Biochemical characterization of cholesterol-3-sulfate as the sole effector for the phosphorylation of HMG1 by casein kinase I in vitro

A MALDI-MSI Approach to the Characterization of Radiation-Induced Lung Injury and Medical Countermeasure Development

Radiation-induced lung injury is highly complex and characterized by multiple pathologies, which occur over time and sporadically throughout the lung. This complexity makes biomarker investigations and medical countermeasure screenings challenging. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has the ability to resolve differences spatially in molecular profiles within the lung following radiation exposure and can aid in biomarker identification and pharmaceutical efficacy investigations. MALDI-MSI was applied to the investigation of a whole-thorax lung irradiation model in non-human primates (NHP) for lipidomic analysis and medical countermeasure distribution.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Biochemical characterization of tau protein and its associated syndapin 1 and protein kinase Cepsilon for their functional regulation in rat brain

BACKGROUND

We recently reported that both sulfatide and cholesterol-3-sulfate (SCS) function as potent stimulators for the GSK-3beta-mediated phosphorylation of tau protein (TP) in vitro [J. Biochem. 143 (2008) 359-367].

METHODS

By means of successive gel filtration on a Superdex 200 pg column and three distinct ion-exchange column chromatographies, TP and its associated proteins were highly purified from the extract of rat brain.

RESULTS

We found that (i) syndapin 1 and novel protein kinase Cepsilon (nPKCepsilon) were identified as the TP-associated proteins; (ii) SCS highly stimulated the phosphorylation of TP and syndapin 1 by nPKCepsilon as well as CK1; (iii) the full phosphorylation of TP and syndapin 1 by nPKCepsilon in the presence of sulfatide resulted in their dissociation; (iv) TP primed by CK1 functioned as an effective phosphate acceptor for GSK-3beta; (v) syndapin 1 highly stimulated the GSK-3beta-mediated phosphorylation of TP; and (vi) TP isoforms were highly expressed in aged brain, whereas syndapin 1 was consistently detected in adult brain, but not in newborn brain.

GENERAL SIGNIFICANCE

These results provided here suggest that (i) TP-associated nPKCepsilon suppresses the GSK-3beta-mediated phosphorylation of TP through the phosphorylation of GSK-3beta by the kinase in vitro; and (ii) SCS act as effective sole mediators to induce the GSK-3beta-mediated high phosphorylation of both TP and its associated syndapin 1 involved in the biochemical processes of neuronal diseases, including Alzheimer's disease.

Characterization of meFucoidan as a selective inhibitor for secretory phospholipase A2-IIA and the phosphorylation of meFucoidan-binding proteins by A-kinase in vitro

The direct interaction of Mekabu fucoidan (meFucoidan) with four functional basic proteins (sPLA2-IIA, bFGF, histone H2B and HBV core protein) and three synthetic FGF-BP peptides (sp5, GE13 and RS6) was characterized in vitro. It was found that (i) meFucoidan inhibited dose-dependently the activity of sPLA2-IIA, but not pPLA2, through its direct binding to the enzyme; (ii) sPLA2-IIA activity was sensitive to meFucoidan rather than heparin, but significantly stimulated by sulfatide; (iii) the A-kinase-mediated phosphorylation of these basic proteins, except sPLA2-IIA, and synthetic peptides, containing potent phosphorylation sites for A-kinase, was inhibited dose-dependently by meFucoidan; and (iv) two consensus meFucoidan-binding motifs (B-B-B-B-X and B-X-B-B-X; B, basic amino acid) in these basic proteins and synthetic peptides could be overlapping to the potent phosphorylation site (B-B-X-S/T) for the kinase in vitro. These results presented here suggest that meFucoidan functions as a selective inhibitor for sPLA2-IIA and the A-kinase-mediated phosphorylation of cellular meFucoidan-binding functional basic proteins in vitro.

A novel consensus phosphorylation motif in sulfatide- and cholesterol-3-sulfate-binding protein substrates for CK1 in vitro

A novel phosphorylation motif for casein kinase 1 (CK1) in response to two sulfated lipids [sulfatide and cholesterol-3-sulfate (SCS)] was determined, using three functional proteins [myelin basic protein (MBP), tau protein (TP) and RhoA (a small GTPase)] and five synthetic MBP peptides as phosphate acceptors for the kinase in vitro. It was found that (i) MBP, p8 (positions 38-118) cleaved from MBP, and a synthetic peptide M103 were effectively phosphorylated by CK1delta in the presence of SCS; (ii) sulfatide in comparison with CH-3S highly enhanced autophosphorylation of CK1delta; (iii) SCS had a high binding affinity with MBP and peptide M103, but not other MBP peptides lacking K-G-R; and (iv) a novel consensus phosphorylation motif (K/R-X-K/R-X-X-S/T) for CK1 was identified among several SCS-binding proteins (SCS-BPs) and three CK1 isoforms (delta, epsilon and gamma). The binding of SCS to two basic brain proteins (MBP and TP) resulted in the high stimulation of their phosphorylation by three CK1 isoforms (alpha, delta and epsilon), but not CK1gamma. In contrast, an acidic protein (RhoA) was effectively phosphorylated by CK1delta in the presence of SCS, and also highly phosphorylated by CK1gamma in the presence of sulfatide. Our results presented here suggest that (i) sulfatide may function as an effective stimulator for autophosphorylation of CK1; and (ii) cellular SCS-binding proteins, containing novel phosphorylation motifs for CK1, may be preferentially phosphorylated by CK1 with isoform specificity at the highly accumulated level of SCS in the brain.

