Faculty Bibliography

Huntington's disease is an autosomal dominant neurodegenerative disorder characterized by abnormalities of motor function, cognition and behavior. The striatum is particularly vulnerable to the disease process with selective loss of medium-sized spiny projection neurons and relative sparing of interneurons. Although the underlying mechanism initiating and propagating neuronal destruction is currently unknown, experimental evidence over the past decade has implicated mitochondrial dysfunction and excititoxicity in the pathogenesis of Huntington disease. The areas that are reviewed in this article include neuopathology, neurophysiology, molecular genetics, and experimental therapeutics in relation to Huntington's disease. The authors argue that the current treatment of Huntington's disease is limited to palliative care with secondary symptomatic management. Recent advances in the understanding of the pathophysiology of this disease that may lead to the development of pharmacotherapeutic and neurosurgical interventions to effectively treat Huntington's disease are discussed.

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments catecholamine-sensitive adenylate cyclase activity in reticulocyte membranes. A highly purified preparation of RCAP, obtained by Sephacryl S-200 chromatography, was used to elucidate further its mechanism of action. The specific activity of the S-200 fraction to augment isoproterenol responsiveness was increased approximately 1,100-fold over the starting material, from 1.2 to 1,300 nmol cAMP formed per mg RCAP. The mol wt of RCAP is approximately 20,000. The effect of RCAP to enhance isoproterenol responsiveness was apparent within 20 sec, virtually abolishing the normal lag time of hormone-activated adenylate cyclase. In addition to its effects on catecholamine-responsive adenylate cyclase, RCAP significantly increased basal [21 +/- 3 (+/- SEM) to 41 +/- 4 pmol/mg protein X 30 min; P less than 0.02], guanyl-5'-yl-imidodiphosphate-associated (3173 +/- 213 to 4339 +/- 365 pmol/mg X 30 min; P less than 0.03), and fluoride-associated (5152 +/- 64 to 5807 +/- 58 pmol/mg X 30 min; P less than 0.05) adenylate cyclase activities. RCAP also altered the characteristics of agonist binding to the beta-adrenergic receptor of reticulocyte membranes, causing an increase in the apparent IC50 for isoproterenol from 0.7 +/- 0.2 to 7.9 +/- 1.6 microM (P less than 0.001). Similar to its effects on reticulocytes, RCAP enhanced isoproterenol- and prostaglandin E2-sensitive adenylate cyclase activity in the wild-type S49 lymphoma cell and shifted the binding isotherm for isoproterenol rightward. In cyc-, the mutant that lacks the stimulatory guanine nucleotide-binding protein (Ns) and in UNC, the mutant in which receptors are uncoupled from N, RCAP was ineffective. Moreover, RCAP decreased agonist affinity for the beta-adrenergic receptor in wild-type S49 cells, but not in cyc- or UNC cells. These observations suggest that RCAP requires a functional Ns unit for its effects on hormone-sensitive adenylate cyclase activity

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments hormone-sensitive adenylate cyclase activity in the rat reticulocyte and other systems. In a previous publication, using a highly purified preparation of RCAP, we reported that the stimulatory guanine nucleotide-binding protein (Ns) was required for the actions of RCAP. We investigated this possibility by studying the actions of RCAP on cholera toxin-dependent ADP ribosylation of Ns. RCAP decreased cholera toxin-dependent ADP ribosylation of the 42,000-dalton subunit of Ns of reticulocyte [40.2 +/- 3.7 (+/-SEM) to 26.5 +/- 3.8 fmol/mg; n = 10; P less than 0.001], S49 wild-type (33.9 +/- 2.4 to 24.9 +/- 2.8 fmol/mg; n = 9; P less than 0.01), and UNC (25.3 +/- 3.5 vs. 17.6 +/- 3.1; n = 5; P less than 0.02) membranes. In contrast, pertussis toxin-dependent ADP-ribosylation of the inhibitory guanine nucleotide binding protein, Ni in reticulocyte, S49 wild-type lymphoma, and its UNC and cyc- variant membranes were all significantly augmented by RCAP. Moreover, when reticulocyte Ni was functionally ablated by exposure to pertussis toxin, RCAP no longer enhanced isoproterenol-responsive adenylate cyclase activity in reticulocyte membranes. These results suggest that RCAP stimulates adenylate cyclase activity by inhibiting Ni function, thus permitting enhanced Ns coupling to the adenylate cyclase enzyme (C)

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments catecholamine-sensitive adenylate cyclase activity in reticulocyte membranes. A partially purified preparation of RCAP was obtained by Sephacryl S-200 chromatography and used to elucidate further its mechanism of action. The specific activity of the S-200 fraction to augment isoproterenol responsiveness is increased approximately 1100-fold over the starting material from 1.2 nmoles to 1300 nmoles cyclic AMP formed per milligram of RCAP. The molecular weight is approximately 20,000. In addition to its effects on catecholamine-responsive adenylate cyclase, RCAP is associated with significant increases in basal (0.9 +/- 0.2 to 1.5 +/- 0.4 nmol/mg; p less than 0.02), guanyl-5'-yl imidodiphosphate [Gpp(NH)p]; (3.9 +/- 0.9 to 4.4. +/- 1.1 nmol/mg; p less than 0.005) and fluoride (4.1 +/- 0.6 to 4.8 +/- 0.6 nmol/mg; p less than 0.005) associated activities. RCAP stimulates isoproterenol responsiveness in wild type S49 cell membranes but is inactive in the mutant line, cyc-. RCAP alters the characteristics of agonist binding to the beta-adrenergic receptor of reticulocyte and wild S49 cell membranes, causing a significant increase in the IC50 for isoproterenol. Direct assessment of Ns and Ni components of the adenylate cyclase complex demonstrates that RCAP inhibits cholera toxin-specific ADP-ribosylation of the 42K subunit of Ns and stimulates pertussis toxin-specific ADP ribosylation of the 39K subunit of Ni