CERAMIDE Ceramide Promotes Stress Fiber Formation

Abstract: Ceramide signaling has been implicated in such processes as programmed cell death, differentiation, and cell proliferation. Hanna et al. provide evidence that ceramide may be one of the mediators of tumor necrosis factor- (TNF-) signaling that results in the formation of stress fibers in Rat2 fibroblasts. Treatment of the cells with TNF-, a cell-permeable ceramide, or sphingomyelinase led to the formation of stress fibers and the tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin. TNF- and ceramide both stimulated the interaction of phosphatidylinositol 3-kinase (PI 3K) with FAK. The formation of stress fibers and paxillin phosphorylation were completely inhibited in cells exposed to ceramide or sphingomyelinase by treatment of the cells with the PI 3K inhibitor LY 294002 and partially inhibited in cells exposed to TNF-. TNF- and ceramide stimulate sphingosine kinase activity, which phosphorylates sphingosine, forming the active compound sphingosine 1-phosphate. If sphingosine kinase activity is inhibited, then stress fiber formation is inhibited in response to TNF- or ceramide. Inhibition of sphingosine kinase also leads to the reorganization of the actin cytoskeleton to form a dense cortical network. Additional experiments indicate that RhoA and Ras guanosine triphosphatases are also involved downstream of the ceramide-induced cytoskeletal rearrangements and that dominant-negative Ras can inhibit the activation of sphingosine kinase. Thus, ceramide and bioactive sphingolipids appear to be involved in the pathway from TNF- to stress fiber formation.

A. N. Hanna, L. G. Berthiaume, Y. Kikuchi, D. Begg, S. Bourgoin, D. N. Brindley, Tumor necrosis factor- induces stess fiber formation through ceramide production: Role of sphingosine kinase. Mol. Biol. Cell 12, 3618-3630 (2001). [Abstract] [Full Text]