Identification of TH1 as an interaction partner of A-Raf kinase

A-Raf is an important intermediate of the growth factor Ras-MAP kinase pathway. In a two-hybrid screen of human fetal liver cDNA library, TH1 was detected as a new interaction partner of A-Raf. TH1 is a highly conserved and widely expressed protein, which was recently cloned by Bonthron DT group. The binding between A-Raf and TH1 was specific, as no binding between TH1 and B-Raf or c-Raf was observed, and the amino-terminal 162 amino acids in the A-Raf regulatory domain were found to be sufficient for this interaction. This specific interaction may have played a critical role in the activation of A-Raf.     

Expression in Escherichia coli, purification and kinetic characterization of human heparan sulfate 3-O-sulfotransferase-1.

Heparan sulfate (HS) glycosaminoglycans are a structurally diverse class of complex biomolecules that modulate many important events at the cell surface and within the extracellular matrix and whose structural heterogeneity derives largely from the sequence-specific N- and O-sulfations catalyzed by an extensive repertoire of sulfating enzymes. We have expressed the human heparan sulfate 3-OST-1 isoform in Escherichia coli and subsequently purified a soluble, active enzyme. To assess its functionality, we determined the kinetic parameters for the recombinant 3-O-sulfotransferase-1 using a radiochemical assay that directly measures the 3-O-sulfation of unlabeled bovine kidney heparan sulfate in vitro using [(35)S]PAPS as the sulfate donor. The apparent K(m) values measured were in the low micromolar range (K(HS)(m) = 4.3 microM; K(PAPS)(m) = 38.6 microM); V(max) values of 18 and 21 pmol sulfate/min/pmol of enzyme for HS and PAPS, respectively. These values were compared with kinetic parameters likewise measured for recombinant 3-OST-1 purified from baculovirus-infected sf9 cells. The two enzymes appear to modify heparan sulfate in vitro to roughly the same extent and with comparable specificities. The expression of 3-OST-1 in E. coli represents an important step in subsequent structure-function studies.     

Stage-specific expression of Smad2 and Smad3 during folliculogenesis

Paracrine and autocrine growth factors can affect many different aspects of ovarian follicle development. Many members of the transforming growth factor beta (TGFbeta) family of growth factors and their receptors are expressed in developing follicles. However, the presence and function of the family of the TGFbeta signaling molecules known as Smads have not been evaluated during follicle development. We have demonstrated that two Smad family members that function as mediators for both activin and TGFbeta are expressed in granulosa cells of preantral follicles but not in large antral follicles. Smad2 expression, but not Smad3 expression, returns in luteal cells. Both Smad2 and Smad3 are translocated to the nucleus of granulosa cells in response to treatment with either TGFbeta or activin. However, Smad2 is more responsive to activin stimulation, and Smad3 is more responsive to TGFbeta stimulation. Stage-specific expression and differing ligand sensitivity of signaling molecules may work together to allow different effects of TGFbeta family ligands using the same signaling pathways over the course of follicular development.     

The morphometry and biomechanical properties of the rat small intestine after systemic treatment with epidermal growth factor

Morphometric and passive biomechanical properties were studied in isolated segments of the duodenum, jejunum and ileum in 22 EGF-treated rats and 12 control rats. The rats were allocated to groups with EGF treatment for 2, 4, 7, and 14 days (n = 6 for each EGF treatment group except n = 4 for the 14 days group) or saline treatment (n = 3 for each group). The intestinal segments were pressurized with Krebs solution from 0 to 8 cmH2O for duodenum and 0 to 6 cmH2O for jejunum and ileum using a ramp distension protocol. The diameter and length were recorded at different pressure levels. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter, pressure and the zero-stress state data. EGF treatment was associated with pronounced morphometric changes, e.g., the wall thickness, wall area, and the circumferential lengths significantly increased during EGF treatment in all intestinal segments (P < 0.05). Histological analysis showed that the thickness and area of the layers increased after EGF treatment. With respect to the biomechanical data, the opening angle increased in all segments during EGF treatment with the highest value in the 14 days EGF treatment group (P < 0.05). The same result was found for residual strain and the residual strain gradient through the intestinal wall. Linear regression analysis demonstrated that the opening angle mainly depended on the mucosa thickness and area. Furthermore, the circumferential stiffness increased in the duodenum and decreased in the jejunum and ileum during EGF treatment. A plateau was reached after 7 days where after it started to normalize (P < 0.01). In the longitudinal direction, all intestinal segments became stiffer after EGF treatment for 7 days. After 14 days the curve started to normalize in duodenum and jejunum but not in the ileum.     

A rapid,nongenomic action of glucocorticoids in rat B103 neuroblastoma cells

We report here a new example in which glucocorticoids (GCs) acted in a rapid, nongenomic way. In rat B103 neuroblastoma cells, 5-hydroxytryptamine (5-HT) was found to evoke an immediate rise in intracellular free calcium concentration ([Ca(2+)](i)). Pre-incubation of B103 cells for 5 min with corticosterone (B) or bovine serum albumin-conjugated corticosterone (B-BSA) concentration-dependently (10(-4)-10(-8) M) inhibited the peak increments in [Ca(2+)](i). Cortisol and dexamethasone had a similar effect, while deoxycorticosterone and cholesterol were ineffective. This rapid inhibitory effect of corticosterone could be mimicked by protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and abolished completely by PKC inhibitors Ro31-8220 or GF-109203X. Neither pertussis toxin (PTX) nor nuclear GC receptor (GR) antagonist RU38486 influenced the rapid action of B. Our results suggest that GCs can modulate the 5-HT-induced Ca(2+) response in B103 cells in a membrane-initiated, nongenomic, and PKC-dependent manner.     

