Maternal Short-Chain Fructooligosaccharide Supplementation Influences Intestinal Immune System Maturation in Piglets

Peripartum nutrition is crucial for developing the immune system of neonates. We hypothesized that maternal short-chain fructooligosaccharide (scFOS) supplementation could accelerate the development of intestinal immunity in offspring. Thirty-four sows received a standard or a scFOS supplemented diet (10 g scFOS/d) for the last 4 weeks of gestation and the 4 weeks of lactation. Colostrum and milk immunoglobulins (Ig) and TGFβ1 concentrations were evaluated on the day of delivery and at d 6 and d 21 postpartum. Piglet intestinal structure, the immunologic features of jejunal and ileal Peyer''s patches, and mesenteric lymph node cells were analysed at postnatal d 21. Short-chain fatty acid concentrations were measured over time in the intestinal contents of suckling and weaned piglets. Colostral IgA (P<0.05) significantly increased because of scFOS and TGFβ1 concentrations tended to improve (P<0.1). IFNγ secretion by stimulated Peyer''s patch and mesenteric lymph node cells, and secretory IgA production by unstimulated Peyer''s patch cells were increased (P<0.05) in postnatal d 21 scFOS piglets. These differences were associated with a higher proportion of activated CD25+CD4α+ T cells among the CD4+ helper T lymphocytes (P<0.05) as assessed by flow cytometry. IFNγ secretion was positively correlated with the population of activated T lymphocytes (P<0.05). Total short-chain fatty acids were unchanged between groups during lactation but were higher in caecal contents of d 90 scFOS piglets (P<0.05); specifically propionate, butyrate and valerate. In conclusion, we demonstrated that maternal scFOS supplementation modified the intestinal immune functions in piglets in association with increased colostral immunity. Such results underline the key role of maternal nutrition in supporting the postnatal development of mucosal immunity.     

Regulators of G Protein Signaling Attenuate the G Protein–mediated Inhibition of N-Type Ca Channels

Regulators of G protein signaling (RGS) proteins bind to the α subunits of certain heterotrimeric G proteins and greatly enhance their rate of GTP hydrolysis, thereby determining the time course of interactions among Gα, Gβγ, and their effectors. Voltage-gated N-type Ca channels mediate neurosecretion, and these Ca channels are powerfully inhibited by G proteins. To determine whether RGS proteins could influence Ca channel function, we recorded the activity of N-type Ca channels coexpressed in human embryonic kidney (HEK293) cells with G protein–coupled muscarinic (m2) receptors and various RGS proteins. Coexpression of full-length RGS3T, RGS3, or RGS8 significantly attenuated the magnitude of receptor-mediated Ca channel inhibition. In control cells expressing α1B, α2, and β3 Ca channel subunits and m2 receptors, carbachol (1 μM) inhibited whole-cell currents by ∼80% compared with only ∼55% inhibition in cells also expressing exogenous RGS protein. A similar effect was produced by expression of the conserved core domain of RGS8. The attenuation of Ca current inhibition resulted primarily from a shift in the steady state dose–response relationship to higher agonist concentrations, with the EC₅₀ for carbachol inhibition being ∼18 nM in control cells vs. ∼150 nM in RGS-expressing cells. The kinetics of Ca channel inhibition were also modified by RGS. Thus, in cells expressing RGS3T, the decay of prepulse facilitation was slower, and recovery of Ca channels from inhibition after agonist removal was faster than in control cells. The effects of RGS proteins on Ca channel modulation can be explained by their ability to act as GTPase-accelerating proteins for some Gα subunits. These results suggest that RGS proteins may play important roles in shaping the magnitude and kinetics of physiological events, such as neurosecretion, that involve G protein–modulated Ca channels.     

Short divalent ethacrynic amides as pro-inhibitors of glutathione S-transferase isozyme Mu and potent sensitisers of cisplatin-resistant ovarian cancers

The linking of ethacrynic acid with ethylenediamine and 1,4-butanediamine gave EDEA and BDEA, respectively, as membrane-permeable divalent pro-inhibitors of glutathione S-transferase (GST). Their divalent glutathione conjugates showed subnanomolar inhibition and divalence-binding to GSTmu (GSTM) (PDB: 5HWL) at ∼0.35 min⁻¹. In cisplatin-resistant SK-OV-3, COC1, SGC7901 and A549 cells, GSTM activities probed by 15 nM BDEA or EDEA revealed 5-fold and 1.0-fold increases in cisplatin-resistant SK-OV-3 and COC1 cells, respectively, in comparison with the susceptible parental cells. Being tolerable by HEK293 and LO2 cells, BDEA at 0.2 μM sensitised resistant SK-OV-3 and COC1 cells by ∼3- and ∼5-folds, respectively, released cytochrome c and increased apoptosis; EDEA at 1.0 μM sensitised resistant SK-OV-3 and A549 cells by ∼5- and ∼7-fold, respectively. EDEA at 1.7 μg/g sensitised resistant SK-OV-3 cells to cisplatin at 3.3 μg/g in nude mouse xenograft model. BDEA and EDEA are promising leads for probing cellular GSTM and sensitising cisplatin-resistant ovarian cancers.     

Intracellular Ca2+ Inhibits Smooth Muscle L-Type Ca2+ Channels by Activation of Protein Phosphatase Type 2B and by Direct Interaction with the Channel

Modulation of L-type Ca²⁺ channels by tonic elevation of cytoplasmic Ca²⁺ was investigated in intact cells and inside-out patches from human umbilical vein smooth muscle. Ba²⁺ was used as charge carrier, and run down of Ca²⁺ channel activity in inside-out patches was prevented with calpastatin plus ATP. Increasing cytoplasmic Ca²⁺ in intact cells by elevation of extracellular Ca²⁺ in the presence of the ionophore A23187 inhibited the activity of L-type Ca²⁺ channels in cell-attached patches. Measurement of the actual level of intracellular free Ca²⁺ with fura-2 revealed a 50% inhibitory concentration (IC₅₀) of 260 nM and a Hill coefficient close to 4 for Ca²⁺- dependent inhibition. Ca²⁺-induced inhibition of Ca²⁺ channel activity in intact cells was due to a reduction of channel open probability and availability. Ca²⁺-induced inhibition was not affected by the protein kinase inhibitor H-7 (10 μM) or the cytoskeleton disruptive agent cytochalasin B (20 μM), but prevented by cyclosporin A (1 μg/ ml), an inhibitor of protein phosphatase 2B (calcineurin). Elevation of Ca²⁺ at the cytoplasmic side of inside-out patches inhibited Ca²⁺ channels with an IC₅₀ of 2 μM and a Hill coefficient close to unity. Direct Ca²⁺-dependent inhibition in cell-free patches was due to a reduction of open probability, whereas availability was barely affected. Application of purified protein phosphatase 2B (12 U/ml) to the cytoplasmic side of inside-out patches at a free Ca²⁺ concentration of 1 μM inhibited Ca²⁺ channel open probability and availability. Elevation of cytoplasmic Ca²⁺ in the presence of PP2B, suppressed channel activity in inside-out patches with an IC₅₀ of ∼380 nM and a Hill coefficient of ∼3; i.e., characteristics reminiscent of the Ca²⁺ sensitivity of Ca²⁺ channels in intact cells. Our results suggest that L-type Ca²⁺ channels of smooth muscle are controlled by two Ca²⁺-dependent negative feedback mechanisms. These mechanisms are based on (a) a protein phosphatase 2B-mediated dephosphorylation process, and (b) the interaction of intracellular Ca²⁺ with a single membrane-associated site that may reside on the channel protein itself.     

Lymphotoxin Alpha-Deficient Mice Clear Persistent Rotavirus Infection after Local Generation of Mucosal IgA

Rotavirus is a major cause of pediatric diarrheal illness worldwide. To explore the role of organized intestinal lymphoid tissues in infection by and immunity to rotavirus, lymphotoxin alpha-deficient (LTα^−/−) mice that lack Peyer''s patches and mesenteric lymph nodes were orally infected with murine rotavirus. Systemic rotavirus was cleared within 10 days in both LTα^−/− and wild-type mice, and both strains developed early and sustained serum antirotavirus antibody responses. However, unlike wild-type mice, which resolved the intestinal infection within 10 days, LTα^−/− mice shed fecal virus for approximately 50 days after inoculation. The resolution of fecal virus shedding occurred concurrently with induction of intestinal rotavirus-specific IgA in both mouse strains. Induction of intestinal rotavirus-specific IgA in LTα^−/− mice correlated with the (late) appearance of IgA-producing plasma cells in the small intestine. This, together with the absence of rotavirus-specific serum IgA, implies that secretory rotavirus-specific IgA was produced locally. These findings indicate that serum IgG responses are insufficient and imply that local intestinal IgA responses are important for the clearance of rotavirus from intestinal tissues. Furthermore, they show that while LTα-dependent lymphoid tissues are important for the generation of IgA-producing B cells in the intestine, they are not absolutely required in the setting of rotavirus infection. Moreover, the induction of local IgA-producing B cell responses can occur late after infection and in an LTα-independent manner.     

Quantitative analysis of APP axonal transport in neurons: role of JIP1 in enhanced APP anterograde transport

Alzheimer''s β-amyloid precursor protein (APP) associates with kinesin-1 via JNK-interacting protein 1 (JIP1); however, the role of JIP1 in APP transport by kinesin-1 in neurons remains unclear. We performed a quantitative analysis to understand the role of JIP1 in APP axonal transport. In JIP1-deficient neurons, we find that both the fast velocity (∼2.7 μm/s) and high frequency (66%) of anterograde transport of APP cargo are impaired to a reduced velocity (∼1.83 μm/s) and a lower frequency (45%). We identified two novel elements linked to JIP1 function, located in the central region of JIP1b, that interact with the coiled-coil domain of kinesin light chain 1 (KLC1), in addition to the conventional interaction of the JIP1b 11–amino acid C-terminal (C11) region with the tetratricopeptide repeat of KLC1. High frequency of APP anterograde transport is dependent on one of the novel elements in JIP1b. Fast velocity of APP cargo transport requires the C11 domain, which is regulated by the second novel region of JIP1b. Furthermore, efficient APP axonal transport is not influenced by phosphorylation of APP at Thr-668, a site known to be phosphorylated by JNK. Our quantitative analysis indicates that enhanced fast-velocity and efficient high-frequency APP anterograde transport observed in neurons are mediated by novel roles of JIP1b.     

Suppression of NF-κB and NF-κB-Regulated Gene Expression by Apigenin through IκBα and IKK Pathway in TRAMP Mice

Aberrant Nuclear Factor-κappaB (NF-κB) activation due to rapid IκBα turnover and high basal IκBα kinase (IKK) activity has been frequently observed in prostate cancer. Apigenin, a naturally occurring plant flavone, exhibits anti-proliferative, anti-inflammatory and anti-carcinogenic activities by inhibiting NF-κB pathway, through a mechanism not fully understood. We found that apigenin feeding in microgram doses (bioavailable in humans) inhibited prostate tumorigenesis in TRAMP mice by interfering with NF-κB signaling. Apigenin feeding to TRAMP mice (20 and 50 μg/mouse/day, 6 days/week for 20 weeks) exhibited significant decrease in tumor volumes of the prostate and completely abolished metastasis, which correlated with inhibition of NF-κB activation and binding to the DNA. Apigenin intake blocked phosphorylation and degradation of IκBα by inhibiting IKK activation, which in turn led to suppression of NF-κB activation. The expression of NF-κB-regulated gene products involved in proliferation (cyclin D1, and COX-2), anti-apoptosis (Bcl-2 and Bcl-xL), and angiogenesis (vascular endothelial growth factor) were also downregulated after apigenin feeding. These events correlated with the induction of apoptosis in tumor cells, as evident by increased cleaved caspase-3 labeling index in the dorsolateral prostate. Our results provide convincing evidence that apigenin inhibits IKK activation and restores the expression of IκBα, preventing it’s phosphorylation in a fashion similar to that elicited by IKK and proteasomal inhibitors through suppression of NF-κB signaling pathway.     

Anion-Sensitive Regions of L-Type CaV1.2 Calcium Channels Expressed in HEK293 Cells

