Dystroglycan (DG) complex, composed of alpha DG and beta DG, provides a link between the extracellular matrix (ECM) and cortical cytoskeleton. Although the proteolytic processing of beta DG was reported in various physiological and pathological conditions, its exact mechanism remains unknown. In this study, we addressed this issue using the cell culture system of rat schwannoma cell line RT4. We found that the Culture medium of RT4 cells was enriched with the protease activity that degrades the fusion protein construct of the extracellular domain of PDG specifically. This activity was Suppressed by the inhibitor of matrix metalloproteinase-2 (MMP-2) and MMP-9, but not by the inhibitors of MMP-1, MMP-3, MMP-8, and MMP-13. Zymography and RT-PCR analysis showed that RT4 cells secreted MMP-2 and MMP-9 into the Culture medium. Finally, active MMP-2 and MMP-9 enzymes degraded the fusion protein construct of the extracellular domain of DG. These results indicate (I) that RT4 cells secrete the protease activity that degrades the extracellular domain of DG specifically and (2) that MMP-2 and MMP-9 may be involved in this process. (c) 2006 Elsevier Inc. All riulits reserved.