Proteomic analysis reveals alterations in the renal kallikrein pathway during hypoxia-induced hypertension

Obstructive sleep apnea syndrome (OSAS), a disorder characterized by episodic hypoxia (EH) during sleep, is associated with systemic hypertension. We used proteomic analysis to examine differences in rat kidney protein expression during EH, and their potential relationship to EH-induced hypertension. Young male Sprague-Dawley rats were exposed to either EH or sustained hypoxia (SH) for 14 (EH14/SH14) and 30 (EH30/SH30) days. Mean arterial blood pressure was significantly increased only in EH30 (p < 0.0002). Kidney proteins were resolved by two-dimensional-PAGE and were identified by MALDI-MS. Renal expression of kallistatin, a potent vasodilator, was down-regulated in all animals. Expression of alpha-1-antitrypsin, an inhibitor of kallikrein activation, was up-regulated in EH but down-regulated in SH. Western blotting showed significant elevation of B(2)-bradykinin receptor expression in all normotensive animals but remained unchanged in hypertensive animals. Proteins relevant to vascular hypertrophy, such as smooth muscle myosin and protein-disulfide isomerase were up-regulated in EH30 but were down-regulated in SH30. These data indicate that EH induces changes in renal protein expression consistent with impairment of vasodilation mediated by the kallikrein-kallistatin pathway and vascular hypertrophy. In contrast, SH-induced changes suggest the kallikrein- and bradykinin-mediated compensatory mechanisms for prevention of hypertension and vascular remodeling. To test the hypothesis suggested by the proteomic data, we measured the effect of EH on blood pressure in transgenic hKLK1 rats that overexpress human kallikrein. Transgenic hKLK1 animals were protected from EH-induced hypertension. We conclude that EH-induced hypertension may result, at least in part, from altered regulation of the renal kallikrein system.     

Mrd1p is required for processing of pre-rRNA and for maintenance of steady-state levels of 40 S ribosomal subunits in yeast

Ribosome biogenesis is a conserved process in eukaryotes that requires a large number of small nucleolar RNAs and trans-acting proteins. The Saccharomyces cerevisiae MRD1 (multiple RNA-binding domain) gene encodes a novel protein that contains five consensus RNA-binding domains. Mrd1p is essential for viability. Mrd1p partially co-localizes with the nucleolar protein Nop1p. Depletion of Mrd1p leads to a selective reduction of 18 S rRNA and 40 S ribosomal subunits. Mrd1p associates with the 35 S precursor rRNA (pre-rRNA) and U3 small nucleolar RNAs and is necessary for the initial processing at the A(0)-A(2) cleavage sites in pre-rRNA. The presence of five RNA-binding domains in Mrd1p suggests that Mrd1p may function to correctly fold pre-rRNA, a requisite for proper cleavage. Sequence comparisons suggest that Mrd1p homologues exist in all eukaryotes.     

Shedding of the interleukin-6 (IL-6) receptor (gp80) determines the ability of IL-6 to induce gp130 phosphorylation in human osteoblasts

Human osteoblasts produce interleukin-6 (IL-6) and respond to IL-6 in the presence of soluble IL-6 receptor (sIL-6R), but the cell surface expression of IL-6R and the mechanism of sIL-6R production are largely unknown. Three different human osteoblast-like cell lines (MG-63, HOS, and SaOS-2) and bone marrow-derived primary human osteoblasts expressed both IL-6R and gp130 as determined by flow cytometry and immunoprecipitation. However, the membrane-bound IL-6R was nonfunctional, as significant tyrosine phosphorylation of gp130 did not occur in the presence of IL-6. Phorbol myristate acetate induced a dramatic increase of both IL-6R shedding (i.e. the production of sIL-6R) and IL-6 release in osteoblast cultures, but the cell surface expression of gp130 remained unchanged. IL-6 complexed with sIL-6R, either exogenously introduced or derived from the nonfunctional cell surface form by shedding, induced rapid tyrosine phosphorylation of gp130. This effect was inhibited by neutralizing antibodies to either sIL-6R or gp130, indicating that the gp130 activation was induced by IL-6/sIL-6R/gp130 interaction. Protein kinase C inhibitors blocked phorbol myristate acetate-induced and spontaneous shedding of IL-6R resulting in the absence of sIL-6R in the culture medium, which in turn also prevented the activation of gp130. In conclusion, human osteoblasts express cell surface IL-6R, which is unable to transmit IL-6-induced signals until it is shed into its soluble form. This unique mechanism provides the flexibility for osteoblasts to control their own responsiveness to IL-6 via the activation of an IL-6R sheddase, resulting in an immediate production of functionally active osteoblast-derived sIL-6R.