Ceramide Activated Protein Phosphatases

Ceramide constitutes a family of closely related molecules that function as bioeffector lipids with roles in the regulation of stress responses and growth/death of various human cancer cells. Critical missing elements in our understanding of ceramide stems from the lack of molecularly-defined targets of action and from defining compartment-specific functions of ceramides. Studies in our lab supported by this project have identified ceramide-activated Ser–Thr phosphatases (CAPPs), specifically PP1 and PP2A as direct targets activated by ceramide in vitro. Studies in cells have also shown that various ceramide-inducing stimuli (e.g. TNF, UV, lipotoxic agents) induce dephosphorylation of several substrates in a ceramide-dependent manner. However, not all stimuli induce all dephosphorylations, presumably due to their activation of distinct pathways in distinct subcellular compartments. Recent results have provided us a breakthrough in defining a specific pathway of ceramide generation at the plasma membrane (PM). Here, we will investigate the hypothesis that ceramide generated at the PM acutely activates PP1ca that leads to the dephosphorylation of ezrin and other proteins. This results in a compartment-specific role for ceramide in regulating cell adhesion and migration. We will address these aims: Aim 1. Define a novel pathway of ceramide generation at the PM leading to ezrin dephosphorylation though activation of PP1ca. Here we will investigate the specific hypothesis that PM ceramide regulates a specific form of dimeric PP1c to mediate ezrin dephosphorylation, independent of raft formation. Aim 2. Identify specific cellular programs coupled to compartmentalized ceramide/CAPPs. Here we will investigate the specific hypothesis that PM ceramide, in contrast to ceramide formed in other compartments, regulates cell adhesion and migration. Taken together, these approaches should result, for the first time, in clearly defining a specific, direct, and relevant target for ceramide action (PP1) with a specific function in mediating the effects of PM ceramide on cell adhesion and migration.