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Biomedical subjects

I Lax

Publications and source records attributed to I Lax.

At least 37 records · Page 2Linked to original sources
PubMed1998

Disulfide bond structure of human epidermal growth factor receptor.

The extracellular domain of the human epidermal growth factor receptor (sEGFR) consists of 621 amino acid residues, including 50 cysteines. The connections of the 25 disulfide bonds in the recombinant sEGFR protein, obtained from Chinese hamster ovary cells, have been determined using N-terminal sequencing and matrix-assisted laser desorption/ionization mass spectroscopy. We identified a basic repeat of eight cysteines with a 1-3, 2-4, 5-6, and 7-8 disulfide pairing pattern in the two cysteine-rich regions of sEGFR. By comparison to other cysteine-rich motifs, it was concluded that the cysteine-rich repeat of sEGFR belongs to the laminin-type EGR-like (LE) structural motif. Three-dimensional structure models of the two cysteine-rich regions have been built, based on the three-dimensional structures of the LE domains from the laminin gamma1 chain and secondary structure predictions for the EGF receptor.

Amino Acid Sequence↗
PubMed1998

Prediction of excess risk of long-term cardiac mortality after radiotherapy of stage I breast cancer.

BACKGROUND AND PURPOSE: Excess cardiac mortality has been reported in long-term follow up of breast cancer patients. Due to these findings it has been emphasized that radiotherapy techniques should be designed to minimize cardiac dose. The present study aims to provide risk figures of long-term excess cardiac mortality following radiotherapy for stage I breast cancer patients, using the relative seriality model. The impact of different modifications of the conventional irradiation technique on the calculated risk value is also analyzed. MATERIAL AND METHODS: One hundred consecutive left-sided stage I breast cancer patients were selected. All patients were treated with post-operative radiotherapy, using tangential 6 MV photon beams. The dose planning of each patient was done by means of a three-dimensional dose planning system. The prescribed mean tumor dose was 50 Gy, 2 Gy/fraction, 5 days a week. For each dose plan the differential heart and myocardium dose-volume histogram (DVH) were calculated. The excess risk of late cardiac mortality was predicted for each patient with the relative seriality model, using a parameter set previously determined. Different methods to decrease the risk of excess cardiac mortality (conventional collimation vs. multileaf collimation (MLC), partial blocking of the target in order to spare the heart and finally a general fluence modulation method) were analyzed. RESULTS AND CONCLUSIONS: The mean value of the calculated excess risk was 1.8%, having the heart as organ at risk, and 2.1% having the myocardium as organ at risk. However, a subgroup of patients where the risk increased up to about 9% (heart) and 12% (myocardium) was found. The risk could be substantially decreased either using an extended blocking of the target or applying the general fluence modulation method.

Breast Neoplasms↗
PubMed1998

Binding of Shp2 tyrosine phosphatase to FRS2 is essential for fibroblast growth factor-induced PC12 cell differentiation.

FRS2 is a lipid-anchored docking protein that plays an important role in linking fibroblast growth factor (FGF) and nerve growth factor receptors with the Ras/mitogen-activated protein (MAP) kinase signaling pathway. In this report, we demonstrate that FRS2 forms a complex with the N-terminal SH2 domain of the protein tyrosine phosphatase Shp2 in response to FGF stimulation. FGF stimulation induces tyrosine phosphorylation of Shp2, leading to the formation of a complex containing Grb2 and Sos1 molecules. In addition, a mutant FRS2 deficient in both Grb2 and Shp2 binding induces a weak and transient MAP kinase response and fails to induce PC12 cell differentiation in response to FGF stimulation. Furthermore, FGF is unable to induce differentiation of PC12 cells expressing an FRS2 point mutant deficient in Shp2 binding. Finally, we demonstrate that the catalytic activity of Shp2 is essential for sustained activation of MAP kinase and for potentiation of FGF-induced PC12 cell differentiation. These experiments demonstrate that FRS2 recruits Grb2 molecules both directly and indirectly via complex formation with Shp2 and that Shp2 plays an important role in FGF-induced PC12 cell differentiation.

