Transcription factor SCIRR69 involved in the activation of brain-derived neurotrophic factor gene promoter II in mechanically injured neurons.

The spinal cord injury and regeneration-related gene #69 (SCIRR69), which was identified in our screen for genes upregulated after spinal cord injury, encode a protein belonging to the cAMP response element-binding protein (CREB)/ATF family of transcription factors. Our previous study showed that SCIRR69 functions as a transcriptional activator. However, the target gene regulated by SCIRR69 and its roles in injured neurons remain unknown. In this study, we showed that SCIRR69 is widely distributed in the central nervous system. Full-length SCIRR69 is an endoplasmic reticulum-bound protein. Following mechanical injury to neurons, SCIRR69 was induced and proteolytically cleaved by site-1 and site-2 proteases, and the proteolytically cleaved SCIRR69 (p60-SCIRR69) was translocated to the nucleus where it bound to brain-derived neurotrophic factor (BDNF) gene promoter II. In addition, loss- and gain-of-function studies confirmed that SCIRR69 is involved in the regulation of BDNF expression in injured neurons. As expected, the culture supernatants of PC12 cells stably expressing p60-SCIRR69 contained higher levels of BDNF, and more remarkably promoted neurite outgrowth in a spinal cord slice culture model in vitro than the supernatants of control cells. These results suggest that SCIRR69 is a novel regulator of the BDNF gene and may play an important role in the repair and/or regeneration of damaged neural tissues by specifically activating BDNF promoter II.

Cloning and characterization of SCIRR69: a novel transcriptional factor belonging to the CREB/ATF family.

The complete cDNA sequence of a novel gene, SCIRR69 (spinal cord injury and regeneration related no. 69 gene), was obtained by RACE technique. It codes for a protein of 521 amino acid residues homologous to human CREB3l2 (also known as BBF2H7) and mouse CREB3l2. The protein contains a basic DNA binding and leucine zipper dimerization (B-ZIP) motif and a hydrophobic region representing a putative transmembrane domain, similar to the structure of other CREB/ATF transcription factors. Monoclonal antibody against SCIRR69 was developed and could recognize the SCIRR69 protein in both native and denatured forms. Constructing of SCIRR69 fusion proteins with the GAL4 DNA-binding domain disclosed that SCIRR69 functioned as a transcriptional activator and its N-terminal 60 amino acids accounted for the activation ability. SCIRR69 resides in the cytoplasm of primary neurons, whereas neuron damage by incision led to the cleavage and translocation from the cytoplasm to the nucleus. These results suggest that SCIRR69 is activated by proteolytic cleavage at the transmembrane domain in response to neuron damage and its amino-terminal cytoplasmic domain translocates into the nucleus to activate the transcription of target genes.

Preparation and characterization of murine monoclonal antibodies against rat spinal cord injury and regeneration related protein no. 69.

Spinal cord injury and regeneration related protein No. 69 (SCIRR69) is a rat transmembrane bZIP transcription factor homologous to mice and human transcription factor CREB3L2. Previous work demonstrated the N-terminal region plays a critical role in its transcriptional activity. In this study, a peptide containing 18 amino acids (5-22aa) at the N-terminus of rat SCIRR69 was synthesized and coupled to the carrier protein as immunogen. One hybridoma cell line was obtained by standard cell fusion technique, followed by enzyme-linked immunosorbent assay (ELISA) and Western blot screening. The newly developed monoclonal antibody (MAb) was designated 4B4, the isotype of which was IgG2a. Immunofluorescence and Western blotting results showed that MAb 4B4 could recognize the SCIRR69 protein in both native and denatured forms. 4B4 will be a useful tool for the functional research of SCIRR69 in future studies.

Identification and characterization of scirr1, a novel gene up-regulated after spinal cord injury.

