Aberrant expression of minichromosome maintenance proteins 2 and 5, and Ki-67 in dysplastic squamous oesophageal epithelium and Barrett's mucosa

Abstract

Background: Minichromosome maintenance (Mcm) proteins are essential for eukaryotic DNA replication, and their expression implies potential for cell proliferation. Expression is dysregulated in dysplastic states but data for oesophageal squamous mucosa and Barrett's mucosa have not been published.

Aim: To test the hypothesis that Mcm proteins are downregulated together with the proliferation marker Ki-67 in differentiating epithelial compartments of non-dysplastic squamous and Barrett's epithelium, and that this process does not occur in dysplastic mucosae. METHODS AND CASES: Forty five patients with Barrett's oesophagus included 20 with glandular dysplasia (10 low grade, eight high grade, two both, and four with invasive adenocarcinoma). Twenty five other patients included 12 with oesophageal squamous dysplasia (three low grade, six high grade, three both, and four with invasive squamous carcinoma). Formalin fixed paraffin embedded tissue sections from biopsy series and resections were immunostained using antibodies to Mcm2, Mcm5, and Ki-67. Percentage of nuclei positive for Mcm2, Mcm5, and Ki-67 was estimated and scored from 0 to 6 as: 0, none +; 1, <10%+; 2, 10-30%+; 3, 30-70%+; 4, 70-90%+; 5, >90%+; 6, all+. Four separate epithelial strata were scored: in squamous epithelium the basal layer and thirds to the surface, in Barrett's mucosa the luminal surface, upper and lower crypt, and deep glands.

Results: In non-dysplastic squamous epithelium and Barrett's mucosa, high level expression of Mcm2, Mcm5, and Ki-67 proteins was largely confined to the proliferative compartments and downregulated in differentiated compartments. Expression persisted up to the mucosal surface in dysplastic squamous epithelium and Barrett's mucosa.

Conclusions: Persistent expression of Mcm2, Mcm5, and Ki-67 proteins in luminal compartments of dysplastic oesophageal squamous epithelium and dysplastic Barrett's mucosa may be diagnostic markers and imply disruption of cell cycle control and differentiation in these dysplastic epithelia.

Figure 1

Graphs of minichromosome maintenance protein (Mcm) and Ki-67 expression in oesophageal squamous epithelium: quartile plots of immunohistochemical scores (range 0–6) for Ki-67, Mcm5, and Mcm2 (rows 1–3). Columns from left to right represent squamous epithelium without dysplasia (none), low grade dysplasia (LGD), and high grade dysplasia (HGD). Epithelial layers are represented as a–d with a=basal; b=suprabasal, lower third; c=suprabasal, middle third; and d=suprabasal, upper third. Filled dots represent medians, bars interquartile range, and small open dots the range.

Figure 2

Graphs of minichromosome maintenance protein (Mcm) and Ki-67 expression in Barrett's mucosa: quartile plots of immunohistochemical scores (range 0–6) for Ki-67, Mcm5, and Mcm2 (rows 1–3). Columns from left to right represent Barrett's mucosa without dysplasia (none), low grade dysplasia (LGD), and high grade dysplasia (HGD). Mucosal layers are represented as a–d with a=deep glands; b=lower crypt; c=upper crypt; and d=mucosal surface. Filled dots represent medians, bars interquartile range, and small open dots the range.

Figure 3

Minichromosome maintenance protein 2 (Mcm2) expression in Barrett's mucosa. On the right of (A), non-dysplastic intestinal type “specialised” Barrett's mucosa shows Mcm2 expression in cells of the proliferative zone beneath the mucosal surface. Expression falls away markedly on the mucosal surface. There is an abrupt transition (arrow) to mucosa showing mild (low grade) dysplasia in which Mcm2 downregulation does not occur. More pronounced but still low grade Barrett's dysplasia (B) shows strong Mcm2 expression in the upper crypt and surface, with weaker expression in deep glands.

Figure 4

Minichromosome maintenance protein 2 (Mcm2) expression in oesophageal squamous epithelium. In normal squamous epithelium (A), maximal expression immediately above a well defined basal layer falls to undetectable levels in the upper third (top). In low grade dysplasia (B), detectable Mcm2 persists to the luminal surface. In (C), there is an abrupt transition between high grade squamous dysplasia (right) and morphologically normal oesophageal squamous epithelium (left). The apparent “island” of Mcm2 expression (small arrow) in the normal epithelium represents tangential sectioning of a submucosal papilla.

Figure 5

Downregulation of minichromosome maintenance protein 2 (Mcm2) with differentiation in dysplastic and neoplastic squamous epithelium. In (A), full thickness squamous dysplasia with Mcm2 expression up to the mucosal surface (on the left of the picture) is associated with a basaloid phenotype. On the right, marked nuclear atypia persists to the mucosal surface but cells towards the surface have more cytoplasm and this morphological change is associated with loss of detectable Mcm2. Similarly, in a moderately differentiated invasive oesophageal squamous carcinoma (B), many carcinoma cells are Mcm2 positive but viable Mcm2 negative carcinoma cells are present within cell nests with morphological features of differentiation (keratinisation).

Figure 6

Minichromosome maintenance protein 2 (Mcm2) expression in an oesophageal adenocarcinoma. This carcinoma was in a Barrett's oesophagus. Malignant glandular acini invade muscularis propria. Most of the carcinoma cells are Mcm2 positive but viable Mcm2 negative carcinoma cells are also present.