An otopetrin family proton channel promotes cellular acid efflux critical for biomineralization in a marine calcifier.

Otopetrins comprise a family of proton-selective channels that are critically important for the mineralization of otoliths and statoconia in vertebrates but whose underlying cellular mechanisms remain largely unknown. Here, we demonstrate that otopetrins are critically involved in the calcification process by providing an exit route for protons liberated by the formation of CaCO3 Using the sea urchin larva, we examined the otopetrin ortholog otop2l, which is exclusively expressed in the calcifying primary mesenchymal cells (PMCs) that generate the calcitic larval skeleton. otop2l expression is stimulated during skeletogenesis, and knockdown of otop2l impairs spicule formation. Intracellular pH measurements demonstrated Zn2+-sensitive H+ fluxes in PMCs that regulate intracellular pH in a Na+/HCO3--independent manner, while Otop2l knockdown reduced membrane proton permeability. Furthermore, Otop2l displays unique features, including strong activation by high extracellular pH (>8.0) and check-valve-like outwardly rectifying H+ flux properties, making it into a cellular proton extrusion machine adapted to oceanic living conditions. Our results provide evidence that otopetrin family proton channels are a central component of the cellular pH regulatory machinery in biomineralizing cells. Their ubiquitous occurrence in calcifying systems across the animal kingdom suggest a conserved physiological function by mediating pH at the site of mineralization. This important role of otopetrin family proton channels has strong implications for our view on the cellular mechanisms of biomineralization and their response to changes in oceanic pH.

Foxp3 expression in pancreatic carcinoma cells as a novel mechanism of immune evasion in cancer.

The forkhead transcription factor Foxp3 is highly expressed in CD4+CD25+ regulatory T cells (Treg) and was recently identified as a key player in mediating their inhibitory functions. Here, we describe for the first time the expression and function of Foxp3 in pancreatic ductal adenocarcinoma cells and tumors. Foxp3 expression was induced by transforming growth factor-beta2 (TGF-beta2), but not TGF-beta1 stimulation in these cells, and was partially suppressed following antibody-mediated neutralization of TGF-beta2. The TGF-beta2 effect could be mimicked by ectopic expression of a constitutively active TGF-beta type I receptor/ALK5 mutant. Down-regulation of Foxp3 with small interfering RNA (siRNA) in pancreatic carcinoma cells resulted in the up-regulation of interleukin 6 (IL-6) and IL-8 expression, providing evidence for a negative transcriptional activity of Foxp3 also in these epithelial cells. Coculture of Foxp3-expressing tumor cells with naive T cells completely inhibited T-cell proliferation, but not activation, and this antiproliferative effect was partially abrogated following specific inhibition of Foxp3 expression. These findings indicate that pancreatic carcinoma cells share growth-suppressive effects with Treg and suggest that mimicking Treg function may represent a new mechanism of immune evasion in pancreatic cancer.

Differential expression of CD126 and CD130 mediates different STAT-3 phosphorylation in CD4+CD25- and CD25high regulatory T cells.

IL-6 is a pleiotropic cytokine involved in T-lymphocyte biology. Following IL-6 binding, the soluble IL-6R (CD126)-IL-6 complex can directly activate cells that express the signal-transducing gp130 (CD130) molecule, which mediates two distinct signals, mitogenesis by mitogen-activated protein kinase (MAPK) activation and anti-apoptosis by signal transducer and activator of transcription 3 (STAT-3) activation. This 'trans-signaling', also mediated by the soluble CD126/IL-6 fusion protein hyper-IL-6 (H-IL-6), contributes to the perpetuation of autoimmune diseases such as Morbus Crohn or rheumatoid arthritis. On the other hand, the homeostasis of cellular immune reactions and its failure leading to autoimmune diseases are critically controlled by regulatory T cells (Tregs). Here, we investigated the differential expression of CD126 and CD130 on subsets of human leukocytes in blood, tonsil and spleen. Among CD4+ T cells, differential expression of CD126 and CD130 was observed on the basis of CD25 expression. CD4+CD25- T cells were strongly CD126+ and CD130+, whereas CD25(high) Tregs expressed CD126 but little CD130. Both CD126 and CD130 were down-modulated on CD4+CD25- T cells following ligand binding, whereas only marginal modulation was observed on Tregs. Interestingly, we observed a correlation between CD126 and CD130 expression with STAT-3 phosphorylation in CD4+CD25- T cells compared with Tregs after stimulation with IL-6 or H-IL-6, whereas the MAPK extracellular signal-regulated kinase 1/2 were not activated by CD130 dimerization. The differential expression of CD126 and CD130 and subsequent STAT-3 phosphorylation might be relevant for the recently described role of IL-6 in the control of Treg activity.