus, binding of MONO to the Go protein does not appear to interfere with release of bound GDP, binding of GTP gamma S or GTP gamma S-induced subunit dissociation. However, we have been unable to induce a similar dissociation of Go using its physiological activator, GTP. Surprisingly, we did not observe any dissociation of Go (bound to MONO) upon dilution in a range from 500 to 5 nM. Since an apparent Kd of alpha o-GDP for binding beta gamma of 340-390 nM has been reported [(1989) J. Biol. Chem. 264, 20688-20696] our results would suggest that binding of MONO to the alpha o-subunit induces an increased affinity of alpha o-GDP for beta gamma. Alternatively, these results could be explained if, under the conditions used, the Kd of alpha o-GDP for beta gamma were at least two orders of magnitude lower than estimated previously.

Animals↗
PubMed1992

The WD-40 repeat.

An amino acid sequence motif, called the WD-40 repeat, has been found as a repeat in a large variety of proteins that do not share any obvious functional properties. At present, the function of the repeated motif is not known for any of these proteins. Interestingly, recent experiments in yeast indicate that several proteins containing the WD-40 repeat are genetically associated with members of the TPR-family, a protein family that is characterized by the presence of another repeated motif of unknown function: the tetratricopeptide repeat. It is conceivable that proteins containing the WD-40 repeat interact physically with members of the TPR-family via their respective repeated motifs.

Amino Acid Sequence↗
PubMed1990

Characterization of a G-protein beta-subunit gene from the nematode Caenorhabditis elegans.

The gene encoding the beta-subunit of guanine nucleotide binding regulatory proteins (G-proteins) has been cloned from the nematode Caenorhabditis elegans. The predicted 340 amino acid sequence matches the highly conserved amino acid sequences of previously isolated G-protein beta-subunits from mammals and Drosophila. The coding region of the C. elegans beta-subunit gene, which has been mapped to the C. elegans chromosome II, is interrupted by eight introns. Southern analysis indicates that C. elegans has only one beta-subunit gene. A 2.8 kb (1 kb = 10(3) bases or base-pairs) transcript derived from this gene could be detected.

Amino Acid Sequence↗
PubMed1986

One adenosine deaminase allele in a patient with severe combined immunodeficiency contains a point mutation abolishing enzyme activity.

We have cloned and sequenced an adenosine deaminase (ADA) gene from a patient with severe combined immunodeficiency (SCID) caused by inherited ADA deficiency. Two point mutations were found, resulting in amino acid substitutions at positions 80 (Lys to Arg) and 304 (Leu to Arg) of the protein. Hybridization experiments with synthetic oligonucleotide probes showed that the determined mutations are present in both DNA and RNA from the ADA-SCID patient. In addition, wild-type sequences could be detected at the same positions, indicating a compound heterozygosity. Studies with ADA expression clones mutagenized in vitro showed that the mutation at position 304 is responsible for ADA inactivation.

Adenosine Deaminase↗
PubMed1985

Adenosine deaminase: characterization and expression of a gene with a remarkable promoter.

Cosmid clones containing the gene for human adenosine deaminase (ADA) were isolated. The gene is 32 kb long and split into 12 exons. The exact sizes and boundaries of the exon blocks including the transcription start sites were determined. The sequence upstream from this cap site lacks the TATA and CAAT boxes characteristic for eukaryotic promoters. Nevertheless, we have shown in a functional assay that a stretch of 135 bp immediately preceding the cap site has promoter activity. This 135-bp DNA fragment is extremely rich in G/C residues (82%). It contains three inverted repeats that allow the formation of cruciform structures, a 10-bp and a 16-bp direct repeat and five G/C-rich motifs (GGGCGGG) disposed in a strikingly symmetrical fashion. Some of these structural features were also found in the promoter region of other genes and we discuss their possible function. Knowledge of the exact positions of the intron-exon boundaries allowed us to propose models for abnormal RNA processing that occurs in previously investigated ADA-deficient cell lines.

Adenosine Deaminase↗