[Stellera chamaejasme extract overcomes multidrug resistance in MCF-7 cells through modulation of MEK/ERK pathway]

This study aims to investigate the action mechanism by which Stellera chamaejasme extract(SCLE) overcomes multidrug resistance(MDR) in breast cancer through the mitogen-activated protein kinase kinase(MEK)/extracellular signal-regulated kinase(ERK) signaling pathway. Sensitive cell line MCF-7 of human breast cancer and its multidrug resistance counterpart MCF-7/adriamycin(ADR) were employed as models. The effect of SCLE on cell proliferation was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay. The transcriptional level of P-glycoprotein(P-gp) was analyzed by quantitative real-time PCR(qPCR). Western blot was employed to detect the expression levels of MEK and ERK, their phosphorylated forms(p-MEK and p-ERK), the drug resistance-related protein P-gp, DNA damage-related proteins including phosphorylated histone H2AX(γ-H2AX) and the tumor suppressor p53(p53), apoptosis-related proteins B-cell lymphoma-2(Bcl-2), Bcl-2-related X protein(Bax), and cleaved caspase-3. Immunofluorescence staining was used to observe the focus formation of DNA damage marker γ-H2AX, and flow cytometry was applied to detect apoptosis. Furthermore, DNA microarray was performed to identify the effect of SCLE on differentially expressed genes(DEGs) in MCF-7/ADR cells. Gene Ontology(GO) function analysis and Kyoto Encyclopedia of Genes and Genomes(KEGG) pathway enrichment analysis were conducted on these DEGs. The MTT results showed that the resistance factor(RF) of MCF-7/ADR cells in the SCLE group was 0.77, which was significantly lower than that observed for vincristine(VCR), paclitaxel(PTX), and ADR. Western blot and qPCR results indicated that SCLE inhibited the activation of the MEK/ERK pathway and significantly downregulated the expression of P-gp at both the protein and transcriptional levels(P<0.05). Concurrently, the SCLE treatment group increased the number of γ-H2AX foci and significantly upregulated the protein expression of p53, Bax, and cleaved caspase-3, while downregulating Bcl-2(P<0.05). Annexin-V/PI double staining revealed a dose-dependent increase in the apoptosis rate of the resistant cells(P<0.05). KEGG and GO analyses corroborated the cellular experimental findings, suggesting that SCLE may concurrently target multiple pathways, including adenosine triphosphate(ATP) binding, endoplasmic reticulum function, the mitogen-activated protein kinase(MAPK) pathway, the mammalian target of rapamycin(mTOR) pathway, and the phosphatidylinositol 3 kinase(PI3K)/protein kinase B(Akt) pathway, to coordinately induce DNA damage and apoptosis. In conclusion, SCLE may play a role in overcoming the MDR effect in breast cancer by inhibiting the activation of MEK/ERK in the core downstream cascade within the MAPK pathway, modulating P-gp levels to enhance intracellular drug accumulation, and subsequently triggering DNA damage and apoptosis.