Microtubule severing by the katanin complex is activated by PPFR-1–dependent MEI-1 dephosphorylation

Katanin is an evolutionarily conserved microtubule (MT)-severing complex implicated in multiple aspects of MT dynamics. In Caenorhabditis elegans, the katanin homologue MEI-1 is required for meiosis, but must be inactivated before mitosis. Here we show that PPFR-1, a regulatory subunit of a trimeric protein phosphatase 4 complex, enhanced katanin MT-severing activity during C. elegans meiosis. Loss of ppfr-1, similarly to the inactivation of MT severing, caused a specific defect in meiosis II spindle disassembly. We show that a fraction of PPFR-1 was degraded after meiosis, contributing to katanin inactivation. PPFR-1 interacted with MEL-26, the substrate recognition subunit of the CUL-3 RING E3 ligase (CRL3^MEL-26), which also targeted MEI-1 for post-meiotic degradation. Reversible protein phosphorylation of MEI-1 may ensure temporal activation of the katanin complex during meiosis, whereas CRL3^MEL-26-mediated degradation of both MEI-1 and its activator PPFR-1 ensure efficient katanin inactivation in the transition to mitosis.     

BAX inhibitor-1 regulates autophagy by controlling the IRE1α branch of the unfolded protein response

Both autophagy and apoptosis are tightly regulated processes playing a central role in tissue homeostasis. Bax inhibitor 1 (BI-1) is a highly conserved protein with a dual role in apoptosis and endoplasmic reticulum (ER) stress signalling through the regulation of the ER stress sensor inositol requiring kinase 1 α (IRE1α). Here, we describe a novel function of BI-1 in the modulation of autophagy. BI-1-deficient cells presented a faster and stronger induction of autophagy, increasing LC3 flux and autophagosome formation. These effects were associated with enhanced cell survival under nutrient deprivation. Repression of autophagy by BI-1 was dependent on cJun-N terminal kinase (JNK) and IRE1α expression, possibly due to a displacement of TNF-receptor associated factor-2 (TRAF2) from IRE1α. Targeting BI-1 expression in flies altered autophagy fluxes and salivary gland degradation. BI-1 deficiency increased flies survival under fasting conditions. Increased expression of autophagy indicators was observed in the liver and kidney of bi-1-deficient mice. In summary, we identify a novel function of BI-1 in multicellular organisms, and suggest a critical role of BI-1 as a stress integrator that modulates autophagy levels and other interconnected homeostatic processes.     

Lipids Modulate the Increase of BK Channel Calcium Sensitivity by the β1 Subunit

Co-expression of the auxiliary β1 subunit with the pore forming α subunit of BK dramatically alters apparent calcium sensitivity. Investigation of the mechanism underlying the increase in calcium sensitivity of BK in smooth muscle has concentrated on the energetic effect of β1′s interaction with α. We take a novel approach, exploring whether β1 modification of calcium sensitivity reflects altered interaction between the channel protein and surrounding lipids. We reconstituted hSlo BK α and BK α+β1 channels into two sets of bilayers. One set contained POPE with POPS, POPG, POPA and POPC, where the length of acyl chains is constant, but surface charge differs. The second set is a series of neutral bilayers formed from DOPE with phosphatidylcholines (PCs) of varying acyl chain lengths: C (14∶1), C (18∶1), C (22∶1) and C (24∶1), and with brain sphingomyelin (SPM), in which surface charge is constant, but bilayer thickness varies. The increase in calcium sensitivity caused by the β1 subunit was preserved in negatively charged lipid bilayers but not in neutral bilayers, indicating that modification of apparent Ca²⁺ sensitivity by β1 is modulated by membrane lipids, requiring negatively charged lipids in the membrane. Moreover, the presence of β1 reduces BK activity in thin bilayers of PC 14∶1 and thick bilayers containing SPM, but has no significant effect on activity of BK in PC 18∶1, PC 22∶1 and PC 24∶1 bilayers. These data suggest that auxiliary β1 subunits fine-tune channel gating not only through direct subunit-subunit interactions but also by modulating lipid-protein interactions.     

Is the biotransformation of chlorinated dibenzo-p-dioxins by Sphingomonas wittichii RW1 governed by thermodynamic factors?

