CLN3 protein regulates lysosomal pH and alters intracellular processing ofAlzheimer's amyloid-beta protein precursor and cathepsin D in human cells

Maintenance of the appropriate pH in the intracellular vacuolar compartment s is essential for normal cell function. Here, we report that CLN3 protein, which is associated with the juvenile form of neuronal ceroid lipofuscinos is (JNCL), participates in lysosomal pH homeostasis in human cells. We show that CLN3 protein increases lysosomal pH in cultured human embryonal kidne y cells, whereas inhibition of CLN3 protein synthesis by antisense approach acidifies lysosomal compartments. These changes in lysosomal pH are suffic ient to exert a significant biological effect and modify intracellular proc essing of amyloid-beta protein precursor and cathepsin D, model proteins wh ose metabolism is influenced by the pH of acidic organelles. Mutant CLN3 pr otein (R334C) that is associated with the classical JNCL phenotype was devo id of biological activities of wild-type CLN3 protein. These data suggest t hat the pathogenesis of juvenile neuronal ceroid lipofuscinosis is associat ed with altered acidification of lysosamal compartments. Furthermore, our s tudy indicates that CLN3 protein affects metabolism of proteins essential f or cell functions, such as amyloid-P protein precursor, implicated in Alzhe imer's disease pathogenesis. (C) 2000 Academic Press.