Huntingtin as an essential integrator of intracellular vesicular trafficking

doi:10.1016/j.tcb.2009.01.005

Trends in Cell Biology

Volume 19, Issue 4, April 2009, Pages 147-155

https://doi.org/10.1016/j.tcb.2009.01.005 Get rights and content

The neurodegenerative disorder Huntington's disease is caused by an expansion in the polyglutamine repeat region of the protein huntingtin. Multiple studies in cellular and animal model systems indicate that this mutation imparts a novel toxic function required for disease pathogenesis. However, the normal function of huntingtin, an essential cellular protein in higher vertebrates, is not yet well understood. Emerging data indicate an important role for wild-type huntingtin in the intracellular transport of vesicles and organelles. Here, we discuss current progress on the role of huntingtin in vesicular trafficking, focusing on the proposal that huntingtin might be a crucial regulator of organelle transport along the cellular cytoskeleton.

Section snippets

Huntingtin: an essential multi-domain protein in health and disease

The devastating neurodegenerative disorder Huntington's disease (HD) is caused by a pathogenic expansion of the polyglutamine repeat region of the protein huntingtin. Extensive research has focused on the defects that result from expression of mutant huntingtin (see Ref. [1] for a comprehensive recent review). Expansion of the polyglutamine repeat in huntingtin is clearly toxic to a subset of mammalian neurons; the primary cell types affected in HD are neurons in the striatum and cerebral

Huntingtin builds a network of interactions with motor and motor-associated proteins

Huntingtin interacts with a diverse array of cellular proteins through multiple interaction domains (for a review, see Refs 11, 12; Figure 1). There are predicted to be up to 36 HEAT repeats spanning most of the huntingtin polypeptide; HEAT repeats are α helix–loop–α helix motifs that mediate protein–protein interactions [13]. Overall, the predicted structure of huntingtin is consistent with a cellular role as a scaffold protein. Several motifs within the polypeptide have been suggested to

Studies of mutant huntingtin pave the way for analyses of wild-type huntingtin function

The polyglutamine repeat expansion mutation in the gene encoding huntingtin causes misfolding and cellular accumulation of the protein, including aggregate formation. Typically, efficient clearance of misfolded and aggregated proteins by the cell depends on trafficking of membranous cargo along the cellular cytoskeleton. Accumulation of aggregates could indicate either an inability to degrade the mutant protein or, alternatively, could indicate an overall inhibition of the cellular trafficking

Insight into huntingtin function from knockout and knockdown studies

Knockout of the gene encoding huntingtin is embryonic lethal in the mouse 6, 7, 8, whereas mice with a single copy of the mouse Hdh gene are grossly normal [7]; however, one line has been reported to display minor cognitive deficits and hyperactivity [6]. Tissue-specific depletion of huntingtin in the forebrain results in progressive neurodegeneration, which is consistent with a post-developmental role for huntingtin in neurons [34]. By contrast, genetic ablation of HAP1 has shown that

Model 1: huntingtin phosphorylation is a molecular switch for microtubule-based bidirectional transport

Two recent studies have proposed that huntingtin is a molecular switch that affects the direction of transport of motile vesicles in neurons 18, 38 (Figure 2a). The motility of post-Golgi secretory vesicles labeled with BDNF–GFP was analyzed to examine the effects of huntingtin phosphorylation in primary neuronal cultures. Depletion of endogenous huntingtin resulted in a bidirectional inhibition of the transport of BDNF-labeled vesicles; transport was restored to normal levels by expression of

Model 2: huntingtin–HAP40 is a switch for cytoskeletal affinity

Endosomal membrane fusion and targeting is regulated by Rab GTPases. Rab5 specifically associates with early endosomes and regulates the motility of early endosomes along microtubules [42]. Pal et al.[25] have recently shown that huntingtin forms a complex with a Rab5 effector that induces a change in the cytoskeletal affinity of early endosomes (Figure 2b). The ability of vesicles to switch from actin, which is most often used for short-range transport, to microtubules, which are used for

Model 3: huntingtin facilitates dynein-mediated vesicle motility

We recently demonstrated that huntingtin binds directly to dynein to enhance dynein-mediated vesicle motility along microtubules [22] (Figure 2c). HeLa cells depleted of huntingtin by RNAi exhibited partial disruption of Golgi stacks, a hallmark for defective dynein function. A similar disruption of Golgi organization induced by depletion of endogenous huntingtin was recently reported by Del Toro et al.[44].

As the most important minus-end-directed motor for vesicular motility, cytoplasmic

Huntingtin, a global coordinator of cytoskeletal vesicular transport?

