The Role of Nuclear Hormone Receptor (NHR) Cofactors in Breast Carcinogenesis

Student thesis: Phd


Identifying the components of the molecular signalling pathways involved in breast cancer metastasis and drug resistance is of vital importance. The role of the nuclear hormone receptor (NHR) cofactors prohibitin 2 (PHB2) and tetratricopeptide repeat domain 5 (TTC5) (also known as the stress-responsive activator of p300 (Strap)) in breast cancer metastasis and drug resistance was investigated in this study. Prohibitin 2 (PHB2) localises in the cytoplasm, nucleus, and mitochondria, and functions as a modulator of the transcriptional activity of the estrogen receptor alpha (ERα) and other transcription factors, as well as a chaperone maintaining optimal mitochondrial respiration. The tetratricopeptide repeat domain 5 (TTC5) facilitates protein-protein interactions and potentially signalling amplification. PHB2 and TTC5 are components of the same multiprotein complex and are associated with important players in breast tumorigenesis (including ERα and p53); however, their precise molecular functions in breast carcinogenesis are not clear. Methods: PHB2 and TTC5 protein levels, interactions, and subcellular localisation under diverse stress conditions were investigated in the breast cancer cell lines MCF-7, T47D, and MDA-MB-231. PHB2 and TTC5 mRNA levels were analysed in normal vs. tumour tissues with different ERα/p53 status in patients with breast cancer. Their functions in relation to the cancer hallmarks of energy metabolism, cell proliferation, and invasion, and metastasis were explored in ERα-positive and ERα-negative breast cancer cells. Results: Diverse types of stress triggered by etoposide, gemcitabine, and IFNγ treatment induced variable PHB2 and TTC5 protein levels in an ERα status-dependent manner. The interaction between the two cofactors was also cell type-dependent. Decreased PHB2 and increased TTC5 mRNA levels were identified in tumours compared to normal breast tissues. Furthermore, silencing of PHB2 or TTC5 gene expression decreased the proliferation of the ERα-positive cells, whereas silencing of PHB2 gene expression led to a significant decrease in the ERα-negative cell proliferation rate, and silencing of TTC5 in these cells increased cell growth. PHB2 and TTC5 mediated energy metabolism was also cell type dependent. Significantly reduced ATP levels were observed in siPHB2 MCF-7 and Hs578T cells whereas no change was seen in koTTC5 cells. siPHB2 Hs578T cells exhibited a significantly decreased cell migratory potential, whereas no change in cell migration was observed in koTTC5 Hs578T cells. Finally, silencing of either PHB2 or TTC5 gene expression resulted in decreased MCF-7 cells’ mammosphere formation. Conclusion: PHB2 and TTC5 could be used as prognostic markers and therapeutic targets for the treatment of both ERα- positive and ERα-negative breast cancer.
Date of Award1 Aug 2023
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorCostas Demonacos (Supervisor) & Ayse Latif (Supervisor)

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