SEL1L, an UPR response protein, a potential marker of colonic cell transformation

Abstract

Background: SEL1L gene product is implicated in the endoplasmic reticulum (ER)-associated protein degradation and Unfolded Protein Response pathways. This gene and associated miRNAs have been indicated as predictive and prognostic markers of pancreatic cancer.

Aim: Explore the role of SEL1L in colorectal cancer (CRC) progression.

Methods: SEL1L expression was analysed immunohistochemically in 153 adenomas and 71 CRCs from African American and North Italian patients. The distribution of stained cells was determined by computing median and inter quartile range. The receiver operating characteristics plot was used as discriminate power of SEL1L expression, CRC diagnosis and the effects on patient survival.

Results: SEL1L was low in normal mucosa and confined to few scattered cells at the base crypt of the villi and in the foveolar glandular compartment. The highest levels were in Paneth cells within the lysosomes. The enterocytic progenitor cells and mature enterocytes showed less cytoplasmic staining. In CRCs, SEL1L expression significantly correlated with the progression from adenoma to carcinoma (P = 0.0001) being stronger in well-to-moderately differentiated cancers. No correlation was found with other clinicopathological characteristics or ethnicity.

Conclusions: SEL1L expression is a potential CRC tissue biomarker since its expression is significantly higher in adenoma cells with respect to normal mucosa. The levels of expression decrease sensibly in undifferentiated CRC cancers. Interestingly, Paneth cells contain high levels of SEL1L protein that could indicate pre-neoplastic mucosa undergoing neoplastic transformation. Since SEL1L's major function lies within ER stress and active ERAD response, it may identify CRCs with differentiated secretory phenotype and acute cellular stress.

Fig. 1

Western blot analysis for SEL1LA of the p38 SEL1L protein lysates obtained from normal tissue mucosa, adenoma and adenocarcinoma from four CRC patients. a An increase of SEL1LA, the ER-resident form of SEL1L, in the adenoma (A) and adenocarcinoma (T) cells when compared to normal mucosa (M) was noted in all four patients (a, lanes: patient 1-A, patient 2-T, patient 3-M and patient 4-A). In addition, a remarkable increase of the p38 SEL1L variant was seen in the neoplastic protein extracts. b Fold of SEL1L proteins increase in the neoplastic versus the normal mucosa cells, the levels were normalized toward the housekeeping p85 protein. Occasionally the p38 variant of SEL1L showed the presence of a post-translationally modified form

Fig. 2

a–j SEL1L expression in CRC progression. a, b Left, Normal colon with decreasing staining ascending the crypt 20X. Right, Normal colon base of crypt (proliferative zone) with cytoplasmic staining, 40X. c, d Left, Cytoplasmic staining in adenoma, 40X. Right, Nuclear staining in adenoma, 40X. e, f Left, Well-differentiated carcinoma, 10X. Right, 40X. g, h Moderately differentiated carcinoma, 10X. Right, 40X. i, j Left, Poorly differentiated carcinoma 10X. Right, 40X

Fig. 3

ROC curve for SEL1L as biomarker for colorectal cancer diagnosis

Fig. 4

SEL1L immunoreactivity in intestinal mucosa Paneth’s cells both at optical (right bottom inset) and ultrastructural level. The electron microscopy shows that the immunoreactivity is concentrated in the secretory granules, as best shown in right top inset by the immunogold technique