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Biomedical subjects

T Velu

Publications and source records attributed to T Velu.

At least 91 records · Page 5Linked to original sources
PubMed1991

The biological activity of the human epidermal growth factor receptor is positively regulated by its C-terminal tyrosines.

The epidermal growth factor receptor (EGF-R) C-terminus contains three conserved tyrosines (Y-1068, Y-1148, Y-1173) which are phosphorylated upon EGF activation. To clarify the functional role of these tyrosines, each has been mutated to phenylalanine and studied as single, double and triple mutants in the full length receptor. EGF-dependent transforming ability of the single point mutants is similar to that of the wild type, while that of double mutants is decreased and an even lower activity is present in the triple mutant. In each bioassay, including EGF-dependent focal transformation, growth in agar and growth in low serum, mutant receptors display a similar hierarchy of activity. The lower activity is intrinsic in the mutants since they are expressed at similar level as the wild type and bind EGF with similar affinity. Deletion mutants lacking the last 19 or 63 amino acids (Velu et al., 1989a) show a similar decline in biological activity when compared to the corresponding point mutants, although the reduction is more pronounced than with the point mutants. Deletion of the last 123 aa, which removes all three tyrosines (Dc123), results in a receptor that is almost inactive biologically. The EGF-R kinase activity is affected by tyrosine substitution since in vitro phosphorylation of exogenous substrates is reduced in the double and triple mutants. Autophosphorylation, in vivo and in vitro, is also reduced, but not totally abolished in the triple point mutant and Dc123 indicating the existence of other autophosphorylation sites. A new site of autophosphorylation is found in the Dc123 mutant. We conclude, therefore, that the tyrosines at the extreme C-terminus positively regulate the biological and transforming activity of the EGF-R, probably via autophosphorylation.

Animals↗
PubMed1990

Over-expression of the epidermal growth factor receptor in human breast cancer cells fails to induce an estrogen-independent phenotype.

An association exists in primary human breast tumors between high epidermal growth factor receptor (EGFR) expression and a reduced number or even absence of estrogen receptors (ER). To determine whether an increase in EGFR expression might alter the estrogen responsiveness of an ER-positive human breast cancer cell line, ZR 75-1 cells were cotransfected with a plasmid containing the full-length cDNA for the human EGFR under the transcriptional control of the Harvey murine sarcoma virus (HaMSV) long terminal repeat (LTR) and with a pSV2neo plasmid. Two of the isolated G418-resistant clones were found to constitutively express EGFR levels 15- to 60-fold higher than those found on nontransfected ZR 75-1 cells. The EGFR in these clones were functionally normal since EGF could increase their autophosphorylation and since EGF could enhance the transphosphorylation of p185erbB-2. No change was seen in either the number or affinity of ER in these clones. In addition, the ability of estrogen to stimulate the anchorage-dependent and anchorage-independent growth of these clones was not significantly modified. These results suggest that an increase in EGFR expression alone is not sufficient to induce a hormone-independent phenotype in vitro in human breast cancer cells.

Blotting, Northern↗
PubMed1990

Effects of substitution of threonine 654 of the epidermal growth factor receptor on epidermal growth factor-mediated activation of phospholipase C.

Addition of epidermal growth factor (EGF) to many cell types activates phospholipase C resulting in increased levels of diacylglycerol and intracellular Ca2+ which may lead to activation of protein kinase C. EGF treatment of cells can also lead to phosphorylation of the EGF receptor at threonine 654 (a protein kinase C phosphorylation site) which appears to attenuate some aspects of receptor signaling. Thus, a feedback loop involving the EGF receptor, phospholipase C, and protein kinase C may regulate EGF receptor function. In this report, the role of phosphorylation of threonine 654 of the EGF receptor in regulation of EGF-stimulated activation of phospholipase C was investigated. NIH-3T3 cells expressing the normal human EGF receptor or expressing EGF receptor in which an alanine residue had been substituted at residue 654 of the receptor were used. Addition of EGF to cells expressing wild-type receptor induced a rapid, but transient, increase in phosphorylation of threonine 654. EGF addition also caused the rapid accumulation of inositol phosphates in these cells. EGF-stimulated accumulation of inositol phosphates was significantly higher in cells expressing Ala-654 receptors compared to control cells. Treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA), which stimulated phosphorylation of threonine 654 to a greater degree than EGF, completely inhibited EGF-dependent inositol phosphate accumulation in cells expressing wild-type receptor, but caused only a 20-30% inhibition in Ala-654 expressing cells. EGF stimulated phosphorylation of phospholipase C-gamma on serine and tyrosine residues in cells expressing wild-type of Ala-654 receptors. However, TPA treatment of cells inhibited EGF-induced tyrosine phosphorylation of phospholipase C-gamma only in cells expressing wild-type receptors. Similarly, TPA inhibited tyrosine-specific autophosphorylation of the EGF receptor and tyrosine phosphorylation of several other proteins in wild-type receptor cells, but not in Ala-654 cells. TPA treatment abolished high affinity binding of EGF to cells expressing wild-type receptors, while decreasing the number of high affinity binding sites 20-30% in Ala-654 cells. These data suggest that phosphorylation of threonine 654 can regulate early events in EGF receptor signal transduction such as phosphoinositide turnover, probably through a feedback mechanism involving protein kinase C. Subsequent dephosphorylation of threonine 654 could reactivate the EGF receptor for participation in later signaling events.

