Actin stabilization by jasplakinolide enhances apoptosis induced by cytokine deprivation

Participation of the actin cytoskeleton in the transduction of proliferativ e signals has been established through the use of compounds that disrupt th e cytoskeleton, To address the possibility that actin also participates in the transduction of an apoptotic signal, we have studied the response of th e murine interleukin 2 (IL-2)-dependent T cell line CTLL-20 to treatment wi th the actin-binding compound jasplakinolide upon IL-2 deprivation, Like ph alloidin, jasplakinolide stabilizes F-actin and promotes actin polymerizati on, Treatment of CTLL-20 cells with jasplakinolide, in the presence or abse nce of recombinant human IL-2, altered actin morphology as assessed by conf ocal fluorescence microscopy. Jasplakinolide was not toxic to CTLL-20 cells , nor was apoptosis induced in the presence of exogenous recombinant human IL-2, However, actin stabilization at the time of IL-2 deprivation enhanced apoptosis by changing the time at which CTLL-20 cells committed to the apo ptotic pathway. This effect of jasplakinolide correlated with its ability t o stabilize polymerized actin, as treatment with a synthetic analog of jasp lakinolide with a greatly reduced ability to bind actin, jasplakinolide B, did not enhance apoptosis. The enhancement occurred upstream of the inducti on of caspase-3-like activity and could be inhibited by the overexpression of the anti-apoptotic protein Bcl-x(L), These data suggest that the actin c ytoskeleton plays an active role in modulating lymphocyte apoptosis induced by cytokine deprivation.