Physical association and functional relationship between protein kinase Cζ and the actin cytoskeleton

Protein kinase C (PKC) was initially identified as a serine/threonine protein kinase dependent on calcium and phospholipids and shown to be involved in intracellular signaling pathways. PKC isoforms have been classified into four groups: Ca2+‐dependent conventional PKC α, βI, βII, γ; Ca2+‐independent, novel PKC δ, ϵ, η, θ; atypical PKCζ, λ, ι which are not activated by Ca2+ or diacylglycerol, and the recently discovered PKCμ. We reported that activation of the ζ PKC isoform is an important step in interleukin‐2 (IL‐2)‐mediated proliferation (Gómez, J., Pitton, C., García, A., Martínez, A., Silva, A. and Rebollo, A., Exp. Cell Res. 1995. 218: 105.). ζPKC is also required for mitogenic activation of fibroblasts and for the maturation pathway activated by insulin and Ras. Contradictory results have been reported regarding the subcellular redistribution of ζPKC upon activation. We report here, using confocal microscopy, that IL‐2 induces expression, translocation and association of ζPKC to a structure coincident with the actin cytoskeleton. Furthermore, we show that ζPKC has a role in maintaining the integrity of the actin cytoskeletal structure in IL‐2‐stimulated cells. On the contrary, ζPKC is not involved in the actin cytoskeleton organization when cells are maintained in IL‐4, confirming our previous results showing that IL‐4‐induced signal transduction is PKC independent.