Animals↗
PubMed1990

[Molecular and diagnostic genetics].

Using the recent developments of molecular biology techniques, our laboratory is offering carrier and prenatal diagnosis for a variety of genetic disorders including cystic fibrosis, phenylketonuria, thalassaemia alpha and beta, sickle cell anaemia, myotonic dystrophy, von Recklinghausen's disease, autosomal polycystic kidney disease, haemophilia A and B, Martin-Bell syndrome (fragile X), Becker and Duchenne muscular dystrophy, etc. It is likely that the rapid advances made in the establishment of the human genetic map will considerably expand the spectrum of diseases for which diagnosis by molecular genetics will become available.

Genetic Carrier Screening↗
PubMed1989

High level expression of p55, a thyroid hormone binding protein which is homologous to protein disulfide isomerase in a retroviral vector.

To develop an efficient system for a high level expression of a human cellular thyroid hormone binding protein (p55) in eukaryotic cells, a full-length p55 cDNA was inserted into a Harvey murine sarcoma virus-derived vector (pHTBr) and transfected into mouse NIH 3T3 cells. The expressed p55 has a molecular weight of 55,000 and is recognized by the human specific anti-p55 monoclonal antibody. Similar to the endogenous p55, the expressed p55 is localized on endoplasmic reticulum and nuclear envelope. Moreover, p55 was specifically labeled by N-bromoacetyl-3,3',5-triiodo-L-thyronine. Thus, the expressed p55 is structurally indistinguishable from the endogeneous p55. pHTBr was packaged into a virus with the aide of an amphotropic virus. Infection by pHTBr-containing virus yielded a 2-11 fold higher expression than the endogeneous p55 in NIH3T3, rat GH3, human HepG2 cells and a mouse monoclonal antibody secreting hybridoma.

Affinity Labels↗
PubMed1989

Signal transduction in hamster fibroblasts overexpressing the human EGF receptor.

Human EGF receptors (HERs) were expressed in CCL39 hamster fibroblasts, a cell line responding only weakly to EGF despite the presence of 10-20,000 EGF receptors per cell. High expression of HERs (800,000 per cell) conferred EGF responsiveness. In these cells EGF is a potent mitogen, induces strong receptor autophosphorylation, phosphorylation of cellular substrates on tyrosine, activates the Na+/H+ exchanger, and weakly stimulates phosphoinositide (PI) turnover. Activation of PI turnover by a mitogen activating a receptor tyrosine kinase has not been observed previously in CCL39 cells. We present evidence, however, that the activation of this signaling pathway which is insensitive to pertussis toxin does not mediate the proliferative response. Unlike NIH 3T3 cells, CCL39 fibroblasts overexpressing HERs are not transformed nor can a transformed phenotype be observed in response to EGF or TGF alpha.

Animals↗
PubMed1988

Daunorubicin in patients with relapsed and refractory acute nonlymphoblastic leukemia previously treated with anthracycline.

While the efficacy of daunorubicin (DNR) in first induction of patients with acute nonlymphoblastic leukemia (ANLL) has been well documented, little data are available concerning the activity of DNR in patients with relapsed and refractory ANLL previously treated with anthracycline. We administered DNR (60 mg/m2/day for 3-5 days) in 21 patients with relapsed (n = 12) or refractory (n = 9) ANLL previously treated with anthracycline. The general response rate was 48%, with a complete response (CR) rate of 38%. Five of 12 patients with relapsed ANLL and 3 of 9 patients with refractory ANLL achieved CR. Among these cases with CR in refractory ANLL, the evolution of one patient is particularly illustrative since he had received previously a large cumulative dose of anthracycline (540 mg/m2) and has been shown to be refractory to high-dose cytosine arabinoside. This study suggests that previous administration of DNR or adriamycin does not induce significant resistance to anthracycline: DNR appears to be almost as efficient in patients with relapsed and refractory ANLL previously treated with anthracycline as in first induction.

Acute Disease↗
PubMed1985

Therapeutic effect of human recombinant interferon-alpha-2C in essential thrombocythaemia.

Human recombinant interferon-alpha 2C was given to 4 patients with essential thrombocythaemia. Three patients achieved a complete remission on day 19 +/- 1 and the 4th achieved a partial remission. After 4 weeks of induction therapy, a maintenance therapy of twice weekly intramuscular injections of 5 X 10(6) or 10 X 10(6) IU was instituted but did not maintain the remission.

Aged↗