Metabolic enzyme PFKFB4 activates transcriptional coactivator SRC-3 to drive breast cancer

Altered re-wiring of cell metabolism and transcriptional programs are both hallmarks of cancer that sustain rapid proliferation and metastasis(1). However mechanisms controlling the interplay between metabolic reprogramming and transcriptional regulation remain elusive. Here we show that metabolic enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4) regulates transcriptional reprogramming by activating the oncogenic steroid receptor coactivator-3 (SRC-3). We employed a method for identifying potential kinases that modulate coactivator functions by integrating kinome-wide RNA interference (RNAi)-based screening coupled to intrinsic SRC-3-transcriptional response. PFKFB4, a regulatory enzyme that synthesizes an allosteric stimulator of glycolysis(2), was found to be a robust stimulator of SRC-3 that co-activates estrogen receptor (ER). PFKFB4 phosphorylates SRC-3 at serine 857 (S857) enhancing its transcriptional activity, whereas either suppression of PFKFB4 or ectopic expression of a phosphorylation-deficient SRC-3 mutant S857A (SRC-3(S857A)) significantly abolishes SRC-3-mediated transcriptional output. Functionally, PFKFB4-driven SRC-3 activation drives glucose flux towards the pentose phosphate pathway enabling purine synthesis by transcriptionally upregulating the expression of enzyme transketolase (TKT). In addition, two enzymes adenosine monophosphate deaminase-1 (AMPD1) and xanthine dehydrogenase (XDH) involved in purine metabolism were identified as SRC-3 targets which may or may not be directly involved in purine synthesis. Mechanistically, phosphorylation at S857 increases coactivator interaction with the transcription factor ATF4 stabilizing SRC-3/ATF4 recruitment to target gene promoters. Ablation of SRC-3 or PFKFB4 suppresses in vivo breast tumor growth and prevents metastasis to the lung from an orthotopic setting as does an SRC-3(S857A) mutant. PFKFB4 and pSRC-3-S857 levels are elevated and significantly correlate in ER positive tumors whereas, in patients with basal subtype, PFKFB4-SRC-3 drives a common protein signature that positively correlates with the poor survival of breast cancer patients. These findings suggest that the Warburg-pathway enzyme PFKFB4 acts as a molecular fulcrum coupling sugar metabolism to transcriptional activation by stimulating SRC-3 critical to promote aggressive metastatic tumors.