Functional dissection of an AP-2 beta2 appendage-binding sequence within the autosomal recessive hypercholesterolemia protein

The autosomal recessive hypercholesterolemia (ARH) protein plays a critical role in regulating plasma low density lipoprotein (LDL) levels. Inherited defects in ARH lead to a hypercholesterolemia that closely phenocopies that caused by a defective LDL receptor. The elevated serum LDL-cholesterol levels typical of ARH patients and the pronounced accumulation of the LDL receptor at the cell surface of hepatocytes in ARH-null mice argue that ARH operates by promoting the internalization of the LDL receptor within clathrin-coated vesicles. ARH contains an amino-terminal phosphotyrosine-binding domain that associates physically with the LDL receptor internalization sequence and with phosphoinositides. The carboxyl-terminal half of ARH contains a clathrin-binding sequence and a separate AP-2 adaptor binding region providing a plausible mechanism for how ARH can act as an endocytic adaptor or CLASP (clathrin-associated sorting protein) to couple LDL receptors with the clathrin machinery. Because the interaction with AP-2 is highly selective for the independently folded appendage domain of the beta2 subunit, we have characterized the ARH beta2 appendage-binding sequence in detail. Unlike the known alpha appendage-binding motifs, ARH requires an extensive sequence tract to bind the beta appendage with comparably high affinity. A minimal 16-residue sequence functions autonomously and depends upon ARH residues Asp253, Phe259, Leu262, and Arg266. We suggested that biased beta subunit engagement by ARH and the only other beta2 appendage selective adaptor, beta-arrestin, promotes efficient incorporation of this mechanistically distinct subset of CLASPs into clathrin-coated buds.     

Real-time fluorescence polarization measurements: interaction of phospholipase A2 with a fluorescent lecithin derivative

We have modified an SLM 4800 fluorometer to allow continuous measurement of fluorescence polarization. The modifications included construction of simple mechanical and electronic accessories which allowed polarizer position to be program-controlled by an HP 9815 calculator. With these modifications we were able to follow the interaction of the fluorescent lipid analog 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminododecanoyl phosphatidylcholine (I) with Naja-naja venom phospholipase A2 (PLA2) (E.C.3.1.1.4). Upon addition of aliquots of PLA2 containing up to 85 ng protein to a cuvette containing 1-2 microM I, the total measured polarization decreased linearly with time for at least 1000 s. Concomitant analyses of equivalent incubation mixtures and analyses of the contents of the cuvette after incubation and collection of fluorescence data revealed time-dependent formation of N-4-nitrobenzo-2-oxa-1,3-diazole-aminododecanoic acid (II). The decrease in total measured polarization was accelerated by Ca2+ and inhibited by EDTA. These data suggest that PLA2 activity in Naja-naja venom can be measured rapidly at low concentrations of both enzyme (0.01 microgram protein) and substrate (1 microM). Since this technique can be used to collect polarization data over time intervals as short as 4 s, it should be possible to measure the early changes in polarization during the interaction of fluorescent probes with proteins or membranes.     

Central activation of thermogenesis and fever by interleukin-1 beta and interleukin-1 alpha involves different mechanisms

Interleukin-1 exists in two forms (alpha and beta) which are assumed to act on the same receptor. Both forms of the molecule stimulated fever and thermogenesis in the rat when injected into the brain, but interleukin-1 beta was more effective, and combined injection of alpha and beta elicited additive responses. The actions of interleukin-1 beta were inhibited by pretreatment of the animals with either a receptor antagonist or monoclonal antibody to corticotrophin releasing factor. The effects of interleukin-1 alpha were unaltered by these treatments. The results indicate that brain corticotrophin releasing factor mediates thermogenesis and fever induced by interleukin-1 beta but not by interleukin-1 alpha.     

Discovery of 3-aryloxy-lactam analogs as potent androgen receptor full antagonists for treating castration resistant prostate cancer

High throughput cell-based screening led to the identification of 3-aryloxy lactams as potent androgen receptor (AR) antagonists. Refinement of these leads to improve the ADME profile and remove residual agonism led to the discovery of 12, a potent full antagonist with greater oral bioavailability. Improvements in the ADME profile were realized by designing more ligand-efficient molecules with reduced molecular weights and lower lipophilicities.     

Clathrin-mediated endocytosis of the epithelial sodium channel. Role of epsin

Here we present evidence that the epithelial sodium channel (ENaC), a heteromeric membrane protein whose surface expression is regulated by ubiquitination, is present in clathrin-coated vesicles in epithelial cells that natively express ENaC. The channel subunits are ubiquitinated and co-immunoprecipitate with both epsin and clathrin adaptor proteins, and epsin, as expected, co-immunoprecipitates with clathrin adaptor proteins. The functional significance of these interactions was evaluated in a Xenopus oocyte expression system where co-expression of epsin and ENaC resulted in a down-regulation of ENaC activity; conversely, co-expression of epsin sub-domains acted as dominant-negative effectors and stimulated ENaC activity. These results identify epsin as an accessory protein linking ENaC to the clathrin-based endocytic machinery thereby regulating the activity of this ion channel at the cell surface.