L-type calcium currents (I_Ca) are influenced by changes in extracellular chloride, but sites of anion effects have not been identified. Our experiments showed that CaV1.2 currents expressed in HEK293 cells are strongly inhibited by replacing extracellular chloride with gluconate or perchlorate. Variance-mean analysis of I_Ca and cell-attached patch single channel recordings indicate that gluconate-induced inhibition is due to intracellular anion effects on Ca²⁺ channel open probability, not conductance. Inhibition of CaV1.2 currents produced by replacing chloride with gluconate was reduced from ∼75%–80% to ∼50% by omitting β subunits but unaffected by omitting α₂δ subunits. Similarly, gluconate inhibition was reduced to ∼50% by deleting an α1 subunit N-terminal region of 15 residues critical for β subunit interactions regulating open probability. Omitting β subunits with this mutant α1 subunit did not further diminish inhibition. Gluconate inhibition was unchanged with expression of different β subunits. Truncating the C terminus at AA1665 reduced gluconate inhibition from ∼75%–80% to ∼50% whereas truncating it at AA1700 had no effect. Neutralizing arginines at AA1696 and 1697 by replacement with glutamines reduced gluconate inhibition to ∼60% indicating these residues are particularly important for anion effects. Expressing CaV1.2 channels that lacked both N and C termini reduced gluconate inhibition to ∼25% consistent with additive interactions between the two tail regions. Our results suggest that modest changes in intracellular anion concentration can produce significant effects on CaV1.2 currents mediated by changes in channel open probability involving β subunit interactions with the N terminus and a short C terminal region.     

Electrophysiological Characterization of the Rat Epithelial Na+ Channel (rENaC) Expressed in MDCK Cells : Effects of Na+ and Ca2+

The epithelial Na⁺ channel (ENaC), composed of three subunits (α, β, and γ), is expressed in several epithelia and plays a critical role in salt and water balance and in the regulation of blood pressure. Little is known, however, about the electrophysiological properties of this cloned channel when expressed in epithelial cells. Using whole-cell and single channel current recording techniques, we have now characterized the rat αβγENaC (rENaC) stably transfected and expressed in Madin-Darby canine kidney (MDCK) cells. Under whole-cell patch-clamp configuration, the αβγrENaC-expressing MDCK cells exhibited greater whole cell Na⁺ current at −143 mV (−1,466.2 ± 297.5 pA) than did untransfected cells (−47.6 ± 10.7 pA). This conductance was completely and reversibly inhibited by 10 μM amiloride, with a Ki of 20 nM at a membrane potential of −103 mV; the amiloride inhibition was slightly voltage dependent. Amiloride-sensitive whole-cell current of MDCK cells expressing αβ or αγ subunits alone was −115.2 ± 41.4 pA and −52.1 ± 24.5 pA at −143 mV, respectively, similar to the whole-cell Na⁺ current of untransfected cells. Relaxation analysis of the amiloride-sensitive current after voltage steps suggested that the channels were activated by membrane hyperpolarization. Ion selectivity sequence of the Na⁺ conductance was Li⁺ > Na⁺ >> K⁺ = N-methyl-d-glucamine⁺ (NMDG⁺). Using excised outside-out patches, amiloride-sensitive single channel conductance, likely responsible for the macroscopic Na⁺ channel current, was found to be ∼5 and 8 pS when Na⁺ and Li⁺ were used as a charge carrier, respectively. K⁺ conductance through the channel was undetectable. The channel activity, defined as a product of the number of active channel (n) and open probability (P _o), was increased by membrane hyperpolarization. Both whole-cell Na⁺ current and conductance were saturated with increased extracellular Na⁺ concentrations, which likely resulted from saturation of the single channel conductance. The channel activity (nP _o) was significantly decreased when cytosolic Na⁺ concentration was increased from 0 to 50 mM in inside-out patches. Whole-cell Na⁺ conductance (with Li⁺ as a charge carrier) was inhibited by the addition of ionomycin (1 μM) and Ca²⁺ (1 mM) to the bath. Dialysis of the cells with a pipette solution containing 1 μM Ca²⁺ caused a biphasic inhibition, with time constants of 1.7 ± 0.3 min (n = 3) and 128.4 ± 33.4 min (n = 3). An increase in cytosolic Ca²⁺ concentration from <1 nM to 1 μM was accompanied by a decrease in channel activity. Increasing cytosolic Ca²⁺ to 10 μM exhibited a pronounced inhibitory effect. Single channel conductance, however, was unchanged by increasing free Ca²⁺ concentrations from <1 nM to 10 μM. Collectively, these results provide the first characterization of rENaC heterologously expressed in a mammalian epithelial cell line, and provide evidence for channel regulation by cytosolic Na⁺ and Ca²⁺.     

