Plays a role in clathrin-mediated endocytosis and trafficking (PubMed:11577110). Involved in regulating AMPA receptor trafficking in the central nervous system in an NMDA-dependent manner (PubMed:12839988, PubMed:17329427). Regulates presynaptic nerve terminal activity (PubMed:17928447). Enhances androgen receptor (AR)-mediated transcription (By similarity). May act as a proapoptotic protein that induces cell death by acting through the intrinsic apoptosis pathway (By similarity). Binds 3-phosphoinositides (via ENTH domain) (By similarity). May act through the ENTH domain to promote cell survival by stabilizing receptor tyrosine kinases following ligand-induced endocytosis (By similarity). May play a functional role in the cell filament networks (By similarity). May be required for differentiation, proliferation, and/or survival of somatic and germline progenitors (PubMed:11604514, PubMed:14998932, PubMed:16967501, PubMed:17928447). Homodimer. Binds actin. Binds HTT (via N-terminus). This interaction is restricted to the brain. Binds to IFT57. In normal conditions, it poorly interacts with IFT57, HIP1 being strongly associated with HTT. However, in mutant HTT proteins with a long poly-Gln region, interaction between HTT and HIP1 is inhibited, promoting the interaction between HIP1 and IFT57. Interacts with CLTB (via N-terminus). Interacts (via coiled coil domain) with AR. Interacts with AP2A1, AP2A2, CLTC and HIP1R (By similarity). Interacts with GRIA1, GRIN2A AND GRIN2B. Shuttles between cytoplasm and nucleus. Nuclear translocation can be induced by AR (By similarity). Most abundantly expressed in brain. In brain, expressed in cortical tissue, hippocampus, the molecular layer of the cerebellum and olfactory bulb. Also expressed in spinal cord and bone marrow (at protein level). Expressed in reproductive tissues. The pseudo DED region (pDED) mediates the interaction with IFT57. Binds F-actin via the talin-like I/LWEQ domain. Mice develop a neurological phenotype by 3 months of age, characterized by wasting, tremor and a gait ataxia secondary to a rigid thoracolumbar kyphosis (PubMed:12839988, PubMed:14998932). Recovery of synaptic transmission following synaptic depression induced by prolonged nerve stimulation is reduced (PubMed:17928447). Paired-pulse facilitation, a form of neuronal plasticity in which delivery of two stimuli within a second of each other produces an increase in the size of the second synaptic response, is enhanced (PubMed:17928447). They also display micro-ophthalmia with nuclear cataracts (PubMed:14998932). Mutant male mice are mostly infertile and exhibit testicular degeneration with increased apoptosis of postmeiotic spermatids (PubMed:11604514, PubMed:16967501). Hip1 and Hip1r double-knockout mice are dwarfed, afflicted with severe vertebral defects and die in early adulthood (PubMed:17452370). Belongs to the SLA2 family.