Biochemical characterization of MLC1 protein in astrocytes and its association with the dystrophin-glycoprotein complex.

MLC1 gene mutations have been associated with megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare neurologic disorder in children. The MLC1 gene encodes a membrane protein (MLC1) with unknown function which is mainly expressed in astrocytes. Using a newly developed anti-human MLC1 polyclonal antibody, we have investigated the biochemical properties and localization of MLC1 in cultured astrocytes and brain tissue and searched for evidence of a relationship between MLC1 and proteins of the dystrophin-glycoprotein complex (DGC). Cultured astrocytes express two MLC1 components showing different solubilisation properties and subcellular distribution. Most importantly, we show that the membrane-associated component of MLC1 (60-64 kDa) localizes in astrocytic lipid rafts together with dystroglycan, syntrophin and caveolin-1, and co-fractionates with the DGC in whole rat brain tissue. In the human brain, MLC1 protein is expressed in astrocyte processes and ependymal cells, where it colocalizes with dystroglycan and syntrophin. These data indicate that the DGC may be involved in the organization and function of the MLC1 protein in astrocyte membranes.