The p.E152K-STIM1 mutation deregulates Ca2+ signaling contributing to chronic pancreatitis

Activation mechanisms and structural dynamics of STIM proteins

The family of stromal interaction molecules (STIM) includes two widely expressed single-pass endoplasmic reticulum (ER) transmembrane proteins and additional splice variants that act as precise ER-luminal Ca2+ sensors. STIM proteins mainly function as one of the two essential components of the so-called Ca2+ release-activated Ca2+ (CRAC) channel. The second CRAC channel component is constituted by pore-forming Orai proteins in the plasma membrane. STIM and Orai physically interact with each other to enable CRAC channel opening, which is a critical prerequisite for various downstream signalling pathways such as gene transcription or proliferation. Their activation commonly requires the emptying of the intracellular ER Ca2+ store. Using their Ca2+ sensing capabilities, STIM proteins confer this Ca2+ content-dependent signal to Orai, thereby linking Ca2+ store depletion to CRAC channel opening. Here we review the conformational dynamics occurring along the entire STIM protein upon store depletion, involving the transition from the quiescent, compactly folded structure into an active, extended state, modulation by a variety of accessory components in the cell as well as the impairment of individual steps of the STIM activation cascade associated with disease.

Functionally deficient TRPV6 variants contribute to hereditary and familial chronic pancreatitis

The recent discovery of TRPV6 as a pancreatitis susceptibility gene served to identify a novel mechanism of chronic pancreatitis (CP) due to Ca²⁺ dysregulation. Herein, we analyzed TRPV6 in 81 probands with hereditary CP (HCP), 204 probands with familial CP (FCP), and 462 patients with idiopathic CP (ICP) by targeted next-generation sequencing. We identified 25 rare nonsynonymous TRPV6 variants, 18 of which had not been previously reported. All 18 variants were characterized by a Ca²⁺ imaging assay, with 8 being identified as functionally deficient. Evaluation of functionally deficient variants in the three CP cohorts revealed two novel findings: (i) functionally deficient TRPV6 variants appear to occur more frequently in HCP/FCP patients than in ICP patients (3.2% vs. 1.5%) and (ii) functionally deficient TRPV6 variants found in HCP and FCP probands appear to be more frequently coinherited with known risk variants in SPINK1, CTRC, and/or CFTR than those found in ICP patients (66.7% vs 28.6%). Additionally, genetic analysis of available HCP and FCP family members revealed complex patterns of inheritance in some families. Our findings confirm that functionally deficient TRPV6 variants represent an important contributor to CP. Importantly, functionally deficient TRPV6 variants account for a significant proportion of cases of HCP/FCP.

Common calcium-sensing receptor (CASR) gene variants do not modify risk for chronic pancreatitis in a Hungarian cohort

The calcium-sensing receptor (CASR) is expressed in the pancreas where it might regulate calcium concentrations in pancreatic secretions. Two independent studies reported conflicting results claiming that commonly occurring missense variants of the CASR gene are risk factors for chronic pancreatitis (CP). Here, we attempted to replicate the association between CASR variants and CP. We analyzed 337 patients and 840 controls from the Hungarian National Pancreas Registry either by direct sequencing of exon 7 and the flanking noncoding regions or by TaqMan SNP genotyping assays. We identified two common missense variants, c.2956G>T (p.A986S), and c.2968A>G (p.R990G), three low-frequency variants, c.3031C>G (p.Q1011E), c.2610G>A (p.E870=) and c.∗60T>A, and 8 rare variants including the novel variant c.1895G>A (p.G632D). When allelic or genotype distributions were considered, none of the CASR variants associated with CP. Subgroup analysis of nonalcoholic versus alcoholic patients revealed no disease association either. Our results demonstrate that common CASR variants do not modify the risk for CP and should not be considered as genetic risk factors in the clinical setting.

First person – Miguel Burgos

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Miguel Burgos is first author on ‘The p.E152K-STIM1 mutation deregulates Ca2+ signaling contributing to chronic pancreatitis’, published in JCS. Miguel conducted the research described in this article while a postdoctoral researcher in Olivier Mignen's lab at the Université de Brest, Brest, France. He is now a senior postdoctoral researcher and Associate Professor in the lab of Alberto Ocaña at Albacete University Hospital and the University of Castilla-La Mancha, Spain, investigating the pathophysiology of calcium homeostasis.