Panoply™ Human STEAP1 Knockdown Stable Cell Line

Overexpression of six-transmembrane epithelial antigen of the prostate 1 (STEAP1) underlies the pathogenesis of numerous human cancers. STEAP1 is expressed on the surface of cancer cells and is an attractive target for antibody or immunotherapy. Here, researchers demonstrate for the first time that STEAP1 transcript levels are significantly elevated in colorectal cancer (CRC) tissue compared with normal colon tissue. Notably, STEAP1 expression is inversely correlated with overall survival based on publicly available gene expression profiling datasets. Loss-of-function approaches in cultured CRC cell lines revealed that STEAP1 silencing inhibits cell growth and increases reactive oxygen species (ROS) production through intrinsic pathways, leading to apoptosis. Mechanistically, STEAP1 inhibition is associated with reduced expression of antioxidant molecules regulated by the transcription factor nuclear erythroid 2-related factor (NRF2) in CRC cells. Taken together, elevated STEAP1 transcript levels lead to reduced ROS production, thereby preventing CRC cell apoptosis through the NRF2 pathway.

To elucidate the mechanism by which STEAP1 knockdown induces cytotoxicity in CRC cell lines, the researchers performed flow cytometric analysis. Annexin V/7-AAD staining revealed increased apoptosis in STEAP1-knockdown DLD-1 (Figure 1a), SW480 (Figure 1b), and LS180 (Figure 1c) CRC cell lines. Previous studies have shown that STEAP1 accelerates tumor invasion by overproduction of ROS in EWS. To assess the role of ROS in apoptosis, the researchers used flow cytometry to investigate whether treatment induced this apoptosis through intrinsic or extrinsic pathways. Caspase 8 activity in STEAP1-knockdown DLD-1 cells was comparable to that observed in control cells (Figure 1d). In contrast, caspase 9 activity was significantly upregulated in STEAP1-knockdown DLD-1 cells (Figure 1e). Furthermore, NAC treatment significantly inhibited the caspase 9 activity induced by STEAP1 knockdown. In conclusion, STEAP1 knockdown-induced apoptosis was stimulated in a ROS-dependent manner and mediated through the intrinsic pathway.

Figure 1. Knock-down of STEAP1 induces intrinsic apoptosis in CRC cell lines. (Nakamura H, et al., 2019)