The lipid raft-bound alkaline phosphatase activity increases and the level of transcripts remains unaffected in liver of merosin-deficient LAMA2dy mouse

Alkaline phosphatase (AP) and other proteins add glycosylphosphatidylinositol (GPI) before addressing to raft domains of the cell membrane. Our previous report showing an increased density of lipid rafts in muscle of dystrophic Lama2dy mice prompted us to compare livers of normal (NL) and dystrophic mice (DL) for their levels of rafts. With this aim, hepatic rafts were isolated as Triton X-100 resistant membranes, and identified by their abundance of flotillin-2, alkaline phosphatase (AP) and other raft markers. The comparable abundance of cholesterol and flotillin-2 in rafts of NL and DL contrasted with the double AP activity both in rafts of DL and whole DL The AP mRNA level was the same in NL and DL Sedimentation analysis profiles revealed AP activity of NL distributed between dimeric (dAP) and monomeric AP (mAP), whose proportions and lectin-binding extent changed in DL The increased AP activity and changed AP glycosylation in DL, the prevalence of mAP in NL and the enhanced stability of dAP in DL demonstrated the critical role that glycosylation and oligomerization play for AP catalysis. The higher AP activity of DL probably arises from dystrophy-associated changes in glycosyl transferases, which alter AP glycosylation and subunit folding with profitable effects for AP stability and catalysis. (c) 2014 Published by Elsevier Ireland Ltd.