Indusible hepsin overexpression activates TGFβ signaling in a Wap-Myc model of breast cancer

To test if ectopic overexpression of hepsin (TMPRSS1) induces TGFβ signaling in the context of tumorigenesis, we made use of a previously published tumor syngraft model of Myc-driven breast cancer (Partanen et al., 2012 PMID: 22308451). Wap-Myc mammary tumor cells, which express high Myc levels, were isolated from donor mice, transduced with the pIND21-HPN lentiviral construct that allows doxycycline (DOX)-induced hepsin overexpression, and subsequentially transplanted into recipient mice. Consistent with the notion that hepsin promotes TGFβ signaling, western blot analysis revealed increased phospho-Smad2/3 and upregulation of the TGFβ signaling downstream target SNAIL in Wap-Myc tumors with DOX-induced hepsin overexpression compared to control (-DOX) tumors. RNAseq analysis of these tumors provided additional evidence for TGFβ pathway upregulation by hepsin as the most significantly upregulated gene signatures corresponded to the TGFβ signaling pathway. The largest cluster of gene signatures affected by hepsin overexpression, however, was related to the ECM and integrins. Isolated Wap-Myc mammary epithelial cells from virgin Wap-Myc mice. Cells were transduced with concentrated pIND21-HPN lentivirus (MOI=10) o/n on the day of cell isolation. Cells were transplanted the next day into the fat pads of recipient mice (105 cells/gland, 3 weeks old). Doxycycline (DOX) was administered in drinking water (2mg/ml 5% sucrose) three days after transplantation. Wap-Myc expression was induced when the mice were 8 weeks old by 2 consecutive pregnancies. Tumor development was monitored once-twice a week after pregnancy. Mice were sacrificed when tumor size reached 1 cm