[Quantification of messenger RNA expression in tumors: which standard should be used for best RNA normalization?]

Alterations in gene expression are frequently encountered in malignant tissues. Quantification of the often quite subtle changes in mRNA content is routinely performed by northern blot hybridization. Practical experience shows that the methodology is subject to considerable error, necessitating the use of an internal mRNA standard for quantification. Many different control mRNAs have been employed over the years, but no systematic study has proven their applicability to comparisons made between tumor cells and normal tissues. The validity of these control RNAs, usually housekeeping genes, must be established to exclude the possibility that they themselves are expressed at different levels in tumor and non-tumor cells. Our experience has revealed that serious discrepancies may arise when incorrect standard genes are used to compare tumor and normal tissues.