An upregulation of SIAH1 after spinal cord injury in adult rats.

E3 ubiquitin ligase SIAH1 is a protein associated with the onset of nontumorigenicy in revertant tumorigenic cell lines and with several apoptotic processes. However, its role in the injury of the central nervous system remains unknown. In this study, we performed acute spinal cord injury (SCI) in adult rats and investigated the protein expression and cellular localization of SIAH1 in the spinal cord. Western blot analysis revealed that SIAH1 was low expressed in normal spinal cord. It increased at 8 h after SCI, peaked at 1 day, remained for another 3 days, then declined to basal levels at 5 days after injury. Immunohistochemistry further confirmed that SIAH1 immunoactivity was expressed at low levels in gray and white matters in normal condition and increased after SCI. Double immunofluorescence staining showed that SIAH1 was coexpressed with NeuN (neuronal marker), CNPase (oligodendroglial marker), GFAP (astroglial marker), and CD11b (microglial marker) at 1 day post-injury and was also coexpressed with active caspase-3 in neurons and glial cells after injury. In addition, double immunofluorescence staining indicated that p-c-Jun NH2-kinase (JNK) coexpressed with SIAH1 in neurons and glial cells. Coimmunoprecipitation further showed that p-JNK and SIAH1 precipitated with each other in the damaged spinal cord. Taken together, these data suggest SIAH1 involvement in the injury response of the adult spinal cord of the rats.