Selection of an internal control gene for quantitation of mRNA in colonic tissues.

Background: GAPDH, beta-actin and 18S rRNA are widely employed as internal control genes, with the assumption that they are expressed constitutively to similar degrees in different cells and tissues and under different experimental conditions. In this study, we tested this assumption by assessment of the transcription of these three genes in human colonic tissues using a quantitative RT-PCR.

Results: GAPDH transcription was significantly greater in both colonic adenomas and cancers than in normal mucosa. In addition, transcription of beta-actin was significantly increased in cancers. The expression of 18S rRNA was essentially constant among these various tissues. Stable expression of 18S rRNA was observed during the growth of colonic cancer cells stimulated with serum, but both GAPDH and beta-actin transcription were up-regulated, coinciding with cell proliferation.

Conclusion: These results indicate that 18S rRNA is more reliable than GAPDH and beta-actin as an internal control gene for quantitative comparison of mRNA in colonic cancers.