Interplay of the proteotoxic CEL-MODY protein and oncogenic KRAS in pancreatic cancer development

Abstract

Challenges in diagnosing and treating pancreatic cancer make it the fourth-leading cause of cancer-related deaths. Survival rates remain dismally low, and the molecular mechanisms driving this malignancy are still inadequately understood. Most pancreatic cancers appear to originate from malignant transformation of pancreatic acinar cells into cancer cells with a ductal phenotype, resulting in what is known as pancreatic ductal adenocarcinoma (PDAC).

Nearly all pancreatic cancers contain a somatic KRAS mutation; however, KRAS alone is insufficient for pancreatic carcinogenesis, and additional mutations or injuries are required. Studies suggest a higher prevalence of endoplasmic reticulum (ER) stress-inducing mutations in digestive enzyme genes of pancreatic cancer patients when compared to healthy controls. Carboxyl-ester lipase (CEL) is one such enzyme secreted by pancreatic acinar cells. The CEL-MODY mutation of the CEL gene is associated with MODY8, a syndrome marked by pancreatic exocrine dysfunction and diabetes. The CEL-MODY mutation affects a variable number tandem repeat (VNTR), resulting in a misfolded CEL protein that triggers ER stress in acinar cells. Hence, we hypothesized that CEL-MODY could contribute to PDAC development.

To investigate the molecular mechanisms through which the pathogenic CEL-MODY variant might promote pancreatic carcinogenesis, we examined pancreatic tissue from mice carrying an oncogenic KRAS mutation expressed in the exocrine pancreas alongside the CEL-MODY mutation (KCC mouse model). The samples were compared with tissue from mice expressing only the KRAS mutation (KC mouse model). Our study employed two experimental approaches to identify differences in protein expression potentially caused by the ER stress-inducing mutation: (1) We focused on immunostaining for markers associated with apoptosis, ductal proliferation and ER stress. (2) We performed a hypothesis-free proteomic analysis of mass spectrometry data obtained from tissue samples of both mouse models.

The experiments validated prior observations of increased acinar to ductal remodeling in the KCC mouse model compared to KC animals. Furthermore, KCC mice exhibited diminished apoptosis and increased ductal proliferation, which are among cancer hallmarks. The proteomic analysis extended these findings by identifying differentially expressed proteins between the two mouse models. This formed the basis for an integrated analysis of signaling and metabolic pathways which predicted stimulation of adenocarcinoma development, suppressed immune system and abnormal RNA processing. However, no distinctions were noted between the two genotypes concerning the CEL protein itself or ER stress levels.

In summary, our findings unveiled differences in the proteome profile between KCC mice and KC animals, confirming our hypothesis that the ER stress-inducing CEL-MODY mutation may contribute to PDAC development. However, experimental validation of the findings from the proteomic analysis results remains necessary.