Biochemical characterization of a N-terminal fragment (p5) cleaved from fibroblast growth factor-binding protein (FGF-BP) in bovine milk in vitro

By means of successive gel filtration on a Superdex 30 pg column and Mono S column chromatography, a 5-kDa polypeptide (p5) was highly purified from the low molecular weight (LMW) fraction separated from the partially purified lactoferrin (bLF) fraction of bovine milk, and biochemically characterized as a phosphate acceptor for two protein kinases [cAMP-dependent protein kinase (PKA) and casein kinase 1delta (CK1delta)] in vitro. Purified p5 was identified as a fragment (N-terminal positions 24-51, 28 amino acid residues) cleaved from fibroblast growth factor-binding protein (FGF-BP, p37). Both purified p5 and synthetic p5 (sp5) were effectively phosphorylated by PKA, and also phosphorylated by CK1delta in the presence of two sulfated lipids [sulfatide or cholesterol-3-sulfate (CH-3S), SCS] in vitro. A novel phosphorylation site (RNRRGS) for CK1delta and a potent SCS-binding site (RNRR) on p5 were identified. The PKA-mediated phosphorylation of p5 was highly stimulated when incubated with either acidic FGF (aFGF) or bLF in vitro, but this phosphorylation was more sensitive to SCS than H-89 (a specific PKA inhibitor). Immunoprecipitate experiments revealed p5, but not the phosphorylated p5, to be directly bound to aFGF in vitro. These results show that (i) p5 has a high binding affinity with aFGF as well as bLF; (ii) the binding of SCS to p5 results in the selective inhibition of its phosphorylation by PKA; and (iii) SCS functions as an effective stimulator for the phosphorylation of p5 by CK1delta in vitro. In addition, p5 may play an important physiological role as a trafficking factor for the physiological interaction between aFGF group including endothelial cell growth factors and their binding proteins in vivo.

Activation of C-Kinase .ETA. through Its Cholesterol-3-sulfate-Dependent Phosphorylation by Casein Kinase I in Vitro

The physiological correlation between casein kinase I (CK-I) and an isoform eta of protein kinase C (C-kinase eta) was investigated in vitro, since it has been reported that (i) cholesterol-3-sulfate (CH-3S) effectively activates C-kinase eta rather than the other isoforms (C-kinase epsilon and C-kinase delta) in vitro; and (ii) CK-I efficiently phosphorylates CH-3S-binding proteins, such as high mobility group protein 1 (HMG1), in the presence of CH-3S in vitro. We found that (i) CK-I phosphorylated Thr in preference to Ser on recombinant human C-kinase isoform eta (rhC-kinase eta) in the presence of CH-3S; (ii) this phosphorylation was selectively inhibited by CK-I-7 (a CK-I inhibitor); and (iii) the activity (phosphorylation of protamine sulfate) of rhC-kinase eta was approx. 3.2-fold stimulated by its full phosphorylation by CK-I in the presence of 3 microM CH-3S. These results suggest that CK-I is a protein kinase responsible for the activation of rhC-kinase eta in the presence of CH-3S in vitro.

The Effects of Cholesterol-3-sulfate (CH-3S) on the Phosphorylation of Human C3a (hC3a) in Vitro and on the Ability of hC3a to Induce Vascular Permeability in Rats

The phosphorylation of human C3a (hC3a, anaphylatoxin) by two distinct protein kinases (PKA and CK-I) and the effect of cholesterol-3-sulfate (CH-3S) on this phosphorylation were biochemically investigated in vitro. It was found that (i) hC3a functions as a phosphate acceptor for PKA and CK-I, but not for CK-II; (ii) the CK-I-mediated phosphorylation of hC3a requires the presence of 3 microM CH-3S in a manner similar to the phosphorylation of HMG1 (CH-3S-binding protein) by CK-I; and (iii) CH-3S inhibits the PKA-mediated phosphorylation of hC3a in a dose-dependent manner (ID50=approximately 2 microM). As expected, hC3a containing high levels of Arg- and Lys-residues stimulated approx. 3-fold CK-II activity (phosphorylation of alpha-casein) in vitro. However, no significant effect of hC3a on CK-II activity was observed when hC3a was preincubated with CH-3S or fully phosphorylated by PKA in vitro. Furthermore, preincubation of hC3a with CH-3S diminished the ability of hC3a to induce vascular permeability in rats. The results provided here suggest that (i) hC3a is a CH-3S-binding protein; and (ii) CH-3S functions as a potent inhibitor for its physiological activities, including phosphorylation by PKA and CK-I, in vitro.

