An essential role of CBL and CBL-B ubiquitin ligases in mammary stem cell maintenance [RESEARCH ARTICLE]

Bhopal Mohapatra, Neha Zutshi, Wei An, Benjamin Goetz, Priyanka Arya, Timothy A. Bielecki, Insha Mustaq, Matthew D. Storck, Jane L. Meza, Vimla Band, and Hamid Band

CBL and CBL-B ubiquitin ligases are negative regulators of tyrosine kinase signaling with established roles in the immune system. However, their physiological roles in epithelial tissues are unknown. Here we used the MMTV-Cre-mediated Cbl gene deletion on a Cbl-b-null background as well as a tamoxifen-inducible mammary stem cell (MaSC)-specific Cbl/Cbl-b double knockout (DKO), using Lgr5-GFP-CreERT, to demonstrate a mammary epithelial cell-autonomous requirement of CBL and CBL-B in the maintenance of MaSCs. Using a newly engineered tamoxifen (TAM)-inducible Cbl/Cbl-b deletion model with a dual fluorescent reporter (Cbl^flox/flox; Cbl-b^flox/flox; Rosa26-CreERT; mT/mG), we show that Cbl/Cbl-b DKO in mammary organoids leads to hyper-activation of AKT-mTOR signaling with depletion of MaSCs. Chemical inhibition of AKT or mTOR rescued MaSCs from Cbl/Cbl-b DKO induced depletion. Our studies reveal a novel, cell-autonomous, requirement of CBL and CBL-B in epithelial stem cell maintenance during organ development and remodeling through modulation of mTOR signaling.

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