The motility of gastrointestinal tract is regulated by classical neurotransmitters, neuropeptides, and humoral agents. Two novel human cDNAs have been cloned based on their sequence similarity to a frog skin secretion protein, Bv8, and a nontoxic protein of mamba snake venom. These human cDNAs encode two secreted proteins of 86 and 81 amino acids. Northern blot hybridization has revealed that these cDNAs are expressed in gastrointestinal tract, particularly the stomach. Recombinant proteins with authentic N-terminal sequences have been produced in Escherichia coli and refolded into functional proteins by careful control of protein aggregation. Mass spectrometry has confirmed the formation of five pairs of disulfide bonds. The refolded recombinant proteins potently contract gastrointestinal smooth muscle with EC(50) values in the subnanomolar range. The contractile effects of the recombinant proteins are specific for gastrointestinal smooth muscle, because they have no effect on vascular or respiratory smooth muscle. To reflect their potent and specific effects on gastrointestinal smooth muscle cells, we have named these recombinant proteins prokineticins. Ligand binding studies with iodinated prokineticin revealed the presence of a high-affinity site in ileal smooth muscle. The displacement of specific binding by GTP gamma S suggests that the prokineticin receptor may belong to the family of G protein-coupled receptors. Experiments with verapamil and nifedipine revealed that calcium influx is essential for the contractile activity of prokineticins on gastrointestinal smooth muscle. In summary, we have identified two novel endogenous regulators of gastrointestinal motility. The availability of recombinant prokineticins should provide novel therapeutic agents for disorders involving impaired gastrointestinal motility.

Proteins that bind to G protein-coupled receptors have recently been identified as regulators of receptor anchoring and signaling. In this study, actin-binding protein 280 (ABP-280), a widely expressed cytoskeleton-associated protein that plays an important role in regulating cell morphology and motility, was found to associate with the third cytoplasmic loop of dopamine D(2) receptors. The specificity of this interaction was originally identified in a yeast two-hybrid screen and confirmed by protein binding. The functional significance of the D(2) receptor-ABP-280 association was evaluated in human melanoma cells lacking ABP-280. D(2) receptor agonists were less potent in inhibiting forskolin-stimulated cAMP production in these cells. Maximal inhibitory responses of D(2) receptor activation were also reduced. Further yeast two-hybrid experiments showed that ABP-280 association is critically dependent on the carboxyl domain of the D(2) receptor third cytoplasmic loop, where there is a potential serine phosphorylation site (S358). Serine 358 was replaced with aspartic acid to mimic the effects of receptor phosphorylation. This mutant (D(2)S358D) displayed compromised binding to ABP-280 and coupling to adenylate cyclase. PKC activation also generated D(2) receptor signaling attenuation, but only in ABP-containing cells, suggesting a PKC regulatory role in D(2)-ABP association. A mechanism for these results may be derived from a role of ABP-280 in the clustering of D(2) receptors, as determined by immunocytochemical analysis in ABP-deficient and replete cells. Our results suggest a new molecular mechanism of modulating D(2) receptor signaling by cytoskeletal protein interaction.

Dysregulated stimulation of microglia, the resident macrophages in the brain, can lead to excessive induction of inflammatory agents and subsequently damage to neurons. Fibrillar b-amyloid peptide (fAb), a major component of senile plaques in Alzheimer's disease (AD) brain, is known to induce microglial-mediated neurotoxicity under certain conditions. Microglial 'priming' by macrophage colony stimulatory factor (MCSF) or interferon-gamma (IFNc) appears to be required for this fAb-induced microglia mediated neurotoxicity in vitro. We report here that while both MCSF and IFNc induce microglial-mediated fAb neurotoxicity, their mechanisms of toxicity differ. The enhancement of neurotoxicity by IFNc or MCSF is not due to enhanced Ab ingestion by microglia or to the direct effect of proinflammatory cytokine production. The neurotoxicity resulting from IFNc/fAb treatment was blocked by pretreatment with nitric oxide synthase inhibitor L-N-5-(1-iminoethyl) ornithine hydrochloride (L-NIO), consistent with a role for nitric oxide in the IFNc-mediated toxicity mechanism. In contrast, no induction of nitric oxide production was detected for microglia treated with MCSF/fAb. Furthermore, inhibiting the generation of reactive oxygen species (ROS) using the specific NADPH oxidase inhibitor apocynin reversed fAb/MCSF-induced neurotoxicity while L-NIO had little effect. As MCSF is endogenously expressed within the brain, and both its level and that of the MCSF receptor are dramatically increased in the AD brain, the neurotoxicity resulting from ROS release by fAb/MCSF coactivated microglia may be a more appropriate model for assessing fAb-induced microglialmediated neuropathology in AD.

This article estimates a partially linear model that permits non-linearities of unspecified form in the school quality-earnings relationship. It examines the joint effect of teacher education and pupil-teacher ratios on 1990 earnings using NLSY data. It finds some evidence of non-linearities in this relationship, and that teacher education has a positive effect on log wages at some points in the pupil-teacher ratio support.

Zellner and Ryu examined several popular specifications of elasticity of scale that characterizes production functions. This note goes further by combining these functional forms and proposing a model-averaged estimator of elasticity of scale. The methodology used in Bayesin Model Averaging, and the procedure is illustrated by an empirical example. Results show that the data clearly prefer some models over the others, but it can be difficult to select a model that overwhelmingly dominates the rest. This model-combined estimator of elasticity of scale is free of choosing a single specification from many competing ones. Moreover, this approach is readily applicable to comparable issues regarding production functions.