Constitutive activation of Jak/STAT proteins in Epstein-Barr virus-infected B-cell lines from patients with posttransplant lymphoproliferative disorder.
BACKGROUND
Posttransplant lymphoproliferative disease (PTLD) is a major complication after bone marrow and solid organ transplantation. The disease encompasses a spectrum of abnormal, Epstein-Barr virus (EBV)-associated B-cell proliferations. We have previously shown that EBV-infected, spontaneous lymphoblastoid cell lines (SLCL) derived from PTLD patients require autocrine interleukin (IL)-10 to proliferate. To determine if cytokine signal transduction is involved in the autonomous growth of the SLCL, the activation states of the Jak/STAT signaling pathway proteins were analyzed in three different SLCL, termed JB7, MF4, and VB4.


METHODS
The tyrosine phosphorylation (P-tyr) states of the Janus kinases (Jaks) and signal transducers and activators of transcription (STAT) proteins were examined by immunoprecipitation and immunoblot. Activated STAT dimer formation was determined by electromobility shift assays.


RESULTS
All three SLCL, but not the Daudi Burkitt's lymphoma B-cell line, expressed the four known Jak kinases constitutively tyrosine phosphorylated, with particularly high levels of P-tyr Jak1 in the JB7 line. STAT1 and STAT3, but not STAT2 or STAT5, are also constitutively activated in all SLCL. The ability of the activated STAT proteins to form DNA-binding dimers was confirmed by electromobility shift assay. The SLCL, but not the Daudi line, express activated STAT complexes composed of STAT1 and STAT3. Another EBV-infected B-cell line, isolated from a lymph node biopsy after kidney transplantation, is phenotypically similar to the other SLCL in both surface antigen and activated STAT1 and STAT3 expression.


CONCLUSIONS
These data support the presence of a constitutively active autocrine signaling pathway consistent with IL-10 in the SLCL.
Nepomuceno
Ronald R
RR
Department of Surgery, Division of Liver Transplantation, Stanford University School of Medicine, CA 94305-5492, USA.
Snow
Andrew L
AL
Robert Beatty
P
P
Krams
Sheri M
SM
Martinez
Olivia M
OM
D015703:Antigens, CD / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D020031:Epstein-Barr Virus Infections / Q000276:immunology*; D006801:Humans; D053613:Janus Kinase 1; D016031:Liver Transplantation / Q000276:immunology*; D008232:Lymphoproliferative Disorders / Q000276:immunology* / Q000821:virology; D020935:MAP Kinase Signaling System / Q000276:immunology*; D008894:Milk Proteins; D019000:Phosphotyrosine / Q000378:metabolism; D011183:Postoperative Complications / Q000276:immunology* / Q000821:virology; D011505:Protein-Tyrosine Kinases / Q000276:immunology*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism*
D015703:Antigens, CD; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; D053613:Janus Kinase 1