HABP4 (hyaluronan binding protein 4) is a 57 kDa regulatory protein that functions primarily in RNA metabolism and transcriptional regulation 1. The protein exhibits RNA-binding activity, specifically binding to poly(U) RNA sequences through its C-terminus, and regulates transcription and pre-mRNA splicing 1. HABP4 displays complex subcellular localization patterns, shuttling between cytoplasm and nucleus, and localizing to nuclear splicing speckles and cytoplasmic stress granules 1. The protein undergoes extensive post-translational modifications including phosphorylation, arginine methylation, and SUMOylation, which regulate its function and localization 12. HABP4 appears to function as a tumor suppressor, particularly in colorectal cancer, where knockout mice develop more and larger tumors following carcinogen treatment 3. In bladder cancer, high HABP4 expression is associated with improved response to BCG immunotherapy and better survival outcomes 45. The protein is also implicated in clear cell renal cell carcinoma, where it is targeted by let-7i-5p microRNA, leading to enhanced cancer cell proliferation and invasion when HABP4 levels are reduced 6. Recent proteomic studies suggest HABP4 may serve as a potential therapeutic target for essential tremor 7.