Other Membrane Receptors

Urokinase-Type Plasminogen Activator Receptors (uPAR) 

More laboratory research, clinical trials, and computer programs would bring us closer to winning the battle against diseases like prostate cancer, but since cancer is increasing in this modern, restless, and hurried society, man also needs to reevaluate and alter his lifestyle. These changes may be small and may even be cheap, but could create an immense difference in the quality of life. 

Akakura, K., Akimoto, S., Furaya, Y., and Ito, H., Incidence and characteristics of antiandrogen withdrawal syndrome in prostate cancer after treatment with chlormadinone acetate. Eur. Urol. 33, 567-571 (1998). 

Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., and Watson, J. D., Molecular Biology of the cell. Garland, New York London, 1994. 

Allegretto,E. A., McClung, M. R.,Lazarchik, S. B., Clem, D. L., Kerner, S. A., etal., Transactivation properties of retinoic acid and retinoid X receptors in mammalian cells and yeast. Correlation with hormone binding and effect of metabolism. J. Biol. Chem. 268, 26625-26633 (1993). 

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The MAPK cascade in the plant s defense against bacterial pathogens is remarkably similar to the innate immune response triggered by bacterial lipopolysac-charide and mediated by the Toll-like receptors in mammals (Fig. 12-30b). Other membrane receptors use similar mechanisms to activate a MAPK cascade, ultimately activating transcription factors and turning on the genes essential to the defense response. 

Rather than direcdy affecting membrane permeability or directly influencing enzyme activity, other membrane receptors affect cell function by linking to an intermediate regulatory protein that is located on the inner surface of the cell s membrane.2,23,45 These regulatory proteins are activated by binding guanine... 

Many proteins found in nature are glycoproteins because they contain covalently linked oligo- and polysaccharide groups. The list of known glycoproteins includes structural proteins, enzymes, membrane receptors, transport proteins, and immunoglobulins, among others. In most cases, the precise function of the bound carbohydrate moiety is not understood. 

Protein toxins acting intracellularly are often composed of two subunits (A/B model). One subunit is catalytic (A-subunit) and the other is responsible for binding and cell entry (B-subunit). Following binding to an extracellular membrane receptor, the toxins are endocytosed. From the endosomes, the A-subunit is directly (pH dqDendent) transferred into the cytosol (e.g., diphtheria toxin and anthrax toxin) or the toxin is transported in a retrograde manner via the golgi to the ER (e.g., cholera toxin), where translocation into the cytosol occurs [1]. 

Besides cytoplasmic protein kinases, membrane receptors can exert protein kinase activity. These so-called receptor tyrosine kinases (RTK) contain a ligandbinding extracellular domain, a transmembrane motif, and an intracellular catalytic domain with specificity for tyrosine residues. Upon ligand binding and subsequent receptor oligomerization, the tyrosine residues of the intracellular domain become phosphory-lated by the intrinsic tyrosine kinase activity of the receptor [3, 4]. The phosphotyrosine residues ftmction as docking sites for other proteins that will transmit the signal received by the RTK. 

There are several major classes of Ca channels (1) receptor-operated Ca channels in plasma membranes (2) ligand-gated Ca " channels in intracellular membranes and (3) voltage-dependent Ca channels that are usually found in plasma membranes or the invaginations of the plasma membrane that are known as transverse tubule membranes. Receptor-dependent or receptor-operated Ca channels (ROCCs) are primarily opened in response to activation of their associated receptors and, by definition, exhibit a certain amount of selectivity for Ca " over other cations. Several potentially different types of ROCCs have been characterized including ATP-sensitive channels in smooth muscle [1], mitogen and IP3-sensitive... 

QUESTION How do you imagine that both a receptor antagonist and an uptake inhibitor would block the effects It would seem that if dopamine is involved, it would either be acting on a membrane receptor or inside, but not both. I would also like to ask a more specific question. You showed that the alpha MT protected effect could be reversed by dopa. And I think you imagined that that was because of dopamine formation. But have you tried dopamine agonists to see if they would antagonize either the protective effect of alpha methyltyrosine or, particularly, the protective effect of the dopamine antagonists to try to verily that those protective effects really have to do with blockade of a dopamine receptor as opposed to some other possibility ... 

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