ASIC4 is a member of the acid-sensing ion channel family that is broadly expressed in the mammalian nervous system, but has no known function. We demonstrate here that transfected ASIC4 is targeted to the plasma membrane in CHO-K1 cells, where it associates with ASIC1a and downregulates exogenous ASIC1a expression. This effect could also be observed on endogenous H+-gated currents in TSA-201 cells and ASIC3 currents in CHO-K1 cells, suggesting a physiological role for ASIC4 in regulating ASIC currents involved in pain mechanisms. Using a yeast two-hybrid assay we found that ASICs interact with proteins involved in diverse functions, including cytoskeletal proteins, enzymes, regulators of endocytosis and G-protein-coupled pathways. ASIC4 is the sole member of this ion channel class to interact strongly with polyubiquitin. The distinct functionally related sets of interacting proteins that bind individual ASICs identified in the yeast two-hybrid screen suggest potential roles for ASICs in a variety of cellular functions.