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Expression of dopamine receptor genes in the periphery
APOPTOSlS INDUCED BY TNF AND BY VIRUSES E. Peterhans, B. Frech, H. Adler, T. Hennet and T.W. Jungi Institute of Veterinary Virology, University of Bern, L~nggassStr. 122, CH-3012 Bern, Switzerland The mechanisms by which viruses cause disease symptoms are highly complex and in addition to direct effects on host cells they include pathology mediated by the immune system. Among the latter, detrimental effects mediated by cytokines have attracted much interest. We recently showed that mouse L929 cells treated with TNF undergo apoptosis. Addition of TNF activates the generation of 02 by mitoohondria, and transfection of the oncogene bcl-2 confers partial protection from TNF-induced cytotoxicity, suggesting that mitochondria may be both a source and a target of a radical-mediated mechanism of apoptosis. Bovine viral diarrhea virus (BVDV), a pestivirus related to hepatitis C virus, exists in two biotypes, cytopathic (cp) and noncytopathic (ncp). Cp BVDV kills fetal turbinate cells and bone-marrow-derived macrophages in an apoptotic fashion. Uninfected macrophages treated with supernatants of cp BVDVinfected macrophages are exquisitely sensitive to killing by LPS or gram-negative bacteria. A factor(s) released from cp, but not ncp, BVDV-infected macrophages sensitizes uninfected macrophages to killing by endotoxin. Direct virus-mediated and factor-mediated priming for cell killing may explain the loss of mononuclear cells observed in lethal mucosal disease. This condition is triggered by cp BVDV in animals that are persistently infected with ncp BVDV and exhibit a specific immunotolerance to the infecting viral strain as a result of infection in early pregnancy. Leakage of endotoxin from the gut may explain why mucosal disease lesions are most prominent in the gastrointestinal tract and particularly in Peyer's patches.
EXPRESSION OF DOPAMINE RECEPTOR GENES IN THE PERIPHERY D.P. Healy Department of Pharmacology, Mount Sinai School of Medicine, New York, NY, USA.
The peripheral effects of low doses of dopamine are mediated by specific dopamine receptors. Based on their pharmacological and physiological properties, peripheral dopamine receptors have been broadly classified into two major subtypes, namely D1 and~D2 (or DA1 and DA2). The predominant systemic effect Of Dt receptor agonists is to produce an increase in renal blood flow and a natriuresis/diuresis, whereas the predominant systemic effect for D2 agonists appears to be a reduction in catecholamine release from sympathetic nerve endings and adrenal chromaffin cells. In the central nervous system, multiple subtypes of the D, and D2 receptor families have been identified by molecular cloning (D,A and D~, D2, D3 and D4). D, receptors positively couple to adenylyl cyclase via the guanine nucleotide binding protein G,, whereas D2, receptors are negatively coupled to adenylyl cyclase via G,. The signal transduction mechanisms for D3 and D4 receptors have not been resolved. At present, peripheral dopamine receptors appear to be the products of the same genes expressed in the CNS. In this overview lecture, I will discuss the current state of our understanding on the molecular identity and expression of dopamine receptor subtypes in peripheral tissues. Particular emphasis will be on expression of doparnine receptors in the kidney.
A P O P T O S I S IN C A N C E R AND C A N C E R T R E A T M E N T , John A Hickman~ School of Biological Sciences, University of Manchester, Manchester M13 9PT, UK. The major human cancers remain resistant to chemotherapy despite advances in the understanding of the details of the molecular mechanisms of action of anticancer drugs. These have focused on how these agents interact with key cellular constituents, such as DNA. The question of why such interactions induce cell death, or not, has not been addressed successfully. The observation that a broad spectrum of drugs, interacting at different cellular loci, all induce cells to die by apoptosis has allowed a reassessment of ideas on how drugs kill cells and, in the major cancers, why they often do not. Apoptosis is an active form of cell death. As well as being important in development and normal tissue homeostasis, apoptosis is initiated in response to cellular damage. This effectively deletes potentially dangerous cells, such as those with damaged DNA. DNA damage appears to drive apoptosis by stabilization of the p53 protein. If p53 can effectively remove DNA damaged cells then how might the process of carcinogenesis be initiated and mutations sustained? There is a hierarchy of response to damage, with different cells having different thresholds: for example, epithelial stem cells from the crypts of the small intestine readily engage apoptosis after DNA damage whereas colonic stem cells do not. The molecular basis of these different thresholds will be discussed, particularly with respect to the expression of the gene bcl-2, which inhibits apoptosis, including that initiated by p53. If certain epithelial cells have a high thresholds for the engagement of cell death (colon versus small intestine), then two predictions might be made: first colonic epithelia may be more susceptible to carcinogenesis in comparison to the small intestine. Indeed, small intestinal tumours constitute < i 0 % of g.i. tract turnouts. Secondly, colonic turnouts, arising from cells with a high threshold for the initiation of cell death, may be resistant to cytotoxic drugs in comparison to tlssues like the small intestine. Colonic stem cells express bcl-2 as do adenomas and carcinomas of the colon. Expression of bcl-2 provides true pleotropic resistance to drug-induced cell death. Lowering the threshold for the engagement of apoptosis in chemoresistant epithelial tumours is critical if they are to be rendered chemoseusitive.
