Differential gene expression in colon cancer of the caecum versus the sigmoid and rectosigmoid

Abstract

Background and aims: There are epidemiological, morphological, and molecular differences between normal mucosa as well as between adenocarcinomas of the right and left side of the large bowel. The aim of this study was to investigate differences in gene expression.

Methods: Oligonucleotide microarrays (GeneChip) were used to compare gene expression in 45 single samples from normal mucosa and sporadic colorectal carcinomas (Dukes' B and C) of the caecum compared with the sigmoid and rectosigmoid. Findings were validated by real time polymerase chain reaction.

Results: Fifty eight genes were found to be differentially expressed between the normal mucosa of the caecum and the sigmoid and rectosigmoid (p<0.01), including pS2, S100P, and a sialyltransferase, all being expressed at higher levels in the caecum. A total of 118 and 186 genes were differentially expressed between normal and right or left sided tumours of the colon, showing more pronounced differences in Dukes' C than B tumours. Thirty genes differentially expressed in tumour tissue were common to adenocarcinomas of both sides, including known tumour markers such as the matrix metalloproteinases. Keratins 8, 19, and 20 as well as carbonic anhydrases (II, IV, VII) showed side specific expression and were downregulated in left sided tumours whereas teratocarcinoma growth factor and cyclooxygenase 2 (COX-2) were upregulated in left sided adenocarcinomas. Immunohistochemical analysis confirmed differences in side specific expression for cytokeratin 20 and COX-2.

Conclusions: Differences in gene expression between normal mucosa as well as between adenocarcinomas of the caecum and sigmoid or rectosigmoid exist and should be taken into account when examining new targeted therapeutic regimens.

Figure 1

Schematic overview of the five different comparison groups (A–E). Comparison (A): normal right sided colon mucosa (N_R) from the caecum versus normal left sided (N_L) colon mucosa from the sigmoid and rectosigmoid. Comparison (B): normal right sided mucosa from the caecum (N_R) versus matched right sided tumours from the caecum (T_R). Comparison (C): normal left sided mucosa (N_L) from the sigmoid and rectosigmoid versus left sided tumour (T_L) from the same region of the colon. Comparison (D): right sided tumours (T_R) from the caecum versus left sided tumours (T_L) from the sigmoid and rectosigmoid. Comparison (E): expression differences from normal mucosa to adenocarcinomas that are common between caecum tumours and left sided tumours in the sigmoid and rectosigmoid (comparing (B) versus (C)).

Figure 2

Comparison of single GeneChip analyses with real time polymerase chain reaction (PCR) analyses. Expression analyses of five selected genes using single samples of normal colon mucosa and adenocarcinomas of Dukes’ stages B and C from the right (A–E) and left (F–J) sides of the colon. Left y axis shows expression intensities “normalised to GAPDH” obtained from reverse transcription (RT)-PCR and the right y axis shows expression intensities “signal” derived from GeneChip analysis. (A, F) X65614 S100P Ca-binding protein; (B, G) Z80345 SCAD; (C, H) M14539 factor XIII subunit a; (D, I) M22324 aminopeptidase N/CD13; (E, J) L12760 PCK1 (phosphoenolpyruvate carboxykinase).

Figure 3

Immunohistochemistry of formalin fixed paraffin embedded sections of Dukes’ B and C adenocarcinomas and their matching normal mucosa (N). Sample numbers of tumours refer to samples previously analysed on microarrays. Cyclooxygenase 2 (COX-2) was moderately expressed in right sided normal mucosa as well as in matching tumours (A). COX-2 was not or very weakly expressed in left sided normal mucosa but moderately to strongly expressed in matching tumours showing a very heterogeneous staining pattern (B) (magnification 20×). Cytokeratin 20 (KRT20) was highly expressed in the luminal epithelium of normal mucosa of both sides. KRT20 was downregulated in only 50% of right sided tumours (C) whereas it was strongly downregulated in 80% of left sided tumours (D) (magnification 10×).