VEGF-induced phosphorylation of Bcl-2 influences B lineage leukemic cell response to apoptotic stimuli.
Post-translational modification of Bcl-2 protein has been described in a variety of cell models with effects varying from enhanced to abrogated function. In this study, we demonstrated that Bcl-2 was constitutively phosphorylated in several hematopoietic tumor cell lines and in primary ALL cells. Increased phosphorylation of Bcl-2 protein in the JM1 ALL cell line, achieved by expression of the phosphomimetic Bcl-2 construct S70E, enhanced JM1 cell chemoresistance. In contrast, initiation of JM1 cell apoptosis was coincident with dephosphorylation of Bcl-2 and elevated protein phosphatase 2A activity. S70E expression also diminished tBid-mediated cytochrome c release and blunted chemotherapy-induced activation of caspases-9 and -3 in JM1 cells. To determine whether soluble factors produced by stromal cells in the bone marrow influence phosphorylation of Bcl-2 protein, a panel of recombinant cytokines was evaluated. Of those tested, vascular endothelial growth factor (VEGF) induced phosphorylation of Bcl-2 protein and blunted cytochrome c release during chemotherapy or tBid treatment of ALL cells. In contrast, JM1 cells transfected with S70A, resulting in expression of Bcl-2 protein that cannot be phosphorylated, were not efficiently rescued from apoptosis by VEGF. These observations suggest that optimal protection of leukemic cells by VEGF may require activation of a pathway that includes Bcl-2 phosphorylation.
Wang
L
L
Department of Pediatrics, Robert C. Byrd Health Sciences Center, School of Medicine, West Virginia University, Morgantown, WV 26506, USA.
Chen
L
L
Benincosa
J
J
Fortney
J
J
Gibson
L F
LF
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D002051:Burkitt Lymphoma / Q000188:drug therapy / Q000378:metabolism*; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000494:pharmacology; D045304:Cytochromes c / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D018922:HL-60 Cells; D019337:Hematologic Neoplasms / Q000235:genetics*; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D017154:Stromal Cells / Q000378:metabolism; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A / Q000493:pharmacokinetics*
D017077:Culture Media, Conditioned; D019253:Proto-Oncogene Proteins c-bcl-2; D042461:Vascular Endothelial Growth Factor A; D045304:Cytochromes c; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases