CBMT-12. FOCAD LOSS IMPACTS MICROTUBULE ASSEMBLY, G2/M PROGRESSION AND PATIENT SURVIVAL IN ASTROCYTIC GLIOMAS

In search of novel genes associated with glioma pathogenesis, we have previously shown that KIAA1797/FOCAD is frequently deleted in malignant gliomas and that the encoded focadhesin functions as a tumor suppressor impacting proliferation and migration of glioma cells in vitro and in vivo. Here, we examine an association of FOCAD copy number loss with overall survival of patients with astrocytic gliomas, and address the molecular mechanisms that govern the suppressive effect of focadhesin on glioma growth. FOCAD loss was associated with inferior outcome in patients with isocitrate dehydrogenase 1 or 2 (IDH)-mutant astrocytic gliomas of WHO grades II-IV. Multivariate analysis considering age at diagnosis, IDH mutation and MGMT promoter methylation status confirmed FOCAD loss as a prognostic factor for overall survival. Using a yeast two-hybrid screen and pull-down assays, we identified tubulin beta-6 and other tubulin family members as novel focadhesin-interacting partners. We demonstrate that tubulins and focadhesin co-localize at the centrosome and that focadhesin is enriched in proximity to centrioles. Focadhesin is recruited to microtubules via its interaction partner SLAIN motif family member 2 and reduces microtubule assembly rates, possibly explaining why focadhesin decreases cell migration. During the cell cycle, focadhesin levels peak in G2/M phase and influence time-dependent G2/M progression possibly via polo like kinase 1 phosphorylation, providing an explanation for focadhesin-dependent cell growth reduction. We conclude that FOCAD loss may promote biological aggressiveness and worsen clinical outcome of diffuse astrocytic gliomas by enhancing microtubule assembly and accelerating G2/M phase progression.

Kongenitale Anomalien der Nieren und ableitenden Harnwege (CA KUT)

Der Begriff CAKUT (Congenital Anomalies of the Kidney and Urinary Tract) bezeichnet diverse angeborene Fehlbildungen der Nieren und ableitenden Harnwege. Da alle CAKUT-Phänotypen zusammengenommen etwa 15–30 % aller pränatal diagnostizierten Fehlbildungen ausmachen und etwa 40 % der Fälle mit terminalem Nierenversagen bei Kindern und Jugendlichen verursachen, sind diese Anomalien epidemiologisch hochrelevant. Die Diagnosestellung erfolgt mit radiologischen Verfahren, insbesondere mit Ultraschall, wobei bei vielen Patienten eine Kombination verschiedener CAKUT-Phänotypen nachgewiesen wird. CAKUT tritt zu etwa 85 % sporadisch auf, zu etwa 15 % familiär. Das Vererbungsmuster ist häufig dominant, kann aber auch rezessiv sein. CAKUT kann isoliert auftreten, aber auch als Teil einer syndromalen Erkrankung. Variable Expressivität und inkomplette Penetranz sind bei CAKUT häufig. CAKUT ist genetisch sehr heterogen. Im Mausmodell wurden bislang über 180 CAKUT-assoziierte Gene beschrieben. Da Mutationen in den etwa 50 bisher bekannten humanen CAKUT-Genen nur ca. 20 % der CAKUT-Fälle erklären und sich verschiedene chromosomale Aberrationen wie Mikrodeletionen in weiteren ca. 15 % der Patienten insbesondere mit syndromalen CAKUT finden, sind exom-/genomweite Screeningverfahren für die Aufklärung genetischer CAKUT-Ursachen besonders geeignet. Bei sporadischen Fällen ist eine Trio-basierte Analyse der Exome/Genome von Patienten-Eltern-Trios zur Identifizierung von De-novo-Aberrationen und biallelischen Varianten vielversprechend. Eine Abklärung der genetischen Ursache ist für die Präzisierung von Wiederholungsrisiken sowie eine gezielte Untersuchung von CAKUT-Patienten im Hinblick auf extrarenale Phänotypen von klinischer Bedeutung.

Whole-exome sequencing identifies mutations of TBC1D1 encoding a Rab-GTPase-activating protein in patients with congenital anomalies of the kidneys and urinary tract (CAKUT)

Congenital anomalies of the kidneys and urinary tract (CAKUT) are genetically highly heterogeneous leaving most cases unclear after mutational analysis of the around 30 causative genes known so far. Assuming that phenotypes frequently showing dominant inheritance, such as CAKUT, can be caused by de novo mutations, de novo analysis of whole-exome sequencing data was done on two patient-parent-trios to identify novel CAKUT genes. In one case, we detected a heterozygous de novo frameshift variant in TBC1D1 encoding a Rab-GTPase-activating protein regulating glucose transporter GLUT4 translocation. Sequence analysis of 100 further CAKUT cases yielded three novel or rare inherited heterozygous TBC1D1 missense variants predicted to be pathogenic. TBC1D1 mutations affected Ser237-phosphorylation or protein stability and thereby act as hypomorphs. Tbc1d1 showed widespread expression in the developing murine urogenital system. A mild CAKUT spectrum phenotype, including anomalies observed in patients carrying TBC1D1 mutations, was found in kidneys of some Tbc1d1 (-/-) mice. Significantly reduced Glut4 levels were detected in kidneys of Tbc1d1 (-/-) mice and the dysplastic kidney of a TBC1D1 mutation carrier versus controls. TBC1D1 and SLC2A4 encoding GLUT4 were highly expressed in human fetal kidney. The patient with the truncating TBC1D1 mutation showed evidence for insulin resistance. These data demonstrate heterozygous deactivating TBC1D1 mutations in CAKUT patients with a similar renal and ureteral phenotype, and provide evidence that TBC1D1 mutations may contribute to CAKUT pathogenesis, possibly via a role in glucose homeostasis.

