Ets2-dependent stromal regulation of mouse mammary tumors

The Ets2 transcription factor is regulated by mitogen-activated protein (MAP) kinase phosphorylation of a single threonine residue. We generated by gene targeting a single codon mutation in Ets2 substituting Ala for the critical Thr-72 phosphorylation site (Ets2(A72)), to investigate the importance of MAP kinase activation of Ets2 in embryo and tumor development. Ets2(A72/A72) mice are viable and develop normally. However, combining the Ets2(A72) allele with a deletion mutant of Ets2 results in lethality at E11.5 and shows that Ets2,472 is a hypomorphic allele. Mammary tumors caused by transgenic polyomavirus middle T antigen, activated Neu (Erbb2), or the combination of Neu and transgenic VEGF (Neu; VEGF-25) were all restricted in Ets2(A72/A72) females. The Ets2(A72/A72) restriction on Neu; VEGF-25 tumor growth was associated with increased p21(CiP1) expression. The size of tumors transplanted into fat pads of mice with Ets2 targeted alleles was correlated directly with Ets2 activity and fewer stromal cells expressing matrix metalloproteinase 9 (MMP-9). Decreased MMP-3 and MMP-9 mRNAs were confirmed in Ets2(A72/A72) macrophages. Activation of Ets2 at Thr-72 acts in the stroma, downstream of vascular endothelial growth factor production, in part through the regulation of macrophage proteases to support the progression of Neu- and polyomavirus middle-T-initiated mammary tumors.