DIFFERENTIAL ACTIVATION OF STAT-3 AND STAT-5 DURING MAMMARY-GLAND DEVELOPMENT

We have investigated the activity of STAT family members throughout a mammary developmental cycle. Transcripts for Stat 5 were upregulated d uring pregnancy whilst STAT1 and STAT3 mRNAs were expressed at constan t levels, DNA binding complexes containing both STAT5a and 5b showed d iffering affinities for two naturally occurring STAT5 binding sites. I n the involuting mammary gland STAT5 activity decreased whereas STAT3 was specifically activated. These observations reveal a complex patter n of activation of STAT factors during mammary growth, differentiation and remodelling and pro,ide the first evidence for the involvement of STAT3 in development of the mammary gland.