Posttranslational modifications affect the structures and functions of proteins and play a crucial role in tumorigenesis (Lu and Hunter, 2009). SUMOylation, the covalent modification of a protein by a small ubiquitin-like modifier (SUMO) peptide on lysine residue, is an important posttranslational modification in the regulation of instrumental cellular processes, such as signal transduction, transcription, and nuclear/cytoplasmic shuttling (Geiss-Friedlander and Melchior, 2007). SUMOylation is also involved in the regulation of cancer progression. Human genome encodes SUMO1–4 proteins, which are covalently bound to substrate lysine residues through an enzymatic cascade similar to ubiquitination (Gareau and Lima, 2010). The SUMOylation process requires E1-activating (SAE1/SAE2) and E2-conjugating (UBC9) enzymes. UBC9 catalyzes the formation of an isopeptide bond between the C-terminus of SUMO and lysine of the target proteins (Flotho and Melchior, 2013). SUMOylation is a reversible process, and de-SUMOylation is mediated by the sentrin-specific proteases (SENPs) (Martin et al., 2007). SUMOylation regulates target protein stability, cellular protein distribution, and protein-protein interactions that are responsible for a variety of biological functions. Increasing numbers of SUMOylated proteins have been shown to be highly expressed in tumors and closely associated with tumor development (Seeler and Dejean, 2017).

The 6-phosphofructo-1-kinase (PFK-1), a rate-limiting enzyme, catalyzes the first irreversible reaction of glycolysis. Fructose 2,6-bisphosphate (F-2,6-BP) is the strongest allosteric activator of PFK1 (Lee et al., 2018, Lee et al., 2017). The concentration of F-2,6-BP is controlled by four 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFBs), a family of bifunctional enzyme that contains a kinase and a phosphatase domain and interconvert fructose 6-phosphate (F-6-P) and F-2,6-BP (Van Schaftingen et al., 1980a, Van Schaftingen et al., 1980b). PFKFB3 has the highest kinase to phosphatase activity ratio and thus sustains high glycolytic rates (Sakakibara et al., 1997). PFKFB3 is ubiquitously expressed, and its expression is upregulated in tumors. Inhibition of PFKFB3 dramatically reduces tumor growth (Hirschey et al., 2015). Regulation of PFKFB3 can be at transcriptional and posttranscriptional levels, which affects PFKFB3 stability and activity (Shi et al., 2017). However, whether PFKFB3 activity is regulated by SUMOylation remains unknown.

In this report, we demonstrate that PFKFB3 is SUMOylated at K302 in glioblastoma (GBM) cells in response to epidermal growth factor receptor (EGFR) activation. This SUMOylation stabilizes PFKFB3 and promotes aerobic glycolysis and proliferation of GBM cells.