Abstract
Housekeeping proteins are essential endogenous controls for normalization as they are expected to be stably expressed. However, the stability of the expression level of housekeeping proteins needs to be assessed considering various experimental conditions. Our study evaluated the degree of variability of 7 commonly used housekeeping proteins with regard to their potential utility as normalizers in 56 pairs of matched colorectal adenocarcinoma (CRC) tissue samples and 6 pairs of hepatocellular carcinoma (HCC) tissue samples using multiple reaction monitoring (MRM) and Western blot analyses. A comprehensive experimental design and strict statistical analysis revealed that the expression levels of these 7 housekeeping proteins were not as stable as expected and they all exhibited upregulations to varying degrees in both the CRC and the HCC tissue samples. Consequently, we verified that using the amount of total protein instead of that of an individual protein can serve as a preferable control for studies of protein expression that require normalization.