We propose that huntingtin facilitates global vesicular trafficking throughout the multiple cytoskeletal superhighways of the cell. Huntingtin is able to coordinate the binding of multiple types of motor proteins to vesicular cargo, most probably by acting as a scaffold that can differentially bind to many proteins. By integrating various signals, huntingtin might have a key role in modulating vesicle transport between the actin and microtubule cytoskeletons (Figure 2c).

After internalization

Acknowledgements

We would like to thank David Howland, Jessica Bryant, Meng-meng Fu and Armen Moughamian for critically reading the manuscript. This work was supported by NIH grant GM48661.

References (52)

M. DiFiglia
Huntingtin is a cytoplasmic protein associated with vesicles in human and rat brain neurons
Neuron
(1995)
J. Nasir
Targeted disruption of the Huntington's disease gene results in embryonic lethality and behavioral and morphological changes in heterozygotes
Cell
(1995)
E. Chevalier-Larsen et al.
Axonal transport and neurodegenerative disease
Biochim. Biophys. Acta
(2006)
P. Harjes et al.
The hunt for huntingtin function: interaction partners tell many different stories
Trends Biochem. Sci.
(2003)
S.H. Li et al.
Huntingtin-protein interactions and the pathogenesis of Huntington's disease
Trends Genet.
(2004)
K.B. Kegel
Huntingtin associates with acidic phospholipids at the plasma membrane
J. Biol. Chem.
(2005)
J.R. McGuire
Interaction of Huntingtin-associated protein-1 with kinesin light chain: implications in intracellular trafficking in neurons
J. Biol. Chem.
(2006)
I. Ferrer
Brain-derived neurotrophic factor in Huntington disease
Brain Res.
(2000)
L.R. Gauthier
Huntingtin controls neurotrophic support and survival of neurons by enhancing BDNF vesicular transport along microtubules
Cell
(2004)
G. Szebenyi
Neuropathogenic forms of huntingtin and androgen receptor inhibit fast axonal transport
Neuron
(2003)

S. Gunawardena

Disruption of axonal transport by loss of huntingtin or expression of pathogenic polyQ proteins in Drosophila

Neuron

(2003)

S. Humbert

The IGF-1/Akt pathway is neuroprotective in Huntington's disease and involves Huntingtin phosphorylation by Akt

Dev. Cell

(2002)

L.A. Ligon

A direct interaction between cytoplasmic dynein and kinesin I may coordinate motor activity

J. Biol. Chem.

(2004)

J.P. Caviston et al.

Microtubule motors at the intersection of trafficking and transport

Trends Cell Biol.

(2006)

S. Imarisio

Huntington's disease: from pathology and genetics to potential therapies

Biochem. J.

(2008)

J.M. Gil et al.

Mechanisms of neurodegeneration in Huntington's disease

Eur. J. Neurosci.

(2008)

C.A. Gutekunst

Identification and localization of huntingtin in brain and human lymphoblastoid cell lines with anti-fusion protein antibodies

Proc. Natl. Acad. Sci. U. S. A.

(1995)

G. Hoffner

Perinuclear localization of huntingtin as a consequence of its binding to microtubules through an interaction with β-tubulin: relevance to Huntington's disease

J. Cell Sci.

(2002)

M.P. Duyao

Inactivation of the mouse Huntington's disease gene homolog Hdh

Science

(1995)

S. Zeitlin

Increased apoptosis and early embryonic lethality in mice nullizygous for the Huntington's disease gene homologue

Nat. Genet.

(1995)

A.L. Lumsden

Huntingtin-deficient zebrafish exhibit defects in iron utilization and development

Hum. Mol. Genet.

(2007)

M.E. MacDonald

Huntingtin: alive and well and working in middle management

Sci. STKE

(2003)

R.S. Atwal

Huntingtin has a membrane association signal that can modulate huntingtin aggregation, nuclear entry and toxicity

Hum. Mol. Genet.

(2007)

A. Yanai

Palmitoylation of huntingtin by HIP14 is essential for its trafficking and function

Nat. Neurosci.

(2006)

E. Colin

Huntingtin phosphorylation acts as a molecular switch for anterograde/retrograde transport in neurons

EMBO J.

(2008)

S. Engelender

Huntingtin-associated protein 1 (HAP1) interacts with the p150Glued subunit of dynactin

Hum. Mol. Genet.

