Expression levels of CMV and GFAP promoters in non-glial and glioblastoma cell lines.

(A) Three cell lines—NIH-3T3, N2A, and U251—were transiently transfected with pCMV-HSVtk-P2A-EGFP or pGFAP-HSVtk-P2A-EGFP, and EGFP-positive cells were observed under an inverted fluorescence microscope. (B) NIH-3T3 had a strong expression level when transfected with the control plasmid, pCMV-HSVtk-P2A-EGFP. No NIH-3T3 cells expressed EGFP when transfected with pGFAP-HSVtk-P2A-EGFP. (C) A strong EGFP expression level was detected in N2A cells transfected with pCMV-HSVtk-P2A-EGFP. (D) Very few EGFP-positive cells were identified in N2A cells transfected with pGFAP-HSVtk-P2A-EGFP. Many EGFP-positive cells were observed in U251 cells transfected with pCMV-HSVtk-P2A-EGFP (E) or pGFAP-HSVtk-P2A-EGFP (F). Scale bar, 200 μm. (G) The proportion of EGFP-positive cells from all live cells was calculated as the expression level of the promotors (n = 5). There was no significant difference in the expression level of NIH-3T3, N2A, and U251 cell lines when transfected with pCMV-HSVtk-P2A-EGFP. By contrast, the expression level of pGFAP-HSVtk-P2A-EGFP was significantly higher in U251 cells than in NIH-3T3 or N2A cells.