Regulation of the Lysosome-Associated Membrane Protein in a Sucrose Model of Lysosomal Storage

Lysosomal biogenesis is a complex process requiring the coordinated expression and colocalization of numerous soluble and membrane proteins. In storage disorders, lysosomal biogenesis is regulated at least partially at, or prior to, the level of mRNA. We have used the sucrosome storage model to determine the sites of regulation of LAMP-1, a major constituent of the lysosomal membrane. A six- to eightfold increase in the level of LAMP-1 mRNA and protein was observed in response to sucrose storage. The half-life of LAMP-1 mRNA was not significantly different in cells grown in the absence or presence of sucrose, implying that the increase observed in mRNA levels reflects an increase in the rate of transcription. The sixfold increase in mRNA did not translate into an increase in LAMP-1 synthesis, indicating an overall decrease in the translational yield in sucrosome cells. The elevation of LAMP-1 protein levels in storage cells was due in large part to a threefold increase in the half-life of the protein. These results are discussed in view of the current understanding of lysosomal biogenesis and how this process is altered during storage.