3T3 Cells↗
PubMed1997

A lipid-anchored Grb2-binding protein that links FGF-receptor activation to the Ras/MAPK signaling pathway.

Activation of the Ras/MAPK signaling cascade is essential for growth factor-induced cell proliferation and differentiation. In this report, we describe the purification, cloning, and characterization of a novel protein, designated FRS2, that is tyrosine phosphorylated and binds to Grb2/Sos in response to FGF or NGF stimulation. We find that FRS2 is myristylated and that this modification is essential for membrane localization, tyrosine phosphorylation, Grb2/Sos recruitment, and MAPK activation. FRS2 functions as a lipid-anchored docking protein that targets signaling molecules to the plasma membrane in response to FGF stimulation to link receptor activation with the MAPK and other signaling pathways essential for cell growth and differentiation. Finally, we demonstrate that FRS2 is closely related and probably indentical to SNT, the long-sought target of FGF and NGF receptors.

3T3 Cells↗
PubMed1997

Kit receptor dimerization is driven by bivalent binding of stem cell factor.

Most growth factors and cytokines activate their receptors by inducing dimerization upon binding. We have studied binding of the dimeric cytokine stem cell factor (SCF) to the extracellular domain of its receptor Kit, which is a receptor tyrosine kinase similar to the receptors for platelet-derived growth factor and colony-stimulating factor-1. Calorimetric studies show that one SCF dimer binds simultaneously to two molecules of the Kit extracellular domain. Gel filtration and other methods show that this results in Kit dimerization. It has been proposed that SCF-induced Kit dimerization proceeds via a conformational change that exposes a key receptor dimerization site in the fourth of the five immunoglobulin (Ig)-like domains in Kit. We show that a form of Kit containing just the first three Ig domains (Kit-123) binds to SCF with precisely the same thermodynamic parameters as does Kit-12345. Analytical ultracentrifugation, light scattering, and gel filtration show that Kit-123 dimerizes upon SCF binding in a manner indistinguishable from that seen with Kit-12345. These data argue that the fourth Ig-like domain of Kit is not required for SCF-induced receptor dimerization and provide additional support for a model in which bivalent binding of the SCF dimer provides the driving force for Kit dimerization.

Chromatography, Gel↗
PubMed1997

Two EGF molecules contribute additively to stabilization of the EGFR dimer.

Receptor dimerization is generally considered to be the primary signaling event upon binding of a growth factor to its receptor at the cell surface. Little, however, is known about the precise molecular details of ligand-induced receptor dimerization, except for studies of the human growth hormone (hGH) receptor. We have analyzed the binding of epidermal growth factor (EGF) to the extracellular domain of its receptor (sEGFR) using titration calorimetry, and the resulting dimerization of sEGFR using small-angle X-ray scattering. EGF induces the quantitative formation of sEGFR dimers that contain two EGF molecules. The data obtained from the two approaches suggest a model in which one EGF monomer binds to one sEGFR monomer, and that receptor dimerization involves subsequent association of two monomeric (1:1) EGF-sEGFR complexes. Dimerization may result from bivalent binding of both EGF molecules in the dimer and/or receptor-receptor interactions. The requirement for two (possibly bivalent) EGF monomers distinguishes EGF-induced sEGFR dimerization from the hGH and interferon-gamma receptors, where multivalent binding of a single ligand species (either monomeric or dimeric) drives receptor oligomerization. The proposed model of EGF-induced sEGFR dimerization suggests possible mechanisms for both ligand-induced homo- and heterodimerization of the EGFR (or erbB) family of receptors.

Animals↗
PubMed1997

Factors influencing the risk for complications following Gamma Knife radiosurgery of cerebral arteriovenous malformations.

