Huntingtin-interacting protein 1

Huntingtin interacting protein 1
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 2NO2, 2QA7, 3I00
Identifiers
Symbols	HIP1 ; HIP-I; ILWEQ; SHON; SHONbeta; SHONgamma
External IDs	OMIM: 601767 HomoloGene: 68463 GeneCards: HIP1 Gene
Gene ontology Molecular function • actin binding • structural constituent of cytoskeleton • protein binding • clathrin binding • phosphatidylinositol binding Cellular component • nucleus • cytoplasm • Golgi apparatus • cytoskeleton • membrane • clathrin-coated vesicle • clathrin-coated vesicle membrane • intracellular membrane-bounded organelle Biological process • transcription, DNA-templated • regulation of transcription, DNA-templated • apoptotic process • activation of cysteine-type endopeptidase activity involved in apoptotic process • cell differentiation • regulation of apoptotic process • positive regulation of receptor-mediated endocytosis • clathrin coat assembly • clathrin-mediated endocytosis • apoptotic signaling pathway Sources: Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	3092	215114
Ensembl	ENSG00000127946	ENSMUSG00000039959
UniProt	O00291	Q8VD75
RefSeq (mRNA)	NM_001243198	NM_146001
RefSeq (protein)	NP_001230127	NP_666113
Location (UCSC)	Chr 7: 75.53 – 75.74 Mb	Chr 5: 135.41 – 135.55 Mb
PubMed search	[1]	[2]

Huntingtin-interacting protein 1 also known as HIP-1 is a protein that in humans is encoded by the HIP1 gene.

Hip-1 is a protein that interacts with the huntingtin protein. It is known to contain a domain homologous to the death effector domains (DED) found on proteins involved in apoptosis. It is believed that accumulation of high levels of the free form of this protein (free as in dissociated from the huntingtin and free to bind other key protein(s)) in the cell is one of the mechanisms by which neuron cell death is caused in Huntington's Disease (via the caspase-3 route). The role of Hip-1 in caspase mediated cell death remains unclear.

Discovery

Huntingtin interacting protein 1 (HIP1) was first identified by Wanker et al. in 1997.

Function

HIP1 was found to bind to Htt in an N-terminal dependent manner, and co-localise with Htt in the CNS although the nature of this interaction with respect to muHtt was not identified. It has since been found that the CAG expansion seen with muHtt results in decreased binding affinity for HIP1, thus causing disruption of HIP1’s usual function, and also an increased in free HIP1. It is likely that this decreased affinity plays a role in mediating HD pathogenesis, due to loss of cytoskeletal integrity and induction of apoptosis. HIP1’s pro apoptotic effect may involve activation of caspase-8 and a novel HIP1 protein interactor HIPPI. HIP1’s non-pathological activity includes clathrin assembly via interaction with clathrin light chains. HIP1 is the human homologue of Sla2p, a membrane protein in the periphery. Sla2p is an actin-binding protein involved in endocytosis, thus indicating HIP1 in this role. Further details suggesting an important role for Hip-1 in endocytosis comes from binding studies looking at Hip-1 binding to actin. Actin binding by Hip-1 is altered depending on whether clathrin is also bound to Hip-1.

Clinical significance

HIP1 has also been found to be overexpressed in some cancers including a subset of colorectal and prostate cancers. This is of specific interest because prostate cancer disease progression involves altered transcription/expression of the androgen receptor (AR). The AR is a nuclear hormone receptor transcription factor that contains polyglutamine repeats. In 2005 Mills and colleagues showed that HIP1 is able to regulate transcription of hormone receptors via the androgen response element (ARE) and also alters the rate of degradation of the AR. It is likely that HIP1 is also able to regulate, or at least interact with proteins that also possess the ARE.