MYC regulation of Glutamine-Proline regulatory axis is key in Luminal B breast cancer

Background: Altered cellular metabolism is a hallmark of cancer and some are reliant on Glutamine for sustained proliferation and survival. We hypothesise that the Glutamine-Proline regulatory axis has a key role in Breast cancer (BC) in the highly proliferative classes.Methods: Glutaminase (GLS), pyrroline-5-carboxylate synthetase (ALDH18A1) and pyrroline-5-carboxylate reductase 1 (PYCR1) were assessed at DNA/mRNA/protein levels in large well-characterised cohorts.Results: Gain of PYCR1 copy number and high PYCR1 mRNA was associated with luminal B tumours. High ALDH18A1 and high GLS protein expression was observed in the ER+/HER2- high proliferation class (Luminal B) compared with ER+/HER2- low proliferation class (Luminal A) (p=0.030 and p=0.022 respectively), however this was not observed with mRNA. Cluster analysis of the Glutamine-Proline regulatory axis genes revealed significant associations with molecular subtypes of breast cancer and patient outcome independent of standard clinicopathological parameters (p=0.012). High protein expression of the Glutamine-Proline enzymes were all associated with high MYC protein in Luminal B tumours only (