Protein kinase C delta and eta isoenzymes control the shedding of the interleukin 6 receptor alpha in myeloma cells.
The soluble interleukin 6 receptor alpha is an agonistic molecule of interleukin 6 (IL-6) and is important in the biology of multiple myeloma. More precisely, it potentiates the deleterious effects of IL-6 during tumour progression, facilitating angiogenesis and bone resorption. Because the mechanisms involved in the shedding of the interleukin 6 receptor alpha (IL-6Ralpha) in multiple myeloma are not known, we have investigated them in the XG-6 human myeloma cell line. Here we provide evidence that PMA-induced IL-6Ralpha shedding is controlled by a metalloproteinase and by protein kinase C (PKC) isoenzymes that do not require Ca(2+) for their activation. We show that XG-6 cells express PKC-delta, -eta and -zeta isoenzymes. However, after stimulation with PMA, only PKC-delta and PKC-eta are activated, as shown by their translocation to the membrane. Treatment with PMA induces an increase in PKC-delta phosphorylation in its active loop. In addition, by using rottlerin, a specific inhibitor of PKC-delta, we demonstrate that PKC-delta is involved in the PMA-induced shedding of IL-6Ralpha. With the use of UO126, a specific inhibitor of the mitogen-activated protein kinase (MAPK) pathway, we show that the PMA-induced IL-6Ralpha shedding is mediated in part by the MAPK pathway. Finally, whereas GF109203X, a general PKC inhibitor, inhibits the activation of ERK1/2 (extracellular signal-regulated protein kinase 1/2), rottlerin has no inhibitory effect, indicating that the Ras/MAPK activation is PKC-dependent but PKC-delta-independent. Taken together, these results suggest that the PMA-induced shedding of IL-6Ralpha is mediated by a PKC isoenzyme network.
Thabard
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U463 Institut de Biologie, 9 quai Moncousu, 44093 Nantes cedex 01, France.
Collette
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Bataille
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Amiot
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D000098:Acetophenones / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001578:Benzopyrans / Q000494:pharmacology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D007527:Isoenzymes / Q000502:physiology*; D020935:MAP Kinase Signaling System; D008856:Microscopy, Fluorescence; D009101:Multiple Myeloma / Q000378:metabolism*; D009389:Neovascularization, Pathologic; D010766:Phosphorylation; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000502:physiology*; D051745:Protein Kinase C-delta; D021381:Protein Transport; D019947:Receptors, Interleukin-6 / Q000378:metabolism*; D013347:Subcellular Fractions; D013755:Tetradecanoylphorbol Acetate; D014407:Tumor Cells, Cultured
D000098:Acetophenones; D000911:Antibodies, Monoclonal; D001578:Benzopyrans; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D020033:Protein Isoforms; D019947:Receptors, Interleukin-6; C085746:rottlerin; C081975:protein kinase C eta; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium