Imagine beyond: recent breakthroughs and next challenges in mammary gland biology and breast cancer research

Abstract

On 8 December 2022 the organizing committee of the European Network for Breast Development and Cancer labs (ENBDC) held its fifth annual Think Tank meeting in Amsterdam, the Netherlands. Here, we embraced the opportunity to look back to identify the most prominent breakthroughs of the past ten years and to reflect on the main challenges that lie ahead for our field in the years to come. The outcomes of these discussions are presented in this position paper, in the hope that it will serve as a summary of the current state of affairs in mammary gland biology and breast cancer research for early career researchers and other newcomers in the field, and as inspiration for scientists and clinicians to move the field forward.

A molecular toolbox to study progesterone receptor signaling

“…Having generated and selected MCF7 and T47D cell lines and culture conditions that are specifically suited for probing PR-mediated signaling questions, we next investigated if and how our readouts with exogenous reporter constructs translated to endogenous target gene induction. The literature reports variable induction of presumed direct PR target genes in PR-expressing cell lines in response to progesterone or R5020 stimulation [ 15 , 17 ]. We therefore selected three known PR-target genes ( WNT4 [ 36 ], RANKL [ 37 ], and FKBP5 [ 18 ]) for qRT-PCR analysis.…”

“…Several factors currently hamper progress in studying PR signaling. A major hurdle that has yet to be taken is the generation of non-transformed, PR-positive breast cell lines, as primary breast epithelial cells typically lose hormone receptor expression when cultured in vitro [ 17 ]. Primary 3D cultures of normal human breast organoids grown in Matrigel that were reported to contain cells with PR expression were unable to induce expression of known PR target genes, including WNT4 and RANKL [ 7 ].…”

“…Even these studies suffer from a scarcity of optimized, sensitive, and specific molecular tools to study PR signaling. For instance, variable progesterone-induced transcriptional responses measured by qRT-PCR have been reported [ 15 , 17 ], and the few available PRE luciferase reporter constructs show low inducibility and high response variation [ 18 – 21 ]. Furthermore, most in vitro studies have used (synthetic) progesterone concentrations in the nM range to study the molecular mechanisms of PR signaling.…”

A molecular toolbox to study progesterone receptor signaling

“…Having generated and selected MCF7 and T47D cell lines and culture conditions that are specifically suited for probing PR-mediated signaling questions, we next investigated if and how our readouts with exogenous reporter constructs translated to endogenous target gene induction. The literature reports variable and unreliable induction of presumed direct PR target genes in PR-expressing cell lines in response to progesterone or R5020 stimulation [15,17]. We therefore selected three known PRtarget genes (WNT4 [33], RANKL [34], and FKBP5 [18]) for qRT-PCR analysis.…”

“…Even these studies suffer from a scarcity of optimized, sensitive, and specific molecular tools to study PR signaling. For instance, inconsistent progesterone induced transcriptional responses measured by qRT-PCR have been reported [15,17], and the few available PRE luciferase reporter constructs show low inducibility and high response variation [18][19][20][21]. Furthermore, most in vitro studies have used (synthetic) progesterone concentrations in the nM range to study the molecular mechanisms of PR signaling.…”