The nuclear hormone receptor cofactors prohibitin-2 (PHB2) and tetratricopeptide repeat domain 5 (TTC5) exert opposite effects in breast tumorigenesis


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Kawther Almazroee1, Constantinos Demonacos1, Ayşe Latif1
1University of Manchester

Abstract

Background

The nuclear hormone receptor (NHR) cofactor prohibitin 2 (PHB2) is overexpressed in multiple cancers including breast cancer contributing to plasma membrane-associated cell signalling processes, mediating NHR transcriptional activity in the nucleus and stabilising respiratory enzymes in mitochondria. The tetratricopeptide repeat domain 5 (TTC5) is a stress responsive protein involved in both the NHR and p53 pathways acting as a facilitator of the assembly of multi-protein networks. Given that PHB2 and TTC5 are components of the same multiprotein complexes in ERα positive MCF-7 breast cancer cells and both associate with ERα and p53 this study aimed to explore their role in the ERα positive and triple negative breast carcinogenesis.  

Method

PHB2 and TTC5 gene expression was explored in normal versus tumour tissues of ERα positive and ERα negative breast cancer patients using the bc-GenExMiner v4.6 tool. PHB2 or TTC5 gene expression was silenced in MCF-7 (ERα positive) or Hs578T (ERα negative) breast cancer cell lines with either siRNA targeting (PHB2) or CRISPR-Cas9 engineering (TTC5). Cell proliferation, clonogenicity, cell cycle regulation, breast cancer stem cells (BCSCs) formation, and epithelial to mesenchymal transition (EMT) were investigated in these cells in the presence or absence of PHB2 or TTC5.

Results

Decreased PHB2 and increased TTC5 mRNA levels were identified in cancer compared to normal breast tissues. Opposite expression patterns were also observed in ERα positive compared to ERα negative breast cancer patients. Decreased cell proliferation rate was observed in both siPHB2 and koTTC5 MCF-7 cells. Significantly decreased proliferation rate was observed in siPHB2 Hs578T cells whereas increased cell growth was monitored in koTTC5 Hs578T cells. Decreased BCSCs formation of MCF-7 cells was recorded in PHB2 or TTC5 silenced MCF-7 cells. PHB2 silenced MCF-7 cells exhibited increased E-cadherin protein levels whereas the opposite was the case in koTTC5 MCF-7 cells. Abolishing PHB2 or TTC5 gene expression in Hs578T cells downregulated vimentin levels.

Conclusion

PHB2 and TTC5 NHR cofactors exert opposing effects in cell proliferation, cell cycle control, BCSCs formation and EMT of breast cancer cells.  

Impact statement

These results provide evidence to support the notion that PHB2 and TTC5 could be prognostic factors and breast cancer type specific therapeutic targets.