Steroid receptors in the human prostate. 1. Estradiol - 17beta binding in benign prostatic hypertrophy.

Agar gel electrophoresis and ultracentrifugation on continuous sucrose gradients revealed the presence of a 4S estradiol 'receptor' in cytosols of samples of human benign hyperplastic prostate tissue. High affinity (charcoal stability) and saturability (disappearance with excess competitor) binding characteristics of the molecular species concerned facilitated its clear distinction from similarly migrating serum albumin-steroid complexes. Our data, obtained with human serum, purified human albumin and albumin-enriched cytosol strongly suggest that agar gel electrophoresis, when used alone, may lack specificity for the quantification of estrogen 'receptors'. Radioligand binding to these molecules may be obscured by similarly migrating albumin-steroid complexes which fail to dissociate during electrophoresis. We advocate the inclusion of competitor experiments to improve the specificity of the method.     

Aphagia in the rat following microinjection of neurotensin into the ventral tegmental area

Neurotensin was microinjected into the lateral cerebral ventricle and the ventral tegmental area of rats which had been deprived of food for 18 hours. Both routes of administration resulted in a significant reduction of food intake compared to vehicle control injections. Additionally, the dose of neurotensin required to produce aphagia following ventral tegmental injection was substantially less than the dose required by the ventricular route. The results are discussed in relation to a possible site and mode of action for this neuropeptide.     

Autoradiographic localization of nicotinic receptor binding in rat brain using [3H]methylcarbamylcholine, a novel radioligand

Light microscopic autoradiography was used to visualize the neuroanatomical distribution of nicotinic receptors in rat brain using a novel radioligand, [3H]methylcarbamylcholine (MCC). Specific [3H]MCC binding to slide-mounted tissue sections of rat brain was saturable, reversible and of high affinity. Data analysis revealed a single population of [3H]MCC binding sites with a Kd value of 1.8 nM and Bmax of 20.1 fmol/mg protein. Nicotinic agonists and antagonists competed for [3H]MCC binding sites in slide-mounted brain sections with much greater potency than muscarinic drugs. The rat brain areas containing the highest densities of [3H]MCC binding were in thalamic regions, the medial habenular nucleus and the superior colliculus. Moderate densities of [3H]MCC binding were seen over the anterior cingulate cortex, the nucleus accumbens, the zona compacta of substantia nigra and ventral tegmental area. Low densities of [3H]MCC binding were found in most other brain regions. These data suggest that [3H]MCC selectively labels central nicotinic receptors and that these receptors are concentrated in the thalamus, the medial habenular nucleus and the superior colliculus of the rat brain.     

A unique FGF23 with the ability to activate FGFR signaling through both αKlotho and βKlotho

Three fibroblast growth factor (FGF) molecules, FGF19, FGF21, and FGF23, form a unique subfamily that functions as endocrine hormones. FGF19 and FGF21 can regulate glucose, lipid, and energy metabolism, while FGF23 regulates phosphate homeostasis. The FGF receptors and co-receptors for these three FGF molecules have been identified, and domains important for receptor interaction and specificity determination are beginning to be elucidated. However, a number of questions remain unanswered, such as the identification of fibroblast growth factor receptor responsible for glucose regulation. Here, we have generated a variant of FGF23: FGF23-21c, where the C-terminal domain of FGF23 was replaced with the corresponding regions from FGF21. FGF23-21c showed a number of interesting and unexpected properties in vitro. In contrast to wild-type FGF23, FGF23-21c gained the ability to activate FGFR1c and FGFR2c in the presence of βKlotho and was able to stimulate glucose uptake into adipocytes in vitro and lower glucose levels in ob/ob diabetic mice model to similar extent as FGF21 in vivo. These results suggest that βKlotho/FGFR1c or FGFR2c receptor complexes are sufficient for glucose regulation. Interestingly, without the FGF23 C-terminal domain, FGF23-21c was still able to activate fibroblast growth factor receptors in the presence of αKlotho. This suggests not only that sequences outside of the C-terminal region may also contribute to the interaction with co-receptors but also that FGF23-21c may be able to regulate both glucose and phosphate metabolisms. This raises an interesting concept of designing an FGF molecule that may be able to address multiple diseases simultaneously. Further understanding of FGF/receptor interactions may allow the development of exciting opportunities for novel therapeutic discovery.     

The inositol 5-phosphatase INPP5B regulates B cell receptor clustering and signaling

Upon antigen binding, the B cell receptor (BCR) undergoes clustering to form a signalosome that propagates downstream signaling required for normal B cell development and physiology. BCR clustering is dependent on remodeling of the cortical actin network, but the mechanisms that regulate actin remodeling in this context remain poorly defined. In this study, we identify the inositol 5-phosphatase INPP5B as a key regulator of actin remodeling, BCR clustering, and downstream signaling in antigen-stimulated B cells. INPP5B acts via dephosphorylation of the inositol lipid PI(4,5)P₂ that in turn is necessary for actin disassembly, BCR mobilization, and cell spreading on immobilized surface antigen. These effects can be explained by increased actin severing by cofilin and loss of actin linking to the plasma membrane by ezrin, both of which are sensitive to INPP5B-dependent PI(4,5)P₂ hydrolysis. INPP5B is therefore a new player in BCR signaling and may represent an attractive target for treatment of B cell malignancies caused by aberrant BCR signaling.