GC-box "b" modulates TRPV1 P2-promoter activity. Comparison of P2-promoter activity in DRG neurons + NGF (A) or +/- NGF-treated PC12 cells (B) directed by: empty pGL3 reporter plasmid (pGL-E); control reporter plasmid (0.4 kb); 0.4 kb reporter with deletion of GC-box "a" (Del-a); 0.4 kb reporter with deletion of GC-box "b" (Del-b) or deletion of both GC-box "a & b". When experiments were repeated under conditions of human Sp4 cDNA over-expression (A,B), P2-promoter activity continued to be lost following deletion of GC-box "a" or GC-box a & b. Loss of GC-box "b" under conditions of Sp4 (A,B) over-expression showed a small decrease of P2-promoter activity that was most evident in NGF treated PC12 cells. Diagram (left) indicates location of GC-box deletions and start site of transcription for P2-promoter expressing firefly luciferase (Luc). Error bars SEM (n = 3) quadruplicate measures. Significant differences: ANOVA (***) p < 0.001; (*) p < 0.05.