Fig 1: ZNF24 suppresses astrocyte activation and decreases CCL8 expression. (A) Human astrocytes activated by a cocktail of IL-1α, TNFα, and C1q. Astrocytes were serum-starved overnight before stimulation. Nuclei were stained with DAPI (blue), and GFAP was visualized in red. Representative 20× images. Scale bar indicates 100 µm. (B) Validation of GFAP mRNA expression in activated astrocytes as indicated by RT-qPCR. (C) Activated astrocytes transfected with ZNF24 plasmid have significantly reduced GFAP expression as indicated by GFAP IF. All slides were imaged at 4× or 20× using the Keyence BZ-X810 microscopes (cat. # BZ-X810 Keyence). At least 300 cells per slide were evaluated to identify GFAP+ cells. Representative 20× images. Scale bar indicates 100 µm. (D) Validation of GFAP reduction and ZNF24 overexpression with ectopic expression of ZNF24. mRNA expression measured by RT-qPCR. (E) ZNF24 binding to the CCL8 promoter in two regions (-69 and -205 bases upstream of the TSS) measured by ChIP-qPCR. (F) Ectopic expression of ZNF24 suppresses CCL8 promoter activity as indicated by dual luciferase reporter assays. (G,H) ZNF24 and CCL8 mRNA expression remains unchanged in breast cancer cells transfected with control or miR-425 mimic. mRNA expression measured by RT-qPCR. Fold change was calculated in panels (B,D–H). Student’s t-test was used in panels (A–H). N = 3 experimental replicates unless otherwise indicated.
Fig 2: miR-425-activated astrocytes secrete CCL8 and SCF to further activate astrocytes and promote mammospheres. (A) Top four highly secreted cytokines in CM from astrocytes overexpressing miR-425 as measured by cytokine arrays. (B) Cytokine stimulation increases GFAP expression (red) in human astrocytes as indicated by GFAP IF. All slides were imaged at 4× or 20× using the Keyence BZ-X810 microscopes (cat. # BZ-X810 Keyence). At least 300 cells per slide were evaluated to identify GFAP+ cells. Nuclei were stained with DAPI (blue). Representative 20× images. Scale bar indicates 100 µm. (C) CCL8, SCF, and MIF stimulation promotes SKBR3 mammospheres. Scale bar indicates 100 µm. (D) CCL8 and SCF promote mammosphere formation of CN34 cells. Scale bar indicates 100 µm. (E) CCL8 and KITLG are upregulated in astrocytes overexpressing miR-425 as measured by RT-qPCR. (F) Human astrocytes stimulated by CM from SKBR3 cells overexpressing miR-425 secrete significantly higher levels of CCL8 compared to astrocytes stimulated with CM from control SKBR3 cells. Secreted CCL8 expression measured by ELISA. (G) Astrocytes stimulated by CM from CN34 overexpressing miR-425 secrete significantly increased levels of CCL8 compared to astrocytes stimulated with CM from control CN34 cells. Secreted CCL8 expression measured by ELISA. (H,I) Astrocytes stimulated by CM from SKBR3 or CN34 cells overexpressing miR-425 secrete high levels of SCF. Secreted SCF expression measured by ELISA. Fold change was calculated in panel (E). Student’s t-test was used in panels (B–I). N = 3 experimental replicates unless otherwise indicated.
Fig 3: The miR-425-ZNF24-CCL8 signaling pathway is upregulated in brain metastases and activated astrocytes of mice intracardially injected with breast cancer cells overexpressing miR-425. (A) Increased EV-miR-425 expression in mouse serum from the SKBR3-Luc-miR-425 group compared to the control group. miR-425 expression measured by RT-qPCR (N = 5 per group). (B) SKBR3-Luc-miR-425 group mouse serum has significantly higher levels of mouse CCL8 as measured by ELISA (N = 7 per group). (C) No significant difference in mouse SCF levels in SKBR3-Luc-miR-425 or control mice serum as measured by ELISA (N = 5 per group). (D,E) GFAP H-score and intratumoral astrocytes are significantly higher in brain metastases from the SKBR3-Luc-miR-425 mouse group than the control in mouse brain sections as measured by IHC (N = 5 per group). (F) Brain metastases from the SKBR3-Luc-miR-425 group have significantly increased Ki-67 positive cells as measured by IHC (N = 5 per group). (G) Tumor-adjacent and infiltrative astrocytes in brain metastases from the SKBR3-Luc-miR-425 group have decreased ZNF24 staining measured by IHC (N = 5 per group). (H) Representative IHC images at 20× magnification. Scale bar indicates 100 µm. (I) Co-staining IF of ZNF24 (green) and GFAP (red) in mouse brain sections containing brain metastases. Nuclei were stained with DAPI (blue). Representative images at 20× magnification. Scale bar indicates 100 µm. (J) Schematic of described mechanism by which breast cancer-derived EV-miR-425 activates astrocytes by suppressing ZNF24, increasing CCL8, and thereby promoting BCBM. Fold change was calculated in panel A. Student’s t-test used in panels (A–G,I).
Fig 4: miR-425 suppresses transcription factor ZNF24 in astrocytes. (A) Predicted miR-425 binding sites within the CREB1, BCOR, and ZNF24 3′-UTRs from TargetScan. (B) ZNF24 mRNA expression is significantly decreased in astrocytes overexpressing miR-425. CREB1 and BCOR mRNA expression is unchanged as measured by RT-qPCR. (C) ZNF24 protein expression is decreased in astrocytes transfected with miR-425 mimic as indicated by Western blot analysis. (D) miR-425 suppresses ZNF24 3′-UTR activity as measured by dual luciferase reporter assay. (E) Ectopic expression of ZNF24 significantly decreases CCL8 and VEGFA mRNA expression, while KITLG is unchanged. mRNA expression measured by RT-qPCR. (F) Ectopic expression of ZNF24 suppresses CCL8 protein expression, but not SCF as indicated by Western blot analysis. (G) ZNF24 knockdown significantly increases CCL8 and VEGFA mRNA expression, but not KITLG. mRNA expression as indicated by RT-qPCR. (H) ZNF24 knockdown increases CCL8 and SCF protein expression as measured by Western blot analysis. Fold change was calculated in panels (B,D,E,G). Student’s t-test was used in panels (B,D,E,G). N = 3 experimental replicates unless otherwise indicated.
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