Cholesterol sulfate in human physiology: what's it all about?

Cholesterol sulfate is quantitatively the most important known sterol sulfate in human plasma, where it is present in a concentration that overlaps that of the other abundant circulating steroid sulfate, dehydroepiandrosterone (DHEA) sulfate. Although these sulfolipids have similar production and metabolic clearance rates, they arise from distinct sources and are metabolized by different pathways. While the function of DHEA sulfate remains an enigma, cholesterol sulfate has emerged as an important regulatory molecule. Cholesterol sulfate is a component of cell membranes where it has a stabilizing role, e.g., protecting erythrocytes from osmotic lysis and regulating sperm capacitation. It is present in platelet membranes where it supports platelet adhesion. Cholesterol sulfate can regulate the activity of serine proteases, e.g., those involved in blood clotting, fibrinolysis, and epidermal cell adhesion. As a result of its ability to regulate the activity of selective protein kinase C isoforms and modulate the specificity of phosphatidylinositol 3-kinase, cholesterol sulfate is involved in signal transduction. Cholesterol sulfate functions in keratinocyte differentiation, inducing genes that encode for key components involved in development of the barrier. The accumulating evidence demonstrating a regulatory function for cholesterol sulfate appears solid; the challenge now is to work out the molecular mechanisms whereby this interesting molecule carries out its various roles.

Characterization of (-)-matairesinol as a potent inhibitor of casein kinase I in vitro

The inhibitory effects of (-)-matairesinol (MTS) isolated from Thujopsis dolabrata var. hondai on the activities of four distinct Ser/Thr-protein kinases [two casein kinases (CK-I and CK-II), A-kinase and C-kinase] were determined in vitro. It was found that (i) MTS inhibits the activities of CK-I and C-kinase alpha (ID(50)=approx. 10 microM) in a dose-depedent manner, but high doses are required to inhibit A-kinase activity (ID(50)=approx. 90 microM); (ii) the autophosphorylation of CK-I is more sensitive to MTS (ID(50)=approx. 0.2 microM); (iii) MTS inhibits CK-I activity in a manner similar to that observed with CK-I-7 (a CK-I inhibitor); and (iv) the compound inhibits CK-I activity by affecting ATP binding in a mixed type manner. These results indicate that MTS is a potent CK-I inhibitor in vitro.

Identification of casein kinase Ialpha interacting protein partners

Casein kinase Ialpha (CKIalpha) belongs to a family of serine/threonine protein kinases involved in membrane trafficking, RNA processing, mitotic spindle formation and cell cycle progression. In this report, we identified several CKIalpha interacting proteins including RCC1, high mobility group proteins 1 and 2 (HMG1, HMG2), Erf, centaurin-alpha1, synaptotagmin IX and CPI-17 that were isolated from brain as CKIalpha co-purifying proteins. Actin, importin-alpha(1), importin-beta, PP2Ac, centaurin-alpha1, and HMG1 were identified by affinity chromatography using a peptide column comprising residues 214-233 of CKIalpha. We have previously shown that centaurin-alpha1 represents a CKIalpha partner both in vitro and in vivo. The nuclear protein regulator of chromosome condensation 1 (RCC1) is a guanosine nucleotide exchange factor for Ran which is involved in nuclear transport and mitotic spindle formation. Here we show that CKIalpha and RCC1 interact in brain and in cultured cells. However, the interaction does not involve residues 217-233 of CKIalpha which are proposed from X-ray structures to represent an anchoring site for CKI partners. Formation of the RCC1/CKIalpha complex is consistent with the association of the kinase with mitotic spindles. In conclusion, we have identified a number of novel CKIalpha protein partners and their relations to CKI are discussed.

Inhibitory effect of glycyrrhizin on the phosphorylation and DNA-binding abilities of high mobility group proteins 1 and 2 in vitro

The physiological correlation between glycyrrhizin (GL) and high mobility group proteins I and 2 (HMG1/2) and the inhibitory effect of GL on their phosphorylation by three protein kinases (CK-I, CK-II and PKC) were investigated biochemically in vitro. It was found that GL binds directly to HMG1/2, because (i) HMG1/2 have a high affinity with a GL-affinity column; and (ii) GL induces the conformational changes in HMG1/2. Both purified HMG1/2 functioned as phosphate acceptors for these two protein kinases (CK-I and PKC), but not phosphorylated by CK-II. Phosphorylation of HMG1/2 by two protein kinases (CK-I and PKC) was completely inhibited by a glycyrrhetinic acid derivative (oGA) at one-tenth the concentration of GL. Also, the DNA-binding abilities of HNG1/2 were reduced by GL in a dose-dependent manner. These results show that the binding of GL to HMG1/2 results in the inhibition of their physiological activities (DNA-binding ability and phosphorylation by PKC or CK-I) in vitro. The GL-induced inhibition of the physiological activities of HMG1/2 may be involved in the anti-inflammatory effect of GL in vivo.