Panoply™ Human GREM1 Over-expressing Stable Cell Line

Gremlin-1 (GREM1) is a bone morphogenetic protein antagonist involved in organogenesis, tissue differentiation, and kidney development. However, the role of GREM1 in cancer progression and its underlying mechanisms remain unclear. Here, researchers found that GREM1 expression is elevated in both breast cancer cells and patient breast cancer tissues. High GREM1 expression correlates with poor prognosis in breast cancer patients, particularly those with estrogen receptor (ER)-negative tumors. Knockdown of GREM1 inhibits breast cancer cell proliferation and the growth of breast tumor xenografts; conversely, GREM1 overexpression enhances cell viability, growth capacity, and invasiveness. Estrogen-related receptor alpha (ERRα), an orphan nuclear hormone receptor, directly interacts with the GREM1 promoter to upregulate GREM1 expression. Meanwhile, GREM1 enhances the promoter activity of the gene encoding ERRα (ESRRA), thereby establishing a positive feedback loop. Notably, GREM1 binds to and activates EGFR, a well-known upstream regulator of ERRα. These findings suggest that the GREM1–ERRα axis serves as a potential therapeutic target for cancer, particularly ER-negative tumors.

Compared with control cell lines, breast cancer cell lines overexpressing GREM1 exhibited significantly higher ERRα transcriptional activity (Figure 1a). Consistent with ERRα activity, mRNA levels of ERRα target genes (KLK3, ENO1, or TAPBPL) were also significantly elevated in GREM1-overexpressing breast cancer cells (Figure 1b). In MCF-7 cells, treatment with recombinant GREM1 protein significantly enhanced the expression of ERRα target genes ENO1 and TAPBPL (Figure 1c). Furthermore, transient transfection of MCF-7 cells with a GREM1 expression plasmid increased ERRα target gene mRNA levels, whereas the ERRα antagonist XCT790 attenuated these effects (Figure 1d). To further determine whether GREM1 enhances ERRα transcriptional activity by activating the EGFR signaling pathway, the researchers examined the effects of inhibitors targeting ERRα, EGFR, Akt, and ERK on GREM1-induced ERRα transcriptional activity. First, ERRα activity was significantly elevated in GREM1-overexpressing SKBR3 cells, and this activity was inhibited by all the tested inhibitors (Figure 1e). Similarly, direct treatment of MCF-7 cells with recombinant GREM1 protein increased ERRα transcriptional activity-an effect comparable to that of the positive control EGF-and this increase was reduced by the aforementioned inhibitors (Figure 1f). As shown in Figure 1g, these inhibitors significantly reduced ERRα target gene mRNA levels in GREM1-overexpressing SKBR3 cells. Moreover, neither the ligand-binding domain (EGFR-ECD) nor the intracellular domain (EGFR-ICD) of EGFR was sufficient to mediate the GREM1-induced enhancement of ERRα activity; instead, a direct interaction between GREM1 and wild-type EGFR (EGFR-WT) played a critical role in ERRα activation (Figure 1h). Collectively, these results indicate that GREM1, acting as a novel target of ERRα, enhances ERRα activity through EGFR activation.

Figure 1. GREM1 increases the transcriptional activity of ERRα and the mRNA levels of ERRα target genes through EGFR activation. (Park S A, et al., 2020)