Secreted Reelin molecules form homodimers

During mammalian brain development, neurons are generated along the ventricle, migrate radially, and become aligned in defined patterns. These precise patterns of neuronal alignment are regulated by an extracellular matrix protein Reelin, and binding of Reelin to its receptors induces tyrosine phosphorylation of the intracellular adaptor protein disabled 1 (Dab1). We recently reported that Reelin molecules assemble to form a homomeric protein complex. Although the number of molecules in the full-length complex is unknown, recombinant N-terminal fragments, which contain the epitope for the function-blocking CR-50 antibody, assembled to form a complex of more than 40 monomers. When the N-terminus was deleted from Reelin, the truncated protein did not form a stable complex. To further characterize the Reelin assembly, we performed biochemical analysis of the full-length Reelin assembly in this study. Here, we report that a full-length Reelin forms a disulfide-linked homodimer. A chemical crosslinking experiment on secreted Reelin confirmed that only dimers are formed by the full-length protein. However, interestingly, chemical crosslinking of the N-terminus-truncated Reelin resulted in the formation of larger complexes, in addition to dimers, suggesting that the tertiary structure required for the proper and stable assembly/dimerization was altered by the truncation. The truncated protein did not induce efficient tyrosine phosphorylation of Dab1, although it bound well to the receptors. These findings demonstrate the functional importance of the N-terminal region of Reelin for proper dimerization and signaling. Proper but not simple extracellular crosslinking of the receptors by these dimers may be important for Reelin signaling to occur.     

IL-6-STAT3 controls intracellular MHC class II alphabeta dimer level through cathepsin S activity in dendritic cells

We found IL-6-STAT3 pathway suppresses MHC class II (MHCII) expression on dendritic cells (DCs) and attenuates T cell activation. Here, we showed that IL-6-STAT3 signaling reduced intracellular MHCII alphabeta dimmer, Ii, and H2-DM levels in DCs. IL-6-mediated STAT3 activation decreased cystatin C level, an endogenous inhibitor of cathepsins, and enhanced cathepsin activities. Importantly, cathepsin S inhibitors blocked reduction of MHCII alphabeta dimer, Ii, and H2-DM in the IL-6-treated DCs. Overexpression of cystatin C suppressed IL-6-STAT3-mediated increase of cathepsin S activity and reduction of MHCII alphabeta dimer, Ii, and H2-DM levels in DCs. Cathepsin S overexpression in DCs decreased intracellular MHCII alphabeta dimer, Ii, and H2-DM levels, LPS-mediated surface expression of MHCII and suppressed CD4(+) T cell activation. IL-6-gp130-STAT3 signaling in vivo decreased cystatin C expression and MHCII alphabeta dimer level in DCs. Thus, IL-6-STAT3-mediated increase of cathepsin S activity reduces the MHCII alphabeta dimer, Ii, and H2-DM levels in DCs, and suppresses CD4(+) T cell-mediated immune responses.     

Cell biology and pathology of liver sinusoidal endothelial cells

Growing evidence revealed that liver sinusoidal endothelial cells (SEC) play several important roles in physiology and pathology of the liver. It has been well understood that their structural characteristics, such as the membrane sieve and lack of basement membrane, facilitate direct contact of soluble and insoluble serum substances with hepatic parenchymal cells, resulting in enhancement of hepatic metabolic activity. In addition, SEC is now regarded as a member of the scavenger endothelial cells, which have potential to eliminate a variety of macromolecules from the blood circulation by receptor-mediated endocytosis. It is reported that molecules preferentially eliminated by SEC are denatured or modified proteins such as advanced glycation end products, extracellular matrix components including hyaluronic acid, and some lipoproteins. The nature of the scavenger receptors corresponding to these molecules remains to be clarified. Recently, it was noted that SEC has an antigen-presenting function similar to dendritic cells. Taken together, it is suggested that SEC, cooperating with Kupffer cells and hepatic dendritic cells, may partake of immunoregulatory functions in the liver. SEC also plays a pivotal role in the pathological process of ischemia-reperfusion injury following liver surgery and liver transplantation. Thus, it is of importance to elucidate the mechanisms of apoptosis and proliferation of SEC. Recent results on the regulation of growth and apoptotic signaling of SEC are discussed.     

