Estimating the size of the active translocation pore of an autotransporter

Autotransporters (ATs) are large virulence factors secreted by Gram-negative bacteria. The passenger domain, carrying the virulence functions, is transported across the bacterial outer membrane in a step that is facilitated by a C-terminal β-domain. This domain folds into a β-barrel with a central aqueous pore of ～1 nm inner diameter according to crystal structures. However, these static dimensions are not compatible with the observed secretion of passengers that may contain natural short-spaced disulfide bonds or artificially fused folded elements. Here, we have systematically analyzed the dimensions of the active AT passenger translocator by inserting peptides of different length and structural complexity in the passenger of the AT hemoglobin protease. The peptides were introduced in a short loop protruding from the main structure and flanked by two single cysteines. Our results show that the attained secondary structure may be more critical for secretion than the length of peptide inserted. Furthermore, the data suggest that, during passenger translocation, at least four extended polypeptides or an extended polypeptide and an α-helix are accommodated in the translocator, indicating that the diameter of the active translocation pore is up to 1.7 nm. If the β-domain functions as the translocator, it must be forced into an expanded conformation during passenger translocation.     

Crosstalk between the nodulation signaling pathway and the autoregulation of nodulation in Medicago truncatula

A subset of CLAVATA3/endosperm-surrounding region-related (CLE) peptides are involved in autoregulation of nodulation (AON) in Medicago truncatula (e.g. MtCLE12 and MtCLE13). However, their linkage to other components of the AON pathways downstream of the shoot-derived inhibitor (SDI) is not understood. We have ectopically expressed the putative peptide ligand encoding genes MtCLE12 and MtCLE13 in M. truncatula which abolished nodulation completely in wild-type roots but not in the supernodulating null mutant sunn-4. Further, root growth inhibition was detected when MtCLE12 was ectopically expressed in wild-type roots or synthetic CLE12 peptide was applied exogenously. To identify downstream genes, roots of wild-type and sunn-4 mutant overexpressing MtCLE12 were used for quantitative gene expression analysis. We found that, in 35S:MtCLE12 roots, NODULE INCEPTION (NIN, a central regulator of nodulation) was down-regulated, whereas MtEFD (ethylene response factor required for nodule differentiation) and MtRR8 (a type-A response regulator thought to be involved in the negative regulation of cytokinin signaling), were up-regulated. Moreover, we found that the up-regulation of MtEFD and MtRR8 caused by overexpressing MtCLE12 is SUNN-dependent. Hence, our data link for the first time the pathways for Nod factor signaling, cytokinin perception and AON.     

Epac- and Ca2+ -controlled activation of Ras and extracellular signal-regulated kinases by Gs-coupled receptors

We have recently reported that two typical Gs-coupled receptors, the beta2-adrenergic receptor and the receptor for prostaglandin E1, stimulate phospholipase C-epsilon (PLC-epsilon) and increase intracellular Ca2+ concentration ([Ca2+]i) in HEK-293 cells and N1E-115 neuroblastoma cells, respectively, by a pathway involving Epac1, a cAMP-activated and Rap-specific guanine nucleotide exchange factor (GEF), and the GTPase Rap2B. Here we have demonstrated that these Gs-coupled receptors use this pathway to activate H-Ras and the extracellular signal-regulated kinases 1 and 2 (ERK1/2). Specifically, agonist activation of the receptors resulted in activation of H-Ras and ERK1/2. The latter action was suppressed by dominant negative H-Ras, but not Rap1A. The receptor actions were independent of protein kinase A but fully mimicked by an Epac-specific cAMP analog as well as by a constitutively active Rap2B mutant. On the other hand, a cAMP-binding-deficient Epac1 mutant, the Rap GTPase-activating proteinII, and a dominant negative Rap2B mutant suppressed receptor- and Epac-mediated activation of H-Ras and ERK1/2. Finally, we have demonstrated that activation of H-Ras and ERK1/2 requires the lipase activity of PLC-epsilon and the subsequent [Ca2+]i increase, suggesting that H-Ras activation is mediated by a Ca2+ -activated GEF. In line with this hypothesis, receptor-mediated activation of H-Ras and ERK1/2 was strongly enhanced by expression of RasGRP1, a Ca2+ -regulated Ras-GEF. Collectively, our data indicated that Gs-coupled receptors can activate H-Ras and subsequently the mitogen-activated protein kinases ERK1/2 by a Ca2+ -activated Ras-GEF, possibly RasGRP1, mediated by cAMP-activated Epac proteins, which then lead via Rap2B and PLC-epsilon stimulation to [Ca2+]i increase.     

Spleen metastasis from thyroid carcinoma. Report of a case with diagnosis by fine needle aspiration cytology

BACKGROUND: Lymphoreticular malignancies are the most common neoplasms involving the spleen. Metastasis can be caused by direct invasion from surrounding tumors or from hematogenous spread. Spleen metastases from thyroid carcinoma are unusual, and only 1 case has been reported; none have been diagnosed by fine needle aspiration cytology (FNAC). CASE: A 75-year-old female was diagnosed 6 months earlier with a poorly differentiated thyroid carcinoma with wide lymphatic and vascular invasion. Abdominal computed tomography (CT) and magnetic resonance imaging showed several spleen nodules. FNAC was performed under CT guidance. Cytologic examination showed atypical epithelial cells with thyroidal characteristics. CONCLUSION: This case had the cytologic findings of a poorly differentiated carcinoma of the thyroid metastatic to spleen. We confirmed the rarity of this pathology and the efficacy of splenic FNAC in the diagnosis.