SDF-1alpha-induced intracellular calcium transient involves Rho GTPase signalling and is required for migration of hematopoietic progenitor cells

Signalling through the chemokine stromal derived factor (SDF)-1alpha and its receptor CXCR4 has been recognized as a key event in the migratory response of hematopoietic stem and progenitor cells (HPC). Small GTPases of the Rho/Rac family might be involved in SDF-1alpha signalling at several different levels. In the present study we report that two toxins from Clostridium species which inhibit the small GTPase Rho suppressed SDF-1alpha-induced generation of intracellular calcium transients in HPC. Chelation of intracellular Ca(2+) with BAPTA or depletion of intracellular Ca(2+) stores with thapsigargin demonstrated that calcium transients are essential for SDF-1alpha-induced chemotactic migration of HPC. Furthermore, transplantation of HPC pretreated with Ca(2+) flux inhibitors into mice revealed a suppression of HPC homing to the bone marrow and increased levels of cells remaining in the bloodstream or circulating to the spleen. Our data indicate that the small GTPase Rho is required for the induction of Ca(2+) transients in HPC, which in turn are necessary for the coordinated migratory response of HPC both in vitro and in vivo.     

Distinct roles of Rab3B and Rab13 in the polarized transport of apical,basolateral, and tight junctional membrane proteins to the plasma membrane

Regulated transport of proteins to distinct plasma membrane domains is essential for the establishment and maintenance of cell polarity in all eukaryotic cells. The Rab family small G proteins play a crucial role in determining the specificity of vesicular transport pathways. Rab3B and Rab13 localize to tight junction in polarized epithelial cells and cytoplasmic vesicular structures in non-polarized fibroblasts, but their functions are poorly understood. Here we examined their roles in regulating the cell-surface transport of apical p75 neurotrophin receptor (p75NTR), basolateral low-density lipoprotein receptor (LDLR), and tight junctional Claudin-1 using transport assay in non-polarized fibroblasts. Overexpression of Rab3B mutants inhibited the cell-surface transport of LDLR, but not p75NTR and Claudin-1. In contrast, overexpression of Rab13 mutants impaired the transport of Claudin-1, but not LDLR and p75NTR. These results suggest that Rab3B and Rab13 direct the cell-surface transport of LDLR and Claudin-1, respectively, and may contribute to epithelial polarization.     

Specific expression of annexin III in rat-small-hepatocytes

Small hepatocytes are cells that express characteristic phenotypes such as a high growth potential and differentiation capacity. In order to identify rat-small-hepatocyte specific proteins, we separated the cellular proteins of isolated small and parenchymal hepatocytes by 2D polyacrylamide gel electrophoresis. Comparison of their profiles revealed a protein with a molecular mass of 37 kDa in the small hepatocytes that was not present in the parenchymal hepatocytes. Proteolytic peptide mass fingerprinting was used to identify the protein and it was found to be annexin III. The validity of the identification was confirmed by Western blot analysis with anti-annexin III antibody.     

Phosphorylation-dependent structural alterations in the small hsp30 chaperone are associated with cellular recovery

Small heat shock proteins (hsps) act as molecular chaperones by preventing the thermal aggregation and unfolding of cellular protein; however, the manner by which cells regulate chaperone activity remains unclear. In the present study, we examined the role of phosphorylation on the chaperone function of the Xenopus small hsp30. Both heat stress and sodium arsenite treatment in A6 cells resulted in a rapid activation of p38alpha and MAPKAPK-2. Surprisingly, the association of MAPKAPK-2 with hsp30 and its subsequent phosphorylation were more prevalent during recovery after heat stress. Treatment of A6 cells with SB203580, an inhibitor of the p38 MAP kinase pathway, resulted in a loss of hsp30 phosphorylation. Phosphorylation resulted in the formation of smaller multimeric hsp30 complexes and resulted in a significant loss of secondary structure. Consequently the phosphorylation-induced structural changes severely compromised the ability of hsp30 to prevent the heat-induced aggregation of citrate synthase and luciferase in vitro. We confirmed that the loss of chaperone activity was coincident with an attenuated binding of phosphorylated hsp30 with target proteins. Our data suggest that phosphorylation may be necessary to regulate the post-heat stress molecular chaperone activity of hsp30.     

