TDP2 negatively regulates axon regeneration by inducing SUMOylation of an Ets transcription factor

Abstract

In Caenorhabditis elegans, the JNK MAP kinase (MAPK) pathway is important for axon regeneration. The JNK pathway is activated by a signaling cascade consisting of the growth factor SVH‐1 and its receptor tyrosine kinase SVH‐2. Expression of the svh‐2 gene is induced by axonal injury in a process involving the transcription factors ETS‐4 and CEBP‐1. Here, we find that svh‐14/mxl‐1, a gene encoding a Max‐like transcription factor, is required for activation of svh‐2 expression in response to axonal injury. We show that MXL‐1 binds to and inhibits the function of TDPT‐1, a C. elegans homolog of mammalian tyrosyl‐DNA phosphodiesterase 2 [TDP2; also called Ets1‐associated protein II (EAPII)]. Deletion of tdpt‐1 suppresses the mxl‐1 defect, but not the ets‐4 defect, in axon regeneration. TDPT‐1 induces SUMOylation of ETS‐4, which inhibits ETS‐4 transcriptional activity, and MXL‐1 counteracts this effect. Thus, TDPT‐1 interacts with two different transcription factors in axon regeneration. The Mxl‐1 transcription factor promotes axon regeneration in C. elegans via inhibition of TDPT‐1, which reduces ETS‐4 SUMOylation and increases svh‐2 transcription. MXL‐1 facilitates axon regeneration by activating axon injury‐induced svh‐2 expression. TDPT‐1, a novel interacting partner of MXL‐1, interacts with ETS‐4 and induces its SUMOylation. SUMOylation of ETS‐4 inhibits its phosphorylation, which is required for the activation of svh‐2 transcription. The Mxl‐1 transcription factor promotes axon regeneration in C. elegans via inhibition of TDPT‐1, which reduces ETS‐4 SUMOylation and increases svh‐2 transcription.