Biomedical subjects

Andrea Hartmann

Publications and source records attributed to Andrea Hartmann.

5 recordsLinked to original sources

PubMed2007

Hemolytic uremic syndrome: a factor H mutation (E1172Stop) causes defective complement control at the surface of endothelial cells.

Defective complement regulation results in hemolytic uremic syndrome (HUS), a disease that is characterized by microangiopathy, thrombocytopenia, and acute renal failure and that causes endothelial cell damage. For characterization of how defective complement regulation relates to the pathophysiology, the role of the complement regulator factor H and also of a mutant factor H protein was studied on the surface of human umbilical vein endothelial cells. The mutant 145-kD factor H protein was purified to homogeneity, from plasma of a patient with HUS, who is heterozygous for a factor H gene mutation G3587T, which introduces a stop codon at position 1172. Functional analyses show that the lack of the most C-terminal domain short consensus repeats 20 severely affected recognition functions (i.e., binding to heparin, C3b, C3d, and the surface of endothelial cells). Wild-type factor H as well as the mutant protein formed dimers in solution as shown by cross-linking studies and mass spectroscopy. When assayed in fluid phase, the complement regulatory activity of the mutant protein was normal and comparable to wild-type factor H. However, on the surface of endothelial cells, the mutant factor H protein showed severely reduced regulatory activities and lacked protective functions. Similarly, with the use of sheep erythrocytes, the mutant protein lacked the protective activity and caused increased hemolysis when it was added to factor H-depleted plasma. This study shows how a mutation that affects the C-terminal region of the factor H protein leads to defective complement control on cell surfaces and damage to endothelial cells in patients with HUS. These effects explain how mutant factor H causes defective complement control and in HUS-particularly under condition of inflammation and complement activation-causes endothelial cell damage.

Cells, Cultured↗

PubMed2006

The CR4 region of EBNA2 confers viability of Epstein-Barr virus-transformed B cells by CBF1-independent signalling.

The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) gene product is the key regulator of the latent genes of EBV and essential for EBV-mediated transformation of human primary B cells. Viral mutants were constructed carrying a deletion of the EBNA2 conserved region 4 (CR4). Primary resting B cells infected with the DeltaCR4-EBNA2 mutant virus were dramatically impaired for B cell transformation. Lymphoblastoid cell lines (LCLs) established with this mutant EBV revealed a prolonged population doubling time when cells were cultivated at low cell densities, which are not critical for wild-type-infected cells. Low-level spontaneous cell death occurred when the cells were cultivated at suboptimal cell densities. The phenotype of B cells and LCLs infected with the DeltaCR4-EBNA2 mutant virus indicated that the CR4 region of EBNA2 specifically contributes to the viability of the cells rather than affecting cell division rates.

B-Lymphocytes↗

PubMed2006

Cellular target genes of Epstein-Barr virus nuclear antigen 2.

Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) is a key determinant in the EBV-driven B-cell growth transformation process. By activating an array of viral and cellular target genes, EBNA-2 initiates a cascade of events which ultimately cause cell cycle entry and the proliferation of the infected B cell. In order to identify cellular target genes that respond to EBNA-2 in the absence of other viral factors, we have performed a comprehensive search for EBNA-2 target genes in two EBV-negative B-cell lines. This screen identified 311 EBNA-2-induced and 239 EBNA-2-repressed genes that were significantly regulated in either one or both cell lines. The activation of most of these genes had not previously been attributed to EBNA-2 function and will be relevant for the identification of EBNA-2-specific contributions to EBV-associated malignancies. The diverse spectrum of EBNA-2 target genes described in this study reflects the broad spectrum of EBNA-2 functions involved in virus-host interactions, including cell signaling molecules, adapters, genes involved in cell cycle regulation, and chemokines.

B-Lymphocytes↗

PubMed2005

Factor H and atypical hemolytic uremic syndrome: mutations in the C-terminus cause structural changes and defective recognition functions.

Atypical hemolytic uremic syndrome is a disease that is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Mutations in the complement regulator factor H are associated with the inherited form of the disease, and >60% of the mutations are located within the C terminus of factor H. The C-terminus of factor H, represented by short consensus repeat 19 (SCR19) and SCR20, harbors multiple functions; consequently, this study aimed to examine the functional effects of clinically reported mutations in these SCR. Mutant factor H proteins (W1157R, W1183L, V1197A, R1210C, R1215G, and P1226S) were recombinantly expressed and functionally characterized. All six mutant proteins showed severely reduced heparin, C3b, C3d, and endothelial cell binding. By peptide spot analyses, four linear regions that are involved in heparin, C3b, and C3d binding were localized in SCR19 and SCR20. A three-dimensional homology model of the two domains suggests that these four regions form a common binding site across both domains. In addition, this structural model identifies two types of residues: Type A residues are positioned on the SCR surface and are represented by mutants W1157R, W1183L, R1210C, and R1215G; and type B residues are buried within the SCR structure and affect mutations V1197A and P1226S. Mutations of both types of residue result in the same functional defects, namely the reduced binding of factor H to surface-attached C3b molecules and reduced complement regulatory activity at the cell surfaces. The buried type B mutations seem to affect ligand interaction of factor H more severely than the surface-exposed mutations.

Amino Acid Sequence↗

PubMed2005

Phosphatidylinositol 3-kinase VPS34 of Candida albicans is involved in filamentous growth, secretion of aspartic proteases, and intracellular detoxification.

The phosphatidylinositol (PI) 3-kinase Vps34p of Candida albicans influences vesicular intracellular transport, filamentous growth and virulence. To get a clearer understanding how these phenomena are connected, we analysed hyphal growth in a matrix under microaerophilic conditions at low temperature, the detoxification of metal ions and antifungal drugs, the secretion of aspartic proteinases (Saps), as well as expression of adhesion-associated proteins of the C. albicans vps34 null mutant strain. The hyphal growth in a matrix, which is repressed in the wild-type strain by Efg1p, was derepressed in the mutant. CZF1, which encodes an activator of hyphal growth in a matrix, was up-regulated in the mutant. In addition, CZF1 expression was pH-dependent in the wild-type. Expression of EFG1 was not changed. Examination of Saps secretion showed a reduction in the vps34 null mutant. Determination of sensitivity against metal ions and antimycotic drugs revealed defects in detoxification. Expression studies indicated that the vps34 mutant reacts to the phenotypical defects with an up-regulation of genes involved in these processes, including the aspartyl proteinases SAP2 and SAP9, adhesion proteins ALS1 and HWP1, and the ABC transporters CDR1 and HST6. We also found an increased expression of the PI 4-kinase LSB6 indicating a complex feed-back mechanism for the compensation of the multiple defects arising from the lack of the PI3-kinase VPS34.

Antifungal Agents↗