Panoply™ Human PNP Knockdown Stable Cell Line

Breast cancer (BC) is a leading cause of cancer-related death among women, a fact largely attributable to tumor metastasis. Here, researchers investigated the role of purine nucleoside phosphorylase (PNP)-a key enzyme in purine metabolism-in the invasive and metastatic behavior of breast cancer. PNP expression was found to be significantly higher in HER-2-positive and triple-negative breast cancers compared to Luminal-type breast cancer. Elevated PNP levels correlated strongly with advanced disease stage, high tumor grade, an epithelial-mesenchymal transition (EMT) phenotype, and poor overall survival. Notably, inhibiting HER-2 downregulated PNP expression, whereas silencing the PNP gene induced HER-2 upregulation, revealing a reciprocal regulatory loop between the two. Simultaneous inhibition of PNP and HER-2 resulted in a more significant reduction in cell viability compared to inhibiting HER-2 alone. Thus, PNP serves as a promising biomarker for assessing breast cancer aggressiveness and progression. Concurrently targeting PNP and HER-2 may offer a novel strategy to improve outcomes for aggressive breast cancer subtypes.

To investigate the regulatory relationship between HER-2 expression and PNP, researchers inhibited HER-2 using trastuzumab; Western blot analysis revealed a significant reduction in PNP levels (a 0.6-fold decrease; see Figures 1A and B). Conversely, inhibiting PNP with BCX-1777 or knocking down PNP resulted in a significant upregulation of HER-2 expression, with increases of approximately 1.45-fold and 2-fold, respectively (see Figures 1C and F). These results suggest the existence of a reciprocal regulatory mechanism: HER-2 promotes PNP expression, whereas PNP inhibits HER-2. This indicates the presence of a negative feedback loop associated with bladder cancer (BC) progression and therapeutic resistance.

Figure 1. Correlation between PNP and HER-2 in SKBR3 cells. (Shakartalla S B, et al., 2025)