Truncated c-Myb expression in the human leukemia cell line TK-6.
The c-MYB proto-oncogene encodes a transcription factor which plays an important role in hematopoiesis. We detected truncated c-MYB mRNA (2.0 kb) and c-Myb protein (55 kDa) in the TK-6 cell line, which was established from a patient with chronic myelogenous leukemia in T cell blast crisis. Mutated c-MYB cDNA clone (WTK-1) was isolated from a TK-6 cell cDNA library and sequenced in its entirety. Compared with the wild-type human c-MYB sequence, the WTK-1 sequence diverged at the 3' ends of exons 9. A termination codon was present as the second codon downstream from the point of divergence and was followed by a previously unknown rearranged sequence. The conceptual protein encoded by WTK-1 (Myb(TK-6)) comprises 402 amino acids and lacks the negative regulatory domain of the normal c-Myb, reminiscent of the activated form of Myb protein. Luciferase reporter assay in NIH3T3 cells showed that the expression vector encoding Myb(TK-6) stimulated Myb-regulated mim-1 promoter more effectively than that encoding wild-type human c-Myb, suggesting that Myb(TK-6) is functional as a transcription factor, and thus as a potential transforming protein. Southern blot and mutant allele-specific polymerase chain reaction analyses showed that the same rearrangement of the c-MYB gene in TK-6 was present in late, but not in early, specimens obtained from the patient, indicating that this mutation had been acquired during disease progression.
Tomita
A
A
First Department of Internal Medicine, Nagoya University School of Medicine, Japan.
Watanabe
T
T
Kosugi
H
H
Ohashi
H
H
Uchida
T
T
Kinoshita
T
T
Mizutani
S
S
Hotta
T
T
Murate
T
T
Seto
M
M
Saito
H
H
D000328:Adult; D001483:Base Sequence; D001752:Blast Crisis / Q000378:metabolism; D002896:Chromosomes, Human, Pair 6 / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D020598:Proto-Oncogene Proteins c-myb; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D004273:DNA, Neoplasm; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators