S100B-mediated inhibition of the phosphorylation of GFAP is prevented by TRTK-12.

S100B belongs to a family of calcium-binding proteins involved in cell cycle and cytoskeleton regulation. We observed an inhibitory effect of S100B on glial fibrillary acidic protein (GFAP) phosphorylation, when stimulated by cAMP or Ca2+/calmodulin, in a cytoskeletal fraction from primary astrocyte cultures. We found that S100B has no direct effect on CaM KII activity, the major kinase in this cytoskeletal fraction able to phosphorylate GFAP. The inhibition of GFAP phosphorylation is most likely due to the binding of S100B to the phosphorylation sites on this protein and blocking the access of these sites to the protein kinases. This inhibition was dependent on Ca2+. However, Zn2+ could substitute for Ca2+. The inhibitory effect of S100B was prevented by TRTK-12, a peptide that blocks S100B interaction with several target proteins including glial fibrillary acidic protein. These data suggest a role for S100B in the assembly of intermediate filaments in astrocytes.

Involvement of the S100B in cAMP-induced cytoskeleton remodeling in astrocytes: a study using TRTK-12 in digitonin-permeabilized cells.

1. Stellation of astrocytes in culture involves a complex rearrangement of microfilaments, intermediate filaments, and microtubules, which reflects in part the plasticity of these cells observed during development or after injury. 2. An astrocytic calcium-binding protein, S100B, has been implicated in the regulation of plasticity due to its ability to interact with cytoskeletal proteins. 3. We used digitonin-permeabilized astrocytes to introduce TRTK-12, a peptide that binds to the C-terminal of S100B and blocks its interaction with cytoskeletal proteins. 4. TRTK-12 was able to block cAMP-induced astrocyte stellation and this effect was dependent on the concentration of the peptide. These results support the idea that S100B has a modulatory role on astrocyte morphology.