title: Enhanced proliferative potential of hematopoietic cells expressing degradation-resistant c-Myb mutants.
abstract: The c-myb gene encodes a transcription factor required for proliferation, differentiation, and survival of hematopoietic cells. Expression of c-Myb is often increased in hematological malignancies, but the underlying mechanisms are poorly understood. We show here that c-Myb has a longer half-life (at least 2-fold) in BCR/ABL-expressing than in normal hematopoietic cells. Such enhanced stability was dependent on a phosphatidylinositol 3-kinase (PI-3K)/Akt/GSKIIIbeta pathway(s) as indicated by the suppression of c-Myb expression upon treatment with PI-3K inhibitors or co-expression with dominant negative Akt or constitutively active GSKIIIbeta. Moreover, inhibition of GSKIIIbeta by LiCl enhanced c-Myb expression in parental 32Dcl3 cells. Compared with wild type c-Myb, three mutants (delta(358-452), delta(389-418), and L389A/L396A c-Myb) of the leucine zipper domain had increased stability. However, only expression of delta(358-452) was not affected by inhibition of the PI-3K/Akt pathway and was not enhanced by a proteasome inhibitor, suggesting that leucine zipper-dependent and -independent mechanisms are involved in the regulation of c-Myb stability. Indeed, delta(389-418) carrying four lysine-to-alanine substitutions (delta(389-418) K387A/K428A/K442A/K445A) was as stable as delta(358-452) c-Myb. Compared with full-length c-Myb, constitutive expression of delta(358-452) and delta(389-418) c-Myb in Lin-Sca-1+ mouse marrow cells increased cytokine-dependent primary and secondary colony formation. In K562 cells, expression of delta(358-452), delta(389-418), and L389A/L396A c-Myb led to enhanced proliferation after STI571 treatment. Thus, enhanced stability of c-Myb by activation of PI-3K-dependent pathway(s) might contribute to the higher proliferative potential of BCR/ABL-expressing and, perhaps, other leukemic cells.
authors.affiliation: Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Francesca
authors.initials: F
authors.lastname: Corradini
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cesi
authors.forename: Viviana
authors.initials: V
authors.lastname: Bartella
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Pani
authors.forename: Rita
authors.initials: R
authors.lastname: Bussolari
authors.forename: Olivia
authors.initials: O
authors.lastname: Candini
authors.forename: Bruno
authors.initials: B
authors.lastname: Calabretta
mesh_terms: D000409:Alanine / Q000737:chemistry; D000818:Animals; D017209:Apoptosis; D001549:Benzamides; D015152:Blotting, Northern; D015153:Blotting, Western; D002453:Cell Cycle; D002454:Cell Differentiation; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D005799:Genes, Dominant; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D000068877:Imatinib Mesylate; D007377:Interleukin-3 / Q000378:metabolism; D020014:K562 Cells; D007930:Leucine / Q000737:chemistry; D018021:Lithium Chloride / Q000494:pharmacology; D008239:Lysine / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D001549:Benzamides; D007377:Interleukin-3; D010879:Piperazines; D020598:Proto-Oncogene Proteins c-myb; D011743:Pyrimidines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D025801:Ubiquitin; D000068877:Imatinib Mesylate; D019869:Phosphatidylinositol 3-Kinases; D018021:Lithium Chloride; D007930:Leucine; D008239:Lysine; D000409:Alanine