HIP1 (huntingtin interacting protein 1) is a multi-domain protein that plays critical roles in clathrin-mediated endocytosis and intracellular trafficking 1. Through its ENTH domain, HIP1 binds phosphoinositide lipids and promotes receptor trafficking by stabilizing receptor tyrosine kinases following ligand-induced endocytosis 2. HIP1 functions in NMDA-dependent AMPA receptor trafficking and regulates presynaptic nerve terminal activity, implicating it in synaptic plasticity. The protein also enhances androgen receptor-mediated transcription and may promote cell survival through receptor stabilization 2. HIP1 has dual roles in cell fate regulation: it can induce proapoptotic cell death via the intrinsic pathway while also being required for somatic and germline progenitor survival 3. In vivo studies demonstrate that combined HIP1 and HIP1-related protein deficiency causes severe developmental defects including dwarfism and vertebral abnormalities, which are rescued by human HIP1 expression, indicating functional conservation 3. Clinically, HIP1 overexpression is associated with multiple human cancers and is involved in cancer-causing translocations 2. Additionally, HIP1 interacts with huntingtin and is implicated in Huntington's disease pathology, where it may influence neuronal trafficking and homeostasis 4. Understanding HIP1's endocytic and signaling functions is relevant to both neurodegenerative disease mechanisms and cancer biology.