LEFTY1 Is a Dual-SMAD Inhibitor that Promotes Mammary Progenitor Growth and Tumorigenesis

Area of Science:

• Cell Biology
• Developmental Biology
• Cancer Research

Background:

• SMAD pathways regulate epithelial cell proliferation and mammary gland development.
• Transforming growth factor-beta (TGF-β) and bone morphogenetic protein (BMP) signaling pathways have distinct roles in mammary homeostasis.
• NODAL/SMAD2 signaling is crucial in various developmental processes.

Purpose of the Study:

• To investigate the role of LEFTY1 in mammary epithelial cell proliferation and breast cancer.
• To elucidate the interaction between LEFTY1, BMP7, and SMAD signaling in mammary development.
• To identify potential therapeutic targets in triple-negative breast cancer.

Main Methods:

• Analysis of LEFTY1 expression in mammary progenitor cells.
• Investigation of LEFTY1's effect on SMAD2 and SMAD5 signaling.
• Study of BMP7's role as a NODAL antagonist.
• Examination of LEFTY1-BMPR2 interaction in breast cancer xenografts.

Main Results:

• LEFTY1, produced by mammary progenitor cells, suppresses SMAD2 and SMAD5 signaling, promoting epithelial cell proliferation.
• BMP7, produced by basal cells, restrains progenitor cell proliferation and opposes LEFTY1 in normal mammary epithelium.
• LEFTY1 binds BMPR2 to inhibit BMP7-induced SMAD5 activation, a mechanism critical for tumor-initiating cells in triple-negative breast cancer.
• LEFTY1 acts as an endogenous dual-SMAD inhibitor.

Conclusions:

• LEFTY1 promotes long-term proliferation of normal and malignant mammary epithelial cells.
• The interaction between LEFTY1 and BMPR2 is specific to tumor-initiating cells and essential for their growth.
• Inhibition of LEFTY1 function presents a potential therapeutic vulnerability in breast cancer.