The FMF phenotype is known to be more severe in patients carrying the p.M694V mutation. This report describes 2 molecules secreted by unconventional secretory pathways, S100A12 and IL-18, whose concentrations correlated with clinical disease activity and genotype in patients with FMF. In this clinically and genetically heterogeneous disease, management of these surrogate markers might help to improve patient care and outcomes.

The septin SEPT11 is a novel member of the highly conserved septin family. Septins are cytoskeletal GTPases, which form heteropolymeric complexes. They are involved in cytokinesis and other cellular processes, such as vesicle trafficking and exocytosis. SEPT11 has strong homology to SEPT8. Previously, we identified the interaction of SEPT5 and SEPT8. Using the yeast two-hybrid system, we now demonstrate that SEPT11 partners with SEPT5. The molecular interaction of SEPT11 with SEPT5 was verified by coprecipitation of SEPT5 and SEPT11 from lysates of the human T-cell leukaemia cell line JURKAT and by fluorescence resonance energy transfer. The interaction between SEPT5 and SEPT11 requires the GTP-binding domain and the C-terminal extension. Western analysis in various mouse and human tissues revealed that expression of SEPT11 is restricted to the same tissues as those expressing SEPT5, suggesting that SEPT11 and SEPT5 are components of a cell-specific septin complex. SEPT5, which is expressed in human umbilical vein endothelial cells (HUVECs), has been reported to play an important role in exocytosis. We now report that HUVECs also express SEPT11. Given the interactivity between SEPT5 and SEPT11 as shown above and their coexpression in HUVECs, it may be that a complex formed by these two proteins is involved in the exocytosis mechanism in HUVECs.

Septins are cytoskeletal GTPases forming heteropolymeric complexes involved in processes characterised by active membrane movement such as cytokinesis, vesicle trafficking, and exocytosis. Septins are expressed in non-mitotic cells such as neurons and platelets. SEPT11 belongs to the SEPT6 group and was identified as interaction partner of SEPT5. We cloned and characterised novel SEPT11 variants and investigated interaction partners of SEPT11 in platelets and human umbilical vein endothelial cells. An endothelial cell library was used for cloning novel SEPT11 variants. Using Northern analysis the different SEPT11 transcripts were illustrated. Interaction studies were performed using yeast two-hybrid system, precipitation, FRET, and immunofluorescence microscopy. We demonstrate that SEPT11 partners with SEPT2, SEPT4 and SEPT7 using yeast two-hybrid system and precipitation. The interaction of SEPT11 with SEPT7 is also demonstrated by FRET. In addition to the known SEPT11 transcript (SEPT11_v1) we identified a novel SEPT11 variant (SEPT11_v2) as interaction partner of SEPT4 and SEPT7. Library screening of an endothelial cell library also revealed the presence of this novel SEPT11_v2 transcript. In addition, a third SEPT11 variant (SEPT11_v3) was identified. Expression of SEPT11_v1 and of SEPT11_v2 and SEPT11_v3 in human brain regions was investigated by Northern analysis. Further interaction partners of SEPT11 are characterised using immunofluorescence. Co-localisation of SEPT2, SEPT4, SEPT7 and SEPT11 with tubulin and transferrin receptor (endocytotic marker) is demonstrated. In addition, co-localisation of SEPT4 and SEPT11 with the vesicle-associated protein synaptobrevin 1 (VAMP1), but not clearly with actin, was shown. Only SEPT2 and SEPT7 definitely co-localised with actin, but not clearly with VAMP1.

Background To analyse the validity of membrane-bound SIGLEC1 (CD169) as a sensitive biomarker for monitoring disease activity in pediatric systemic lupus erythematosus (SLE). Methods 27 children and adolescents with SLE were followed for a mean of 13.5 months. During consecutive routine visits SLEDAI-2k, C3, C4 and ds-DNA values were determined. Additionally, expression of SIGLEC1 on monocytes was determined by flow cytometry. The amount of PE-labelled CD169 mAb bound per monocyte was analyzed using QuantiBRITE™ PE tubes. Associations between biomarkers and the clinical course were investigated by regression analysis. Results In general, SIGLEC1 expression is high on SLE-derived monocytes (mean 6 359 (SD 6 056) molecules/monocyte, cut-off 2 500 molecules/monocyte), all patients with newly diagnosed SLE exhibit elevated expression (mean 13366 (SD 7 750) molecules/monocyte). Changes (Δ) in SIGLEC1 levels during the clinical course is the only biomarker that significantly correlates with the change in SLEDAI-2k (betaST = 0.28, p = 0.001). At follow-up visit, a clinically important worsening was experienced by 47.6% of patients with a Δ SIGLEC1 > 2 151 molecules/cell (OR 5.31) and 72.4% with a Δ SIGLEC1 > 756 molecules/cell (OR 8.90). Conversely, 36.4% of patients with a Δ SIGLEC1 < -2 818 molecules/cell (OR 4.16, percentiles as cut-off criteria) and 50.0% of patients with a Δ SIGLEC1 < -1 370 molecules/cell (OR 3.55, application of Youden index) showed clinical improvement. SIGLEC1 expression correlates inversely with the amount of therapeutically applied hydroxychloroquine (p < 0.001). Conclusions SIGLEC1 expression on monocytes is a sensitive biomarker for adjusting disease activity in childhood SLE and represents a promising and easily applicable tool for disease monitoring.

The septin SEPT11 is a novel member of the highly conserved septin family. Septins are GTP-binding proteins which form heteropolymeric complexes. In non-dividing cells (such as platelets and neurons) septins are implicated in exocytosis. The septins SEPT4, SEPT5 and SEPT8 are expressed in platelets. Platelets from a SEPT5 knockout mouse showed an altered serotonin secretion and platelet aggregation suggesting that SEPT5 is involved in secretion in platelets. Transmission electron microscopy of platelets revealed that SEPT4, SEPT5 and SEPT8 are localized surrounding alpha-granules suggesting that the three septins may be components of the septin complex in platelets and contribute in such a way to platelet biology. Activation of platelets by agonists resulted in the translocation of SEPT4 and SEPT8 to the platelet surface indicating a possible functional role of these proteins in granular secretion. Previously, we had identified the interaction of the septins SEPT5 and SEPT8. The aim of this study was to identify other interaction partners of the human septin SEPT5. Using the yeast two-hybrid system we now demonstrate that SEPT11 partners with SEPT5. Western analysis revealed that SEPT11 is also expressed in platelets. The molecular interaction of SEPT11 with SEPT5 was verified by precipitation of the SEPT5/SEPT11 complex from lysates of human platelets. In addition, using Western analysis and immunofluorescence analysis, the co-expression of SEPT5 and SEPT11 is shown in human endothelial cells (HUVECs). The Western analyses of various mouse tissues showed that the expression pattern of SEPT11 matches with the expression pattern of SEPT5 suggesting that SEPT11 and SEPT5 are components of the corresponding cell specific septin complex. Since SEPT5 and SEPT11 are members of the same septin complex and since SEPT5 has been reported to play an important role in exocytosis, the SEPT5/SEPT11-complex may be involved in exocytosis in platelets and HUVECs.