High <i>ABCC2</i> and Low <i>ABCG2</i> Gene Expression Are Early Events in the Colorectal Adenoma-Carcinoma Sequence

<div><p>Development of colorectal cancer (CRC) may result from a dysfunctional interplay between diet, gut microbes and the immune system. The ABC transport proteins ABCB1 (P-glycoprotein, Multidrug resistance protein 1, MDR1), ABCC2 (MRP2) and ABCG2 (BCRP) are involved in transport of various compounds across the epithelial barrier. Low mRNA level of <i>ABCB1</i> has previously been identified as an early event in colorectal carcinogenesis (Andersen et al., PLoS One. 2013 Aug 19;8(8):e72119).</p><p><i>ABCC2</i> and <i>ABCG2</i> mRNA levels were assessed in intestinal tissue from 122 CRC cases, 106 adenoma cases (12 with severe dysplasia, 94 with mild-moderate dysplasia) and from 18 controls with normal endoscopy.</p><p>We found significantly higher level of <i>ABCC2</i> in adenomas with mild to moderate dysplasia and carcinoma tissue compared to the levels in unaffected tissue from the same individual (P = 0.037, P = 0.037, and P<0.0001) and in carcinoma and distant unaffected tissue from CRC cases compared to the level in the healthy individuals (P = 0.0046 and P = 0.036). Furthermore, <i>ABCG2</i> mRNA levels were significantly lower in adenomas and carcinomas compared to the level in unaffected tissue from the same individuals and compared to tissue from healthy individuals (P<0.0001 for all). The level of <i>ABCB2</i> in adjacent normal tissue was significantly higher than in tissue from healthy individuals (P = 0.011).</p><p>In conclusion, this study found that <i>ABCC2</i> and <i>ABCG2</i> expression levels were altered already in mild/moderate dysplasia in carcinogenesis suggesting that these ABC transporters are involved in the early steps of carcinogenesis as previously reported for <i>ABCB1</i>. These results suggest that dysfunctional transport across the epithelial barrier may contribute to colorectal carcinogenesis.</p></div