Identification and validation of novel targets of regulated IRE1-dependent decay in triple negative breast cancer
Bolger, Alice
Bolger, Alice
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Publication Date
2023-08-16
Type
Thesis
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Abstract
Breast cancer is the most commonly diagnosed cancer in women. Triple-negative breast cancer (TNBC) refers to a subtype which lacks oestrogen receptors (ESR1), progesterone receptors (PR) and does not overexpress Human Epidermal Growth Factor Receptor 2 (HER2). TNBC accounts for 15-20% of all breast cancer subtypes, lacks targeted therapies and has a worse prognosis than other breast cancer subtypes, highlighting an urgent need for new therapeutic targets and strategies. Recently, our laboratory showed that the endoplasmic reticulum (ER) transmembrane protein IRE1α is constitutively activated in TNBC, which promotes growth and survival of tumours. IRE1α possesses both kinase and endoribonuclease (RNase) domains; the main characterised target of IRE1α’s RNase activity is X-box-binding protein 1 (XBP1) messenger RNA (mRNA), however it can also cleave other RNAs through a process known as regulated IRE1-dependent decay (RIDD). As IRE1α RNase inhibition emerges as a potential mode of treatment for TNBC, focus has turned to identifying novel genes that are regulated by the IRE1α-RIDD pathway, in order to fully understand the consequences of IRE1α inhibition for these cells. Recent work from our lab has shown that JUP mRNA is a target of IRE1α cleavage by RIDD in TNBC cell line MDA-MB-231. This leads to depletion of JUP protein, a component of cell-cell junctions, which our lab has shown significantly increases migratory capacity of the cells. This thesis examines JUP mRNA regulation by IRE1α in TNBC in more detail. We assess the sequence-specificity of JUP mRNA cleavage by IRE1α, examine the role of XBP1s in JUP mRNA levels in MDA-MB 231 and analyse the effects of IRE1α activity on JUP mRNA expression in other TNBC cell lines. In addition, we also searched for novel RIDD targets in MDA-MB 231, using RT-qPCR analysis to examine the influence of IRE1α activity on the expression of potential target genes, and validated cleavage of their transcripts by IRE1 in vitro. This research identifies CDK11A and MATR3 as potential RIDD targets in TNBC and contributes to our understanding of IRE1α as a potential therapeutic target in TNBC.
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NUI Galway