(1997)

Cited by (207)

Huntingtin protein–protein interactions: From biology to therapeutic targets
2024, Huntington's Disease: Pathogenic Mechanisms and Implications for Therapeutics
Huntingtin (HTT) is a largely alpha-helical protein that is ubiquitously expressed in many tissues and cell types. This protein has been extensively studied because an abnormally expanded polyglutamine (polyQ) stretch, located at its N-terminus, leads to Huntington's disease (HD), an inherited, late-onset neurodegenerative disease with severe motor, cognitive and psychiatric symptoms. To elucidate HTT function and its role in disease, numerous protein–protein interaction (PPI) mapping studies have been performed, which have revealed ∼3400 HTT candidate interaction partners. Here, we provide an overview of HTT interaction mapping efforts and an integrated computational analysis of HTT interacting proteins (HIPs) based on currently available literature. We discuss and apply various PPI selection criteria as well as highlight potential hub interacting proteins and complexes for defining “high-confidence” HIPs for further functional characterization and potential therapeutic efforts.
Early whole-body mutant huntingtin lowering averts changes in proteins and lipids important for synapse function and white matter maintenance in the LacQ140 mouse model
2023, Neurobiology of Disease
Expansion of a triplet repeat tract in exon 1 of the HTT gene causes Huntington’s disease (HD). The mutant HTT protein (mHTT) has numerous aberrant interactions with diverse, pleiomorphic effects. Lowering mHTT is a promising approach to treat HD, but it is unclear when lowering should be initiated, how much is necessary, and what duration should occur to achieve benefits. Furthermore, the effects of mHTT lowering on brain lipids have not been assessed. Using a mHtt-inducible mouse model, we analyzed mHtt lowering initiated at different ages and sustained for different time-periods. mHTT protein in cytoplasmic and synaptic compartments of the striatum was reduced 38-52%; however, there was minimal lowering of mHTT in nuclear and perinuclear regions where aggregates formed at 12 months of age. Total striatal lipids were reduced in 9-month-old LacQ140 mice and preserved by mHtt lowering. Subclasses important for white matter structure and function including ceramide (Cer), sphingomyelin (SM), and monogalactosyldiacylglycerol (MGDG), contributed to the reduction in total lipids. Phosphatidylinositol (PI), phosphatidylserine (PS), and bismethyl phosphatidic acid (BisMePA) were also changed in LacQ140 mice. Levels of all subclasses except ceramide were preserved by mHtt lowering. mRNA expression profiling indicated that a transcriptional mechanism contributes to changes in myelin lipids, and some but not all changes can be prevented by mHtt lowering. Our findings suggest that early and sustained reduction in mHtt can prevent changes in levels of select striatal proteins and most lipids, but a misfolded, degradation-resistant form of mHTT hampers some benefits in the long term.
A comprehensive perspective of Huntington's disease and mitochondrial dysfunction
2023, Mitochondrion
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease. It is caused by the expansion of the CAG trinucleotide repeat sequence in the HTT gene. HD mainly manifests as involuntary dance-like movements and severe mental disorders. As it progresses, patients lose the ability to speak, think, and even swallow. Although the pathogenesis is unclear, studies have found that mitochondrial dysfunctions occupy an important position in the pathogenesis of HD. Based on the latest research advances, this review sorts out and discusses the role of mitochondrial dysfunction on HD in terms of bioenergetics, abnormal autophagy, and abnormal mitochondrial membranes. This review provides researchers with a more complete perspective on the mechanisms underlying the relationship between mitochondrial dysregulation and HD.
Palmitate-mediated disruption of the endoplasmic reticulum decreases intracellular vesicle motility
2023, Biophysical Journal
Essential cellular processes such as metabolism, protein synthesis, and autophagy require the intracellular transport of membrane-bound vesicles. The importance of the cytoskeleton and associated molecular motors for transport is well documented. Recent research has suggested that the endoplasmic reticulum (ER) may also play a role in vesicle transport through a tethering of vesicles to the ER. We use single-particle tracking fluorescence microscopy and a Bayesian change-point algorithm to characterize vesicle motility in response to the disruption of the ER, actin, and microtubules. This high-throughput change-point algorithm allows us to efficiently analyze thousands of trajectory segments. We find that palmitate-mediated disruption of the ER leads to a significant decrease in vesicle motility. A comparison with the disruption of actin and microtubules shows that disruption of the ER has a significant impact on vesicle motility, greater than the disruption of actin. Vesicle motility was dependent on cellular region, with greater motility in the cell periphery than the perinuclear region, possibly due to regional differences in actin and the ER. Overall, these results suggest that the ER is an important factor in vesicle transport.
Huntingtin S421 phosphorylation increases kinesin and dynein engagement on early endosomes and lysosomes
2023, Biophysical Journal
Huntingtin (HTT) is a scaffolding protein that recruits motor proteins to vesicular cargoes, enabling it to regulate kinesin-1, dynein, and myosin-VI-dependent transport. To maintain the native stoichiometry of HTT with its interacting partners, we used CRISPR/Cas9 to induce a phosphomimetic mutation of the endogenous HTT at S421 (HTT-S421D). Using single-particle tracking, optical tweezers, and immunofluorescence, we examined the effects of this mutation on the motility of early endosomes and lysosomes. In HTT-S421D cells, lysosomes exhibit longer displacements and higher processive fractions compared with wild-type (HTT-WT) cells. Kinesins and dyneins exert greater forces on early endosomes and lysosomes in cells expressing HTT-S421D. In addition, endosomes bind to microtubules faster and are more resistant to detachment under load. The recruitment of kinesins and dyneins to microtubules is enhanced in HTT-S421D cells. In contrast, overexpression of HTT had variable effects on the processivity, displacement, and directional bias of both early endosomes and lysosomes. These data indicate that phosphorylation of the endogenous HTT causes early endosomes and lysosomes to move longer distances and more processively by recruiting and activating both kinesin-1 and dynein.
Treatment with THI, an inhibitor of sphingosine-1-phosphate lyase, modulates glycosphingolipid metabolism and results therapeutically effective in experimental models of Huntington's disease
2023, Molecular Therapy
Huntington’s disease (HD) is a fatal neurodegenerative disorder with no effective cure currently available. Over the past few years our research has shown that alterations in sphingolipid metabolism represent a critical determinant in HD pathogenesis. In particular, aberrant metabolism of sphingosine-1-phosphate (S1P) has been reported in multiple disease settings, including human postmortem brains from HD patients. In this study, we investigate the potential therapeutic effect of the inhibition of S1P degradative enzyme SGPL1, by the chronic administration of the 2-acetyl-5-tetrahydroxybutyl imidazole (THI) inhibitor. We show that THI mitigated motor dysfunctions in both mouse and fly models of HD. The compound evoked the activation of pro-survival pathways, normalized levels of brain-derived neurotrophic factor, preserved white matter integrity, and stimulated synaptic functions in HD mice. Metabolically, THI restored normal levels of hexosylceramides and stimulated the autophagic and lysosomal machinery, facilitating the reduction of nuclear inclusions of both wild-type and mutant huntingtin proteins.