Existence of a small population of IL-2Rβhi TCRint cells in SCG and MRL-lpr/lpr mice which produce normal Fas mRNA and Fas molecules from the lpr gene

Mice carrying the lpr gene, SCG and MRL-lpr/lpr mice, were used to characterize the phenotype and lpr gene of abnormally proliferating T cells in these mice. A major population which expanded in these mice were T cells expressing intermediate (int) levels of T cell receptor (TCR) (and CD3) and the phenotype of interleukin-2 receptor (IL-2R)β^lo α^? (possibly abnormal TCR^int cells). The levels of TCR^hi cells of thymic origin (generated through the mainstream of T cell differentiation in the thymus) profoundly decreased after the onset of disease. However, a small population of normal TCR^int cells (i.e. IL-2Rβ^hi α^?) were also found to exist in all tested organs. For example, the majority of abnormal IL-2Rβ^lo TCR^int cells were CD4^?8^? CD2^?, while normal IL-2Rβ^hi TCR^int cells were a mixture of single-positive cells (mainly CD8⁺), CD4^?8^? cells and CD2⁺ cells. Moreover, normal TCR^int cells preferentially produced normal Fas mRNA and Fas molecules from the lpr gene. This phenomenon explains the leaky appearance of normal Fas mRNA and Fas molecules in mice carrying the lpr gene. It is suggested that a small population of IL-2Rβ^hiTCR^int cells are resistant to the lpr genetic abnormality.     

Diverse functions of the p75 neurotrophin receptor

The pan-neurotrophin receptor p75NTR belongs to a large family of receptors, which includes tumor necrosis factor receptors, Fas and approximately 25 other members. The p75NTR is the first receptor to be cloned molecularly. Recent years have seen the emergence of a consensus regarding the signaling pathways activated by p75NTR and its potential biological function, although receptor characterization had not been targeted for some years. We now know that p75NTR has surprisingly diverse effects, ranging from cell death to regulation of axon elongation. This diversity can be explained by the complex formation of p75NTR with other receptors and multiple signaling molecules that interact with the intracellular domain of p75NTR.     

Primary osteosarcoma of the uterine corpus: case report and review of the literature

A rare case of rapidly growing osteosarcoma that developed in the uterine corpus of a 62-year-old woman is presented. The tumor occupied almost the entire pelvic cavity and extended into the abdominal cavity, with marked involvement of the intestines. Histopathologically, the tumor was composed of an osteoblastic component, accompanied by conspicuous bone formation, and a fibroblastic component. The tumor cells were positive for vimentin and osteocalcin, as well as desmin, alpha-smooth muscle actin and muscle-specific actin, but negative for h-caldesmon. The results indicated myofibroblastic differentiation in a part of the tumor. A review of 14 reported cases and our case of uterine osteosarcoma revealed that this tumor has a biologically aggressive nature, although its histopathological and immunohistochemical features are similar to those of osteosarcomas in soft tissue and bone. As the prognosis of patients with this tumor is poor, it is of importance to differentiate this tumor from other types of tumors arising from the uterine corpus.     

Microdissection is essential for gene expression profiling of clinically resected cancer tissues.

The gene expression array method enables us to achieve expression profiling with thousands of genes. Clinically resected bulk cancer tissues, however, contain not only cancer cells but also stromal cells, which may affect gene expression profiling and hamper accurate analysis of the cancer cells per se. Therefore, a procedure for dissecting specific cells, such as laser capture microdissection, is neededfor the clinical application of a gene expression array. There has been no study actually comparing 2 gene expression profiles, one obtained using RNA extractedfrom cancer cells by laser capture microdissection and one obtained using RNA extractedfrom bulk cancer tissues. Wefirst demonstrated the difference in expression patterns between them, without any amplification procedures. In addition, differential expression analysis between tumor and nontumor tissue yielded quite different patterns between the 2 methods. We conclude that microdissection is essential for gene expression profiling of clinical specimens.     

Peripheral hepatolithiasis incidentally found at autopsy

Summary Hepatolithiasis is a common disease in East Asia though very rare in the West. Four cases of hepatolithiasis in which calculi were incidentally found in the peripheral branches of the intrahepatic biliary tree at autopsy are described and compared with hepatolithiasis involving the major branches of the intrahepatic biliary tree. These four cases were all elderly, three patients were male and one female. The calculi were brown pigment stones in each case, as seen in the major branch type. The stone-containing ducts showed mild fibrosis and glandular proliferation with inflammatory changes in three cases; these changes were marked in the fourth case. The hepatic parenchyma around the stone-containing ducts was atrophic or collapsed in all four cases. The major branches of the intrahepatic biliary tree as well as the extrahepatic tree failed to show findings suggestive of bacterial infections or biliary anomalies. These data suggest that brown pigment stones develop primarily in the peripheral ducts in the liver. It remains uncertain whether the peripheral type eventually progresses to the major type or not.     

Characterization of enteropathogenic and enteroaggregative Escherichia coli isolated from diarrheal outbreaks.

Virulence characteristics of diarrheal outbreak-associated Escherichia coli O55:NM, O126:NM, and O111:NM were examined. The E. coli O55:NM strains were atypical enteropathogenic E. coli (EPEC), while the E. coli O126:NM and O111:NM strains should be classified as enteroaggregative E. coli (EAggEC). The contributions of EPEC and EAggEC to the human disease burden in Japan might be significantly greater than is currently appreciated.