effect of PPA2 knockdown on gene expression under normoxia or hypoxia of DLD1 colerectal cancer cells
Metastatic colorectal cancer (mCRC) is the major cause of death in patients with CRC. Hypoxia is a hallmark of solid tumors that promotes cell metabolic adaptation and metastasis. However, the mechanism linking mCRC to hypoxia-regulated metabolic adaptation remains unclear. Here, we found that inorganic pyrophosphatase 2 (PPA2) suppresses mCRC progression via its phosphatase function. PPA2 is expressed at low levels in mCRC specimens and lowly expressed PPA2 mediates better responses to hypoxia to enhance CRC glycolysis and metastasis by promoting hypoxia-inducible factor-1a (HIF-1a) signaling. Mechanistically, PPA2 decreases HIF-1a stability through noncanonical ubiquitin-mediated proteasomal degradation via recruitment of E3 ligase neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4), which inhibits glycolysis and metastasis-related gene expression. Furthermore, PPA2 directly interacts with NEDD4 and dephosphorylates NEDD4 at the T758 residue, leading to the increased interaction between NEDD4 and HIF-1a. Under hypoxic stress, NAD-dependent protein deacetylase sirtuin-5 (SIRT5) promotes the dissociation of PPA2 and NEDD4 by inducing PPA2 desuccinylation at the K176 residue, which ultimately contributes to the improved stability of HIF-1a under hypoxic conditions. Our findings reveal the suppressive role of PPA2 in HIF-1a-dependent mCRC, suggesting that the SIRT5-PPA2-NEDD4-HIF-1a axis can be assessed for integrated prognosis evaluation and represents a potential therapeutic target. Overall design: PPA2-depleted DLD1 cells were establised by shRNA, and were incobated under normoxia (HO) or hypoxia (LO) for 12h before sample collection.