GENETIC AND ACQUIRED DETERMINANTS OF DOPAMINE AVAILABILITY FOR ITS CARDIOVASCULAR AND RENAL ACTION. O.Kuchel. Clinical Research Institute of Montreal and HtteI-Dieu Hospital, University of Montreal, 110 Pine Ave West, Montreal, Quebec, Canada H2W 1 R7. The considerable genetic influences on dopamine available for its receptor action are substantiated by the cloning and location of all the enzymes involved in dopamine synthesis, reuptake and metabolism. Peripheral dopamine mostly originates in autocrineparacrine sources. The expression of genes of enzymes, determining dopamine availability, is modulated by multiple environmental and pharmacological influences. These influences on the ratelimiting tyrosine-hydroxylase, aromatic acid decarboxylase, dopamine 13-hydroxylase on one hand and the dopamine transporter, monoaminoxidase, catechol-ortomethyltransferase, phenol sulfotransferase and sulfatase on the other, will be outlined. Of particular interest is the catecholamine-sulfating and desulfating system, the latter under the influence of sulfatase and representing the only reversible metabolic pathway regenerating biologically active free dopamine from dopamine sulfate These findings represent newly identified determinants of dopamine availability for its peripheral cardiovascular and renal actions and potential sites of their physiological and pharmacological modulation.
EXPRESSION OF DOPAMINE RECEPTOR GENES IN THE PERIPHERY D.P. Healy Department of Pharmacology, Mount Sinai School of Medicine, New York, NY, USA.
The peripheral effects of low doses of dopamine are mediated by specific dopamine receptors. Based on their pharmacological and physiological properties, peripheral dopamine receptors have been broadly classified into two major subtypes, namely D1 and~D2 (or DA1 and DA2). The predominant systemic effect Of Dt receptor agonists is to produce an increase in renal blood flow and a natriuresis/diuresis, whereas the predominant systemic effect for D2 agonists appears to be a reduction in catecholamine release from sympathetic nerve endings and adrenal chromaffin cells. In the central nervous system, multiple subtypes of the D, and D2 receptor families have been identified by molecular cloning (D,A and D~, D2, D3 and D4). D, receptors positively couple to adenylyl cyclase via the guanine nucleotide binding protein G,, whereas D2, receptors are negatively coupled to adenylyl cyclase via G,. The signal transduction mechanisms for D3 and D4 receptors have not been resolved. At present, peripheral dopamine receptors appear to be the products of the same genes expressed in the CNS. In this overview lecture, I will discuss the current state of our understanding on the molecular identity and expression of dopamine receptor subtypes in peripheral tissues. Particular emphasis will be on expression of doparnine receptors in the kidney.
A P O P T O S I S IN C A N C E R AND C A N C E R T R E A T M E N T , John A Hickman~ School of Biological Sciences, University of Manchester, Manchester M13 9PT, UK. The major human cancers remain resistant to chemotherapy despite advances in the understanding of the details of the molecular mechanisms of action of anticancer drugs. These have focused on how these agents interact with key cellular constituents, such as DNA. The question of why such interactions induce cell death, or not, has not been addressed successfully. The observation that a broad spectrum of drugs, interacting at different cellular loci, all induce cells to die by apoptosis has allowed a reassessment of ideas on how drugs kill cells and, in the major cancers, why they often do not. Apoptosis is an active form of cell death. As well as being important in development and normal tissue homeostasis, apoptosis is initiated in response to cellular damage. This effectively deletes potentially dangerous cells, such as those with damaged DNA. DNA damage appears to drive apoptosis by stabilization of the p53 protein. If p53 can effectively remove DNA damaged cells then how might the process of carcinogenesis be initiated and mutations sustained? There is a hierarchy of response to damage, with different cells having different thresholds: for example, epithelial stem cells from the crypts of the small intestine readily engage apoptosis after DNA damage whereas colonic stem cells do not. The molecular basis of these different thresholds will be discussed, particularly with respect to the expression of the gene bcl-2, which inhibits apoptosis, including that initiated by p53. If certain epithelial cells have a high thresholds for the engagement of cell death (colon versus small intestine), then two predictions might be made: first colonic epithelia may be more susceptible to carcinogenesis in comparison to the small intestine. Indeed, small intestinal tumours constitute < i 0 % of g.i. tract turnouts. Secondly, colonic turnouts, arising from cells with a high threshold for the initiation of cell death, may be resistant to cytotoxic drugs in comparison to tlssues like the small intestine. Colonic stem cells express bcl-2 as do adenomas and carcinomas of the colon. Expression of bcl-2 provides true pleotropic resistance to drug-induced cell death. Lowering the threshold for the engagement of apoptosis in chemoresistant epithelial tumours is critical if they are to be rendered chemoseusitive.
GENETIC AND ACQUIRED DETERMINANTS OF DOPAMINE AVAILABILITY FOR ITS CARDIOVASCULAR AND RENAL ACTION. O.Kuchel. Clinical Research Institute of Montreal and HtteI-Dieu Hospital, University of Montreal, 110 Pine Ave West, Montreal, Quebec, Canada H2W 1 R7. The considerable genetic influences on dopamine available for its receptor action are substantiated by the cloning and location of all the enzymes involved in dopamine synthesis, reuptake and metabolism. Peripheral dopamine mostly originates in autocrineparacrine sources. The expression of genes of enzymes, determining dopamine availability, is modulated by multiple environmental and pharmacological influences. These influences on the ratelimiting tyrosine-hydroxylase, aromatic acid decarboxylase, dopamine 13-hydroxylase on one hand and the dopamine transporter, monoaminoxidase, catechol-ortomethyltransferase, phenol sulfotransferase and sulfatase on the other, will be outlined. Of particular interest is the catecholamine-sulfating and desulfating system, the latter under the influence of sulfatase and representing the only reversible metabolic pathway regenerating biologically active free dopamine from dopamine sulfate These findings represent newly identified determinants of dopamine availability for its peripheral cardiovascular and renal actions and potential sites of their physiological and pharmacological modulation.