c-Myb is an essential downstream target for homeobox-mediated transformation of hematopoietic cells.
Abdominal-type HoxA genes in combination with Meis1 are well-documented on-cogenes in various leukemias but it is unclear how they exert their transforming function. Here we used a system of conditional transformation by an inducible mixed lineage leukemia-eleven-nineteen leukemia (MLL-ENL) oncoprotein to overexpress Hoxa9 and Meis1 in primary hematopoietic cells. Arrays identified c-Myb and a c-Myb target (Gstm1) among the genes with the strongest response to Hoxa9/Meis1. c-Myb overexpression was verified by Northern blot and quantitative reverse transcription-polymerase chain reaction (RT-PCR). Also MLL-ENL activated c-Myb through up-regulation of Hoxa9 and Meis1. Consequently, short-term suppression of c-Myb by small inhibitory RNA (siRNA) efficiently inhibited transformation by MLL-ENL but did not impair transformation by transcription factor E2A-hepatic leukemia factor (E2A-HLF). The anti c-Myb siRNA effect was abrogated by coexpression of a c-Myb derivative with a mutated siRNA target site. The introduction of a dominant-negative c-Myb mutant had a similar but weaker effect on MLL-ENL-mediated transformation. Hematopoietic precursors from mice homozygous for a hypo-morphic c-Myb allele were more severely affected and could be transformed neither by MLL-ENL nor by E2A-HLF. Ectopic expression of c-Myb induced a differentiation block but c-Myb alone was not transforming in a replating assay similar to Hoxa9/Meis1. These results suggest that c-Myb is essential but not sufficient for Hoxa9/Meis1 mediated transformation.
Hess
Jay L
JL
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, USA.
Bittner
Claudia B
CB
Zeisig
Deniz T
DT
Bach
Christian
C
Fuchs
Uta
U
Borkhardt
Arndt
A
Frampton
Jon
J
Slany
Robert K
RK
D000818:Animals; D015152:Blotting, Northern; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D020869:Gene Expression Profiling; D015973:Gene Expression Regulation, Leukemic / Q000235:genetics; D005982:Glutathione Transferase / Q000235:genetics; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics*; D007938:Leukemia / Q000235:genetics*; D051379:Mice; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins / Q000235:genetics; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015854:Up-Regulation
D005982:Glutathione Transferase; D018398:Homeodomain Proteins; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins; D020598:Proto-Oncogene Proteins c-myb; C000616392:Meis1 protein, mouse; C097899:homeobox protein HOXA9