Density functional theory (DFT) calculations were used to explore the relationship between the biotransformation of dibenzo-p-dioxin and selected chlorinated derivatives by resting cells of Sphingomonas wittichii RW1 and measuring the thermodynamic properties of the biotransformation substrates. Sphingomonas wittichii RW1 can aerobically catabolize dibenzo-p-dioxin as well as 2,7-dichloro-, 1,2,3-trichloro-, 1,2,3,4-tetrachloro-, and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin; however, neither the 2,3,7-trichloro- nor the 1,2,3,7,8-pentachlorodibenzo-p-dioxin was transformed to its corresponding metabolic intermediate. The experimental biotransformation rates established were apparently governed by the selected thermodynamic properties of the substrates tested.     

AREL1 resists the apoptosis induced by TGF-β by inhibiting SMAC in vascular endothelial cells

Abnormal apoptosis of vascular endothelial cells is an important feature of arteriosclerosis (AS). Here, we induced apoptosis in human umbilical vein endothelial cells (HUVECs) using transforming growth factor-β (TGF-β), and investigated the role of antiapoptotic E3 ubiquitin ligase (AREL1) in the apoptosis of vascular endothelial cells. We proved that AREL1 is downregulated in TGF-β treated HUVECs. The overexpression of AREL1 inhibits the activation of Caspase-3 and Caspase-9 and attenuates cell apoptosis induced by TGF-β. According to the result of coimmunoprecipitation, AREL1 interacts with the proapoptotic proteins the second mitochondria-derived activator of caspases (SMAC) in TGF-β treated HUVECs. In addition, miR-320b inhibits the expression of AREL1, and the overexpression of AREL1 attenuates the apoptosis induced by miR-320b mimics in HUVECs. In conclusion, AREL1 is downregulated by miR-320b. AREL1 overexpression inhibits TGF-β induced apoptosis through downregulating SMAC in vascular endothelial cells. Our study explores pathogenesis regulation mechanism and new biological therapeutic targets for vascular disease.     

On the inhibition of HIV-1 protease by hydrazino-ureas displaying the N→CO interaction

To create novel HIV-1 protease (HIV PR) inhibitors, we have extended our investigations of the N→CO interaction as a moiety that reproduces electrostatic properties of the transition state of peptidolysis. Consequently, we prepared a series of compounds with an unusual hydrazino-urea core. In polar protic media, these adopt solely a cyclic constitution displaying the interaction on one side of the molecule while offering a urea moiety on the opposite side meant to hydrogen-bond with the enzyme flaps. Each inhibitor candidate was obtained via a key series of three synthetic steps employing carbonyl-di-imidazole (CDI). It was thus possible to efficiently fuse two independent building blocks, a hydrazine and a protected aminoaldehyde in a convergent manner. NMR and UV analysis proved that all compounds, when dissolved in polar protic media, existed exclusively in the cyclic constitution exhibiting the N→CO interaction. In total, five inhibitor candidates were tested with HIV PR for their potency. The one carrying the least bulk in peripheral substituents showed the highest activity. Its very low molecular weight (365 g/mol) holds great promise for future improvements in affinity without violating Lipinski’s rule of remaining within the limit of 500 g/mol.     

Inhibition of F1-ATPase Rotational Catalysis by the Carboxyl-terminal Domain of the ? Subunit

Escherichia coli ATP synthase (F₀F₁) couples catalysis and proton transport through subunit rotation. The ϵ subunit, an endogenous inhibitor, lowers F₁-ATPase activity by decreasing the rotation speed and extending the duration of the inhibited state (Sekiya, M., Hosokawa, H., Nakanishi-Matsui, M., Al-Shawi, M. K., Nakamoto, R. K., and Futai, M. (2010) Single molecule behavior of inhibited and active states of Escherichia coli ATP synthase F₁ rotation. J. Biol. Chem. 285, 42058–42067). In this study, we constructed a series of ϵ subunits truncated successively from the carboxyl-terminal domain (helix 1/loop 2/helix 2) and examined their effects on rotational catalysis (ATPase activity, average rotation rate, and duration of inhibited state). As expected, the ϵ subunit lacking helix 2 caused about ½-fold reduced inhibition, and that without loop 2/helix 2 or helix 1/loop 2/helix 2 showed a further reduced effect. Substitution of ϵSer¹⁰⁸ in loop 2 and ϵTyr¹¹⁴ in helix 2, which possibly interact with the β and γ subunits, respectively, decreased the inhibitory effect. These results suggest that the carboxyl-terminal domain of the ϵ subunit plays a pivotal role in the inhibition of F₁ rotation through interaction with other subunits.     

