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Type 1 autoimmune pancreatitis (AIP) is the pancreatic manifestation of a systemic fibroinflammatory IgG4-related disease. It is often misdiagnosed as pancreatic cancer.1, 2, Full size image

Subcellular localization of βCGRP

Consistent with the wild-type recombinant CALCB, the fluorescence signal of the Flag-labeled mutant (S30P- and IR [1]-) βCGRP recombinant didnot coincided with the green fluorescent signals of the endoplasmic reticulum (ER) marker (Figure 5a) and the red signal of the Golgi apparatus marker (Figure 5b) in HEK293 cells, that is, only very few zones of yellow which would indicate co-localization with ER and Golgi apparatus in S30P and IR [1] mutants compared with wild-type. Thus, in vitro, the mutant βCGRP propeptides were fall to location with ER and Golgi.

Located of Trypsin/PAR2/ERK/VEGFR2

In particular, the PAR2 receptor is activated by tryptase that cleaves the N-terminal domain of the receptor and signaling through the ERK/VEGFR2 pathway. To examine this possibility, we initially performed immunohistochemical (IHC) studies to determine whether CALCB_p.S30P mutations affect the co-localization of trypsin and PAR2 in the inflamed pancreas of IgG4-related AIP patients. We found that trypsin does co-expresses with PAR2 in the pancreatic tissues neither from patients with CALCB_p.S30P mutations (Figure 5a) and that of wild-type (Figure 5b). The cellular localization of the PAR2/ERK signaling pathway showed a rare overlap of ERK and PAR2 (yellow staining in the merged image) (Figures 5c and d) in the mutant-type (Figure 5c) than that of wild-type (Figure 5d) indicating that CALCB_p.S30P may affect the localization of ERK and PAR-2. Double staining of AKT with PI3K showed that AKT co-expresses with PI3K in the tissues with CALCB mutation (Figure 5e) and that of wild-type (Figure 5f). Intriguingly, ERK and VEGFR2 slightly co-localized in the tissues with CALCB_p.S30P mutation (Figure 5g) than that in wild-type (Figure 5h).

βCGRP activates the phosphorylation of ERK1/2 resulting in autoimmune inflammation

To examine whether CALCB mutations effect on βCGRP activates the phosphorylation of ERK1/2, we performed a Western blot on the cell lysates from HEK293 cells transfected with empty vector, wild-type CALCB, p.S30P, and p.IR CALCB mutations, which indicated that p.S30P and p.IR CALCB mutations induced a decrease in the phosphorylation of ERK1/2 (Figure 6).

Figure 6
figure 6

CALCB mutation effect the phosphorylation of ERK1/2. Phosphorylation of AKT1 on serine 473 (pAKT1, S473), total AKT1 protein. Phosphorylation of ERK1/2 (phospho-T202/204) and total ERK1/2 protein. GAPDH levels were assessed as a control for loading

In this study, we also found that the distribution of CD4+Foxp3+ (Treg) cells was significantly different in pancreatic tissues from CALCB_p.S30P mutations and wild-type. A majority of the Treg cells were distributed around pancreatic ductal or blood vessels in the tissues with CALCB mutations (Figure 7a), while they were scattered in wild-type from chronic pancreatitis (Figure 7b).

Figure 7
figure 7

CALCB mutation effect the Treg cells dispense. Co-localization of DNA (blue), CD4 (red), and Foxp3 (green) indicates Treg cells formation. Original magnification: × 400. WT denotes wild-type