PKC-δ mediates interferon-α-induced apoptosis through c-Jun NH2-terminal kinase activation

IFN-α caused activation of PKC-δ in Daudi B lymphoma cells and myeloma U266 cells, as detected by Western blotting using a monoclonal antibody specific for the phosphorylated form of PKC-δ. The dominant-negative form of mutant PKC-δ (dnPKC-δ) reduced the IFN-α-induced JNK1 activation, TRAIL promoter activity, loss of mitochondrial membrane potential (ΔΨm), and increase in propidium iodide (PI) positive cells. The IFN-α-induced activation of JNK1 and the TRAIL promoter was also attenuated by the PKC-δ inhibitor rottlerin. Moreover, a constitutively active form of mutant PKC-δ enhanced the IFN-α-induced TRAIL promoter activity and loss of ΔΨm in Daudi B lymphoma cells. In addition, IFN-α-induced Ser727 phosphorylation of Stat1 was also abrogated by dnPKC-δ.IFN-α induced JNK1 activation via PKC-δ, leading to upregulation of TRAIL. The interaction of the consequent enhanced TRAIL expression with TRAIL-receptor results in a loss of ΔΨm and increase in PI positive cells. The IFN-α-induced apoptotic events may also be affected by the Ser727-Stat1 induced by PKC-δ-mediated signaling component(s).Type I interferon-α (IFN-α) has been employed for treatment of patients with some tumors including hairy cell leukemia, chronic myelogenous leukemia, melanoma, and renal cell cancer [1,2]. The anti-tumor action of IFN-α is mediated at least by induction of apoptosis or inhibition of cell growth [3-6]. However, the detailed molecular mechanism(s) by which IFN-α induces apoptosis remain largely unclear. The interaction of IFN-α with its receptor results in transphosphorylation of receptor-associated Janus kinases (Jak1 and Tyk2), leading to tyrosine phosphorylation of critical residues on the receptors [7,8]. The activated Jak1/Tyk2 phosphorylate and activate signal transducers and activators of transcription (STAT), which in turn translocates to the nucleus to regulate gene transcription [8].In addition to Jak/Stat pathways, mitogen-activated protein kinases (MAPKs) including extrace