Abstract 3305: Hippo kinases LATS1/2 control human breast cell fate
Authors: Britschgi Adrian , Duss Stephan , Kim Sungeun , Brinkhaus Heike , Pinto Couto Joana , De Silva Duvini , Miraglia Loren , Stadler Michael B. , Orth Anthony P. , Bonamy Ghislain M.C. , Reddy Venkateshwar A. , Bentires-Alj Mohamed 
Published: July 2016

Abstract
Cellular differentiation and lineage commitment in adult tissues is a tightly regulated, yet highly dynamic process. It is of crucial importance to understand how different cell fates are maintained and how cellular plasticity is regulated: In the context of normal development but also in the light of the fact that perturbations acting as cell fate switches are the underlining cause for many human diseases. Still, the regulation of cell fate in many tissues, including the breast, remains largely elusive. We performed a high-content confocal image-based loss-of-function screen for regulators of primary breast cell fate. We infected primary human breast cells with a shRNA tumor suppressor library in serum-free suspension culture in an arrayed format and assessed a variety of phenotypic parameters using automated confocal imaging. We found that removal of tumor-suppressor genes increased the number of progenitor cells and promoted self-renewal potential. Unexpectedly, these effects were particularly linked to an increase in the number of cells of the luminal lineage. Redundant shRNA activity (RSA) and pathway analysis revealed that activation of the Hippo pathway was significantly associated with this increase in self-renewal and the luminal phenotype. We focused on the Hippo core kinases LATS1/2 (LATS), which were among the highest scored hits in the initial screen. Depletion of LATS in normal breast cells derived from several independent donors promoted self-renewal, luminal fate and increased the numbers of luminal progenitors. Luminal progenitors have been shown to include the cell-of-origin of most human breast cancers and supporting this hypothesis, we found that LATS protein expression was low or absent in most human breast cancers. Furthermore, we generated a gene signature of LATS depleted primary breast cells, which revealed a high enrichment in genes belonging to luminal A and B subtypes of breast cancer. Surprisingly, endogenous activation of the Hippo pathway via removal of its core kinases LATS only resulted in modest upregulation of its canonical targets YAP/TAZ, but rather triggered a pronounced increase in the expression of luminal and luminal progenitor genes. These findings challenge the current observation that Hippo effectors YAP/TAZ are associated with mammary basal cell fate and uncover a novel YAP/TAZ-independent role of LATS in the regulation on breast cell fate.
Citation Format: Adrian Britschgi, Stephan Duss, Sungeun Kim, Heike Brinkhaus, Joana Pinto Couto, Duvini De Silva, Loren Miraglia, Michael B. Stadler, Anthony P. Orth, Ghislain M.C. Bonamy, Venkateshwar A. Reddy, Mohamed Bentires-Alj. Hippo kinases LATS1/2 control human breast cell fate. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3305.