Ctr2 Regulates Mast Cell Maturation by Affecting the Storage and Expression of Tryptase and Proteoglycans

Abstract

Copper (Cu) is essential for multiple cellular functions. Cellular uptake of Cu+ is carried out by the Ctr1 high affinity Cu transporter. The mobilization of endosomal Cu pools is regulated by a protein structurally similar to Ctr1, called Ctr2. It was recently shown that ablation of Ctr2 caused an increase in the concentration of Cu localized to endolysosomes. However, the biological significance of excess endolysosomal Cu accumulation has not been assessed. Here we addressed this issue by investigating the impact of Ctr2 deficiency on mast cells, a cell type unusually rich in endolysosomal organelles (secretory granules). We show that Ctr2−/− mast cells have increased intracellular Cu concentrations and that the absence of Ctr2 results in increased metachromatic staining, the latter indicating an impact of Ctr2 on the storage of proteoglycans in the secretory granules. In agreement with this, the absence of Ctr2 caused a skewed ratio between proteoglycans of heparin and chondroitin sulfate type, with increased amounts of heparin accompanied by a reduction of chondroitin sulfate. Moreover, transmission electron microscopy analysis revealed a higher number of electron dense granules in Ctr2−/− mast cells than in wild-type cells. The increase in granular staining and heparin content is compatible with an impact of Ctr2 on mast cell maturation and, in support of this, the absence of Ctr2 resulted in markedly increased mRNA expression, storage and enzymatic activity of tryptase. Taken together, the present study introduces Ctr2 and Cu as novel actors in the regulation of mast cell maturation and granule homeostasis.

Acidic pH is essential for maintaining mast cell secretory granule homeostasis

“…For this purpose we used the fast garnet assay, a method that detects trypsin-like activity. 14 However, the fast garnet method will detect a range of proteases with trypsin-like activity, that is, not just mast cell tryptase, and to evaluate to what extent mast cell tryptase accounts for the total trypsin-like activity in mast cells we therefore subjected both wild-type and tryptase-deficient (mMCP6 −/− ) mast cells to fast garnet staining. As seen in Figure 8 , wild-type mast cells stained strongly and the staining showed a distinct granular appearance, in agreement with the location of tryptase within the secretory granules.…”

Copper Regulates Maturation and Expression of an MITF:Tryptase Axis in Mast Cells

“…bacteria and yeast) and there is also evidence supporting that copper can regulate neutrophil and macrophage function [16, 21]. As regards mast cells, it was shown in a previous study that mast cells lacking Ctr2, a protein implicated in copper transport, exhibited altered homeostasis [22]. However, the direct impact of copper on mast cells has not been investigated.…”

Copper transporters and chaperones CTR1, CTR2, ATOX1, and CCS as determinants of cisplatin sensitivity

“…Yeast CTR2 has been shown to regulate internal pools of Cu under low Cu conditions 8, 9 , suggesting that the human homolog may have a similar Cu regulatory function. Recent studies found that CTR2 plays a role in mast cell maturation and hemostasis 10 , and that CTR1 protects CTR2 protein from degradation 11 .…”