Connexin43 Expression Increases in the Epithelium and Stroma along the Colonic Neoplastic Progression Pathway: Implications for Its Oncogenic Role

Abstract

Connexins (Cxs) are critical for normal tissue development, differentiation, and cell proliferation. Normal expression and function of Cxs are considered to play a role in tumor suppression, but abnormal localization and abnormally increased expression of Cxs have been found in a variety of carcinomas. Of the Cx family, Cx43 is a most prevalent member and has been known as a downstream target of β-catenin, a key component of Wnt signaling pathway. We evaluated the expression of Cx43 in the colonic neoplasia progression sequence with additional attention to the stromal component. Resections of 50 colonic adenocarcinomas were stained immunohistochemically for Cx43 on paraffin embedded sections. Cx43 cytoplasmic expression increased progressively in the colonic adenocarcinoma sequence in both the epithelial [normal (4 ± 1), adenomatous (20 ± 2), cancerous (124 ± 10) (P < 0.01)], and stromal [normal (19 ± 1), cancerous (45 ± 4) (P < 0.01)] components. In the epithelial component, Cx43 was expressed lower in stage I adenocarcinomas (69 ± 12) compared to stage III/IV (158 ± 10, P < 0.01). Additionally, Cx43 was relatively increased in the adenocarcinoma at the invasive tumor front in all stages. Cx43 may play a critical role in the pathogenesis of colon cancer via gap junction or other gap junction independent mechanisms such as the Wnt/β-catenin pathway.

Figure 1

The expression of Cx43 in colonic adenocarcinoma was evaluated according to the intensity of the staining as follows: 1, very weak expression (1+); 2, moderate expression (2+); 3, strong expression (3+) (Original magnification ×200).

Figure 2

The expression of Cx43 in normal colonic mucosa, tubular adenoma, and severe dysplasia (Original magnification ×200). There is an increase in cytoplasmic Cx43 expression from normal epithelium (Cx43 score 4 ± 1) to tubular adenoma/severe dysplasia (Cx43 score 20 ± 2).

Figure 3

The difference in Cx43 expression in stage I and stage III/IV colonic adenocarcinoma (original magnification ×200). A higher level of Cx43 expression was significantly associated with AJCC stage III/IV adenocarcinomas (Cx43 score 158 ± 10), as compared to AJCC stage I (Cx43 score 69 ± 12).

Figure 4

The expression of Cx43 in colonic stroma was evaluated according to the intensity of the staining as follows: 1, very weak expression (1+); 2, moderate expression (2+); 3, strong expression (3+) (original magnification ×200).

Figure 6

The difference in Cx43 expression in the stromal component in normal mucosa and colonic adenocarcinoma (original magnification ×200). Cx43 reactivity was stronger in the stromal components adjacent to cancerous epithelium than benign epithelium: normal (Cx43 score 19 ± 1), cancer (Cx43 score 45 ± 4).

Figure 5

The relationship between Cx43 expression and nuclear beta-catenin expression in colonic adenocarcinoma (original magnification ×200). (a) Coexpression of Cx43 (brown cytoplasmic staining) and nuclear beta-catenin (red nuclear staining). Note. Peritumoral stromal cells exhibited only Cx43 but not beta-catenin reactivity. (b) Tumoral tissue exhibited heterogeneous expression of Cx43 and nuclear beta-catenin. (c) Tumoral tissue with expression of Cx43 only. (d) Tumoral tissue with expression of beta-catenin only. (e) Tumoral tissue with no expression of Cx43 or beta-catenin.