ERK5 S496 phosphorylation, but not ERK5 kinase activation, promotes senescence-associated cell growth (SACG) and inflammation of myeloid cells and atherosclerosis via upregulating SUMOylation at a novel site (K518) on NRF2 and aryl hydrocarbon receptor

ERK5 is a dual kinase-transcription factor, which contains an N-terminal kinase domain and transactivation domains in the C-terminal half. Many ERK5 kinase inhibitors have been developed and tested to treat cancer and inflammatory diseases. However, recent data have raised questions regarding the functional role of ERK5 kinase inhibitors. We aimed to investigate how ERK5 reprograms myeloid cells (MC) to the senescence-associated secretory phenotype (SASP), consequently leading to atherosclerosis. We showed that atherosclerosis was inhibited in ERK5 S496A (dephosphorylation mimic) knock-in (KI) mice. Furthermore, ERK5 S496 phosphorylation was required for not only SASP but also senescence-associated cell growth (SACG) observed in the plaque via upregulation of aryl hydrocarbon receptor (AHR). We also discovered a key effect of ERK5 S496 phosphorylation on SUMOylation at a novel site of NRF2 (i.e., K518), which inhibited NRF2 transcriptional activity without affecting ERK5 kinase activity and antagonized oxidized LDL (oxLDL)-induced SASP. Specific ERK5 kinase inhibitors (AX15836 and XMD8-92) both inhibited oxLDL-induced ERK5 S496 phosphorylation, suggesting that ERK5 S496 phosphorylation was involved at least in part of the effects of these inhibitors. We have discovered a novel mechanism, in which ERK5 S496 phosphorylation directly inhibits NRF2 activity by upregulating NRF2 K518 SUMOylation, and induces SACG and atherosclerosis. We prepared the tissue section from the plaques in wild-type, and ERK5 S496A KI mice fed a high-fat diet (HFD) or normal chow diet (NCD) for 12 weeks after AAV8-PCSK9 injection.