Elevated levels of members of the STAT family of transcription factors in breast carcinoma nuclear extracts.

The transcription factor, milk protein binding factor (MPBF/Stat5), is a member of the STAT family of signalling molecules which mediates prolactin signal transduction in lactating mammary gland by binding to GAS (gamma-interferon activation site) DNA elements. We have determined the levels of STAT factors in nuclear extracts from a variety of human breast tissues including carcinoma and normal 'resting' breast by electrophoretic mobility-shift assay. The results show that the level of STAT binding activity is low in normal 'resting' breast and benign lesions while carcinoma samples have significantly higher (P < 0.01) amounts of STAT binding activity. Supershift analysis suggests that Stat1 and possibly other members of the STAT family of signalling factors, including Stat3, are activated in breast cancer tissues.