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2018 ; 11
(1
): 35
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The pioneer factor activity of c-Myb involves recruitment of p300 and induction
of histone acetylation followed by acetylation-induced chromatin dissociation
#MMPMID29954426
Fuglerud BM
; Ledsaak M
; Rogne M
; Eskeland R
; Gabrielsen OS
Epigenetics Chromatin
2018[Jun]; 11
(1
): 35
PMID29954426
show ga
BACKGROUND: The concept of pioneer transcription factors is emerging as an
essential part of the epigenetic regulation, taking place during cell development
and differentiation. However, the precise molecular mechanism underlying pioneer
factor activity remains poorly understood. We recently reported that the
transcription factor c-Myb acts as a pioneer factor in haematopoiesis, and a
point mutation in its DNA binding domain, D152V, is able to abrogate this
function. RESULTS: Here, we show that specific histone modifications, including
H3K27ac, prevent binding of c-Myb to histone tails, representing a novel effect
of histone modifications, namely restricting binding of a pioneer factor to
chromatin. Furthermore, we have taken advantage of the pioneer-defect D152V
mutant to investigate mechanisms of c-Myb's pioneer factor activity. We show that
c-Myb-dependent transcriptional activation of a gene in inaccessible chromatin
relies on c-Myb binding to histones, as well as on c-Myb interacting with the
histone acetyltransferase p300. ChIP assays show that both wild type and the
D152V mutant of c-Myb bind to a selected target gene at its promoter and
enhancer, but only wild-type c-Myb causes opening and activation of the locus.
Enhancement of histone acetylation restores activation of the same gene in the
absence of c-Myb, suggesting that facilitating histone acetylation is a crucial
part of the pioneer factor function of c-Myb. CONCLUSIONS: We suggest a pioneer
factor model in which c-Myb binds to regions of closed chromatin and then
recruits histone acetyltransferases. By binding to histones, c-Myb facilitates
histone acetylation, acting as a cofactor for p300 at c-Myb bound sites. The
resulting H3K27ac leads to chromatin opening and detachment of c-Myb from the
acetylated chromatin. We propose that the latter phenomenon, acetylation-induced
chromatin dissociation, represents a mechanism for controlling the dynamics of
pioneer factor binding to chromatin.