OPUS 4 | Universitätspublikationen

HuR promotes tumorigenic characteristics in hepatocellular carcinoma (2012)

Kathrin Schulz

In the absence of apparent mutations, alteration of gene expression patterns represents the key mechanism by which normal cells evolve to cancer cells. Gene expression is tightly regulated by posttranscriptional processes. Within this context, RNA-binding proteins (RBPs) represent fundamental factors, since they control mechanisms, such as mRNA-stabilization, -translation and -degradation. Human antigen R (HuR) was among the first RBPs that have been directly associated to carcinogenesis. HuR modulates the stability and translation of mRNAs which encode proteins facilitating various ‘hallmarks of cancer’, namely proliferation, evasion of growth suppression, angiogenesis, cell death resistance, invasion and metastasis. Furthermore, it is well established that tumor-promoting inflammation contributes to tumorigenesis. In this process, monocytes are attracted to the site of the tumor and educated towards a tumor-promoting macrophage phenotype. While HuR has been extensively studied in various tumor cell types, little is known about HuR in hepatocellular carcinoma (HCC). Thus, the aim of my work was to characterize the contribution of HuR to the development of cancer characteristics in HCC. I was particularly interested to investigate if HuR facilitates tumor-promoting inflammation, since a role for HuR has not been described in this context. To this end, I depleted HuR in HepG2 cells (HuR k/d) and used a co-culture model of HepG2 tumor spheroids and infiltrating monocytes to study the impact of HuR on the tumor microenvironment. I could show that depletion of HuR resulted in the reduction of cell numbers. Additionally, the expression of proliferation marker KI-67 and proto-oncogene c-Myc was reduced, supporting a proliferative role of HuR. Furthermore, exposure to cytotoxic staurosporine elevated apoptosis in HuR k/d cells compared to control cells. Concomitantly, the expression of the anti-apoptotic mediator B-cell lymphoma protein-2 (Bcl-2) was markedly reduced in the HuR k/d cells, pointing to an involvement of HuR in cell survival processes. Accordingly, a pro-survival function of HuR was also observed in tumor spheroids, since HuR k/d spheroids exhibited a larger necrotic core region at earlier time points and showed elevated numbers of dead cells compared to control (Ctr.) spheroids. Interestingly, HuR k/d spheroids isplayed reduced numbers of infiltrated macrophages, suggesting that HuR contributes to a tumor-promoting, inflammatory microenvironment by recruiting monocytes/macrophages to the tumor site. Aiming at identifying HuR-regulated factors responsible for the recruitment of monocytes, I found reduced levels of the chemokine interleukin 8 (IL-8) in supernatants of HuR k/d spheroids, supporting a critical involvement of HuR in the chemoattraction of monocytes. Analyzing supernatants of co-cultures of macrophages and HuR k/d or Ctr. spheroids revealed additional differences in chemokine secretion patterns. Interestingly, protein levels of many chemokines were elevated in co-cultures of HuR k/d spheroids compared to control co-cultures. Albeit enhanced chemokine secretion was observed, less monocytes are recruited into HuR k/d spheroids, further underlining the necessity of HuR in cancer related monocyte/macrophage attraction and infiltration. Differences between chemokine profiles of mono- and co-cultured spheroids could be attributable to changes in spheroid-derived chemokines as a result of the crosstalk with the immune cells. Provided the chemokines originate from monocytes/macrophages, the different secretion patterns suggest that HuR contributes to the modulation of the functional phenotype of infiltrated macrophages, since the tumorenvironment is critically involved in the shaping of macrophage phenotypes. Regions of low-oxygen (hypoxia) represent another critical feature of tumors. Therefore, I next analyzed the impact of HuR on the hypoxic response. Loss of HuR attenuated hypoxia-inducible factor (HIF) 2α expression after exposure to hypoxia, while HIF-1α protein levels remained unaltered. Considering previous results of our group, showing that HIF-2α depletion (HIF-2α k/d) resulted in the enhanced expression of HIF-1α protein, I aimed to determine the involvement of HuR in the compensatory upregulation of HIF-1α protein in HIF-2α k/d cells. I could demonstrate that not only total HuR protein levels, but specifically cytoplasmic HuR was elevated in HIF-2α depleted cells pointing to enhanced HuR activity. Silencing HuR in HIF-2α deficient cells attenuated enhanced HIF-1α protein expression, thus confirming a direct role of HuR in the compensatory upregulation of HIF-1α. This as also reflected on HIF-1α target gene expression. I further investigated the mechanism underlying the compensatory HIF-1α expression in HIF-2α deficient cells. Analyzing HIF-1α mRNA expression, I excluded enhanced HIF1-α transcription and stability to account for elevated HIF-1α expression in HIF-2α k/d cells. HIF-1α promoter activity assays confirmed the mRNA data. Furthermore, HIF-1α protein half-life was not elevated in HIF-2α k/d cells compared to control cells, indicating that HIF-1α protein stability is not altered in HIF-2α k/d cells. Analysis of the association of HIF-1α with the translational machinery using polysomal fractionation finally revealed an increased istribution of HIF-1α mRNA in the heavier polysomal fractions in HIF-2α k/d cells compared to control cells. Since augmented ribosome occupancy is an indicator for more efficient translation, I propose enhanced HIF-1α translation as underlying principle of the compensatory increase in HIF-1α protein levels in HIF-2α k/d cells. In summary, my results demonstrate that HuR is critical for the development of cancer characteristics in HCC. Future work analyzing the impact of HuR on tumor-promoting inflammation, specifically macrophage attraction and activation could provide new trategies to inhibit macrophage-driven tumor progression. Furthermore, I provide evidence that HuR contributes to the hypoxic response by regulating the expression of HIF-1α and HIF-2α. Targeting single HIF-isoforms for tumor therapy should be carefully considered, because of their compensatory regulation when one α-subunit is depleted. Thus, therapeutic strategies targeting factors such as HuR that control both α-subunits and at the same time prevent compensation might be more promising.

Atomic-Level Structure Characterization of an Ultrafast Folding Mini-Protein Denatured State (2012)

Per Rogne Przemysław Ozdowy Christian Richter Krishna Saxena Harald Schwalbe Lars T. Kuhn

Atomic-level analyses of non-native protein ensembles constitute an important aspect of protein folding studies to reach a more complete understanding of how proteins attain their native form exhibiting biological activity. Previously, formation of hydrophobic clusters in the 6 M urea-denatured state of an ultrafast folding mini-protein known as TC5b from both photo-CIDNP NOE transfer studies and FCS measurements was observed. Here, we elucidate the structural properties of this mini-protein denatured in 6 M urea performing 15N NMR relaxation studies together with a thorough NOE analysis. Even though our results demonstrate that no elements of secondary structure persist in the denatured state, the heterogeneous distribution of R2 rate constants together with observing pronounced heteronuclear NOEs along the peptide backbone reveals specific regions of urea-denatured TC5b exhibiting a high degree of structural rigidity more frequently observed for native proteins. The data are complemented with studies on two TC5b point mutants to verify the importance of hydrophobic interactions for fast folding. Our results corroborate earlier findings of a hydrophobic cluster present in urea-denatured TC5b comprising both native and non-native contacts underscoring their importance for ultra rapid folding. The data assist in finding ways of interpreting the effects of pre-existing native and/or non-native interactions on the ultrafast folding of proteins; a fact, which might have to be considered when defining the starting conditions for molecular dynamics simulation studies of protein folding.

Iodido(tri-tert-butylphosphane-κP)gold(I) (2012)

Inge Sänger Hans-Wolfram Lerner Tanja Sinke Michael Bolte

The AuI atom of the title compound, [AuI(C12H27P)], shows an almost linear coordination, with a P—Au—I angle of 178.52 (3)° [Au—P = 2.2723 (14) Å and Au—I = 2.5626 (6) Å].

trans-Dichloridobis(triphenylphosphane-κP)palladium(II) benzene hemisolvate (2012)

Frank Meyer-Wegner Hans-Wolfram Lerner Tanja Sinke Michael Bolte

The title complex, [PdCl2(C18H15P)2]·0.5C6H6, has the PdII ion in a square-planar coordination mode (r.m.s. deviation for Pd, P and Cl atoms = 0.024 Å) with the PPh3 and Cl ligands mutually trans. The benzene solvent molecule is located about a crystallographic inversion centre. The title complex is isostructural with trans-dichloridobis(triphenylphosphane)palladium(II) 1,4-dichlorobenzene sesquisolvate [Kitano et al. (1983 [triangle]). Acta Cryst. C39, 1015–1017].

