KCNE4 is a transmembrane regulatory subunit of voltage-gated potassium channels with context-dependent modulatory functions. As an ancillary subunit, KCNE4 exhibits diverse effects depending on its α-subunit partner: it inhibits KCNQ1, KCNQ4, Kv4.2, and Kv4.3 channels, while modulating Kv1.3 activation kinetics and accelerating C-type inactivation 123. KCNE4 contains an N-terminally extended isoform (221 residues) widely conserved in vertebrates, with distinct functional properties from shorter variants 1. Mechanistically, KCNE4 associates with target channels through its C-terminus and transmembrane domain, with calmodulin-dependent dimerization regulating its membrane trafficking and Kv1.3 interaction 43. KCNE4 polymorphisms (rs12621643) represent independent risk factors for atrial fibrillation in both Uygur and Han Chinese populations 56. Beyond cardiac function, KCNE4 is highly expressed in colorectal cancer tissues and correlates with advanced tumor stage, lymph node metastasis, and poor prognosis; elevated KCNE4 promotes radioresistance through PI3K/AKT pathway activation 7. KCNE4 also regulates immune responses through Kv1.3 modulation in leukocytes, with variants linked to autoimmune pathologies 48. These findings establish KCNE4 as a multifunctional channel regulator with significant cardiac and oncological implications.