The role of hBCATc in breast cancer progression through IGF-1 and insulin signalling cascades

Shafei, Mai

Abstract

Introduction and Aims:

Breast cancer remains the leading cause of cancer mortality in women globally, despite advances in the development of targeted therapies. Driven by oncogenic signals, cancer cells undergo metabolic reprogramming, upregulating metabolite transporters and shuttling nutrients to promote proliferation and migration. The expression of key metabolic enzymes involved in BCAA metabolism (hBCATc and hBCATm), isocitrate dehydrogenase (IDH1 and IDH2) and serine metabolism (PHGDH) have been demonstrated to be upregulated in breast cancer. However, the expression patterns and the role of these metabolic proteins in breast cancer tumourigenesis remains to be elucidated. This research hypothesises that these metabolic pathways converge in tumour cells, whereby particular metabolic pathways are favoured differentially between breast cancer subtypes, which could lead to the identification of novel therapeutic targets. In breast cancer insulin/IGF-1 signalling has been demonstrated to contribute to tumourigenesis through the activation of growth signalling effectors which is mediated by two chief pathways: Akt/mTOR and RAS/MAPK. As nutrient levels of BCAAs particularly leucine, substrates of hBCAT, regulate the mTOR pathway hBCAT was hypothesised to play a role in
the regulation of proliferation and migration of triple-negative breast cancer (TNBC) cells through the IGF-1 and insulin signalling pathways.

Methods:

Using immunohistochemistry, the expression profile of the metabolic proteins was assessed between breast cancer subtypes. The impact of hBCATc expression on proliferation, migration, invasion, apoptosis and modulation of PI3K/Akt and RAS/MAPK signalling was assessed using molecular biological investigations, Western blot and confocal analysis.

Results and discussion:

Using serial sections, hBCATm was found to be significantly associated with IDH1 expression, indicating that these two metabolic pathways are activated concomitantly. Expression of hBCATm and IDH1 correlated with luminal A breast cancer and smaller breast tumours, indicating better prognosis. Differentially, hBCATc expression was found to be significantly associated with the more aggressive HER2+ and TNBC subtypes. For the first time, knockdown of hBCATc was demonstrated to significantly reduce insulin and IGF-1-mediated proliferation, migration and invasion in TNBC cells. An analysis of this pathway showed that when overexpressed hBCATc regulates proliferation through the PI3K/Akt/mTO axis, whilst simultaneously attenuating the Ras/MAPK pathway, indicating that hBCATc acts as a conduit between these two pathways. Overexpression of hBCATc ultimately led to the increase in FOXO3a, Nrf2 and GRP78, which play fundamental roles in cell proliferation, cell survival and protein folding. Therefore, hBCATc has been demonstrated to provide TNBC cells with metabolic plasticity to alter dependence on the RAS/MAPK and PI3K/Akt/mTOR signalling cascades, in response to IGF-1/insulin, to promote tumour survival and progression.

• Thesis Type: Thesis
• Deposit Date: Oct 1, 2019
• Publicly Available Date: Sep 10, 2020
• Public URL: https://uwe-repository.worktribe.com/output/3429539
• Award Date: Sep 10, 2020