Complex modulation of peptidolytic activity of cathepsin D by sphingolipids

Cathepsin D is an aspartic peptidase involved in cellular processes including proliferation and apoptosis and implicated in human pathologies such as cancer and neurodegeneration. Our knowledge about the relationship between proteolysis and bioactive sphingolipids is still very limited. Here, we describe a complex pattern of modulation of the peptidolytic activity of cathepsin D by sphingolipids. A panel of sphingolipid derivatives was screened in a FRET-based assay; these molecules demonstrated negative or positive modulation of cathepsin D peptidolytic activity, depending on the sphingolipid structure. Certain sphingosines and ceramides inhibited cathepsin D in the submicromolar range, and structural requirements for this inhibitory effect were evaluated. The interaction of cathepsin D with sphingolipids was also demonstrated by fluorescence polarization measurements and determined to follow a competitive inhibition mode. In contrast, monoester phosphosphingolipids, especially ceramide-1-phosphate, were identified as activators of cathepsin D peptidolytic activity at submicromolar concentrations. Thus, sphingolipids and phosphosphingolipids, known to be antagonistic in their cell-signaling functions, displayed opposite modulation of cathepsin D. Sphingolipid-based modulators of cathepsin D are potentially involved in the control of cathepsin D-dependent processes and might serve as a scaffold for the development of novel regulators of this therapeutic target.