View all citing articles on Scopus

View full text

Trends in Cell Biology

ReviewHuntingtin as an essential integrator of intracellular vesicular trafficking

Section snippets

Huntingtin: an essential multi-domain protein in health and disease

Huntingtin builds a network of interactions with motor and motor-associated proteins

Studies of mutant huntingtin pave the way for analyses of wild-type huntingtin function

Insight into huntingtin function from knockout and knockdown studies

Model 1: huntingtin phosphorylation is a molecular switch for microtubule-based bidirectional transport

Model 2: huntingtin–HAP40 is a switch for cytoskeletal affinity

Model 3: huntingtin facilitates dynein-mediated vesicle motility

Huntingtin, a global coordinator of cytoskeletal vesicular transport?

Acknowledgements

Neuron

Cell

Biochim. Biophys. Acta

Trends Biochem. Sci.

Trends Genet.

J. Biol. Chem.

J. Biol. Chem.

Brain Res.

Cell

Neuron

Neuron

Dev. Cell

J. Biol. Chem.

Trends Cell Biol.

Huntington's disease: from pathology and genetics to potential therapies

Biochem. J.

Mechanisms of neurodegeneration in Huntington's disease

Eur. J. Neurosci.

Identification and localization of huntingtin in brain and human lymphoblastoid cell lines with anti-fusion protein antibodies

Proc. Natl. Acad. Sci. U. S. A.

Perinuclear localization of huntingtin as a consequence of its binding to microtubules through an interaction with β-tubulin: relevance to Huntington's disease

J. Cell Sci.

Inactivation of the mouse Huntington's disease gene homolog Hdh

Science

Increased apoptosis and early embryonic lethality in mice nullizygous for the Huntington's disease gene homologue

Nat. Genet.

Huntingtin-deficient zebrafish exhibit defects in iron utilization and development

Hum. Mol. Genet.

Huntingtin: alive and well and working in middle management

Sci. STKE

Huntingtin has a membrane association signal that can modulate huntingtin aggregation, nuclear entry and toxicity

Hum. Mol. Genet.

Palmitoylation of huntingtin by HIP14 is essential for its trafficking and function

Nat. Neurosci.

Huntingtin phosphorylation acts as a molecular switch for anterograde/retrograde transport in neurons

EMBO J.

Huntingtin-associated protein 1 (HAP1) interacts with the p150Glued subunit of dynactin

Hum. Mol. Genet.

Review
Huntingtin as an essential integrator of intracellular vesicular trafficking