Fig 2: FABP7 knockdown (FABP7-Kd) and hypoxic exposure induced UCP1 expression in cancer cells. a FABP7, PRDM16, PGC-1α, and UCP1 expression in controls (Ctrl) and FABP7-Kd after 48 h normoxia or hypoxia (0.1% O2). b Representative western blots of FABP7, UCP1, PRDM16, PGC-1α, phosphorylated CREB (pCREB), and CREB after 48 h normoxia or hypoxia (0.1% O2). UCP1 bands appeared at 32 kD (monomer) and 64 kD (dimer). Four different PRDM16 isoforms were detected. c UCP1 expression (green) in cells cultured under normoxia or hypoxia (0.1% O2) for 48 h. Nuclei were stained with DAPI (blue). Scale bars; 20 μm. d Proportion of UCP1-expressing cells in Ctrl and FABP7-Kd after 48 h normoxia or hypoxia (0.1% O2). Error bars, SD; *p < 0.05, **p < 0.01, ***p < 0.001; n = 3

Fig 3: Mutual exclusivity between FABP7 and UCP1 expression in primary breast cancer tissues. a Association of FABP7, UCP1, and hypoxia median score in the METABRIC (n = 1904, upper panels) and TCGA (n = 960, lower panels) breast cancer cohorts. X and y axes show UCP1 and FABP7 expression, respectively. Hypoxia median score quartiles are indicated using different colors (orange, green, blue, and purple). b Correlation analyses of hypoxia score with FABP7 (upper panels) and UCP1 expression (lower panels)

Fig 4: FABP7 knockdown (FABP7-Kd) inhibited cancer cell growth after hypoxia or ionizing radiation. a Comparison of cell proliferation between control (Ctrl) and FABP7-Kd under normoxia and hypoxia (0.1% O2). b–d Clonogenic assay performed under normoxia and under hypoxia-reoxygenation (72 h of 0.1% O2 followed by normoxia). b Representative image of colonies. c Distributions of colony size. Red bars show averaged colony size. d Plating efficacy of Ctrl and FABP7-Kd. e, f Clonogenic assay performed with/without ionizing radiation. e Representative image of colonies. f Calculated surviving fractions of Ctrl and FABP7-Kd. Error bars, SD; *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.001; n = 3

Fig 5: FABP7 knockdown (FABP7-Kd) increased oxygen consumption, proton leak, and glycolysis. a Oxygen consumption rate (OCR) curve of controls (Ctrl) and FABP7-Kd cells. Oligomycin (Oligo), FCCP, and rotenone/antimycin A (Rot/AA) were added sequentially. b Estimated mitochondrial basal respiration (upper left), maximal respiration (upper right), proton leak (lower left), and coupling efficacy (lower right) of Ctrl and FABP7-Kd. c Extracellular acidification rate (ECAR) curve of Ctrl and FABP7-Kd. Glucose (Glu), oligo, and 2-deoxy-glucose (2-DG) were added sequentially. d Estimated glycolysis and glycolytic capacity of Ctrl and FABP7-Kd. Error bars, SD; *p < 0.05, ***p < 0.001, ****p < 0.0001; n = 3. Each experiment consisted of 20 technical replicates for each condition