CTCF, also known as CCCTC-binding factor, contains 11 zinc finger (ZF) binding domains that allow it to bind different DNA target sequences and proteins. This multifunctional protein can act as a transcriptional activator or repressor. As a transcriptional repressor, CTCF, binds to promoters of vertebrate c-myc gene. It also binds to the PLK and PIM1 promoters. CTCF may prevent the access of transcriptional activators to enhancers. CTCF also acts as a transcriptional activator of APP. It is involved in different aspects of gene regulation including promoter activation or repression, hormone-responsive gene silencing, methylation-dependent chromatin insulation, and genomic imprinting. Mutations of CTCF in this gene have been associated with invasive breast cancers, prostate cancers, and Wilms tumors, suggesting a role for CTCF may as a tumor suppressor.