Changes of Src-suppressed C kinase substrate expression in cytokine induced reactive C6 glioma cells

Role of A-Kinase Anchoring Protein 12 in the Central Nervous System

A-kinase anchoring protein (AKAP) 12 is a scaffolding protein that anchors various signaling proteins to the plasma membrane. These signaling proteins include protein kinase A, protein kinase C, protein phosphatase 2B, Src-family kinases, cyclins, and calmodulin, which regulate their respective signaling pathways. AKAP12 expression is observed in the neurons, astrocytes, endothelial cells, pericytes, and oligodendrocytes of the central nervous system (CNS). Its physiological roles include promoting the development of the blood-brain barrier, maintaining white-matter homeostasis, and even regulating complex cognitive functions such as long-term memory formation. Under pathological conditions, dysregulation of AKAP12 expression levels may be involved in the pathology of neurological diseases such as ischemic brain injury and Alzheimer's disease. This minireview aimed to summarize the current literature on the role of AKAP12 in the CNS.

Expression of SRC suppressed C kinase substrate in rat neural tissues during inflammation

Src-suppressed C kinase substrate (SSeCKS), an in vivo and in vitro protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein which markedly upregulated in several organs, including brain, lung, heart, kidney etc., indicating a possible role of SSeCKS in inflammatory process. However, the expression and biological function of SSeCKS during neuronal inflammation remains to be elucidated, so we established an inflammatory model injected with LPS to investigate the gene expression patterns of SSeCKS in neural tissues by using TaqMan quantitative real-time PCR and immunohistochemistry in rat. Real-time PCR showed that LPS stimulated the expression of SSeCKS mRNA in a dose- and time-dependent manner in sciatic nerves, spinal cords and dorsal root ganglions. Immunohistochemistry showed that SSeCKS colocalized with nerve fibers in sciatic nerve after LPS administration, but there was no colocalization between SSeCKS and Schwann cells. In addition, SSeCKS colocalized with neurons which existed in dorsal root ganglions and spinal cords. These findings indicated that SSeCKS might play some important roles in sciatic nerve fibers and neurons in spinal cords and dorsal root ganglions after LPS injection.

The relationship between Src-suppressed C kinase substrate and β-1,4 galactosyltransferase-I in the process of lipopolysaccharide-induced TNF-α secretion in rat primary astrocytes

Src-suppressed C kinase substrate (SSeCKS), a protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein. In addition, β-1,4 Galactosyltransferase-I (β-1,4-GalT-I) also plays an important role in the inflammation reactions of nervous system. It was reported that both SSeCKS and β-1,4-GalT-I were involved in the LPS-induced tumor necrosis factor-alpha (TNF-α) expression in rat primary astrocytes. However, the functional interaction between SSeCKS and β-1,4-GalT-I in the LPS-induced TNF-α secretion remains unclear. Therefore, in this study, using the inflammation model of astrocytes treated by LPS in vitro, we found that the changed expressions of SSeCKS and β-1,4-GalT-I participated in LPS-induced TNF-α secretion through p38, JNK, and ERK signal transduction pathways in rat primary astrocytes. Knockdown by small-interfering RNAs (siRNAs) or overexpression of SSeCKS and β-1,4-GalT-I could influence Mitogen-activated protein kinases (MAPKs) signaling pathways activation and TNF-α secretion. Besides, we confirmed that knockdown of SSeCKS could prevent the induction of β-1,4-GalT-I in this process. Inversely, β-1,4-GalT-I had no significant effect on SSeCKS expression in the same way. In summary, our data indicated that SSeCKS could regulate LPS-induced TNF-α secretion through β-1,4-GalT-I in rat primary astrocytes.

Involvement of SRC-suppressed C kinase substrate in neuronal death caused by the lipopolysaccharide-induced reactive astrogliosis

Src-suppressed C kinase substrate (SSeCKS), a protein kinase C substrate, is a major lipopolysaccharide (LPS) response protein, regulating the inflammatory process. In the process of spinal inflammatory diseases by LPS intraspinal injection, expression of SSeCKS in the spinal cord was increased, mainly in active astrocytes and neurons. Induced SSeCKS was colabeled with terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling (an apoptosis maker) in the late inflammation processes. These results indicated that SSeCKS might correlate with the inflammatory reaction and late neurodegeneration after LPS injection. A cell type-specific action for SSeCKS was further studied within C6 cells and PC12 cells. Knockdown of SSeCKS by small-interfering RNAs (siRNAs) blocked the LPS-induced inducible nitric oxide synthase (iNOS) expression in C6 cells, while overexpression SSeCKS enhanced iNOS expression. SSeCKS is also participated in regulation of PC12 cell viability. Loss of SSeCKS rescued PC12 cell viability, and excessive SSeCKS exacerbated the cell death upon conditioned medium and tumor necrosis factor-alpha exposure. This study delineates that SSeCKS may be important for host defenses in spinal inflammation and suggests a valuable molecular mechanism by which astrocytes modify neuronal viability during pathological states.