Fig. 5.

SP1 transactivation is prevented by in vitro methylation. a In silico analysis revealed conserved SP1 binding sites (boxed) within CpG I. CpG dinucleotides are underlined and “CCGG”-motifs are marked in gray. b SP1 overexpression resulted in elevated KIBRA protein levels detected by western blot. c Transcription of KIBRA is stimulated by SP1. SP1 overexpression in IHKE cells resulted in significant transcriptional activation of P1aI, and P1aII promoter constructs harboring CpG I compared to pCMV5 mock-control. d In vitro methylation of promoter fragments by SssI prevented the stimulatory SP1 effect significantly, while partial methylation by HpaII selectively affected P1aI. Figures are representative for experiments (n = 3); western blot densitometry is based on three individual experiments. **p < 0.01, ***p < 0.001, ns not significant