Inhibition of phosphatidylinositol 3'-kinase/AKT signaling promotes apoptosis of primary effusion lymphoma cells.
OBJECTIVE
Phosphatidylinositol 3'-kinase (PI3'-kinase) can be activated by the K1 protein of Kaposi sarcoma-associated herpes virus (KSHV). However, the role of PI3'-kinase in KSHV-associated primary effusion lymphoma (PEL) is not known. To assess this, we studied survival and apoptosis in PEL cell lines following inhibition of PI3'-kinase.


METHODS
Constitutive activation of several targets of PI3-kinase and apoptotic proteins were determined by Western blot analysis using specific antibodies. We used LY294002 to block PI3'-kinase/AKT activation and assess apoptosis by flow cytometric analysis.


RESULTS
Blocking PI3'-kinase induced apoptosis in PEL cells, including BC1, BC3, BCBL1, and HBL6, whereas BCP1 was refractory to LY294002-induced apoptosis. LY294002-induced apoptosis did not seem to involve Fas/Fas-L but had an additive effect to CH11-mediated apoptosis. We also show that AKT/PKB is constitutively activated in all PELs and treatment with LY294002 causes complete dephosphorylation in all cell lines except BCP1 where a residual AKT phosphorylation remained after 24 hours of treatment. FKHR and GSK3 were also constitutively phosphorylated in PELs and treatment with LY294002 caused their dephosphorylation. Although inhibition of PI3'-kinase induced cleavage of BID in all cell lines, cytochrome c was released from the mitochondria and caspase-9 and caspase-3 were activated in LY294002-induced apoptotic BC1 but not in resistant BCP1. Similarly, XIAP, a target of AKT, was down-regulated after LY294002 treatment only in sensitive PEL cells.


CONCLUSIONS
Our data show that the PI3'-kinase pathway plays a major role in survival of PEL cells and suggest that this cascade may be a promising target for therapeutic intervention in primary effusion lymphomas.
Uddin
Shahab
S
King Fahad National Center for Children's Cancer and Research, Riyadh, Saudi Arabia. shahab@kfshrc.edu.sa
Hussain
Azhar R
AR
Al-Hussein
Khaled A
KA
Manogaran
Pulicat S
PS
Wickrema
Amitha
A
Gutierrez
Marina I
MI
Bhatia
Kishor G
KG
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry / Q000379:methods; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008223:Lymphoma / Q000201:enzymology / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D016066:Pleural Effusion, Malignant / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor / Q000276:immunology
D000911:Antibodies, Monoclonal; D002867:Chromones; D045304:Cytochromes c; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D038362:Glycogen Synthase Kinase 3; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014157:Transcription Factors; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor; C085126:FOXO1 protein, human; C496866:XIAP protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human