BAD regulates mammary gland morphogenesis by 4E-BP1-mediated control of localized translation in mouse and human models

John Maringa Githaka,David A Kramer,Raven Kirschenman,Nika N Danial,Lin Fu Zhu,Ing Swie Goping,D Alan Underhill,Namita Tripathi,Richard P Fahlman,Vrajesh Pandya,Rachel Montpetit,Namrata Patel,Nahum Sonenberg

doi:10.1038/s41467-021-23269-8

John Maringa Githaka, David A Kramer + Show 11 more

Open Access

https://doi.org/10.1038/s41467-021-23269-8

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Abstract

Elucidation of non-canonical protein functions can identify novel tissue homeostasis pathways. Herein, we describe a role for the Bcl-2 family member BAD in postnatal mammary gland morphogenesis. In Bad3SA knock-in mice, where BAD cannot undergo phosphorylation at 3 key serine residues, pubertal gland development is delayed due to aberrant tubulogenesis of the ductal epithelium. Proteomic and RPPA analyses identify that BAD regulates focal adhesions and the mRNA translation repressor, 4E-BP1. These results suggest that BAD modulates localized translation that drives focal adhesion maturation and cell motility. Consistent with this, cells within Bad3SA organoids contain unstable protrusions with decreased compartmentalized mRNA translation and focal adhesions, and exhibit reduced cell migration and tubulogenesis. Critically, protrusion stability is rescued by 4E-BP1 depletion. Together our results confirm an unexpected role of BAD in controlling localized translation and cell migration during mammary gland development.

Highlights

Elucidation of non-canonical protein functions can identify novel tissue homeostasis pathways
This work identifies BAD as a modulator of mammary gland morphogenesis and shows a regulatory link to localized translation that is critical for pubertal stage-specific cell migration
We used 3 genetic engineered mouse models to explore the role of BAD in postnatal mammary gland development; knock-out Bad−/−, knock-in BadS155A and Bad3SA where 3SA indicates alanine substitutions at S112/136/155 of the endogenous Bad allele[7,8,10]

Summary

Introduction

Elucidation of non-canonical protein functions can identify novel tissue homeostasis pathways. Together our results confirm an unexpected role of BAD in controlling localized translation and cell migration during mammary gland development. The BH3-only Bcl-2-associated agonist of death protein BAD1 is best known as an apoptosis sensitizer, but has complex roles in vivo[2,3,4] It is regulated by coordinated phosphorylation of three serine (S) residues S112, 136, and 155 (75, 99, and 118 in humans) that differentially modulate activity in a tissue-specific manner[5,6]. Unbiased proteomic screens identify that Bad3SA dysregulates the mRNA translational repressor protein 4E-BP1, focal adhesion and actin binding components, which together suggest defects to the cell motility machinery. This work identifies BAD as a modulator of mammary gland morphogenesis and shows a regulatory link to localized translation that is critical for pubertal stage-specific cell migration

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