Mycalolide-B, a novel and specific inhibitor of actomyosin ATPase isolated from marine sponge

AbstractA toxin isolated from marine sponge, mycalolide-B, inhibited smooth muscle contractions without changing cytosolic Ca2+ levels. It also inhibited Ca2+-induced contraction in permeabilized smooth muscles. In native actomyosin prepared from chicken gizzard, mycalolide-B inhibited superprecipitation and Mg2+-ATPase activity stimulated by Ca2+ without changing myosin light chain phosphorylation. In the permeabilized muscle and native actomyosin preparation thiophosphorylated with ATPγS, mycalolide-B inhibited ATP-induced contraction and Mg2+-ATPase activity, respectively, in the absence of Ca2+. Mycalolide-B also inhibited Mg2+-ATPase activity of skeletal muscle native actomyosin. Mycalolide-B had no effect on calmodulin-stimulated (Ca2+Mg2+)-ATPase activity of erythrocyte membranes. These results suggest that mycalolide-B selectively inhibits actin—myosin interaction

Cyclic ADP-ribose as an endogenous inhibitor of the mTOR pathway downstream of dopamine receptors in the mouse striatum

The role of cyclic ADP-ribose (cADPR) as a second messenger and modulator of the mTOR pathway downstream of dopamine (DA) receptors and/or CD38 was re-examined in the mouse. ADP-ribosyl activity was low in the membranes of neonates, but DA stimulated it via both D1- and D2-like receptors. ADP-ribosyl cyclase activity increased significantly during development in association with increased expression of CD38. The cADPR binding proteins, FKBP12 and FKBP12.6, were expressed in the adult mouse striatum. The ratio of phosphorylated to non-phosphorylated S6 kinase (S6K) in whole mouse striatum homogenates decreased after incubation of adult mouse striatum with extracellular cADPR for 5 min. This effect of cADPR was much weaker in MPTP-treated Parkinson’s disease model mice. The inhibitory effects of cADPR and rapamycin were identical. These data suggest that cADPR is an endogenous inhibitor of the mTOR signaling pathway downstream of DA receptors in the mouse striatum and that cADPR plays a certain role in the brain in psychiatric and neurodegenerative diseases. © 2016 Springer-Verlag WienEmbargo Period 12 month

Amyloid-Beta (Aβ) D7H Mutation Increases Oligomeric Aβ42 and Alters Properties of Aβ-Zinc/Copper Assemblies

Amyloid precursor protein (APP) mutations associated with familial Alzheimer's disease (AD) usually lead to increases in amyloid β-protein (Aβ) levels or aggregation. Here, we identified a novel APP mutation, located within the Aβ sequence (AβD7H), in a Taiwanese family with early onset AD and explored the pathogenicity of this mutation. Cellular and biochemical analysis reveal that this mutation increased Aβ production, Aβ42/40 ratio and prolonged Aβ42 oligomer state with higher neurotoxicity. Because the D7H mutant Aβ has an additional metal ion-coordinating residue, histidine, we speculate that this mutation may promote susceptibility of Aβ to ion. When co-incubated with Zn2+ or Cu2+, AβD7H aggregated into low molecular weight oligomers. Together, the D7H mutation could contribute to AD pathology through a “double punch” effect on elevating both Aβ production and oligomerization. Although the pathogenic nature of this mutation needs further confirmation, our findings suggest that the Aβ N-terminal region potentially modulates APP processing and Aβ aggregation, and further provides a genetic indication of the importance of Zn2+ and Cu2+ in the etiology of AD

Vesicular GABA Uptake Can Be Rate Limiting for Recovery of IPSCs from Synaptic Depression

Synaptic efficacy plays crucial roles in neuronal circuit operation and synaptic plasticity. Presynaptic determinants of synaptic efficacy are neurotransmitter content in synaptic vesicles and the number of vesicles undergoing exocytosis at a time. Bursts of presynaptic firings depress synaptic efficacy, mainly due to depletion of releasable vesicles, whereas recovery from strong depression is initiated by endocytic vesicle retrieval followed by refilling of vesicles with neurotransmitter. We washed out presynaptic cytosolic GABA to induce a rundown of IPSCs at cerebellar inhibitory cell pairs in slices from rats and then allowed fast recovery by elevating GABA concentration using photo-uncaging. The time course of this recovery coincided with that of IPSCs from activity-dependent depression induced by a train of high-frequency stimulation. We conclude that vesicular GABA uptake can be a limiting step for the recovery of inhibitory neurotransmission from synaptic depression

Stellettamide-A, a novel inhibitor of calmodulin, isolated from a marine sponge

1. Stellettamide A (ST-A), a novel marine toxin isolated from a marine sponge, inhibited high K(+)(72.7 mM)-induced contraction in the smooth muscle of guinea-pig taenia coli with an IC(50) of 88 μM. 2. In the taenia permeabilized with Triton X-100, ST-A inhibited Ca(2+) (3 and 10 μM)-induced contractions with an IC(50) of 46 μM for 3 μM Ca(2+) and 105 μM for 10 μM Ca(2+). In the permeabilized taenia, calyculin-A (300 nM), a potent inhibitor of type-1 and type-2A phosphatases, induced sustained contraction in the absence of Ca(2+). ST-A had no effect on this contraction. 3. ST-A inhibited Mg(2+)-ATPase activity in native actomyosin prepared from chicken gizzard with an IC(50) of 25 μM. 4. In a reconstituted smooth muscle contractile system containing calmodulin, myosin light chain (MLC) and MLC kinase, ST-A inhibited MLC phosphorylation with an IC(50) of 152 μM. The inhibitory effect of ST-A was antagonized by increasing the concentration of calmodulin. 5. ST-A inhibited calmodulin activity, assessed by Ca(2+)/calmodulin-dependent enzymes, (Ca(2+)-Mg(2+))-ATPase of erythrocyte membrane, with an IC(50) of 100 μM and phosphodiesterase prepared from bovine cardiac muscle with an IC(50) of 52 μM. The inhibitory effect on phosphodiesterase activity was antagonized by increasing the calmodulin concentration. 6. Interaction between ST-A and calmodulin was demonstrated by instantaneous quenching of the intrinsic tyrosine fluorescence of calmodulin by ST-A (3–300 μM). Similar results were obtained in the presence or absence of Ca(2+) suggesting that ST-A binds to calmodulin and that Ca(2+) is not essential for the binding of ST-A to calmodulin. 7. These results suggest that ST-A, isolated from marine metabolites, is a novel inhibitor of calmodulin

Atypical Familial Mediterranean Fever Complicated with Gastrointestinal Amyloidosis Diagnosed due to Paroxysmal Arthralgia and Intractable Diarrhea, Successfully Treated with Tocilizumab

A 53-year-old man with recurrent episodes of large joint pain and a low-grade fever at irregular intervals for 16 years developed right knee and ankle arthralgia, watery diarrhea, and abdominal pain. Following an ileum and colon biopsy, he was diagnosed with gastrointestinal amyloidosis. We suspected familial Mediterranean fever (FMF) based on his history and administered colchicine; his symptoms subsequently improved. Thus, he was diagnosed with atypical FMF. After tocilizumab administration, the amyloid deposits disappeared. This case suggests that physicians should consider FMF even in cases with atypical symptoms in order to prevent the progression of amyloidosis and that amyloid deposits can be eliminated by interleukin (IL)-6 inhibition