14-3-3γ affects dynamics and integrity of glial filaments by binding to phosphorylated GFAP

Recent findings indicated a protective role of GFAP in ischemic brain, injured spinal cord, and in neurodegenerative disease. We previously demonstrated that 14-3-3gamma, once thought to be neuronal specific, was up-regulated by ischemia in astrocytes and may play a specific protective role in astrocytes. Here we report that 14-3-3gamma associates with both soluble and filamentous GFAP in a phosphorylation- and cell-cycle-dependent manner in primary cultured astrocytes. The amount of association increases during G2/M phase due to more phosphorylated GFAP. Moreover, this interaction is independent of vimentin, another type III intermediate filament protein in astrocytes which forms glial filaments with GFAP. A series of domain deletion mutants and substitution mutations at phosphorylation sites (from serine to alanine) on GFAP demonstrated that serine 8 in the head domain is essential for the direct association of GFAP to 14-3-3gamma. Overexpression of 14-3-3gamma destroyed the integrity and affected the movement of GFAP intermediate filaments. This data demonstrates that 14-3-3gamma contributes to the regulation of dynamics of GFAP filaments, which may contribute to the stability of the cytoskeleton and the mechanisms of central nervous system neurodegenerative disease.