Poly[[μ-ethane-1,2-diyl bis-(pyridine-3-carboxyl-ate)](μ-tetra-fluorido-borato)silver(I)] (2012)

Javier Vallejos Iván Brito Alejandro Cárdenas Michael Bolte

In the title compound, [Ag(BF4)(C14H12N2O4)]n, the coordination of the Ag+ ion is trigonal–bipyramidal with the N atoms of two ethane-1,2-diyl bis(pyridine-3-carboxylate) ligands in the apical positions and three F atoms belonging to different tetrafluoridoborate anions in the equatorial plane. The material consists of infinite chains of [Ag(C14H12N2O4)] units running along [001], held together by BF4 − bridging anions.

Bromido(2,4,6-trimethylphenyl)mercury(II) (2012)

Frank Meyer-Wegner Tanja Sinke Hans-Wolfram Lerner Michael Bolte

Molecules of the title compound, [HgBr(C9H11)], are located on a crystallographic twofold rotation axis. Due to the molecular symmetry, the HgII atom is linearly coordinated by the ipso-C of the mesityl group and the Br atom. In the crystal, molecules lie in planes parallel to (001).

Dimethyl 6-bromo-2-methyl-1,2-dihydroquinoline-2,4-dicarboxylate (2012)

Zeynep Gültekin Michael Bolte Tuncer Hökelek

In the title compound, C14H14BrNO4, the dihydropyridine ring adopts a screw-boat conformation. In the crystal, pairs of N—H[cdots, three dots, centered]O hydrogen bonds link the molecules into inversion R 2 2(10) dimers.

Dimethyl 6-acetyl-2-methyl-1,2-dihydroquinoline-2,4-dicarboxylate (2012)

Zeynep Gültekin Michael Bolte Tuncer Hökelek

In the title compound, C16H17NO5, the dihydropyridine ring adopts a sofa conformation. In the crystal, intermolecular N—H[cdots, three dots, centered]O hydrogen bonds link the molecules into chains running along the b axis.

Space group revsion of the triclinic polymorph of salicyl-aldehyde azine (2012)

Aamer Saeed Michael Bolte Muhammad Arshad

The structure of the title compound, C14H12N2O2 {systematic name: 2,2′-[hydrazinediylidenebis(methanylylidene)]diphenol}, has already been determined in the triclinic space group P An external file that holds a picture, illustration, etc. Object name is e-68-0o255-efi1.jpg with Z = 4 [El-Medani, Aboaly, Abdalla & Ramadan (2004 [triangle]). Spectrosc. Lett. 37, 619–632]. However, the correct space group should be P21/c with Z = 4. This structure is a new polymorph of the already known monoclinic polymorph of salicyladehyde azine, which crystallizes in space group P21/n with Z = 2. The benzene rings form a dihedral angle of 46.12 (9)°. Two intramolucular O—H[cdots, three dots, centered]N hydrogen bonds occur.

1-Decyl-6-nitro-1H-benzimidazol-2(3H)-on (2012)

Younes Ouzidan Youssef Kandri Rodi El Mokhtar Essassi Santiago V. Luis Michael Bolte Lahcen El Ammari

The title molecule, C17H25N3O3, is built up from fused six- and five-membered rings linked to a –C10H21 chain. The fused-ring system is essentially planar, the largest deviation from the mean plane being 0.009 (2) Å. The chain is roughly perpendicular to this plane, making a dihedral angle of 79.5 (2)°. In the crystal, N—H[cdots, three dots, centered]O hydrogen bonds build infinite chains along [010]. There are channels in the structure containing disordered hexane. The contribution of this solvent to the scattering power was suppressed using the SQUEEZE option in PLATON [Spek (2009 [triangle]). Acta Cryst. D65, 148–155].

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