Membrane receptors with protein-tyrosine kinase activity

Investigation on the interaction behavior of afatinib, dasatinib, and imatinib docked to the BCR-ABL protein

Chronic myeloid leukemia (CML) is a pathological condition associated with the uncontrolled proliferation of white blood cells and respective loss of function. Imatinib was the first drug that could effectively treat this condition, but its use is hindered by the development of mutations of the BCR-ABL protein, which are the cause of resistance. Therefore, dasatinib and afatinib present similarities that can be explored to discover new molecules capable of overcoming the effects of imatinib. Afatinib exhibited electronic and docking behavior, indicating that a replacement with some minor modifications could design a new potential inhibitor. The amide group in each candidate is clearly of pharmacophoric importance, and it needs to concentrate a negative region. Sulfur group presents a good pharmacophoric profile, which was shown by dasatinib results, adding to the influence of the Met318 residue in the target protein active site configuration. This behavior suggests that the sulfur atom and other fragments that have an affinity for the methionine sidechain may provide a significant positive effect when present in TKI molecules such as afatinib or dasatinib.

Pharmacokinetics of genistein distribution in blood and retinas of diabetic and non-diabetic rats

Genistein, a natural tyrosine kinase inhibitor, may act as an intraocular antiangiogenic agent. Its therapeutical use, however, is limited by its nonlinear pharmacokinetics. We aimed to determine genistein's kinetics and retinal tissue distributions in normal and diabetic rats. We developed an isocratic, reverse-phase C18 HPLC system to measure genistein concentration in blood and retinas of streptozotocin (65 mg/kg IV)-diabetic and non-diabetic rats receiving two types of genistein-rich diet (150 and 300 mg/kg) for ten days. Genistein's decay exhibited a two-compartmental open model. Half-lives of distribution and elimination were 2.09 and 71.79 min, with no difference between groups. Genistein steady-state concentration in blood for 150 and 300 mg/kg diet did not differ between diabetic (0.259 ± 0.07 and 0.26 ± 0.06 μg/ml) and non-diabetic rats (0.192 ± 0.05 and 0.183 ± 0.09 μg/ml). In retina, genistein concentration was significantly higher in diabetic rats (1.05 ± 0.47 and 0.997 ± 0.47 μg/gm wt. vs. 0.087 ± 0.11 and 0.314 ± 0.18 μg/gm wt., p < 0.05). The study determined that increasing genistein dose did not change its bioavailability, perhaps due to the poor aqueous solubility. The retina's increased genistein could be due to increased permeability of blood-retinal barrier that occurs early in diabetes.

Mechanical stress-initiated signal transduction in vascular smooth muscle cells in vitro and in vivo

Increasing evidence has been demonstrated that hypertension-initiated abnormal biomechanical stress is strongly associated with cardio-/cerebrovascular diseases e.g. atherosclerosis, stroke, and heart failure, which is main cause of morbidity and mortality. How the cells in the cardiovascular system sense and transduce the extracellular physical stimuli into intracellular biochemical signals is a crucial issue for understanding the mechanisms of the disease development. Recently, collecting data derived from our and other laboratories showed that many kinds of molecules in the cells such as receptors, ion channels, caveolin, G proteins, cell cytoskeleton, kinases and transcriptional factors could serve as mechanoceptors directly or indirectly in response to mechanical stimulation implying that the activation of mechanoceptors represents a non-specific manner. The sensed signals can be further sorted and/or modulated by processing of the molecules both on the cell surface and by the network of intracellular signaling pathways resulting in a sophisticated and dynamic set of cues that enable cardiovascular cell responses. The present review will summarise the data on mechanotransduction in vascular smooth muscle cells and formulate a new hypothesis, i.e. a non-specific activation of mechanoceptors followed by a variety of signal cascade activation. The hypothesis could provide us some clues for exploring new therapeutic targets for the disturbed mechanical stress-initiated diseases such as hypertension and atherosclerosis.

