BCR gene expression blocks Bcr-Abl induced pathogenicity in a mouse model.
It is well accepted that the Bcr-Abl oncoprotein encoded by the Philadelphia chromosome is responsible for causing chronic myelogenous leukemia (CML). We have previously demonstrated that expression of Bcr interferes with the oncogenic effects of Bcr-Abl. To examine the effects of increased Bcr expression on Bcr-Abl oncogenic effects in a more physiological system, we tested the leukemogenic potential of a clone of K562 cells (K6 K562) containing an inducible BCR gene in NOD/scid mice. In this clone, the BCR gene was placed under the control of a tetracycline (Tet) repression system with a cytomegalovirus (CMV) promoter. Induction of exogenous Bcr protein by removal of Tet from the culture medium caused a dramatic increase in Bcr serine kinase activity, yielding predominantly phosphoserine Bcr, despite the presence of Bcr-Abl in the kinase reaction mixture. Prior to induction, the endogenous Bcr was predominantly in the phosphotyrosine form because of phosphorylation by Bcr-Abl, which we previously have shown suppresses Bcr serine/threonine kinase activity. Injection of K6 K562 cells into NOD/scid mice under conditions where BCR expression was suppressed resulted in death or terminal illness in 100% of the mice within 35 days after injection. These mice had a severe wasting syndrome characterized by atrophy of bone marrow hematopoiesis, and/or neoplasia of liver, bone marrow and spleen. Neoplastic spleens from these mice usually contained b3a2 Bcr-Abl transcripts. In contrast, induction of BCR expression at the time of injection allowed 80% survival; these healthy mice had no detectable microscopic lesions in blood forming organs. This difference in survival was significant with P<0.0001. Of interest, mice that were fed Tet for 19 days to initiate the disease syndrome and then released from the BCR transcriptional block had a significantly better survival pattern than mice exposed to Tet throughout the entire period. Moreover, 30% of these mice (three mice) survived through day 50. We conclude from these findings that BCR gene expression strongly inhibits the oncogenic effects of Bcr-Abl in NOD/scid mice, yielding healthy mice in most cases.
Lin
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Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA.
Monaco
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G
Sun
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Liu
J
J
Lin
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H
Stephens
C
C
Belmont
J
J
Arlinghaus
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RB
D000818:Animals; D016044:Fusion Proteins, bcr-abl / Q000633:toxicity*; D005786:Gene Expression Regulation; D006801:Humans; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics*; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D015513:Oncogene Proteins / Q000235:genetics*; D009857:Oncogenes; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051562:Proto-Oncogene Proteins c-bcr; D012333:RNA, Messenger / Q000032:analysis; D012694:Serine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D014443:Tyrosine; D012694:Serine; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl; C496613:BCR protein, human; C496614:Bcr protein, mouse; D051562:Proto-Oncogene Proteins c-bcr