BACKGROUND AND PURPOSE: We reported previously a model predicting the risk for radiation-induced complications following Gamma Knife radiosurgery for AVM. No factor other than the dose distribution was related to the risk. The aim of this study was to define if other parameters are of importance for the risk of complications. MATERIAL AND METHODS: The model above was used to calculate the risk for complications in all 1128 AVM patients Gamma Knife-treated at the Karolinska Hospital 1970-1993. The number of predicted complications was compared to the number of observed ones for a number of different parameters. RESULTS: The model underestimated the risk of complications for patients previously given radiation with multiple or single fractions. Neither age nor gender influenced the risk of complications. Centrally located AVM had a higher, and peripheral a lower incidence of complications as compared to the calculated risk, and a previous hemorrhage reduced the risk of complications. From the observed number of complications, parameters in the model were determined by a fitting procedure separately for three groups of AVM: central and peripheral with and without a previous hemorrhage. It is also shown that the assumption of a serial functional architecture is valid in the model. This was investigated by the use of a relative seriality model with a combined serial-parallel functional architecture. CONCLUSIONS: The risk of complications following radiosurgical treatment of AVM is dependent on the clinical history, AVM location and whether the patient has received radiation earlier.

Adolescent↗
PubMed1997

Procedure for accurate fabrication of tissue compensators with high-density material.

An accurate method for producing compensating filters using high-density material (Cerrobend) is described. The procedure consists of two cutting steps in a Styrofoam block: (i) levelling a surface of the block to a reference level; (ii) depth-modulated milling of the levelled block in accordance with pre-calculated thickness profiles of the compensator. The calculated thickness (generated by a dose planning system) can be reproduced within acceptable accuracy. The described compensator thickness manufactured according to this procedure is reproduced to within 0.1 mm, corresponding to a 0.5% change in dose at a beam quality of 6 MV. The results of our quality control checks performed with the technique of stylus profiling measurements show an accuracy of 0.04 mm (1 sigma) in the milling process over an arbitrary profile along the milled-out Styrofoam block.

Equipment Design↗
PubMed1997

Ligand-binding enhances the affinity of dimerization of the extracellular domain of the epidermal growth factor receptor.

We studied the dimerization of the recombinant soluble extracellular domain of the epidermal growth factor receptor (sEGFR) in response to EGF-binding using multi-angle laser light scattering with size exclusion chromatography (SEC-MALLS). In the absence of EGF, sEGFR behaved as a monomer. However, upon EGF-binding, sEGFR formed a dimer with the stoichiometry of two EGF molecules bound to two sEGFR molecules [(EGF)2-(sEGFR)2]. We analyzed the chemical equilibrium of the dimer formation by SEC-MALLS using a dissociation constant of 0.25 microM for the binding of EGF to sEGFR. The calculated dissociation constant for EGF-induced sEGFR dimerization was found to be 2.4 +/- 0.9 microM. These experiments demonstrated that EGF induces receptor dimerization and that two EGF molecules are bound to an EGF-receptor dimer.

Binding Sites↗
PubMed1997

Radiosurgical lesions in the normal human brain 17 years after gamma knife capsulotomy.

OBJECTIVE: To our knowledge, this is the first long-term follow-up study of high-dose single-session irradiation to the human brain and provides new data concerning late tissue reactions after irradiation to small target volumes. The long-term lesional brain changes in 14 patients subjected to bilateral gamma knife capsulotomy for otherwise intractable anxiety disorders were retrospectively analyzed by magnetic resonance imaging. METHODS: The prototype gamma unit was used for the radiosurgical procedure, and the collimators provided rectangular cross-sectional fields with an anteroposterior diameter of 3 mm and a transverse diameter of 5 or 11 mm. Maximum target doses were 120 to 180 Gy. Magnetic resonance imaging was performed 15 to 18 years (mean, 17 yr) after treatment, and dose-volume histograms were calculated for the dose distributions. RESULTS: One patient had been irradiated twice on one side. In all but one of the remaining 27 targets, lesions with a volume of less than 100 mm3 were revealed by magnetic resonance imaging. The volumes of the lesions were confined within the volume corresponding to a minimum dose of approximately 110 Gy, with one exception. In one of three targets receiving a maximum dose of 120 Gy, no lesion was detected. There were no late radiation effects such as cyst formations, telangiectasias, hemorrhagic infarctions, or neoplasms. CONCLUSION: This investigation indicates that a minimum dose of 110 Gy, with the currently used 4-mm collimator, to the edge of the target volume is required to create a lesion. The results prove that gamma knife surgery can be used in functional neurosurgery for producing small permanent lesions in the normal human brain.

Adult↗
PubMed1997

Tumour cell proliferation after failed ruthenium plaque radiotherapy for posterior uveal melanoma.

Enucleation following ruthenium plaque radiotherapy for posterior uveal melanoma indicates failure of treatment. This study focused on the histopathological findings and remaining tumour cell growth fraction in 42 of 46 patients with failed ruthenium plaque treatment (of 266 patients treated) for melanoma of the choroid or ciliary body. The cause for enucleation was clinically detected tumour regrowth in 27 (64%) patients, treatment-related ocular side effects in 12 (29%) cases and the patient's personal preference in three (7%) cases. The median time elapsing from plaque radiotherapy to enucleation was not significantly different for patients with recurrent tumour growth (23 months) compared to those enucleated without clinical signs of regrowth (19 months). While all tumours showed some regressive features by histopathological examination, only five melanomas were completely necrotic and viable-appearing tumours cells were present in all of the remaining 37 (88%) irradiated tumours. Microwave processed PC-10 immunostainings increased the sensitivity to detect cycling cells compared to the sole use of mitotic cell counts. By the former technique, proliferating tumour cells were detected in 17 of 23 (74%) studied melanomas of eyes enucleated for tumour regrowth following brachytherapy. Also, the number of cycling melanoma cells was similar to that of non-irradiated controls managed solely by enucleation. In contrast, the proliferative compartments of irradiated, but non-recurrent, posterior uveal melanomas were significantly reduced compared to those of matched controls. Still, cycling tumour cells were present in four of 13 (31%) irradiated melanomas, clinically assumed to be successfully treated.

Adult↗
PubMed1997

Results following episcleral ruthenium plaque radiotherapy for posterior uveal melanoma. The Swedish experience.

The Swedish experience of ruthenium 106 plaque radiotherapy for posterior uveal melanoma includes 266 patients treated between 1979 and 1995. The median dose delivered at the tumour apex was 100 Gy and the median follow-up after radiotherapy was 3.6 years (range = 0.5 to 12.5 years) with no patient being lost to follow-up. Visual acuity deteriorated moderately following treatment but appeared to stabilize after 5 to 6 years. Treatment failure defined as enucleation following plaque treatment occurred in 46 of the 266 (17%) studied patients. The cumulative 5-year probability of retaining the eye after radiotherapy was 82% and by univariate analysis tumour height, tumour diameter and tumour stage each predicted subsequent treatment failure, whereas in multivariate analysis no single covariate retained a predictive value. Forty-five of the 266 patients died of any cause during follow-up; 27 of these deaths were melanoma-related. The cumulative 5-year survival proportion (based on melanoma-related deaths only) was 86%. Death in metastatic disease appeared to be more common among patients that failed ruthenium plaque radiotherapy, however these patients also tended to have large tumours.

Adult↗
PubMed1997

Evaluation of irradiated heart volumes in stage I breast cancer patients treated with postoperative adjuvant radiotherapy.