Alteration of Water Structure by Peptide Clusters Revealed by Neutron Scattering in the Small-Angle Region (below 1???1)

Solution scattering of neutrons and x-rays can provide direct information on local interactions of importance for biomolecular folding and structure. Here, neutron scattering experiments are combined with molecular-dynamics simulation to interpret the scattering signal of a series of dipeptides with varying degrees of hydrophobicity (GlyAla, GlyPro, and AlaPro) in concentrated aqueous solution (1:20 solute/water ratio) in which the peptides form large segregates (up to 50–60 amino acids). Two main results are found: 1), the shift to lower Q of the so-called water-ring peak (Q ≈ 2 Å⁻¹) arises mainly from an overlap of water-peptide and peptide-peptide correlations in the region of 1.3 < Q < 2 Å⁻¹, rather than from a shift of the water signal induced by the presence of the clusters; and 2), in the low-Q region (Q ≈ 0.6 Å⁻¹) a positive peak is observed originating from both the solute-solute correlations and changes in the water structure induced by the formation of the clusters. In particular, the water molecules are found to be more connected than in the bulk with hydrogen-bonding directions tangential to the exposed hydrophobic surfaces, and this effect increases with increasing peptide hydrophobicity. This work demonstrates that important information on the (hydrophobic) hydration of biomolecules can be obtained in the very-small-angle region.     

Control of yeast cell type by the mating type locus: Positive regulation of the α-specific STE3 gene by the MATα 1 product

The mating type locus (MAT) determines the three yeast cell types, a, α, and a/α. It has been proposed that alleles of this locus, MATa and MATα, encode regulators that control expression of unlinked genes necessary for mating and sporulation. Specifically, the α1 product of MATα is proposed to be a positive regulator of α-specific genes. To test this view, we have assayed RNA production from the α-specific STE3 gene in the three cell types and in mutants defective in MATα. The STE3 gene was cloned by screening a yeast genomic clone bank for plasmids that complement the mating defect of ste3 mutants. Using the cloned STE3 gene as a probe, we find that a cells produce STE3 RNA, whereas a and a/a cells do not. Furthermore, matα 1 mutants do not produce STE3 RNA, whereas matα 2 mutants do. These results show that the STE3 gene, required for mating only by α cells, is expressed only in α cells. They show also that production of RNA from the STE3 gene requires the α1 product of MATα. Thus α1 positively regulates at least one α-specific gene by increasing the level of that gene's RNA product.     

Regulation of IGF-1 but not TGF-β1 by NGF in the smooth muscle of the inflamed urinary bladder

Intraperitoneal injection of cyclophosphamide (CYP) causes hemorrhagic cystitis with excess growth of muscular layer leading to bladder hypertrophy; this could be attributable to changes in the expression profiles of growth factors in the inflamed urinary bladder. The growth factors characterized in the current study include nerve growth factor (NGF), insulin-like growth factor (IGF)-1, and transforming growth factor (TGF)-β1. We found that following CYP injection for 8 h and 48 h, the mRNA levels of all three factors were increased in the inflamed bladder when compared to control. The level of NGF mRNA was mainly increased in the urothelium layer while the levels of IGF-1 mRNA and TGF-β1 mRNA were increased in the smooth muscle layer. The level of NGF high affinity receptor TrkA mRNA was also increased in both the urothelium and the smooth muscle layers during bladder inflammation. When we blocked NGF action with NGF neutralizing antibody in vivo, we found that the up-regulation of IGF-1 in the inflamed bladder was reversed while the up-regulation of TGF-β1 was not affected by NGF neutralization. The effect of NGF on regulating IGF-1 expression was further confirmed in bladder smooth muscle culture showing that exogenous NGF increased the mRNA level of IGF-1 after 30 min to 1 h stimulation. These results suggested that bladder inflammation induced region-specific changes in the expression profiles of NGF, IGF-1 and TGF-β1. The up-regulation of NGF in the urothelium may have a role in affecting bladder smooth muscle cell physiology by regulating IGF-1 expression.