Transformation of hematopoietic cells by BCR/ABL requires activation of a PI-3k/Akt-dependent pathway.
The BCR/ABL oncogenic tyrosine kinase activates phosphatidylinositol 3-kinase (PI-3k) by a mechanism that requires binding of BCR/ABL to p85, the regulatory subunit of PI-3k, and an intact BCR/ABL SH2 domain. SH2 domain BCR/ABL mutants deficient in PI-3k activation failed to stimulate Akt kinase, a recently identified PI-3k downstream effector with oncogenic potential, but did activate p21 RAS and p70 S6 kinase. The PI-3k/Akt pathway is essential for BCR/ABL leukemogenesis as indicated by experiments demonstrating that wortmannin, a PI-3k specific inhibitor at low concentrations, suppressed BCR/ABL-dependent colony formation of murine marrow cells, and that a kinase-deficient Akt mutant with dominant-negative activity inhibited BCR/ABL-dependent transformation of murine bone marrow cells in vitro and suppressed leukemia development in SCID mice. In complementation assays using mouse marrow progenitor cells, the ability of transformation-defective SH2 domain BCR/ABL mutants to induce growth factor-independent colony formation and leukemia in SCID mice was markedly enhanced by expression of constitutively active Akt. In retrovirally infected mouse marrow cells, the BCR/ABL mutant lacking the SH2 domain was unable to upregulate the expression of c-Myc and Bcl-2; in contrast, expression of a constitutively active Akt mutant induced Bcl-2 and c-Myc expression, and stimulated the transcription activation function of c-Myc. Together, these data demonstrate the requirement for the BCR/ABL SH2 domain in PI-3k activation and document the essential role of the PI-3k/Akt pathway in BCR/ABL leukemogenesis.
Skorski
T
T
Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.
Bellacosa
A
A
Nieborowska-Skorska
M
M
Majewski
M
M
Martinez
R
R
Choi
J K
JK
Trotta
R
R
Wlodarski
P
P
Perrotti
D
D
Chan
T O
TO
Wasik
M A
MA
Tsichlis
P N
PN
Calabretta
B
B
D000818:Animals; D001853:Bone Marrow / Q000473:pathology; D001854:Bone Marrow Cells; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D004789:Enzyme Activation; D016044:Fusion Proteins, bcr-abl / Q000235:genetics*; D019254:Genes, bcl-2; D016259:Genes, myc; D007942:Leukemia, Experimental / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D008099:Liver / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D013154:Spleen / Q000473:pathology
D016044:Fusion Proteins, bcr-abl; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt