Genetic Analysis of Human Chymotrypsin-Like Elastases 3A and 3B (CELA3A and CELA3B) to Assess the Role of Complex Formation between Proelastases and Procarboxypeptidases in Chronic Pancreatitis

Abstract

Human chymotrypsin-like elastases 3A and 3B (CELA3A and CELA3B) are the products of gene duplication and share 92% identity in their primary structure. CELA3B forms stable complexes with procarboxypeptidases A1 and A2 whereas CELA3A binds poorly due to the evolutionary substitution of Ala241 with Gly in exon 7. Since position 241 is polymorphic both in CELA3A (p.G241A) and CELA3B (p.A241G), genetic analysis can directly assess whether individual variability in complex formation might alter risk for chronic pancreatitis. Here we sequenced exon 7 of CELA3A and CELA3B in a cohort of 225 subjects with chronic pancreatitis (120 alcoholic and 105 non-alcoholic) and 300 controls of Hungarian origin. Allele frequencies were 2.5% for CELA3A p.G241A and 1.5% for CELA3B p.A241G in controls, and no significant difference was observed in patients. Additionally, we identified six synonymous variants, two missense variants, a gene conversion event and ten variants in the flanking intronic regions. Variant c.643-7G>T in CELA3B showed an association with alcoholic chronic pancreatitis with a small protective effect (OR = 0.59, 95% CI = 0.39-0.89, p = 0.01). Functional analysis of missense variants revealed no major defects in secretion or activity. We conclude that variants affecting amino-acid position 241 in CELA3A and CELA3B are not associated with chronic pancreatitis, indicating that changes in complex formation between proelastases and procarboxypeptidases do not alter pancreatitis risk.

A Pilot Genome‐Wide Analysis Study Identifies Loci Associated With Response to Obeticholic Acid in Patients With NASH

“…The elastase 3B isoform can be measured in stool as a measure of pancreatic exocrine function . A variant in CELA3B has a possible protective effect on the risk of chronic alcoholic pancreatitis, and hypermethylation of the gene promoter may be associated with pancreatic cancer . However, no data are currently available on the role of CELAB3 in liver disease.…”

The reversion variant (p.Arg90Leu) at the evolutionarily adaptive p.Arg90 site in CELA3B predisposes to chronic pancreatitis

“…Second, the pLI score for CELA3B in genomAD (http://gnomad.broadinstitute.org/; as of 13 November 2020) is 0, suggesting that the gene is completely tolerant of heterozygous loss-of-function variants. In this regard, it is pertinent to mention that a CELA3B intronic variant, c.643-7G>T (rs61777963), manifests an association with alcoholic CP with a small protective effect (allele frequency: 13.8% in patients vs. 21.3% in controls; OR = 0.59, 95% CI 0.39 to 0.89; P = 0.01) 29 . However, as acknowledged by the original authors, the number (n = 120) of alcoholic CP patients analyzed was small, and no association was found in a small cohort (n = 105) of non-alcoholic CP (allele frequency: 18.6% in patients vs. 21.3% in controls; OR = 0.84, 95% CI 0.56 to 1.26; P = 0.4) 29 .…”

“…The ≥2 single nucleotide substitutions in each case were confirmed to be in cis by a newly developed next-generation sequencing method (detailed method will be published elsewhere), with the original sequencing data being deposited in the NCBI Sequence Read Archive (SRA) database (https://www.ncbi.nlm.nih.gov/sra) under accession numbers SAMN16675587, SAMN16675586 and SAMN1667558. c.736_742delACCCGCAinsTTCATCT has previously been shown to be a gene conversion event 29 . c.[71G>A;73C>T;91A>C] and c.[529G>C;536T>G] probably also arose via gene conversion 30 as, in each case, a putative donor sequence is present at the aligned positions of the highly homologous and tandemly linked CELA3A gene on human chromosome 1p36.12.…”

“…In this regard, it is pertinent to mention that a CELA3B intronic variant, c.643-7G>T (rs61777963), manifests an association with alcoholic CP with a small protective effect (allele frequency: 13.8% in patients vs. 21.3% in controls; OR = 0.59, 95% CI 0.39 to 0.89; P = 0.01) 29 . However, as acknowledged by the original authors, the number (n = 120) of alcoholic CP patients analyzed was small, and no association was found in a small cohort (n = 105) of non-alcoholic CP (allele frequency: 18.6% in patients vs. 21.3% in controls; OR = 0.84, 95% CI 0.56 to 1.26; P = 0.4) 29 . We extracted corresponding data from our patients and controls, showing no significant association (allele frequency: 17.2% (222/1288) vs. 17.1% (194/1132); OR = 1.01, 95% CI 0.81 to 1.24; P = 1.0).…”

“…The ≥2 single nucleotide substitutions in each case were confirmed to be in cis by a newly developed next-generation sequencing method (detailed method will be published elsewhere), with the original sequencing data being deposited in the NCBI Sequence Read Archive (SRA) database (https://www.ncbi.nlm.nih.gov/sra) under accession numbers SAMN16675587, SAMN16675586 and SAMN1667558. c.736_742delACCCGCAinsTTCATCT has previously been shown to be a gene conversion event 29 Calculation was based on allele frequency in patients vs. that in controls. c A gene conversion event that can be alternatively termed c.71_91conNM_005747.5:c.71_91; deposited in the NCBI Sequence Read Archive database under the accession number SAMN16675587.…”