Publication Date

2019-05-08

Availability

Embargoed

Embargo Period

2021-05-07

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Cancer Biology (Medicine)

Date of Defense

2018-12-10

First Committee Member

Karoline J. Briegel

Second Committee Member

Anthony Capobianco

Third Committee Member

Dorraya El-Ashry

Fourth Committee Member

Merce Jorda

Fifth Committee Member

Ralf Landgraf

Abstract

Clinically aggressive basal-like triple negative breast cancers (B-TNBC) disproportionally contribute to cancer deaths, but lack effective treatment options due to absence of expression of key therapeutic targets. New evidence suggests that B-TNBC may originate from luminal breast epithelial cells through luminal-to-basal cell lineage conversion and dedifferentiation. However, the factors that reprogram cell fate and differentiation states during the development of B-TNBC remain poorly understood. Our laboratory has identified a novel WNT/ß-Catenin target and transcriptional regulator, Limb-Bud-and Heart (LBH), which is majorly overexpressed in aggressive B-TNBC harboring WNT hyperactivation. We previously showed in vivo that LBH is a key stem cell and basal lineage regulator essential for normal mammary gland development. Using crosses between MMTV-Wnt1 transgenic mice and conditional LBH knockout mice, we tested if LBH is a critical effector of WNT-driven basaloid breast cancer, and whether its inhibition may prevent and/or attenuate B-TNBC formation and progression. In our in vivo mouse model, LBH inactivation in the basal mammary epithelium using a Keratin 14/K14-Cre deleter strain significantly attenuated MMTV-Wnt1-induced mammary gland hyperplasia and led to a delay in tumor onset. Surprisingly, tumor volume or burden were not changed, indicating that LBH is not required for WNT-driven tumorigenesis. Ubiquitous Lbh ablation delayed tumor onset even more drastically without affecting tumor volume. LBH-deficient MMTV-Wnt1-transgenic tumors did not exhibit significant histopathological differences compared to LBH WT MMTV-Wnt1-transgenic tumors; Whereas MMTVWnt1+; K14Cre;Lbh WT tumors were highly vascularized, disorganized, with mixed basal and luminal cell identity; tumors from MMTV-Wnt1+;K14Cre;Lbh KO mice were more organized, differentiated, and predominantly luminal Keratin 8 positive. The attenuation of mammary gland hyperplasia and tumor onset suggested that LBH deficiency may negatively affect WNT-induced stem cell expansion, which we were able to confirm in vitro using human breast cancer cell lines and in vivo using a transgenic GFP-reporter line. We also confirmed that LBH overexpression caused a luminal-to-basal conversion using a human breast cancer cell line. Our data indicate that LBH is an essential cell fate regulator downstream of WNT signaling that maintains basal lineage identity in B-TNBC. LBH inhibition may be a potential novel strategy to treat B-TNBC patients through differentiation therapy.

Keywords

cancer biology, molecular biology, breast cancer, triple negative breast cancer, Wnt, LBH

Available for download on Friday, May 07, 2021

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