Portal sensing of intestinal gluconeogenesis is a mechanistic link in the diminution of food intake induced by diet protein

Protein feeding is known to decrease hunger and subsequent food intake in animals and humans. It has also been suggested that glucose appearance into portal vein, as occurring during meal assimilation, may induce comparable effects. Here, we connect these previous observations by reporting that intestinal gluconeogenesis (i.e., de novo synthesis of glucose) is induced during the postabsorptive time (following food digestion) in rats specifically fed on protein-enriched diet. This results in glucose release into portal blood, counterbalancing the lowering of glycemia resulting from intestinal glucose utilization. Comparable infusions into the portal vein of control postabsorptive rats (fed on starch-enriched diet) decrease food consumption and activate the hypothalamic nuclei regulating food intake. Similar hypothalamic activation occurs on protein feeding. All these effects are absent after denervation of the portal vein. Thus, portal sensing of intestinal gluconeogenesis may be a novel mechanism connecting the macronutrient composition of diet to food intake.     

Exogenously added fibroblast growth factor 2 (FGF-2) to NIH3T3 cells interacts with nuclear ribosomal S6 kinase 2 (RSK2) in a cell cycle-dependent manner

Fibroblast growth factor 2 (FGF-2) has been detected in the nuclei of many tissues and cell lines. Here we demonstrate that FGF-2 added exogenously to NIH3T3 cells enters the nucleus and interacts with the nuclear active 90-kDa ribosomal S6 kinase 2 (RSK2) in a cell cycle-dependent manner. By using purified proteins, FGF-2 is shown to directly interact through two separate domains with two RSK2 domains on both sides of the hydrophobic motif, namely the NH2-terminal kinase domain (residues 360-381) by amino acid Ser-117 and the COOH-terminal kinase domain (residues 388-400) by amino acids Leu-127 and Lys-128. Moreover, this interaction leads to maintenance of the sustained activation of RSK2 in G1 phase of the cell cycle. FGF-2 mutants (FGF-2 S117A, FGF-2 L127A, and FGF-2 K128A) that fail to interact in vitro with RSK2 fail to maintain a sustained RSK2 activity in vivo.     

CDK1/cyclin B regulation during oocyte maturation in two closely related lugworm species, Arenicola marina and Arenicola defodiens

The molecular mechanisms underlying oocyte maturation in the annelid polychaetes Arenicola marina and Arenicola defodiens were investigated. In both species, a hitherto unidentified hormone triggers synchronous and rapid transition from prophase to metaphase, a maturation process which can be easily reproduced in vitro. Activation of a roscovitine- and olomoucine-sensitive M-phase-specific histone, H1 kinase, occurs during oocyte maturation. Using affinity chromatography on immobilized p9CKShs1, we purified CDK1 and cyclin B from oocyte extracts prepared from both phases and both species. In prophase, CDK1 is present both as an inactive, but Thr161-phosphorylated monomer, and as an inactive (Tyr15-phosphorylated) heterodimer with cyclin B. Prophase to metaphase transition is associated with complete tyrosine dephosphorylation of the cyclin B-associated CDK1, with phosphorylation of cyclin B, and with dramatic activation of the kinase activity of the CDK1/cyclin B complex. We propose that Arenicola oocytes may provide an ideal model system to investigate the acquisition of the ability of oocytes to be fertilized that occurs as oocyte shift from prophase to metaphase, an important physiological event, probably regulated by active CDK1/cyclin B.     

PrPSc binding antibodies are potent inhibitors of prion replication in cell lines

Conversion of the cellular alpha-helical prion protein (PrP(C)) into a disease-associated isoform (PrP(Sc)) is central to the pathogenesis of prion diseases. Molecules targeting either normal or disease-associated isoforms may be of therapeutic interest, and the antibodies binding PrP(C) have been shown to inhibit prion accumulation in vitro. Here we investigate whether antibodies that additionally target disease-associated isoforms such as PrP(Sc) inhibit prion replication in ovine PrP-inducible scrapie-infected Rov cells. We conclude from these experiments that antibodies exclusively binding PrP(C) were relatively inefficient inhibitors of ScRov cell PrP(Sc) accumulation compared with antibodies that additionally targeted disease-associated PrP isoforms. Although the mechanism by which these monoclonal antibodies inhibit prion replication is unclear, some of the data suggest that antibodies might actively increase PrP(Sc) turnover. Thus antibodies that bind to both normal and disease-associated isoforms represent very promising anti-prion agents.     

B cell-activating factor belonging to the TNF family acts through separate receptors to support B cell survival and T cell-independent antibody formation

The TNF-related ligand, B cell-activating factor belonging to the TNF family (BAFF), is necessary for normal B cell development and survival, and specifically binds the receptors transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), B cell maturation Ag (BCMA), and BAFF-R. Similarities between mice completely lacking BAFF and A/WySnJ strain mice that express a naturally occurring mutant form of BAFF-R suggest that BAFF acts primarily through BAFF-R. However, the nearly full-length BAFF-R protein expressed by A/WySnJ mice makes unambiguous interpretation of receptor function in these animals impossible. Using homologous recombination we created mice completely lacking BAFF-R and compared them directly to A/WySnJ mice and to mice lacking BAFF. BAFF-R-null mice exhibit loss of mature B cells similar to that observed in BAFF(-/-) and A/WySnJ mice. Also, mice lacking both TACI and BCMA simultaneously exhibit no B cell loss, thus confirming that BAFF-R is the primary receptor for transmitting the BAFF-dependent B cell survival signal. However, while BAFF-R-null mice cannot carry out T cell-dependent Ab formation, they differ from BAFF-deficient mice in generating normal levels of Ab to at least some T cell-independent Ags. These studies clearly demonstrate that BAFF regulates Ab responses in vivo through receptors in addition to BAFF-R.     

In vivo adjuvant-induced mobilization and maturation of gut dendritic cells after oral administration of cholera toxin

Although dendritic cells (DCs) regulate immune responses, they exhibit functional heterogeneity depending on their anatomical location. We examined the functional properties of intestinal DCs after oral administration of cholera toxin (CT), the most potent mucosal adjuvant. Two CD11c+ DC subsets were identified both in Peyer's patches and mesenteric lymph nodes (MLN) based on the expression of CD8alpha (CD8+ and CD8- DCs, respectively). A third subset of CD11c+CD8int was found exclusively in MLN. Feeding mice with CT induced a rapid and transient mobilization of a new CD11c+CD8- DC subset near the intestinal epithelium. This recruitment was associated with an increased production of the chemokine CCL20 in the small intestine and was followed by a massive accumulation of CD8int DCs in MLN. MLN DCs from CT-treated mice were more potent activators of naive T cells than DCs from control mice and induced a Th2 response. This increase in immunostimulating properties was accounted for by CD8int and CD8- DCs, whereas CD8+ DCs remained insensitive to CT treatment. Consistently, the CD8int and CD8- subsets expressed higher levels of costimulatory molecules than CD8+ and corresponding control DCs. Adoptive transfer experiments showed that these two DC subsets, unlike CD8+ DCs, were able to present Ags orally coadministered with CT in an immunostimulating manner. The ability of CT to mobilize immature DCs in the intestinal epithelium and to promote their emigration and differentiation in draining lymph nodes may explain the exceptional adjuvant properties of this toxin on mucosal immune responses.