Spinal cord injury and regeneration involves transcriptional activity of many genes, of which many remain unknown. Using the rat spinal cord full- transection model, bioinformatics, cloning, expression assays, fusion proteins, and transfection techniques, we identified and characterized one such differentially expressed gene, termed scirr1 (spinal cord injury and/or regeneration related gene 1). Fourteen orthologs were found in 13 species from echinoderm to insect and human by Blast search of NCBI protein reference sequence database. However, no further information is available for these homologues. Using whole-mount in situ hybridization, mouse scirr1 mRNA was expressed temporally and spatially in accordance with the early development sequence of the central nervous system. In adult rat spinal cord, expression of scirr1 mRNA was localized to neurons of gray matter by in situ hybridization. Using immunohistochemistry, SCIRR1 protein was found to be up-regulated and expressed more highly in spinal cord neurons farther from the epicenter of injury. Although the precise function of SCIRR1 is unknown, its unique pattern of expression during CNS early development and up-regulation after spinal cord injury suggest that SCIRR1 should be involved in the succeeding injury and/or repair processes of the injured spinal cord. Also, the typical F-box and leucine-rich repeat (LRR) architecture of rat SCIRR1 indicated that it may play an important substrate recruiting role in the pleiotropic ubiquitin/proteasome pathway. All these make scirr1 a new interesting start to study the spinal cord injury and regeneration mechanism.

Identification of up-regulated genes after complete spinal cord transection in adult rats.

Spinal cord injury (SCI) initiates a cascade of events and these responses to injury are likely to be mediated and reflected by changes in mRNA concentrations. As a step towards understanding the complex mechanisms underlying repair and regeneration after SCI, the gene expression pattern was examined 4.5 days after complete transection at T8-9 level of rat spinal cord. Improved subtractive hybridization was used to establish a subtracted cDNA library using cDNAs from normal rat spinal cord as driver and cDNAs from injured spinal cord as tester. By expressed sequence tag (EST) sequencing, we obtained 73 EST fragments from this library, representing 40 differentially expressed genes. Among them, 32 were known genes and 8 were novel genes. Functions of all annotated genes were scattered in almost every important field of cell life such as DNA repair, detoxification, mRNA quality control, cell cycle control, and signaling, which reflected the complexity of SCI and regeneration. Then we verified subtraction results with semiquantitative RT-PCR for eight genes. These analyses confirmed, to a large extent, that the subtraction results accurately reflected the molecular changes occurring at 4.5 days post-SCI. The current study identified a number of genes that may shed new light on SCI-related inflammation, neuroprotection, neurite-outgrowth, synaptogenesis, and astrogliosis. In conclusion, the identification of molecular changes using improved subtractive hybridization may lead to a better understanding of molecular mechanisms responsible for repair and regeneration after SCI.

cDNA microarray analysis of spinal cord injury and regeneration related genes in rat.

The acute traumatic spinal cord injury (SCI) is a commonly seen and severe case in clinic. However, the repair and regeneration of injured spinal cord is limited. This is likely due to that different kinds of factors are involved in regeneration after SCI. In the present study, we used complementary DNA microarray consisting of 4 041 specific probes from rat to identify genes that were differentially expressed after SCI. The animals were subjected to complete transection injury of the thoracic spinal cord (T8-T9). Sham operated animals received only a laminectomy. Four and a half days later, rat spinal cord was dissected out for total RNA isolation. The fluorescent (Cy3 and Cy5) labeled probes were prepared and hybridized to the microarray. Genes that showed 2-fold difference in SCI tissue were identified. Sixty-five up-regulated genes consisted of 21 known genes, 30 known expressed sequence tags (ESTs) and 14 unknown genes. Seventy-nine down-regulated genes comprised 20 known genes, 42 known ESTs and 17 unknown genes. In 41 differentially expressed known genes, 5 up-regulated genes, i.e., tissue inhibitor of metalloproteinase 1 (Timp1), transgelin (Tagln), vimentin (Vim), Fc gamma receptor, cathepsin S (Ctss), and 3 down-regulated genes, i.e., stearyl-CoA desaturase, coagulation factor II (F2), endosulfin alpha (Ensa), were further confirmed by reverse transcription polymerase chain reaction (RT-PCR). These genes may play a role in the response to tissue damage or repair following SCI and characterization of them might be helpful to elucidate the molecular mechanisms of spinal cord injury and regeneration.