TGF ‐β1 targets Smad, p38 MAPK , and PI 3K/Akt signaling pathways to induce PFKFB 3 gene expression and glycolysis in glioblastoma cells

In human cancers, transforming growth factor‐β1 ( TGF ‐β1) plays a dual role by acting as both a tumor suppressor and a promoter of tumor metastasis. Although TGF ‐β1 contributes to the metabolic reprogramming of cancer cells and tumor‐associated stromal cells, little is known of the molecular mechanisms connecting this cytokine with enhanced glycolysis. PFKFB 3 is a homodymeric bifunctional enzyme, belonging to the family of 6‐phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatases, that controls the conversion of fructose‐6‐phosphate (Fru‐6‐P) to fructose‐2,6‐bisphosphate (Fru‐2,6‐P 2 ). This metabolite is important for the dynamic regulation of glycolytic flux by allosterically activating phosphofructokinase‐1, a rate‐limiting enzyme in glycolysis. The PFKFB 3 gene is involved in cell proliferation via its role in carbohydrate metabolism. Here, we studied the mechanisms connecting TGF ‐β1, glucose metabolism, and PFKFB 3 in glioblastoma cell lines. We demonstrate that TGF ‐β1 upregulates PFKFB 3 mRNA and protein expression resulting in an increase in fructose 2,6‐bisphosphate concentration, glucose uptake, glycolytic flux and lactate production. Moreover, these increases in PFKFB 3 mRNA and protein expression and Fru‐2,6‐P 2 concentration were reduced when the Smad3, p38 mitogen‐activated protein kinase ( MAPK ), and phosphoinositide 3‐kinase ( PI 3K)/Akt signaling pathways were inhibited. We demonstrate that inhibition of PFKFB 3 activity with 3 PO or si RNA ‐mediated knockdown of PFKFB 3 significantly eliminated the capacity of the T98G cells to form colonies by TGF ‐β1, one of the hallmarks of transformation. Taken together, these results show that TGF ‐β1 induces PFKFB 3 expression through activation of the p38 MAPK and PI 3K/Akt signaling pathways that complement and converge with early activation of Smad signaling. This suggests that PFKFB 3 induction by TGF ‐β1 can be one of the main mechanisms mediating the reprogramming of glioma cells.