c-Myb and p300 Regulate Hematopoietic Stem Cell Proliferation and Differentiation

Abstract

Precise control of hematopoietic stem cell (HSC) proliferation and differentiation is needed to maintain a lifetime supply of blood cells. Using genome-wide ENU mutagenesis and phenotypic screening, we have identified a mouse line that harbors a point mutation in the transactivation (TA) domain of the transcription factor c-Myb (M303V), which reduces c-Myb-dependent TA by disrupting its interaction with the transcriptional coactivator p300. The biological consequences of the c-Myb(M303V/M303V) mutation include thrombocytosis, megakaryocytosis, anemia, lymphopenia, and the absence of eosinophils. Detailed analysis of hematopoiesis in c-Myb(M303V/M303V) mice reveals distinct blocks in T cell, B cell, and red blood cell development, as well as a remarkable 10-fold increase in the number of HSCs. Cell cycle analyses show that twice as many HSCs from c-Myb(M303V/M303V) animals are actively cycling. Thus c-Myb, through interaction with p300, controls the proliferation and differentiation of hematopoietic stem and progenitor cells.

Mutations in Multiple Domains of c-Myb Disrupt Interaction with CBP/p300 and Abrogate Myeloid Transforming Ability

“…The M303V mutation has also been reported to alter the ability of c-Myb to recruit the highly homologous p300 coactivator, resulting in decreased transactivation (5). Loss of transforming activity of these mutants is similarly accompanied by severely impaired transactivation abilities as shown by our data and previous reports (5,38).…”

“…6) were carried out. The M303V and L302A mutations have been shown to decrease or abolish the transactivation ability of the protein (5,38). As expected, c-Myb CT3 and c-Myb L3,4P showed enhanced transactivation abilities compared with WT (36), and we confirmed that the L302A mutation abolishes transactivation by Myb (Fig.…”

“…1B. The L302A and M303V mutations have been reported previously to interfere with the binding of CBP/p300 to c-Myb (5,38,39). The c-Myb 3M mutant has three amino acid substitutions in the DBD (I91N, L106H, and V117D) and has been reported to decrease the interaction of c-Myb with the N-CoR, mSin3a, and c-Ski corepressor molecules (23).…”

“…c-myb-null mice display abnormal fetal liver hematopoiesis and die by day 15 of gestation due to severe anemia (3). Moreover, ENU mutagenesis studies in mice revealed point mutations in myb that resulted in hypomorphic alleles and consequent hematopoietic irregularities (4,5).…”

Expansion of hematopoietic stem/progenitor cells

“…In 1999, GATA proteins were found to occupy the b3/b4 region of PU.1 to block PU.1 interaction with its coactivator c-Jun and thereby inhibit the transcription of PU.1 [39]. In addition to PU.1 and GATA, cMyb was reported to control the proliferation and differentiation of HSPCs through interaction with transcriptional coactivator p300 [40]. C-Myb M303V/M303V mouse line that harbors a point mutation in the transcription factor c-Myb (M303V) contained 5-to 10-fold more phenotypic HSCs.…”