TRPS1 maintains luminal progenitors in the mammary gland by repressing SRF/MRTF activity [01d_bulk_rna_seq_lum_prog_vs_mature]

The GATA transcription factor TRPS1 is a context-dependent oncogene in breast cancer. In the mammary gland, TRPS1 activity is restricted to the luminal population and sustains the initial branching of the mammary ducts at puberty as well as the lactogenic differentiation during pregnancy. Its function in the resting mammary gland however, remains unclear. To evaluate whether it could be a target for cancer therapy, we investigated TRPS1 function in the healthy resting mammary gland using a conditional ubiquitous depletion mouse model where long-term depletion does not affect fitness. we show that TRPS1 activity is critical to maintain a functional luminal progenitor compartment and that this involves the repression of the SRF/MRTF and the YAP/TAZ transcriptional program. Mechanistically, this repression involves Krt8-dependent RhoA modulation. Our work uncovers a hitherto undisclosed function of TRPS1 in luminal progenitors which is intrinsically linked to mechanotransduction in the mammary gland. It also provides new insights into the oncogenic functions of TRPS1 since luminal progenitors are likely the cells of origin of many breast cancers.