Dissecting the genotype in syndromic intellectual disability using whole exome sequencing in addition to genome-wide copy number analysis

When a known microimbalance affecting multiple genes is detected in a patient with syndromic intellectual disability, it is usually presumed causative for all observed features. Whole exome sequencing (WES) allows questioning this assumption. In this study of three families with children affected by unexplained syndromic intellectual disability, genome-wide copy number and subsequent analyses revealed a de novo maternal 1.1 Mb microdeletion in the 14q32 imprinted region causing a paternal UPD(14)-like phenotype, and two inherited 22q11.21 microduplications of 2.5 or 2.8 Mb. In patient 1 carrying the 14q32 microdeletion, tall stature and renal malformation were unexplained by paternal UPD(14), and there was no altered DLK1 expression or unexpected methylation status. By WES and filtering with a mining tool, a novel FBN1 missense variant was found in patient 1 and his mother, who both showed clinical features of Marfan syndrome by thorough anthropometric assessment, and a novel EYA1 missense variant as a probable cause of the renal malformation in the patient. In patient 2 with the 22q11.21 microduplication syndrome, skin hypo- and hyperpigmentation and two malignancies were only partially explained. By WES, compound heterozygous BLM stop founder mutations were detected causing Bloom syndrome. In male patient 3 carrying a 22q11.21 microduplication inherited from his unaffected father, WES identified a novel missense variant in the OPHN1 X-linked intellectual disability gene inherited from the unaffected mother as a possible additional cause for developmental delay. Thus, WES seems warranted in patients carrying microdeletions or microduplications, who have unexplained clinical features or microimbalances inherited from an unaffected parent.

Characterization of the Interaction Between the Small Regulatory Peptide SgrT and the EIICBGlc of the Glucose-Phosphotransferase System of E. coli K-12

Escherichia coli is a widely used microorganism in biotechnological processes. An obvious goal for current scientific and technical research in this field is the search for new tools to optimize productivity. Usually glucose is the preferred carbon source in biotechnological applications. In E. coli, glucose is taken up by the phosphoenolpyruvate-dependent glucose phosphotransferase system (PTS). The regulation of the ptsG gene for the glucose transporter is very complex and involves several regulatory proteins. Recently, a novel posttranscriptional regulation system has been identified which consists of a small regulatory RNA SgrS and a small regulatory polypeptide called SgrT. During the accumulation of glucose-6-phosphate or fructose-6-phosphate, SgrS is involved in downregulation of ptsG mRNA stability, whereas SgrT inhibits glucose transport activity by a yet unknown mechanism. The function of SgrS has been studied intensively. In contrast, the knowledge about the function of SgrT is still limited. Therefore, in this paper, we focused our interest on the regulation of glucose transport activity by SgrT. We identified the SgrT target sequence within the glucose transporter and characterized the interaction in great detail. Finally, we suggest a novel experimental approach to regulate artificially carbohydrate uptake in E. coli to minimize metabolic overflow in biotechnological applications.

The structure of Mlc titration factor A (MtfA/YeeI) reveals a prototypical zinc metallopeptidase related to anthrax lethal factor

MtfA of Escherichia coli (formerly YeeI) was previously identified as a regulator of the phosphoenolpyruvate (PEP)-dependent:glucose phosphotransferase system. MtfA homolog proteins are highly conserved, especially among beta- and gammaproteobacteria. We determined the crystal structures of the full-length MtfA apoenzyme from Klebsiella pneumoniae and its complex with zinc (holoenzyme) at 2.2 and 1.95 Å, respectively. MtfA contains a conserved H(149)E(150)XXH(153)+E(212)+Y(205) metallopeptidase motif. The presence of zinc in the active site induces significant conformational changes in the region around Tyr205 compared to the conformation of the apoenzyme. Additionally, the zinc-bound MtfA structure is in a self-inhibitory conformation where a region that was disordered in the unliganded structure is now observed in the active site and a nonproductive state of the enzyme is formed. MtfA is related to the catalytic domain of the anthrax lethal factor and the Mop protein involved in the virulence of Vibrio cholerae, with conservation in both overall structure and in the residues around the active site. These results clearly provide support for MtfA as a prototypical zinc metallopeptidase (gluzincin clan).

The phosphoenolpyruvate-dependent glucose-phosphotransferase system from Escherichia coli K-12 as the center of a network regulating carbohydrate flux in the cell

The phosphoenolpyruvate-(PEP)-dependent-carbohydrate:phosphotransferase systems (PTSs) of enteric bacteria constitute a complex transport and sensory system. Such a PTS usually consists of two cytoplasmic energy-coupling proteins, Enzyme I (EI) and HPr, and one of more than 20 different carbohydrate-specific membrane proteins named Enzyme II (EII), which catalyze the uptake and concomitant phosphorylation of numerous carbohydrates. The most prominent representative is the glucose-PTS, which uses a PTS-typical phosphorylation cascade to transport and phosphorylate glucose. All components of the glucose-PTS interact with a large number of non-PTS proteins to regulate the carbohydrate flux in the bacterial cell. Several aspects of the glucose-PTS have been intensively investigated in various research projects of many groups. In this article we will review our recent findings on a Glc-PTS-dependent metalloprotease, on the interaction of EIICB(Glc) with the regulatory peptide SgrT, on the structure of the membrane spanning C-domain of the glucose transporter and on the modeling approaches of ptsG regulation, respectively, and discuss them in context of general PTS research.