Abstract
BackgroundHuntington's disease, spinal and bulbar muscular atrophy, and spinocerebellar ataxia 17 (SCA17) are caused by expansions in the polyglutamine (polyQ) repeats in Huntingtin protein (Htt), androgen receptor protein (AR), and TATA-binding protein (TBP), respectively. Htt-associated protein 1 (HAP1), a component of neuronal cytoplasmic stigmoid bodies (STBs), can sequester polyQ-expanded Htt and AR in STBs, thereby antagonizing formation of the nuclear aggregates associated with apoptotic neuron loss and disease progression.ResultsClones of HAP1 were isolated from unbiased two-hybrid screens for proteins that interact with TBP. Domain mapping showed that regions between amino acids 157 and 261 and between amino acids 473 and 582 of mouse HAP1 both bind specifically to the conserved C-terminal TBPCORE domain, away from the TBP N-terminal polyQ region. When fluorescently tagged versions of HAP1 or TBP were expressed independently in COS-7, 293, or Neuro-2a cells, all TBP localized to the nucleus and all HAP1 assembled into cytoplasmic stigmoid-like bodies (STLBs). When co-expressed, a portion of the TBP was assembled into the HAP1 STLBs while the remainder was localized to the nucleus. Although the TBP N terminus, including the polyQ region, was unnecessary for TBP-HAP1 interaction, in mammalian cells, removal of the TBP Qrepeat reduced the proportion of TBP that assembled into STLBs, whereas expansion of the Qrepeat had no significant affect on TBP subcellular localization.ConclusionHAP1 can sequester a subset of TBP protein away from the nucleus; extranuclear TBP sequestration is quantitatively influenced by the TBP polyQ repeat. These results suggest HAP1 could provide protection from SCA17 neuropathology.
Highlights
Huntington's disease, spinal and bulbar muscular atrophy, and spinocerebellar ataxia 17 (SCA17) are caused by expansions in the polyglutamine repeats in Huntingtin protein (Htt), androgen receptor protein (AR), and TATA-binding protein (TBP), respectively
Identification of Httassociated protein 1 (HAP1) as a TBP interacting protein To identify proteins that interacted with TBP, we screened a mixture of oligo(dT)-primed placental and whole pregnant uteri cDNA libraries (50% of each library was used) or a random-primed library which consisted of 50% placental and 50% whole pregnant mouse uteri cDNAs
Sub-cellular co-localization studies indicated that HAP1-induced stigmoid-like bodies (STLBs) could sequester a subset of overexpressed TBP, but not other overexpressed nuclear proteins, away from the nucleus
Summary
Huntington's disease, spinal and bulbar muscular atrophy, and spinocerebellar ataxia 17 (SCA17) are caused by expansions in the polyglutamine (polyQ) repeats in Huntingtin protein (Htt), androgen receptor protein (AR), and TATA-binding protein (TBP), respectively. HD is a member of a family of diseases in which expanded polyglutamine (polyQ) repeat regions in an otherwise functionally diverse group of proteins results in neurodegenerative disorders [1,3,6] This family includes dentatorubral-palidoluysian atrophy (DRPLA), caused by polyQ expansion in atrophin 1; [7,8], spinal and bulbar muscular atrophy (SBMA or Kennedy's disease), caused by polyQ expansion in the androgen receptor, AR; [9,10,11], and spinocerebellar ataxias 1–3, 6, 7, and 17 (SCAs), caused by polyQ expansions in various proteins [1,3]. TBP is generally a low abundance protein in normal somatic cells [21,22], the nuclear aggregates in SCA17 accumulate to high levels [23], suggesting that the pathological state is associated with increased accumulation of nuclear TBP
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