Huntingtin facilitates polycomb repressive complex 2.
Huntington's disease (HD) is caused by expansion of the polymorphic polyglutamine segment in the huntingtin protein. Full-length huntingtin is thought to be a predominant HEAT repeat alpha-solenoid, implying a role as a facilitator of macromolecular complexes. Here we have investigated huntingtin's domain structure and potential intersection with epigenetic silencer polycomb repressive complex 2 (PRC2), suggested by shared embryonic deficiency phenotypes. Analysis of a set of full-length recombinant huntingtins, with different polyglutamine regions, demonstrated dramatic conformational flexibility, with an accessible hinge separating two large alpha-helical domains. Moreover, embryos lacking huntingtin exhibited impaired PRC2 regulation of Hox gene expression, trophoblast giant cell differentiation, paternal X chromosome inactivation and histone H3K27 tri-methylation, while full-length endogenous nuclear huntingtin in wild-type embryoid bodies (EBs) was associated with PRC2 subunits and was detected with trimethylated histone H3K27 at Hoxb9. Supporting a direct stimulatory role, full-length recombinant huntingtin significantly increased the histone H3K27 tri-methylase activity of reconstituted PRC2 in vitro, and structure-function analysis demonstrated that the polyglutamine region augmented full-length huntingtin PRC2 stimulation, both in Hdh(Q111) EBs and in vitro, with reconstituted PRC2. Knowledge of full-length huntingtin's alpha-helical organization and role as a facilitator of the multi-subunit PRC2 complex provides a novel starting point for studying PRC2 regulation, implicates this chromatin repressive complex in a neurodegenerative disorder and sets the stage for further study of huntingtin's molecular function and the impact of its modulatory polyglutamine region.
Seong
Ihn Sik
IS
Center for Human Genetic Research, Massachusetts General Hospital, 185 Cambridge Street, Boston, MA 02114, USA.
Woda
Juliana M
JM
Song
Ji-Joon
JJ
Lloret
Alejandro
A
Abeyrathne
Priyanka D
PD
Woo
Caroline J
CJ
Gregory
Gillian
G
Lee
Jong-Min
JM
Wheeler
Vanessa C
VC
Walz
Thomas
T
Kingston
Robert E
RE
Gusella
James F
JF
Conlon
Ronald A
RA
MacDonald
Marcy E
ME
D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
C086055:HTT protein, human; D006657:Histones; C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins