Cell cycle arrest induced by engagement of B7-H4 on Epstein-Barr virus-positive B-cell lymphoma cell lines.
B7-H4 is a recently discovered B7 family member that has inhibitory effects on T-cell immunity. However, the reverse signalling mechanism of the B7-H4-expressing cells remains unclear. Previous work has shown that B7-H4 expression was enhanced on B cells following Epstein-Barr virus (EBV) infection, and engagement of cell-surface-expressed B7-H4 induces cell death of EBV-transformed B cells. Here we found that B7-H4 was constitutively expressed on EBV-positive lymphoma cells, Raji and IM-9 cells, but was not expressed on EBV-negative lymphoma cells (Ramos). Engagement of B7-H4 significantly reduced cell growth of Raji and IM-9 cells and resulted in cell cycle arrest at G0-G1 phase in a dose- and time-dependent manner. To clarify the mechanism of cell cycle arrest via activation of B7-H4, cell cycle regulatory factors were examined by reverse transcription-polymerase chain reaction and immunoblotting. We found that B7-H4 triggered down-regulation of CDK4/6 and up-regulation of p21 expression at both protein and RNA levels. Furthermore, CDK2 and cyclin E/D expression was down-regulated by B7-H4 triggering. Additionally, the down-regulation of phospho-AKT and phospho-cyclin E were clearly detected in B7-H4-activated Raji cells, but the phosphorylation of p53 was constitutively maintained. These results indicate that B7-H4-mediated signalling on EBV-positive B-cell lymphoma cells modulates the cell cycle through down-regulation of the AKT pathway. Consequently, B7-H4 may be a new potential target for use in EBV-positive lymphoma therapy.
Park
Ga Bin
GB
Department of Anatomy and Tumour Immunology, Inje University College of Medicine, Busan, Korea.
Song
Hyunkeun
H
Kim
Yeong-Seok
YS
Sung
Minjung
M
Ryu
Jeoung W
JW
Lee
Hyun-Kyung
HK
Cho
Dae-Ho
DH
Kim
Daejin
D
Lee
Wang J
WJ
Hur
Dae Y
DY
D000911:Antibodies, Monoclonal; D017209:Apoptosis; D018122:B7-1 Antigen / Q000276:immunology*; D002453:Cell Cycle; D002460:Cell Line; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000235:genetics; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D020031:Epstein-Barr Virus Infections / Q000276:immunology* / Q000378:metabolism; D004854:Herpesvirus 4, Human / Q000276:immunology*; D006801:Humans; D016393:Lymphoma, B-Cell / Q000276:immunology / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D060907:V-Set Domain-Containing T-Cell Activation Inhibitor 1
D000911:Antibodies, Monoclonal; D018122:B7-1 Antigen; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D060907:V-Set Domain-Containing T-Cell Activation Inhibitor 1; C475826:VTCN1 protein, human; D051058:Oncogene Protein v-akt