Identification and Characterization of Deubiquitinases and Long Non-coding RNAs as Novel Regulators of Breast Cancer

Abstract

Abstract

Cancer initiation and progression is orchestrated by a complicated web of signaling pathways with numerous effector proteins and RNAs. My studies focus on identifying and characterizing the novel regulators of cancer-related processes and pathways from two aspects.

First, I aimed to identify the deubiquitinases (DUBs) controlling the degradation of SLUG/SNAI2, a protein that promotes cancer initiation and metastasis through upregulating stem cell activity, migration, invasion, and survival of cancer cells. SLUG is unstable and degraded through the ubiquitin proteasome system; however, the molecular mechanisms regulating SLUG stability during cancer development remain poorly understood. Thus, to identify the DUBs that deubiquitinate SLUG and protect it from proteasomal degradation, I conducted comprehensive screenings of a human DUB cDNA library of 65 genes and a siRNA library of 98 genes. USP20 was a positive hit from both screenings, and was validated as the bona fide DUB for regulating endogenous SLUG ubiquitination and stability. Further investigations on USP20 demonstrated its function in promoting migration, invasion and metastasis. Clinical studies suggested that the protein levels of USP20 and SLUG are positively correlated, and higher USP20 expression is associated with poorer prognosis in ER- breast cancer patients. Since so far there is no effective approach to directly target SLUG pharmaceutically, the identified enzyme USP20 may serve as a potential drug target for reducing SLUG level.

Second, I aimed to identify the novel long non-coding RNAs (lncRNAs) involved in the transforming growth factor β (TGFβ) signaling pathway, which is a pivotal pathway in the regulation of normal development, homeostasis, as well as cancer initiation and progression. Although this pathway has been extensively studied, the role of lncRNAs in TGFβ signaling is largely unknown. To achieve my goal, I performed a genome-wide gene expression profiling of TGFβ treated human epithelial cells (MCF10A, HaCaT, and HPL1) using microarray. Preliminary investigations highlighted lncRNA-75 as a promising candidate regulating cell proliferation, senescence and cell cycle progression, and studies are ongoing to unveil the molecular mechanisms underlying lncRNA-75’s function. This study also provides a groundwork for future efforts to further elucidate the role of lncRNAs in TGFβ signaling.