Actin-binding proteins involved in the capping of epidermal growth factor receptors in A431 cells

A capping process of epidermal growth factor receptors (EGF-Rs) was used for the study of the relation between the receptors and the actin-binding proteins (spectrin, vinculin, annexin I) that may be involved in EGF-R-cytoskeleton interaction. In intact, adherent A431 cells, EGF-Rs were diffusively distributed on the cell surface. Spectrin, vinculin, and annexin I were located beneath the plasma membrane. An abundance of EGF-Rs as well as submembrane proteins was observed in regions of membrane ruffles and cell-cell contacts. Annexin I was localized also in cytoplasm being attached to filamentous structures surrounding the nucleus and extending to the cell periphery. Under polyvalent ligand treatment, EGF-Rs of adherent cells were aggregated on one side of the cell. Spectrin, vinculin, and annexin I dislocated together with EGF-Rs and were concentrated under plasma membrane at regions where cap formation took place. In suspended A431 cells only spectrin was located under the plasma membrane whereas annexin I and vinculin were diffusively distributed through the cells. During cap formation only spectrin was colocalized with EGF-Rs. The results confirmed the major role of spectrin as a receptor-microfilament linking protein.

Basic fibroblast growth factor is a substrate for protein phosphorylation and is phosphorylated by capillary endothelial cells in culture

A phosphorylated basic fibroblast growth factor (FGF) can be detected in extracts of bovine capillary endothelial cells and human hepatoma cells. Accordingly, human basic FGF contains consensus sequences that account for its phosphorylation on Thr-112 by the catalytic subunit of the cAMP-dependent protein kinase A (PK-A) and on Ser-64 by the calcium- and phospholipid-dependent protein kinase C (PK-C). A kinetic analysis of both of these reactions revealed that basic FGF is among the better substrates for these enzymes. Although the kinase responsible for the phosphorylation in vivo has not yet been identified, we examined the effects of phosphorylation on the biological activity, heparin-binding capacity, and receptor-binding capacity of phosphorylated basic FGF. No effects of phosphorylation were observed when the mitogen was phosphorylated by PK-C. In contrast, when basic FGF was phosphorylated in the receptor-binding domain with PK-A, the growth factor was 3-8 times better at displacing radiolabeled basic FGF in the radioreceptor assay. No effects were seen on the binding of this FGF to immobilized heparin or cell-associated glycosaminoglycans, suggesting that this phosphorylation modifies the affinity of basic FGF for its receptor. Biological assays for basic FGF failed to identify differences between the phosphorylated and unphosphorylated forms of recombinant basic FGFs presumably because of the presence of ectophosphatases and the experimental conditions of proliferation and mitogenic assays (37 degrees C, 24-96 hr). Because the relative affinity of basic FGF for its receptor and cell-associated glycosaminoglycans may regulate its activity, the identification of a modified form of basic FGF may be of particular importance in understanding the mechanisms that regulate its biological activity, bioavailability, and processing to and from the extracellular matrix.

Analysis of the protein glycosylation defect of a temperature-sensitive cell cycle mutant by the use of mutant cells overexpressing the human epidermal growth factor receptor after transfection of the gene

A temperature-sensitive mutant with a defect in glycoprotein synthesis and a cell cycle (G1)-specific arrest at the nonpermissive temperature (Tenner et al., J. Cell. Physiol., 90:145-160, 1977; Tenner and Scheffler, J. Cell. Physiol., 98:251-266, 1979) was investigated further after a human epidermal growth factor (EGF) receptor gene had been transfected and amplified in these cells. While a temperature shift-up lead to an immediate arrest in the biosynthesis of mature EGF receptor and its appearance on the plasma membrane, the observed turnover of the preexisting receptor was too slow to account for the arrest of DNA synthesis in these mutant cells. Tunicamycin could in fact mimic the effect of a temperature shift on the biosynthesis of EGF receptor, but it did not have the same rapid effect on DNA synthesis and cell cycle progression. These mutants have also been shown to induce a set of stress proteins or glucose-regulated proteins, GRPs (Lee et al., J. Cell. Physiol., 129:277-282, 1986). The question is addressed whether the defect in glycoprotein synthesis is the primary defect and a possible cause of the induction of the GRPs, or whether a more basic defect at the level of the endoplasmic reticulum (ER) is responsible for the complex phenotype of the mutant. Our results argue in favor of a primary defect which indirectly affects N-linked glycosylation of proteins, as well as several other functions associated with the ER. We hypothesize that the defect affects the calcium distribution between ER and cytosol, since the calcium ionophore A23187 has an effect similar to that of a temperature shift.