Rab11b resides in a vesicular compartment distinct from Rab11a in parietal cells and other epithelial cells

The Rab11 family of small GTPases is composed of three members, Rab11a, Rab11b, and Rab25. While recent work on Rab11a and Rab25 has yielded some insights into their function, Rab11b has received little attention. Therefore, we sought to examine the distribution of endogenous Rab11b in epithelial cells. In rabbit gastric parietal cells, unlike Rab11a, Rab11b did not colocalize or coisolate with H(+)/K(+)-ATPase. In MDCK cells, endogenous Rab11b localized to an apical pericentrisomal region distinct from Rab11a. The microtubule agents nocodazole and taxol dramatically alter Rab11a's localization in the cell, while effects on Rab11b's distribution were less apparent. These results indicate that in contrast to Rab11a, the Rab11b compartment in the apical region is not as dependent upon microtubules. While Rab11a is known to regulate transferrin trafficking in nonpolarized cells and IgA trafficking in polarized cells, Rab11b exhibited little colocalization with either of these cargoes. Thus, while Rab11a and Rab11b share high sequence homology, they appear to reside within distinct vesicle compartments.     

Fish microsporidia: fine structural diversity and phylogeny

Structural diversity of fish microsporidian life cycle stages and of the host-parasite interface is reviewed. In the infected cell of the fish host, microsporidia may either cause serious degradation of the cytoplasm and demise of the cell, or they may elicit host cell hypertrophy, producing a parasite-hypertrophic host cell complex, the xenoma. The structure of the xenoma and of its cell wall may differ according to the genus of the parasite, and seems to express properties of the parasite rather than those of the host. In merogony, the parasite cell surface interacts with the host cell in diverse ways, the most conspicuous being the production of thick envelopes of different types. Sporogony stages reveal different types of walls or membranes encasing the sporoblasts and later the spores and these envelopes may be of host or parasite origin. Nucleospora differs from all other fish microsporidia by its unique process of sporogony. Except for the formation of conspicuous xenomas, there are no essentially different structures in fish-infecting microsporidia compared with microsporidia from other hosts. Although the structures associated with the development of fish microsporidia cannot be attributed importance in tracing the phylogeny, they are relevant for practical determination and assessing the relation to the host. The possibility of the existence of an intermediate host is discussed. Higher-level classification of Microsporidia is briefly discussed and structure and evolutionary rates in microsporidian rDNA are reviewed. Discussion of rDNA molecular phylogeny of fish-infecting microsporidia is followed by classification of these parasites. Most form a rather cohesive clade. Outside this clade is the genus Nucleospora, separated at least at the level of Order. Within the main clade, however, there are six species infecting hosts other than fish. Based on data available for analysis, a tentative classification of fish-infecting microsporidia into five groups is proposed. Morphologically defined groups represent families, others are referred to as clades. Group 1, represented by family Pleistophoridae, includes Pleistophora, Ovipleistophora and Heterosporis; Vavraia and Trachipleistophora infect non-fish hosts. Group 2, represented by family Glugeidae, is restricted to genus Glugea and Tuzetia weidneri from crustaceans. Group 3 comprises three clades: Loma and a hyperparasitic microsporidian from a myxosporean; Ichthyosporidium and Pseudoloma clade and the Loma acerinae clade. For the latter species a new genus has to be established. Group 4 contains two families, Spragueidae with the genus Spraguea and Tetramicridae with genera Microgemma and Tetramicra, and the Kabatana and Microsporidium seriolae clade. Group 5 is represented by the family Enterocytozoonidae with the genus Nucleospora and mammal-infecting genus Enterocytozoon.     

Organization of the Rab-GDI/CHM superfamily: the functional basis for choroideremia disease

Choroideremia is an X-chromosome-linked disease that leads to the degeneration of the choriocapillaris, the retinal pigment epithelium and the photoreceptor layer in the eye. The gene product defective in choroideremia, CHM, is identical to Rab escort protein 1 (REP1). CHM/REP1 is an essential component of the catalytic geranylgeranyltransferase II complex (GGTrII) that delivers newly synthesized small GTPases belonging to the RAB gene family to the catalytic complex for post-translational modification. CHM/REP family members are evolutionarily related to members of the guanine nucleotide dissociation inhibitor (GDI) family, proteins involved in the recycling of Rab proteins required for vesicular membrane trafficking through the exocytic and endocytic pathways, forming the GDI/CHM superfamily. Biochemical and structural analyses have now revealed a striking parallel in the organization and function of these two families allowing us to generate a general model for GDI/CHM superfamily function in health and disease.     

