P12.09.B Extracellular vesicle derived-miR-146a increases melanoma brain metastasis progression via Notch signalling pathway dysregulation

Background

Melanoma has the highest tropism of any cancer to metastasize to the brain, and 40% of late-stage patients develop brain metastasis. Invasion, survival, and progression of tumors is dependent on the support of the surrounding microenvironment; therefore, modulation of neighboring cells is a key factor in metastasis. Extracellular vesicles (EVs) are important in cell-to-cell signalling, shuttling proteins, RNA and DNA to alter the surroundings into a favorable tumor microenvironment. Our aims were to investigate the role of melanoma brain metastasis (MBM) derived EVs in MBM development to find possible contributing mechanisms to cancer progression for eventual therapeutic targeting.

Material and Methods

MBM-EVs isolated via sequential ultracentrifugation were injected into mice as a pre-treatment prior to intracardial injection of MBM cells. EVs were co-cultured with normal human astrocytes (NHA) to investigate phenotypic changes. MiRNA sequencing was performed on EVs collected from MBM cells and compared to NHA and melanocytes to determine a candidate miRNA for targeting. In situ hybridization was utilized to evaluate the level of miRNA in clinical patient MBM samples. Functional in vivo validation was performed by injecting miRNA knockout MBM cells into mice. Sequencing of NHA in the presence or absence of target miRNA mimic was used to determine downstream targets.

Results

Mice primed with EVs had a significant increase in MBM tumor burden, compared to non-primed mice. Co-culture with MBM-EVs resulted in NHA activation in vitro, with increased proliferation, invasion, cytokine production, and upregulation of GFAP. MiR-146a was highly upregulated in MBM EVs, and miR-146a mimics activated NHA. Patient samples had a significant increase in miR-146a expression, compared to healthy brain controls. MiR-146a knockdown in MBM mice models reduced MBM burden and prolonged animal survival. Sequencing of NHA determined NUMB, an inhibitor of the Notch signalling pathway, as a target of miR-146a. Numb and other downstream Notch proteins expression was significantly altered in NHA in the presence of both MBM-EVs and miR-146a.

Conclusion

In conclusion, EVs are important regulators of MBM and establish tumor-supporting reactive astrocytes by delivery of miR-146a. MiR-146a alters Notch signalling in astrocytes via inhibition of the tumor suppressor gene NUMB. Elevated miR-146a levels in patients suggests a potential clinical intervention is possible via miR-146a targeting.

Folding and self-assembly of herpes simplex virus type 1 thymidine kinase

Thymidine kinase from herpes simplex virus type 1 (HSV1 TK) has been postulated to be a homodimer throughout the X-ray crystallography literature. Our study shows that HSV1 TK exists as a monomer-dimer equilibrium mixture in dilute aqueous solutions. In the presence of 150 mM NaCl, the equilibrium is characterized by a dissociation constant of 2.4 microm; this constant was determined by analytical ultracentrifugation and gel filtration experiments. Dimerization seems to be unfavorable for enzymatic activity: dimers show inferior catalytic efficiency compared to the monomers. Moreover, soluble oligomers formed by self-assembly of TK in the absence of physiological salt concentrations are even enzymatically inactive. This study investigates enzymatic and structural relevance of the TK dimer in vitro. Dissociation of the dimers into monomers is not accompanied by large overall changes in secondary or tertiary structure as shown by thermal and urea-induced unfolding studies monitored by circular dichroism and fluorescence spectroscopy. A disulfide-bridge mutant TK (V119C) was designed bearing two cysteine residues at the dimer interface in order to crosslink the two subunits covalently. Under reducing conditions, the properties of V119C and wild-type HSV1 TK (wt HSV1 TK) were identical in terms of expression yield, denaturing SDS PAGE gel electrophoresis, enzyme kinetics, CD spectra and thermal stability. Crosslinked V119C (V119Cox) was found to have an increased thermal stability with a t(m) value of 59.1(+/-0.5) degrees C which is 16 deg. C higher than for the wild type protein. This is thought to be a consequence of the conformational restriction of the dimer interface. Furthermore, enzyme kinetic studies on V119Cox revealed a K(m) for thymidine of 0.2 microm corresponding to wt HSV1 TK, but a significantly higher K(m) for ATP. The present findings raise the question whether the monomer, not the dimer, might be the active species in vivo.

