Department of Molecular and Cell Biology, Henry M. Goldman School of Dental Medicine, Boston University, Boston, Massachusetts, USA.
Gut. 2013 Nov;62(11):1616-24. doi: 10.1136/gutjnl-2012-303090. Epub 2012 Sep 1.
The digestive enzyme chymotrypsin C (CTRC) protects against pancreatitis by promoting degradation of trypsinogen, thereby curtailing potentially harmful trypsinogen activation. Loss-of-function variants in CTRC increase the risk for chronic pancreatitis. The aim of the present study was to perform comprehensive functional analysis of all missense CTRC variants identified to date.
We investigated secretion, activity and degradation of 27 published and five novel CTRC mutants. We also assessed the effect of five mutants on endoplasmic reticulum (ER) stress.
None of the mutants exhibited a gain of function, such as increased secretion or activity. By contrast, 11 mutants showed marked loss of function, three mutants had moderate functional defects, whereas 18 mutants were functionally similar to wild-type CTRC. The functional deficiencies observed were diminished secretion, impaired catalytic activity and degradation by trypsin. Mutants with a secretion defect caused ER stress that was proportional to the loss in secretion. ER stress was not associated with loss-of-function phenotypes related to catalytic defect or proteolytic instability.
Pathogenic CTRC variants cause loss of function by three distinct but mutually non-exclusive mechanisms that affect secretion, activity and proteolytic stability. ER stress may be induced by a subset of CTRC mutants, but does not represent a common pathological mechanism of CTRC variants. This phenotypic dataset should aid in the classification of the clinical relevance of CTRC variants identified in patients with chronic pancreatitis.
糜蛋白酶 C（CTRC）通过促进胰蛋白酶原的降解来保护胰腺免受胰腺炎的侵害，从而阻止潜在的有害胰蛋白酶原激活。CTRC 的功能丧失变体增加了慢性胰腺炎的风险。本研究的目的是对迄今为止发现的所有错义 CTRC 变体进行全面的功能分析。
我们研究了 27 个已发表和 5 个新的 CTRC 突变体的分泌、活性和降解。我们还评估了 5 个突变体对内质网（ER）应激的影响。
没有一个突变体表现出功能获得，例如分泌或活性增加。相比之下，11 个突变体表现出明显的功能丧失，3 个突变体具有中度功能缺陷，而 18 个突变体的功能与野生型 CTRC 相似。观察到的功能缺陷表现为分泌减少、催化活性受损和被胰蛋白酶降解。具有分泌缺陷的突变体引起内质网应激，其程度与分泌减少成正比。内质网应激与催化缺陷或蛋白水解不稳定性相关的功能丧失表型无关。
致病性 CTRC 变体通过三种不同但非排他性的机制导致功能丧失，这些机制影响分泌、活性和蛋白水解稳定性。内质网应激可能由一组 CTRC 突变体诱导，但不是 CTRC 变体的常见病理机制。该表型数据集应有助于对慢性胰腺炎患者中发现的 CTRC 变体的临床相关性进行分类。
