GRP78 regulates EGFR expression at the transcriptional level. (A) Correlation between GRP78 and EGFR mRNA expression levels in a panel of 207 lung cancer cell lines from DepMap. (B) RT-qPCR analysis of GRP78, EGFR, and KRAS mRNA levels in the indicated cell lines treated with siCtrl or si78 for 48 h (n = 3). (C) HEK293AD cells were transfected with EGFR-Luc reporter gene and siCtrl or si78 for 48 h. GRP78 and EGFR protein levels were analyzed by Western blots with GAPDH serving as loading control, and EGFR promoter activity was measured by the dual luciferase assay in (D). (E) Similar to (C) except HEK293AD cells were transfected with the EGFR-Luc reporter gene and empty vector or F-78 expression construct, and EGFR promoter activity was measured in (F). (G) Similar to (C) except HEK293AD cells were transfected with EGFR-Luc reporter gene and siCtrl or si78 in combination with empty vector or F-78 expression construct as indicated and EGFR promoter activity was measured in (H). Data are presented as mean ± SEM. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001 (Student’s t test). See also SI Appendix, Fig. S2.