Transcriptional repressor and activator. Binds to CACCC-boxes promoter elements. Also binds the GT-box of cyclin D1 promoter and mediates cell cycle progression at G(1) phase as a downstream target of focal adhesion kinase (FAK) (By similarity). Interacts with corepressor CtBP2. Interacts with PIAS1, PIAS2, AND PIAS4; the interaction with each ligase sumoylates KLF8 (By similarity). The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. In KLF8, the motif is inactive. Sumoylation at Lys-64 represses transcriptional activity and reduces cell cycle progression into the G(1) phase. Has no effect on subcellular location. Belongs to the Sp1 C2H2-type zinc-finger protein family.