S100A12 is expressed exclusively by granulocytes and acts independently from MRP8 and MRP14

Changes in cytosolic calcium concentrations regulate a wide variety of cellular processes, and calcium-binding proteins are the key molecules in signal transduction, differentiation, and cell cycle control. S100A12, a recently described member of the S100 protein family, has been shown to be coexpressed in granulocytes and monocytes together with two other S100 proteins, MRP8 (S100A8) and MRP14 (S100A9), and a functional relationship between these three S100 proteins has been suggested. Using Western blotting, calcium overlays, intracellular flow cytometry, and cytospin preparations, we demonstrate that S100A12 expression in leukocytes is specifically restricted to granulocytes and that S100A12 represents one of the major calcium-binding proteins in these cells. S100A12, MRP8, and MRP14 translocate simultaneously from the cytosol to cytoskeletal and membrane structures in a calcium-dependent manner. However, no evidence for direct protein-protein interactions of S100A12 with either MRP8 or MRP14 or the heterodimer was found by chemical cross-linking, density gradient centrifugation, mass spectrometric measurements, or yeast two hybrid detection. Thus, S100A12 acts individually during calcium-dependent signaling, independent of MRP8, MRP14, and the heterodimer MRP8/MRP14. This granulocyte-specific signal transduction pathway may offer attractive targets for therapeutic intervention with exaggerated granulocyte activity in pathological states.

Analysis of the MRP8-MRP14 protein-protein interaction by the two-hybrid system suggests a prominent role of the C-terminal domain of S100 proteins in dimer formation

Calcium-binding S100 proteins are thought to play a central role in calcium-mediated signal transduction pathways. They consist of two helix-loop-helix, calcium-binding EF-hand domains. A characteristic feature is their tendency to form homo- and/or heterodimeric complexes. This report presents for the first time a functional "in vivo" approach to the analysis of S100 protein dimerization. Using the two-hybrid system we analyzed the dimerization of MRP8 (S100A8) and MRP14 (S100A9), two S100 proteins expressed in myeloid cells. It is reported that the MRP8-MRP14 heteromer is the clearly preferred complex in both man and mouse. The ability to homodimerize, however, appears to be restricted to the murine MRPs. Interaction analysis of chimeric murine/human MRP14 proteins indicates, that the C-terminal EF-hand domain plays a prominent role in MRP8-MRP14 interaction and determines the specificity of dimerization. Site-directed mutagenesis of four evolutionary conserved hydrophobic amino acids, which have been recently supposed to be essential for S100 protein dimerization, suggests that at least one of these, namely the most N-terminal located residue, is not critical for dimerization.

Biochemical characterization of the murine S100A9 (MRP14) protein suggests that it is functionally equivalent to its human counterpart despite its low degree of sequence homology

Due to the low degree of sequence similarity it has been speculated that murine and human S100A9 (MRP14), an inflammatory marker protein belonging to the S100 protein family, may have different cellular functions in mouse and man. The present study was undertaken to investigate the murine S100A9 protein (mS100A9) biochemically. We demonstrate that in murine peripheral CD11b+ cells up to 20% of the protein of the cytosolic fraction consists of mS100A9 and that several minor mS100A9 isoforms are present. Cell fractionation experiments with CD11b+ murine leukocytes showed that mS100A9 is found in the cytosol as well as in the insoluble fraction. Transient expression of a green fluorescence protein-mS100A9 fusion in mammalian cells revealed that mS100A9 is localized in neither the nucleus nor the vesicles. Recombinantly expressed murine S100A9 interacts in vitro with murine and human S100A8 in an in vitro glutathione S-transferase pull-down assay. Homodimerization was not observed. For further biochemical analysis the myeloid 32D cell line is presented as a suitable model, to study murine myeloid expressed S100 proteins. Both murine S100A9 and its dimerization partner mS100A8 are expressed at the onset of granulocyte-colony stimulating factor induced myeloid differentiation. Substantial amounts of this complex are constitutively secreted by granulocytic 32D cells into the medium. In summary, these data suggest, that the human and murine S100A9 may share a higher degree of functional homology than of sequence similarity.

