Panoply™ Human MUC1 Over-expressing Stable Cell Line

Breast cancer is the most common cancer in women and often exhibits intrinsic drug insensitivity, even in the absence of drug resistance. MUC1, a heavily glycosylated transmembrane protein, is overexpressed in breast cancer, leading to tumorigenesis and poor prognosis. Here, researchers investigated the natural flavonoid apigenin, known for its antitumor activity and widespread availability. MUC1 knockout (KO) significantly increased the sensitivity of breast cancer cells to apigenin's cytotoxicity both in vitro and in vivo. Both genetic and pharmacological inhibition significantly enhanced the chemosensitivity of breast cancer cells to apigenin and clinical drugs, while MUC1 overexpression, in turn, exacerbated this resistance. Reexpression of wild-type MUC1 in knockout cells restored drug resistance; however, deletion of the transmembrane domain did not rescue this phenotype. Notably, further investigation revealed that membrane-dependent drug resistance is dependent on extracellular glycosylation. Removal of O-glycosylation sites by inhibitors, enzymatic cleavage, or knockout of GCNT3 (MUC1-associated O-glycosyltransferase) significantly restored chemosensitivity in wild-type cells but had no effect in knockout cells. Conversely, inserting O-glycosylated sites to MUC1-N increased the drug tolerance, whereas the O-glycosylated deletant (Ser/Thr to Ala) maintained high susceptibility to drugs. Importantly, UPLC analysis of the intracellular concentration and fluorescence distribution of apigenin clearly revealed increased drug permeability in MUC1-knockout cells and BAG-pretreated cells.

To investigate the differences between wild-type (WT) and knockout (KO) cells, researchers compared quantitative mRNA profiles of cells treated with apigenin with those not treated with apigenin. The results revealed a significant downregulation of oxidative phosphorylation in MUC1 KO cells, particularly the mitochondrial respiratory chain (MRC) (Figure 1E). Using CCCP as a positive control, apigenin-induced JC aggregates decreased in MUC1 KO cells, but JC monomers increased, indicating a more severe collapse of the mitochondrial membrane potential (MMP), an indicator of mitochondrial damage (Figure 1F). Subsequently, ATP levels in apigenin-treated MUC1 KO cells decreased dramatically due to impaired mitochondrial integrity (Figure 1G). Importantly, these observations were confirmed in mouse xenograft experiments. Mice inoculated with MUC1 knockout cells showed significantly enhanced sensitivity to apigenin, with a significant reduction in tumor volume and weight (Figures 1H-J). To further clarify the role of MUC1 in apigenin sensitivity, the researchers overexpressed MUC1 in MCF-7 cells for validation. As expected, MUC1-overexpressing cells (OE) showed significantly reduced sensitivity to apigenin, especially at high doses (Figures 1K, L). Taken together, these results strongly suggest that targeting MUC1 can significantly enhance drug sensitivity and cellular efficacy.

Figure 1. MUC1 KO enhanced the cytotoxic sensitivity to apigenin in MCF-7 cells. (Xi X, et al., 2022)