The effect of substrate binding on the conformation and structural stability of Herpes simplex virus type 1 thymidine kinase

The structure of Herpes simplex virus type 1 thymidine kinase (TK(HSV1)) is known at high resolution in complex with a series of ligands and exhibits important structural similarities to the nucleoside monophosphate (NMP) kinase family, which are known to show large conformational changes upon binding of substrates. The effect of substrate binding on the conformation and structural stability of TK(HSV1), measured by thermal denaturation experiments, far-UV circular dichroism (CD) and fluorescence is described, and the results indicate that the conformation of the ligand-free TK(HSV1) is less ordered and less stable compared to the ligated enzyme. Furthermore, two crystal structures of TK(HSV1) in complex with two new ligands, HPT and HMTT, refined to 2.2 A are presented. Although TK(HSV1):HPT does not exhibit any significant deviations from the model of TK(HSV1):dT, the TK(HSV1):HMTT complex displays a unique conformationally altered active site resulting in a lowered thermal stability of this complex. Moreover, we show that binding affinity and binding mode of the ligand correlate with thermal stability of the complex. We use this correlation to propose a method to estimate binding constants for new TK(HSV1)substrates using thermal denaturation measurements monitored by CD spectroscopy. The kinetic and structural results of both test substrates HPT and HMTT show that the CD thermal denaturation system is very sensitive to conformational changes caused by unusual binding of a substrate analog.

Kinetics and crystal structure of the wild-type and the engineered Y101F mutant of Herpes simplex virus type 1 thymidine kinase interacting with (North)-methanocarba-thymidine

Kinetic and crystallographic analyses of wild-type Herpes simplex virus type 1 thymidine kinase (TK(HSV1)) and its Y101F-mutant [TK(HSV1)(Y101F)] acting on the potent antiviral drug 2'-exo-methanocarba-thymidine (MCT) have been performed. The kinetic study reveals a 12-fold K(M) increase for thymidine processed with Y101F as compared to the wild-type TK(HSV1). Furthermore, MCT is a substrate for both wild-type and mutant TK(HSV1). Its binding affinity for TK(HSV1) and TK(HSV1)(Y101F), expressed as K(i), is 11 microM and 51 microM, respectively, whereas the K(i) for human cytosolic thymidine kinase is as high as 1.6 mM, rendering TK(HSV1) a selectivity filter for antiviral activity. Moreover, TK(HSV1)(Y101F) shows a decrease in the quotient of the catalytic efficiency (k(cat)/K(M)) of dT over MCT corresponding to an increased specificity for MCT when compared to the wild-type enzyme. Crystal structures of wild-type and mutant TK(HSV1) in complex with MCT have been determined to resolutions of 1.7 and 2.4 A, respectively. The thymine moiety of MCT binds like the base of dT while the conformationally restricted bicyclo[3.1.0]hexane, mimicking the sugar moiety, assumes a 2'-exo envelope conformation that is flatter than the one observed for the free compound. The hydrogen bond pattern around the sugar-like moiety differs from that of thymidine, revealing the importance of the rigid conformation of MCT with respect to hydrogen bonds. These findings make MCT a lead compound in the design of resistance-repellent drugs for antiviral therapy, and mutant Y101F, in combination with MCT, opens new possibilities for gene therapy.

Highly purified recombinant varicella Zoster virus thymidine kinase is a homodimer

Recombinant varicella zoster virus (VZV) thymidine kinase (TK) was isolated in a fast and gentle two-step procedure from Escherichia coli. The TK was expressed as a PreScission-cleavable fusion protein and purified by glutathione and ATP affinity chromatography, yielding homogeneous, highly pure VZV TK. The purified enzyme displays enzymatic activities with K(m) values of 0.3 +/- 0.06 microM for the natural substrate thymidine and 11.6 +/- 3.2 microM for ATP, indicating the biochemical equivalence with the viral VZV TK expressed in infected cells. Determinations of the native molecular weight by size exclusion chromatography and native polyacrylamide gel electrophoresis revealed that the pure enzyme is biologically active as a homodimer.

Substrate diversity of herpes simplex virus thymidine kinase. Impact Of the kinematics of the enzyme

Herpes simplex virus type 1 (HSV 1) thymidine kinase (TK) exhibits an extensive substrate diversity for nucleobases and sugar moieties, in contrast to other TKs. This substrate diversity is the crucial molecular basis of selective antiviral and suicide gene therapy. The mechanisms of substrate binding of HSV 1 TK were studied by means of site-directed mutagenesis combined with isothermal calorimetric measurements and guided by theoretical calculations and sequence comparison. The results show the link between the exceptionally broad substrate diversity of HSV 1 TK and the presence of structural features such as the residue triad His-58/Met-128/Tyr-172. The mutation of Met-128 into a Phe and the double mutant M128F/Y172F result in mutants that have lost their activity. However, by exchanging His to form the triple mutant H58L/M128F/Y172F, the enzyme regains activity. Strikingly, this triple mutant becomes resistant toward acyclovir. Furthermore, we give evidence for the importance of Glu-225 of the flexible LID region for the catalytic reaction. The data presented give new insights to understand mechanisms ruling substrate diversity and thus are crucial for both the development of new antiviral drugs and engineering of mutant TKs apt to accept novel substrate analogs for gene therapeutic approaches.