Identification and characterization of a novel Chlamydia trachomatis reticulate body protein

The genome of the obligate intracellular bacterium Chlamydia trachomatis comprises 894 genes predicted by computer-based analysis. As part of a large-scale proteome analysis of C. trachomatis, a small abundant protein encoded by a previously unrecognized novel 204-bp open reading frame was identified by tandem mass spectrometry. No homology of this protein was observed to proteins from other organisms. The protein was conserved in C. trachomatis but not found in Chlamydia pneumoniae. Using proteomics, we show that the expression of the protein is initiated at the middle of the developmental cycle. The protein is rapidly degraded and is only present in reticulate or intermediate bodies, suggesting a possible function in the intracellular stage of C. trachomatis development. We have termed the protein '7-kDa reticulate body protein'.     

Modulation of HeLa cells spreading by the non-receptor tyrosine kinase ACK-2

The CDC42 regulated non-receptor tyrosine kinase ACK-2 has been associated with integrin signaling. In this report, the effect of ACK-2 on the modulation of cell spreading and motility was examined. HeLa cells expressing epitope-tagged wild type ACK-2 showed a slower rate of spreading on fibronectin when compared with untransfected cells. An ACK-2 protein lacking its SH3 domain was still capable of modulating HeLa cell spreading suggesting that its tyrosine kinase activity is sufficient to induce the observed phenotype. The ACK-2 effect on the rate of cell spreading did not involve inhibition of integrin-mediated activation of PI-3K signaling, since it did not alter membrane translocation of a GFP-PH-AKT domain (AKT pleckstrin homology domain) used as a reporter for PI-3K products induced by cell adhesion. The ACK-2 effect appears to be upstream from the adapter protein CrkII, since co-expression of CrkII and ACK-2 results in a neutralization of ACK-2 mediated effects on HeLa cell spreading. Similarly, co-expression of p130Cas, which interacts with the adapter protein CrkII, with ACK-2, also results in a partial reversion of the ACK-2 effects on cell spreading. CrkII mediated reversal of the ACK-2 induced phenotype requires the activity of the small GTPase, Rap1. Co-expression of ACK-2 and CrkII with a dominant negative form of Rap1 reverses the neutralization by CrkII suggesting that CrkII mediated activation of Rap1 is required. However, an active form of Rap1 is not sufficient to reverse the ACK-2 phenotype by itself. A role for Rac1 in ACK-2 effects was also established. An activated Rac1 protein neutralized the ACK-2 mediated inhibition of cell spreading. A direct measurement of cell motility by either a modified Boyden chamber or wounding assay demonstrates that ACK-2 overexpression increases the motility of the cells. These results suggest that ACK-2 modulates HeLa cells spreading upstream of pathways regulated by CrkII and that ACK-2 may regulate cell motility by controlling the activation of small GTPases such as Rap1 and Rac1.     

Effect of epidermal growth factor on intestinal adaptation after allogeneic small bowel transplantation in rats

We reported that epidermal growth factor (EGF) stimulated graft adaptation in a rat model of syngeneic small bowel transplantation. However, graft rejection is a severe problem with clinical small bowel transplantation, because small intestinal wall contains large amounts of lymphoid tissue. Studies were performed to investigate the effect of EGF on allogeneic graft adaptation after small bowel transplantation in rats treated with an immunosuppressant FK506. The transplanted animals received intraperitoneally EGF or saline (untreated) after surgery and were examined for analysis one week later. EGF-treated group markedly enhanced the water absorption and induction of sodium glucose cotransporter (SGLTI) as compared with EGF-untreated group. EGF-treated group also increased the mucosal crypt depth and its cell proliferating rate, although there was no significant difference in the mucosal villus height between the two groups. These results indicate that EGF accelerates intestinal allograft adaptation in part by the recovery of mucosal structure and function after small bowel transplantation in rats. EGF may have relevance to promote graft function in clinical small intestinal transplantation.