PURPOSE: To quantify the proportion of heart volumes that received at least 25 Gy with tangential photon fields in patients with left-sided stage I (T1 NOMO) breast cancer treated with breast-conserving surgery. METHODS AND MATERIALS: The dose planning of 100 consecutive patients was reviewed. All were irradiated with tangential photon fields that covered the left breast only. A three-dimensional computed tomographic (CT)-based dose planning was made for each patient. The prescribed dose to the tumor was 50 Gy. For each patient, the proportion of the heart included in the 50% isodose was determined from the cumulative dose-volume histogram (DVH). The same volume determination was made for the left-sided breast cancer patients treated with tangential fields during the first Stockholm Breast Cancer Trial. RESULTS: The mean irradiated heart volume that received at least 25 Gy was 5.7% (SD = 4.5%) for the whole group and 11.9% (SD = 3.7%) in those with the highest volumes. The mean irradiated heart volume included in the 50% isodose for patients in the Stockholm Trial was 25% (SD = 11.9%). CONCLUSION: In this study, the majority of patients with left-sided T1NOMO breast cancer did not receive irradiation to substantial heart volumes. However, in 6% of all studied patients, the proportion of irradiated heart volume was close to the irradiated heart volumes with one of the treatment techniques used in the Stockholm Trial for patients with left-sided tumors. That technique has been associated with significantly increased cardiac mortality during long-term follow-up evaluation in a previous study. The CT-based three-dimensional treatment-planning system (TMS) represents a valuable tool in identifying such patients; thus, treatment may be conformed to reduce the irradiated heart volume.

Breast Neoplasms↗
PubMed1996

Prediction of results following Gamma Knife surgery for brain stem and other centrally located arteriovenous malformations: relation to natural course.

Two models for predicting the results of Gamma Knife surgery for brain stem and other centrally located arteriovenous malformations (AVMs) are presented. By using these models, the probability of total obliteration and the risk of complications can be predicted. The model to predict the probability for obliteration is based on the following two observations. First, there is a positive relationship between the minimum dose given to the AVM nidus and the incidence of obliteration. Second, there is a negative relationship between the AVM nidus volume and the minimum dose given in the obliterated cases. The risk estimation model is also based on two observations. First, centrally located AVMs carry a higher risk of complications than those located peripherally. Second, the average dose to volumes which are large for radiosurgery is related to the incidence of complications. The findings of this study may be used to estimate the consequences of Gamma Knife treatment for every individual case prior to the treatment. This makes a comparison between different treatment options and no treatment possible. The risk of hemorrhage without any treatment is also quantified.

Adolescent↗
PubMed1996

Long-term cardiac mortality after radiotherapy of breast cancer--application of the relative seriality model.

Effects on the heart constitute a potentially significant and serious clinical problem in primary radiation therapy of early breast cancer. Increased cardiac mortality among irradiated patients may offset the potential benefit in terms of a reduced risk of recurrence or of death from breast cancer. Clinical data on long-term cardiac mortality among breast cancer patients included in two randomized trials (the Stockholm and Oslo studies) of radiation therapy as an adjunct to primary surgery were analysed using the relative seriality model of radiation response. Five different radiation therapy techniques were used in the trials. The original treatment plans were recalculated on a group of model patients using a three-dimensional treatment planning system. A mean dose-volume histogram (DVH) was calculated for each treatment technique. Both heart and myocardium, i.e. excluding circulating blood within the heart, were separately investigated as risk organs. Model parameters, (D50, i.e. the dose giving 50% complication probability; gamma, i.e. the maximum relative slope of the dose-response curve; s, describing the organ relative seriality) were determined by a chi 2 fitting of the calculated probability of excess cardiac mortality, based on the DVHs, to the incidence data. Computed complication probabilities for each treatment technique were modelled within the 95% confidence interval (CI) of the clinical incidence data. It was shown that the relative seriality model, assuming a homogeneous radiation sensitivity within the volume of the heart/myocardium can be used to describe the incidence data. A small dependence on the volume was found. The results do not, however, exclude the possibility that more sensitive structures within the myocardium are the main target for radiation.

Breast Neoplasms↗
PubMed1996

Prediction of complications in gamma knife radiosurgery of arteriovenous malformation.

The incidence of complications following radiosurgical treatment of arteriovenous malformations (AVM) is presented. A simple relationship exists between average dose and risk of complications, and on this basis a model is presented that gives a qualitatively correct description of this relationship. The parameters of the model have been determined using a clinical material of 862 AVM treatments to give a quantitatively correct description of the risk of complications. The dose-response curve is described by a double-exponential function. An accurate description of the dose-response curve at high dose levels is shown to be very important in radiosurgery.

Algorithms↗