Role of protein kinase C-delta (PKC-delta) in the generation of the effects of IFN-alpha in chronic myelogenous leukemia cells.
OBJECTIVE
The mechanisms by which interferon alpha (IFN-alpha) induces antileukemic responses in chronic myelogenous leukemia (CML) cells are not known. We examined whether a member of the protein kinase C (PKC) family of proteins, PKC-delta, is activated during treatment of BCR-ABL cells with IFN-alpha and participates in the induction of interferon responses.


METHODS
Immunoblots and immune complex kinase assays were performed to study the phosphorylation and activation of PKC-delta in response to IFN-alpha in CML-derived cell lines. The effects of pharmacological inhibition of PKC-delta on the suppressive effects of IFN-alpha on leukemic CFU-GM progenitors from CML patients were assessed by clonogenic assays in methylcellulose.


RESULTS
IFN-alpha treatment of the sensitive CML-derived KT-1 cell line resulted in phosphorylation of PKC-delta and activation of its kinase domain. Such phosphorylation/activation of PKC-delta was required for phosphorylation of Stat1 on serine 727, as inhibition of PKC-delta activity blocked the IFN-alpha-dependent serine phosphorylation of Stat1 and IFN-alpha-inducible gene transcription. IFN-alpha treatment strongly inhibited leukemic CFU-GM progenitor colony formation from bone marrow or peripheral blood of patients with CML, and such inhibition was reversed by concomitant treatment of the cells with the PKC-delta pharmacologic inhibitor rottlerin.


CONCLUSIONS
Taken altogether, our data demonstrate that PKC-delta plays a critical role in Type I IFN signaling in BCR-ABL expressing cells, acting as a serine kinase for Stat1, to regulate transcriptional activation of interferon-regulated genes and induction of antileukemic responses.
Kaur
Surinder
S
Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Northwestern University Medical School and Lakeside Veterans Affairs Medical Center, Chicago, Ill. 60611, USA.
Parmar
Simrit
S
Smith
Jessica
J
Katsoulidis
Efstratios
E
Li
Yongzhong
Y
Sassano
Antonella
A
Majchrzak
Beata
B
Uddin
Shahab
S
Tallman
Martin S
MS
Fish
Eleanor N
EN
Platanias
Leonidas C
LC
D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D047468:Immunoprecipitation; D016898:Interferon-alpha / Q000494:pharmacology* / Q000627:therapeutic use; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051745:Protein Kinase C-delta; D050794:STAT1 Transcription Factor; D012694:Serine / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism
D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D012694:Serine; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta