Proteomic differential distribution of 53BP1 in serrated and conventional adenomas validated by histological characterisation

INTRODUCTION: Sessile serrated adenoma/polyp (SSA/p) is a precancerous lesion, mostly located in the right side of the colon (cecum, ascending and transverse colon). The difficulty is to visualize this lesion during colonoscopy because of its subtle appearance.
MATERIAL AND METHOD: We compared proteomes of serrated polyps (SSA/p) and conventional adenomas using residual human formalin fixed paraffin embedded (FFPE) samples. FFPE-FASP method was applied on samples before label free proteomic analysis. Immunohistochemistry (IHC) characterisation of one candidate marker was performed for tissue validation on an independent set of samples including: conventional adenomas (low and high-grade dysplasia), serrated polyps (hyperplastic polyps, SSA/p and traditional serrated adenoma) and finally normal colon (taken at the margin of colorectal cancer (CRC) or of diverticular disease).
RESULTS: Proteomics provided 765 proteins (out of 5992 proteins identified) significantly discriminating conventional adenomas from serrated lesions. We selected 53BP1 (Tumor suppressor p53-binding protein 1) among these for IHC validation, because of its tumor suppressor gene function and role as a mediator of DNA damage checkpoint. 53BP1 appeared significantly up-regulated in proteomes of low and high grade adenomas compared to these of normal tissue and SSA/p. 53BP1 IHC signal was located in the nucleus and the percentage of positive nucleus decreased in serrated polyps, especially in crypts and in the border epithelium, confirming part of the proteomic results.
CONCLUSION: This study highlights potential marker proteins, including 53BP1 from which IHC signal was strongly decreased in some serrated polyps. The loss of 53BP1 has been associated with tumour progression and poor prognosis, while little is currently known about its involvement in precancerous CRC lesions. 53BP1 decrease of expression in the nucleus and therefore possible loss of function in some epithelial cells could reflect important changes occurring during dysplasia to neoplasia progression in serrated lesions.