Common exonic missense variants in the C2 domain of the human KIBRA protein modify lipid binding and cognitive performance

The human KIBRA gene has been linked to human cognition through a lead intronic single-nucleotide polymorphism (SNP; rs17070145) that is associated with episodic memory performance and the risk to develop Alzheimer's disease. However, it remains unknown how this relates to the function of the KIBRA protein. Here, we identified two common missense SNPs (rs3822660G/T [M734I], rs3822659T/G [S735A]) in exon 15 of the human KIBRA gene to affect cognitive performance, and to be in almost complete linkage disequilibrium with rs17070145. The identified SNPs encode variants of the KIBRA C2 domain with distinct Ca(2+) dependent binding preferences for monophosphorylated phosphatidylinositols likely due to differences in the dynamics and folding of the lipid-binding pocket. Our results further implicate the KIBRA protein in higher brain function and provide direction to the cellular pathways involved.

[Importance of cellular tight junction complexes in the development of periprosthetic leakage after prosthetic voice rehabilitation]

BACKGROUND

The use of voice prostheses is currently the gold standard in voice rehabilitation after total laryngectomy. This method combines low complication rates and excellent rehabilitation results; however, approximately 30% of patients show periprosthetic leakage or severe fistula enlargement after laryngectomy and prosthetic voice restoration within the first 4 years. The development of this enlargement is controversially discussed in the literature but recently published studies have shown that high esophageal reflux plays a key role in this process, which leads to an inflammatory reaction and disturbs the intercellular tight junctions in the sense of an epithelial mesenchymal transition (EMT).

MATERIAL AND METHODS

A total of 44 patients underwent 24 h pH monitoring, a sample biopsy from the region of the fistula and a subsequent biomolecular examination for intracellular junction proteins as well as a correlation between the severity of reflux and tracheoesophageal fistula problems before and after antireflux therapy with proton pump inhibitors (PPI).

RESULTS

Immunohistochemical staining revealed decreases in membrane E-cadherin and β-catenin and a significant increase in the cytoplasmic fraction, depending on the severity of inflammation in the fistula tissue. In patients with an improvement of clinical fistula problems under oral PPI treatment an increase of membrane E-cadherin could be shown, whereas patients with persisting fistula enlargement demonstrated a further decrease of E-cadherin.

CONCLUSION

The data indicate a central role of EMT in the development of fistula enlargement after total laryngectomy. Patients with periprosthetic leakage showed a loss of membrane bound E-cadherin and β-catenin with an up-regulation of vimentin expression. In patients with mild or no leakage problems EMT could be resolved by aggressive antireflux treatment, whereas patients without any effect of PPI treatment on the fistula showed no reversal of EMT. These data contribute to the understanding of treatment resistant fistula enlargement after total laryngectomy.

[Abelson interactor 1 (Abi1) in colorectal cancer. From synaptic plasticity to tumor cell migration]

BACKGROUND

Invasion and metastatic dissemination of tumor cells defines the prognosis of patients with colorectal cancer (CRC). The Abelson interactor 1 (Abi1), a 65 kD substrate of the eponymous Abelson tyrosine kinase, interacts with phosphatidylinositol-3-kinase (PI3K) and heterogeneous nuclear ribonucleoprotein K (hnRNP K) and is a key regulator of cytoskeletal reorganization during synaptic maturation and cellular migration.

AIM

The aim of this study was the analysis of Abi1 expression patterns and to elucidate the role in cytoskeletal reorganization in colorectal carcinoma cells.

MATERIAL AND METHODS

The methods used in this study were immunohistochemistry; immunofluorescence microscopy; liposomal transfection and protein analysis by Western blotting.

RESULTS

The results showed that Abi1 is expressed at the invasive front of colorectal carcinomas and localizes to the leading edge of lamellipodia in cultured colorectal carcinoma cells. A phosphorylated isoform of Abi1 that stains positively in these microcompartments disappears after treatment with the tyrosine kinase inhibitor STI571 (Glivec®). The RNA interference (RNAi) approach knockdown of Abi1 as well as treatment with STI571 induce a shift in cellular morphology from broad lamellipodia-like to thin filopodia-like cellular protrusions.

DISCUSSION

The initial results support a central role for phosphorylated Abi1 in the formation of lamellipodia-like cellular protrusions as a prerequisite for cellular migration of colorectal carcinoma cells. As phosphorylation of Abi1 could be pharmaceutically targeted with STI571, this indicates a possible therapeutic option to prevent the gain of a metastatic phenotype in colorectal cancer. This possibility will be further evaluated in ongoing research.