Characterisation of ACBD3 and PI4Kβ expression in breast cancer and the effects of ACBD3 overexpression

Abstract

Targeted breast cancer treatments are essential for increasing chemotherapy effectiveness whilst simultaneously reducing side effects and are the focus of a whole generation of drug development in cancer and elsewhere. The ACBD3 gene encodes an essential structural tether protein of the same name that has an unusually large number of cellular roles, diverse binding partners, and few redundancies. Chromosome 1q is frequently amplified in breast cancer and the ACBD3 locus (1q42.12) was previously found to be amplified in multiple breast cell lines and primary breast tumours. Previous research found that ACBD3 mRNA was upregulated in breast tumour tissue matched against adjacent normal tissue and that ACBD3 overexpression promoted cancer stem cell renewal and activated the Wnt/β-Catenin signalling pathway in breast cancer cell lines. Due to the broad functions of ACBD3 and its contextual role in cells it was hypothesised that ACBD3 expression may have other affects in breast cancer. ACBD3 was overexpressed at the mRNA and protein level in breast cancer patient tumours compared to normal tissue and mRNA expression over the median value was detrimental for breast cancer patient survival, relapse free survival and distant metastasis free survival. IHC staining of breast cancer and normal breast tissue cores found that ACBD3 was highly expressed in epithelial ductal cells. ACBD3 mRNA and protein expression was higher in a panel of breast cancer cell lines compared to a normal like breast cell line and ER+ cell lines had the highest protein expression of ACBD3. ACBD3 mRNA and protein expression was upregulated in a previously engineered T47D everolimus chemotherapy resistant cell, the T47D breast cancer cell line was transfected with eGFP-ACBD3 but this did not affect everolimus resistance. ACBD3 overexpression did increase cell growth and there were also a number of expression changes to oncoproteins. A GOLD domain deletion mutant of ACBD3 was constructed and this led to more oncoprotein expression changes when expressed in the T47D cell line. Transcriptional and translational regulation are sensitive to cell density which has implications for all ex vivo study of ACBD3 and several compounds have been found that augment ACBD3 expression. ACBD3 was hypothesised to be a marker of progression in breast cancer and may promote a Luminal B pathology over Luminal A. its overexpression increased growth in a Luminal A cell line, increased expression of proteins associated with inflammation and secretion and reduced immunogenic protein expression. Luminal B patients had the largest reduction in relapse free survival when ACBD3 mRNA expression was high. ACBD3 expression appears to be a biomarker for breast cancer patient outcomes and may have some validity in predicting response to therapy and was also associated with ER+ and signalling. New mechanisms by which ACBD3 might cause inflammation were determined in addition to known roles for ACBD3 in redox stress and in iron import. ACBD3 also reduced immunogenic proteins when overexpressed. ACBD3 is certainly associated with worse outcomes and with progression in breast cancer and ACBD3 dependent pathways should be considered as a target for treatment in the future. The consensus of these results agree that ACBD3 expression in breast cancer is associated with characteristics of stemness and that ACBD3 may decrease immune system detection in addition to Wnt signalling.