Temperature Dependences of Torque Generation and Membrane Voltage in the Bacterial Flagellar Motor

In their natural habitats bacteria are frequently exposed to sudden changes in temperature that have been shown to affect their swimming. With our believed to be new methods of rapid temperature control for single-molecule microscopy, we measured here the thermal response of the Na⁺-driven chimeric motor expressed in Escherichia coli cells. Motor torque at low load (0.35 μm bead) increased linearly with temperature, twofold between 15°C and 40°C, and torque at high load (1.0 μm bead) was independent of temperature, as reported for the H⁺-driven motor. Single cell membrane voltages were measured by fluorescence imaging and these were almost constant (∼120 mV) over the same temperature range. When the motor was heated above 40°C for 1–2 min the torque at high load dropped reversibly, recovering upon cooling below 40°C. This response was repeatable over as many as 10 heating cycles. Both increases and decreases in torque showed stepwise torque changes with unitary size ∼150 pN nm, close to the torque of a single stator at room temperature (∼180 pN nm), indicating that dynamic stator dissociation occurs at high temperature, with rebinding upon cooling. Our results suggest that the temperature-dependent assembly of stators is a general feature of flagellar motors.     

DNA-Dependent Protein Kinase Phosphorylation of IκBα and IκBβ Regulates NF-κB DNA Binding Properties

Regulation of the IκBα and IκBβ proteins is critical for modulating NF-κB-directed gene expression. Both IκBα and IκBβ are substrates for cellular kinases that phosphorylate the amino and carboxy termini of these proteins and regulate their function. In this study, we utilized a biochemical fractionation scheme to purify a kinase activity which phosphorylates residues in the amino and carboxy termini of both IκBα and IκBβ. Peptide microsequence analysis by capillary high-performance liquid chromatography ion trap mass spectroscopy revealed that this kinase was the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). DNA-PK phosphorylates serine residue 36 but not serine residue 32 in the amino terminus of IκBα and also phosphorylates threonine residue 273 in the carboxy terminus of this protein. To determine the biological relevance of DNA-PK phosphorylation of IκBα, murine severe combined immunodeficiency (SCID) cell lines which lack the DNA-PKcs gene were analyzed. Gel retardation analysis using extract prepared from these cells demonstrated constitutive nuclear NF-κB DNA binding activity, which was not detected in extracts prepared from SCID cells complemented with the human DNA-PKcs gene. Furthermore, IκBα that was phosphorylated by DNA-PK was a more potent inhibitor of NF-κB binding than nonphosphorylated IκBα. These results suggest that DNA-PK phosphorylation of IκBα increases its interaction with NF-κB to reduce NF-κB DNA binding properties.     

IκB Is a Substrate for a Selective Pathway of Lysosomal Proteolysis

In lysosomes isolated from rat liver and spleen, a percentage of the intracellular inhibitor of the nuclear factor κ B (IκB) can be detected in the lysosomal matrix where it is rapidly degraded. Levels of IκB are significantly higher in a lysosomal subpopulation that is active in the direct uptake of specific cytosolic proteins. IκB is directly transported into isolated lysosomes in a process that requires binding of IκB to the heat shock protein of 73 kDa (hsc73), the cytosolic molecular chaperone involved in this pathway, and to the lysosomal glycoprotein of 96 kDa (lgp96), the receptor protein in the lysosomal membrane. Other substrates for this degradation pathway competitively inhibit IκB uptake by lysosomes. Ubiquitination and phosphorylation of IκB are not required for its targeting to lysosomes. The lysosomal degradation of IκB is activated under conditions of nutrient deprivation. Thus, the half-life of a long-lived pool of IκB is 4.4 d in serum-supplemented Chinese hamster ovary cells but only 0.9 d in serum-deprived Chinese hamster ovary cells. This increase in IκB degradation can be completely blocked by lysosomal inhibitors. In Chinese hamster ovary cells exhibiting an increased activity of the hsc73-mediated lysosomal degradation pathway due to overexpression of lamp2, the human form of lgp96, the degradation of IκB is increased. There are both short- and long-lived pools of IκB, and it is the long-lived pool that is subjected to the selective lysosomal degradation pathway. In the presence of antioxidants, the half-life of the long-lived pool of IκB is significantly increased. Thus, the production of intracellular reactive oxygen species during serum starvation may be one of the mechanisms mediating IκB degradation in lysosomes. This selective pathway of lysosomal degradation of IκB is physiologically important since prolonged serum deprivation results in an increase in the nuclear activity of nuclear factor κ B. In addition, the response of nuclear factor κ B to several stimuli increases when this lysosomal pathway of proteolysis is activated.