抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Experimental introduction of RNA into cells can be used in certain biological systems to interfere with the function of an endogenous gene Such effects have been proposed to result from a simple antisense mechanism that depends on hybridization between the injected RNA and endogenous messenger RNA transcripts RNA interference has been used in the nematode Caenorhabditis elegans to manipulate gene expression Here we investigate the requirements for structure and delivery of the interfering RNA To our surprise, we found that double-stranded RNA was substantially more effective at producing interference than was either strand individually After injection into adult animals, purified single strands had at most a modest effect, whereas double-stranded mixtures caused potent and specific interference The effects of this interference were evident in both the injected animals and their progeny Only a few molecules of injected double-stranded RNA were required per affected cell, arguing against stochiometric interference with endogenous mRNA and suggesting that there could be a catalytic or amplification component in the interference process

Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans

Ligand: a versatile computerized approach for characterization of ligand-binding systems.

Cell signaling by receptor-tyrosine kinases

The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stressresponse or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole. (Endocrine Reviews 21: 55‐ 89, 2000)

/pdf/how-do-glucocorticoids-influence-stress-responses-4egr3fa2k0.pdf

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

Phosphorylation of the beta-adrenergic receptor (beta AR) is closely associated with homologous desensitization of the beta-adrenergic receptor-coupled adenylate cyclase system. Homologous desensitization and receptor phosphorylation also occur in cell mutants which are deficient in their cAMP-dependent protein kinase (kin- mutant of S49 lymphoma cells). beta AR phosphorylation is mediated by a cAMP-independent protein kinase which phosphorylates the receptor only when it is occupied by a beta-agonist. During the time course of desensitization the beta AR kinase (beta ARK) activity is translocated from a cytoplasmic to a plasma membrane location. beta ARK translocation can also be effected by prostaglandin E1 (PGE1) suggesting that this beta ARK may represent a more general enzyme capable of phosphorylating other adenylate cyclase-coupled receptors. Thus, beta ARK may play a key role in the process of homologous desensitization of adenylate cyclase coupled receptors. Extracellular hormones interact with specific receptors at the outer surface of the plasma membrane and thus initiate a cellular response. One of the best studied transmembrane signalling systems known to be coupled to the occupancy of cell surface receptors is adenylate cyclase. The adenylate cyclase system is composed of various components all of which have been purified to homogeneity (Shorr et al., 1982; Homcy et al., 1983; Benovic et al., 1984; Codina et al., 1984; Northup et al., 1980; Sternweis et al., 1981; Bokoch et al., 1984; Pfeuffer et al., 1985). Initially, agonist binding to the receptor promotes coupling of the occupied receptor to one of the guanine nucleotide binding regulatory proteins. These proteins are members of a family of heterotrimeric proteins consisting of alpha, beta and gamma subunits. Stimulatory receptors like the beta-adrenergic (Cerione et al., 1984) or glucagon (Iyengar et al., 1979) receptors couple to the stimulatory regulatory protein Ns (or Gs) whereas inhibitory receptors like the alpha 2-adrenergic (Jacobs et al., 1976) or M2-muscarinic (Harden et al., 1982) receptors couple to the inhibitory regulatory protein Ni (or Gi). Prolonged exposure to agonist hormones, either stimulatory or inhibitory, results in an attenuation of the response to the hormonal activation, a phenomenon called tachyphylaxis or desensitization (Harden, 1983; Sibley and Lefkowitz, 1985; Sharma et al., 1975). One of the best studied models for desensitization is the beta-adrenergic receptor-coupled adenylate cyclase system. In this system two different forms of desensitization have been characterized.(ABSTRACT TRUNCATED AT 400 WORDS)

The beta-adrenergic receptor kinase: role in homologous desensitization in S49 lymphoma cells.

Activation of adenylate cyclase by beta-adrenergic receptors: investigation of rate limiting steps by simultaneous assay of high affinity agonist binding and GDP release.

The beta-adrenergic signaling cascade is an important regulator of myocardial function. Numerous abnormalities occur in this pathway and are associated with impaired cardiac contractility in patients with congestive heart failure (CHF). These signaling defects include downregulation of beta-adrenergic receptors (beta ARs) and increased levels of beta-adrenergic receptor kinase (beta ARK), an enzyme that phosphorylates and uncouples only agonist-bound receptors. Our laboratory has been testing the hypothesis that reversal of these beta-adrenergic defects may be able to restore cardiac inotropy to normal in patients with depressed systolic function. Transgenic mice with cardiac overexpression of beta 2ARs or an inhibitor of beta ARK have enhanced cardiac function as compared to wildtype littermates. Adenoviral vectors encoding the beta 2AR or beta ARK inhibitor potentiate beta AR signaling in cultured adult rabbit ventricular myocytes. However, a controversy has developed in the literature regarding whether increasing beta-adrenergic signaling would be beneficial or detrimental for patients with CHF. Those cautioning against this approach note that increased sympathetic activity is dangerous in CHF. Elevated catecholamine levels predict mortality and beta-agonists are not beneficial for survival, while recent studies suggest that beta-antagonists do improve outcome. Supporting these concerns is the demonstration that transgenic mice with cardiac overexpression of Gs alpha and enhanced myocardial responsiveness to isoproterenol develop myocardial fibrosis. This article summarizes this controversy; highlights important differences between overexpression of beta ARs or a beta ARK inhibitor, overexpression of Gs alpha, and administration of beta-agonists; and develops the hypothesis that these strategies may differ in their therapeutic efficacy in treating CHF.

Potentiation of beta-adrenergic signaling by gene transfer.

MARC G. CARON,+ MICH~LE BEAULIEU,~ VINCENT RAYMOND,~ BERNARD GAGN~, JACQUES DROUIN,§ ROBERT J. LEFKOWITZ,~ AND FERNAND LABRIE/~ From the Medical Research Council Group in Molecular Endocrinology, Le Centre Hospitalier de 1’Universite Laval, Quebec GlV 4G2 and Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710 The ergot alkaloid [“Hldihydroergocryptine, a potent do- paminergic agonist, has been used to study binding sites in bovine anterior pituitary membranes. One function of the anterior pituitary gland, prolactin secretion, as we show is under typical dopaminergic control and was measured in uitro in another series of experiments using rat anterior pituitary cells

Dopaminergic Receptors in the Anterior Pituitary Gland

Erratum: Localization of the fourth membrane spanning domain as a ligand binding site in the human platelet α2-adrenergic receptor (Biochemistry (1989) 28, 9, (4125-4130))

Robert J. Lefkowitz

Papers

The beta-adrenergic receptor kinase: role in homologous desensitization in S49 lymphoma cells.

Activation of adenylate cyclase by beta-adrenergic receptors: investigation of rate limiting steps by simultaneous assay of high affinity agonist binding and GDP release.

Potentiation of beta-adrenergic signaling by gene transfer.

Dopaminergic Receptors in the Anterior Pituitary Gland

Erratum: Localization of the fourth membrane spanning domain as a ligand binding site in the human platelet α2-adrenergic receptor (Biochemistry (1989) 28, 9, (4125-4130))