SP1 and cancer: Because BRCA1 has an inhibitory control of the IGF-I-R promoter as well as repressing the Sp1-induced transactivation of the IGF-I-R gene, this suggests that methylated BRCA1 state (as observed in our cancer cell lines and breast tumor tissues) allows for decreased BRCA1-Sp1 binding which could be part of a regulatory mechanism of the IGF-I-R gene expression.