Plays a role in clathrin-mediated endocytosis and trafficking (PubMed:11532990, PubMed:11577110, PubMed:11889126). Involved in regulating AMPA receptor trafficking in the central nervous system in an NMDA-dependent manner (By similarity). Regulates presynaptic nerve terminal activity (By similarity). Enhances androgen receptor (AR)-mediated transcription (PubMed:16027218). May act as a proapoptotic protein that induces cell death by acting through the intrinsic apoptosis pathway (PubMed:11007801). Binds 3-phosphoinositides (via ENTH domain) (PubMed:14732715). May act through the ENTH domain to promote cell survival by stabilizing receptor tyrosine kinases following ligand-induced endocytosis (PubMed:14732715). May play a functional role in the cell filament networks (PubMed:18790740). May be required for differentiation, proliferation, and/or survival of somatic and germline progenitors (PubMed:11007801, PubMed:12163454). 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. Interacts with GRIA1, GRIN2A AND GRIN2B. Shuttles between cytoplasm and nucleus. Nuclear translocation can be induced by AR. Ubiquitously expressed with the highest level in brain. Expression is up-regulated in prostate and colon cancer. The pseudo DED region (pDED) mediates the interaction with IFT57. Binds F-actin via the talin-like I/LWEQ domain. A chromosomal aberration involving HIP1 is found in a form of chronic myelomonocytic leukemia (CMML). Translocation t(5;7)(q33;q11.2) with PDGFRB (PubMed:9616134). The chimeric HIP1-PDGFRB transcript results from an in-frame fusion of the two genes (PubMed:9616134). The reciprocal PDGFRB-HIP1 transcript is not expressed (PubMed:9616134). The affinity of the huntingtin protein-HIP1 interaction is inversely correlated to the length of the polyglutamine tract added to the huntingtin protein in Huntington disease. Belongs to the SLA2 family.