Activation of adenosine deaminase in MCF-7 cells through IGF-estrogen receptor α crosstalk

Adenosine deaminase (ADA) regulates cellular levels of adenosine and deoxyadenosine, and 17β-estradiol (E₂) induces ADA mRNA in MCF-7 human breast cancer cells. IGF-I also induces ADA gene expression in these cells, and induction of this response through IGF activation of estrogen receptor α (ERα) was further investigated. IGF and other polypeptide growth factors induce reporter gene expression in MCF-7 cells contransfected with ERα expression plasmid and pADA211, a construct containing the - 211 to +11 region of the ADA gene promoter which is required for high basal and E₂-inducible activity. Deletion analysis of this promoter demonstrates that IGF activates ERα/Sp1 interactions with multiple GC-rich sites in the promoter and this response is abrogated in cells transfected with ERα containing mutations at Ser¹¹⁸ or Ser¹⁶³. IGF induces both MAPK (mitogen-activated protein kinase) and P13-K (phosphatidylinositol-3-kinase) phosphorylation cascades in MCF-7 cells; however, using a series of inhibitors and dominant negative constructs, our results show that induction of ADA by IGF activation of ERα/Sp1 is dependent on the MAPK signaling pathway.