Journal of Cell Science, Vol 112, Issue 5 631-640, Copyright © 1999 by Company of Biologists

JOURNAL ARTICLES

Phosphatidylinositol 3-kinase translocation to the nucleus is induced by interleukin 1 and prevented by mutation of interleukin 1 receptor in human osteosarcoma Saos-2 cells

A Bavelloni, S Santi, A Sirri, M Riccio, I Faenza, N Zini, S Cecchi, A Ferri, P Auron, NM Maraldi and S Marmiroli
Laboratory of Cell Biology and Electron Microscopy, IOR, and Institute of Normal and Pathological Cytomorphology, CNR c/o IOR, Bologna 40136, Italy.

Although interleukin 1 (IL-1) functions have been extensively characterized, the mechanisms by which IL-1 signals are transduced from the plasma membrane to the nucleus are less known. Recent evidence indicates that phosphatidylinositol 3-kinase (PI3-kinase) could be activated by a direct association with the activated IL-1 receptor. In this study we analyzed the effects of IL-1 on the intracellular distribution of PI3-kinase in wild-type Saos-2 human osteosarcoma cells, and in cell clones overexpressing type I IL-1 receptor (IL-1RI). PI3-kinase intracellular distribution displays two distinct patterns. In quiescent cells, PI3-kinase is distributed through the cytoplasm, although a portion is present in the nucleus; following stimulation with IL-1, PI3-kinase is redistributed, increasing in the nuclear compartment. Both immunoblotting and immunofluorescence data indicate that IL-1 causes a rapid and transient translocation of PI3-kinase from the cytoplasm to the nucleus. This phenomenon is prevented by PI3-kinase inhibitors, suggesting that the maintenance of PI3-kinase activity is essential for IL-1-induced translocation. Indeed, in cell clones stably transfected with Y479F receptor mutant, in which the binding of the enzyme to the activated receptor is blocked, IL-1-induced PI3-kinase translocation to the nucleus is completely prevented. These data suggest that PI3-kinase translocation to the nucleus upon IL-1R activation is an early event in IL-1 signaling mechanism, and may be involved in transcriptional activation.
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