Fig. 3

KMO enzyme expression and activity in HC and various BrCa subtypes. a All BrCa tissues expressed KMO mRNA more highly than the HC, with HER2-enriched tissues showing most expression in the METABRIC dataset. b KMO activity (as reflected by the ratio of 3HK to KYN concentration, 3HK/K ratio) is upregulated in all BrCa patient sera relative to HC, with HER2-enriched BrCa patient serum showing the highest KMO activity. c KMO protein immunohistochemistry in BrCa tissues shows that KMO expression is highest in the HER2-enriched BrCa subtype. Representative images of KMO staining in BrCa tumor tissue subtypes with semi-quantification (n = 10 each subtype; scale bar, 1000 μM). d KMO mRNA expression increased only in TN BrCa cells (2-fold change) after 24 h IFN-γ treatment (n = 3, in triplicate). e The low 3HK/KYN ratio observed in the TN BrCa cell lines could potentially be due to the elevated production of substrate KYN induced by IFN-γ treatment. KP metabolite analysis was performed using uHPLC in BrCa cell supernatants and cell pellets (n = 3, in triplicate) or in human plasma samples, HC (n = 98), luminal (n = 138), TN (n = 143), and HER2-enriched (n = 127). The error bars in d and e indicate the standard deviation from the triplicates of cell culture treatment. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001