HPRT is a housekeeping
enzyme involved in recycling
guanine and
inosine in the
purine salvage pathway. As a housekeeping gene,
HPRT has been widely used as an endogenous control for molecular studies evaluating changes in gene expression. Yet, recent evidence has shown that
HPRT exhibits high variability within malignant samples. We designed this study to determine whether this observed upregulation is consistently found, therefore rendering
hprt an unsuitable normalization control in
cancer. Utilizing
protein and
RNA-seq expression, we found that malignant and normal patient samples vary significantly both within the same tissue type and across organ sites. Upon staining for
HPRT via immunohistochemistry, we found that expression is highly variable in malignant samples (Lung; 89.2-111.8, Breast; 66.7-98.3, Colon; 85.3-129.7, Prostate; 90.8-155.4, Pancreas; 74.1-132.1). Similarly, we observed high variability across cell lines via western blotting (p < 0.0001) which was further confirmed using
RNA sequencing. Comparing normal and malignant patient samples, we observed consistent upregulation of
HPRT expression within malignant samples relative to normal samples (p = 0.0001). These data indicate that
HPRT is unsuitable as an endogenous control for
cancer-related studies because its expression is highly variable and exceeds that of an appropriate control; therefore, we recommend its discontinued use as a normalization gene.