Moonlight human ribosomal protein L13a downregulation is associated with p53 and HER2/neu expression in breast cancer

Breast cancer is the most common malignancy among females worldwide. Recent studies have shown extra-ribosomal roles of the moonlight ribosomal proteins in the development of human cancers. Accurate quantification of the gene expression level is based on the selection of the reference genes whose expression is independent of cancer properties and patient's characteristics. The aim of this study was the evaluation of the expression level of a previously proposed ribosomal protein as moonlight, L13a (RPL13A), in breast cancer samples and their adjacent tissues. Its association with genes of known roles in developing cancers was also investigated. Traditionally used housekeeping genes were selected and their expression was analyzed in 80 surgically excised breast tissue specimens (40 tumors and 40 tumor-adjacent tissues) by applying three software tools including GeNorm, NormFinder, and BestKeeper to select the most stable reference genes. Then, mRNA expression levels of RPL13A and p53 were evaluated. Additionally, protein expression levels of RPL13A were measured. It was demonstrated that PUM1 and ACTB are the most reliable reference genes and RPL13A is the least stable gene. There was a positive correlation between RPL13A and p53 mRNA expression levels in all the tumor samples. Moreover, significant downregulation of RPL13A expression levels was revealed in HER2+ tumor samples compared to HER2- ones. There was also a marked decrease in p53 mRNA expression levels in HER2+ tumor subtypes. Our results suggest that there is a probable relationship between RPL13A decreased expression with p53 and HER2/neu expression in the breast cancer.