The most pathogenic transthyretin variant, L55P, forms amyloid fibrils under acidic conditions and protofilaments under physiological conditions

The L55P transthyretin (TTR) familial amyloid polyneuropathy-associated variant is distinct from the other TTR variants studied to date and the wild-type protein in that the L55P tetramer can dissociate to the monomeric amyloidogenic intermediate and form fibril precursors under physiological conditions (pH 7.0, 37 degrees C). The activation barrier associated with L55P-TTR tetramer dissociation is lower than the barrier for wild-type transthyretin dissociation, which does not form fibrils under physiological conditions. The L55P-TTR tetramer is also very sensitive to acidic conditions, readily dissociating to form the monomeric amyloidogenic intermediate between pH 5.5-5.0 where the wild-type TTR adopts a nonamyloidogenic tetrameric structure. The formation of the L55P monomeric amyloidogenic intermediate involves subtle tertiary structural changes within the beta-sheet rich subunit as discerned from Trp fluorescence, circular dichroism analysis, and ANS binding studies. The assembly of the L55P-TTR amyloidogenic intermediate at physiological pH (pH 7.5) affords protofilaments that elongate with time. TEM studies suggest that the entropic barrier associated with filament assembly (amyloid fibril formation) is high in vitro, amyloid being defined by the laterally assembled four filament structure observed by Blake upon isolation of "fibrils" from the eye of a FAP patient. The L55P-TTR protofilaments formed in vitro bind Congo red and thioflavin T (albeit more weakly than the fibrils produced at acidic pH), suggesting that the structure observed probably represents an amyloid precursor. The structural continuum from misfolded monomer through protofilaments, filaments, and ultimately fibrils must be considered as a possible source of pathology associated with these diseases.

Interaction of the recombinant herpes simplex virus type 1 thymidine kinase with thymidine and aciclovir: a kinetic study

Herpes Simplex Virus type 1 thymidine kinase (HSV 1 TK) is a key target for antiviral therapy and it phosphorylates a broad spectrum of nucleosides and nucleotides. We report the results from kinetic and inhibition experiments with HSV 1 TK, and show that there is a preferred, but not exclusive, binding order of substrates, i.e. dT binds prior to ATP. Furthermore, the results provide new informations on the mechanism of binding suggesting that HSV1 TK undergoes conformational changes during the catalytic cycle.

Comparison of two extraction procedures for urinary organic acids prior to gas chromatography-mass spectrometry

We have compared a new isolation procedure for urinary organic acids using strong anion-exchange columns with a solvent partition (ethyl acetate) method. Urinary samples from two healthy children and from nine children with organic acidurias were analysed by both procedures. Although the solid-phase extraction is more efficient for polyhydroxy acids, some polar acids, and some glycine derivatives, clinically important compounds such as oxalic, methylcitric, pyruvic, glyoxylic and 2-ketoglutaric acids, are not recovered or are only poorly recovered. However, both procedures may be used as a routine method for the diagnosis of the organic acidurias included in this study.

Oxcarbazepine disposition: preliminary observations in patients

We describe a preliminary retrospective study based on the concentration of two hydroxylated metabolites of oxcarbazepine (OCZ), a new anticonvulsant substance, measured in the plasma of 15 patients with epilepsy. Their ages ranged from 8 to 68 years, 6 of them also received phenobarbital and/or phenytoin as co-medication. The concentration of 10-hydroxy-10,11-dihydrocarbamazepine (HCBZ) or of trans-10,11-dihydroxy-10,11-dihydrocarbamazepine (DHCBZ), the metabolites measured, are significantly correlated with the dose of OCZ (p less than 0.05 and p less than 0.01, respectively). DHCBZ concentrations, standardized to a constant OCZ dose or to a constant HCBZ concentration, are significantly higher during co-medication (p less than 0.01 and p less than 0.05, respectively); HCBZ levels are unaffected. These results confirm that enzyme-inducing drugs, although accelerating the oxidation HCBZ, do not induce its formation. Since HCBZ is the active metabolite, such drug interaction seems unlikely to alter OCZ pharmacological activity.