Suppression of apoptosis and granulocyte colony-stimulating factor-induced differentiation by an oncogenic form of Cbl.
OBJECTIVE
The retroviral oncogene v-Cbl causes pre-B cell lymphomas and myeloid leukemias in mice, and its Drosophila homologue is oncogenic, causing enhanced receptor tyrosine kinase signaling. The human Cbl gene resides at 11q23. The aim of this study is to determine the effect of oncogenic Cbl on growth-regulating responses.


METHODS
The oncogenic mutant of Cbl (CblDelta1-357) was transfected into factor-dependent 32Dcl3 myeloid cells. Consequently, cell survival and differentiation were measured. Lyn, Syk, MAP kinase, and phosphatidylinositol 3'(PI3')-kinase activities, protein phosphorylation, Bcl-2 promoter activity, ubiquitination, and levels of Bcl-2, Bax, Bad, and Bcl-x(L) were determined. In addition, the effect of v-Cbl on TF-1 cell survival upon granulocyte-macrophage colony-stimulating factor withdrawal was studied.


RESULTS
32Dcl3 and TF-1 cells expressing v-Cbl showed resistance to apoptosis upon growth factor withdrawal, and 32Dcl3 cells completely failed to respond to granulocyte colony-stimulating factor's induction of differentiation. Basal activities of Lyn, Syk, and PI3'-kinase were elevated in the v-Cbl line. There was neither enhanced tyrosine phosphorylation of cellular protein content, Cbl, or Jak2, nor serine phosphorylation of MAP kinase or Akt. After factor withdrawal, the level of Bcl-2 was greater in v-Cbl cells than in control cells.


CONCLUSIONS
Neither increased Bcl-2 promoter activity nor decreased ubiquitination of Bcl-2 could account for increased Bcl-2 levels. v-Cbl-expressing 32Dcl3 cells were resistant to differentiation. v-Cbl suppresses apoptosis and differentiation, possibly through enhancement of Lyn, Syk, and PI3'-kinase activities and Bcl-2.
Sinha
S
S
Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
Jancarik
J
J
Roginskaya
V
V
Rothermund
K
K
Boxer
L M
LM
Corey
S J
SJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002470:Cell Survival / Q000187:drug effects; D002880:Chromosomes, Human, Pair 11; D004330:Drosophila; D004792:Enzyme Precursors / Q000378:metabolism; D019254:Genes, bcl-2; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D050722:Oncogene Protein v-cbl; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics / Q000502:physiology*; D017384:Sequence Deletion; D000072377:Syk Kinase; D014452:Ubiquitins / Q000378:metabolism; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; D019061:src-Family Kinases / Q000378:metabolism
C494819:BAD protein, human; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C494820:Bad protein, mouse; C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D002352:Carrier Proteins; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D050722:Oncogene Protein v-cbl; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D015682:Retroviridae Proteins, Oncogenic; D014452:Ubiquitins; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D020928:Mitogen-Activated Protein Kinases