BIK (BCL2 interacting killer) is a pro-apoptotic BH3-only protein that accelerates programmed cell death through multiple mechanisms 1. The protein is predominantly localized in the endoplasmic reticulum (ER) and induces apoptosis via the mitochondrial pathway by mobilizing calcium from the ER to mitochondria and remodeling mitochondrial cristae 1. BIK-mediated apoptosis occurs through selective activation of BAX 1. Beyond apoptosis regulation, BIK plays a critical role in controlling low-grade inflammation by enhancing proteasomal degradation of nuclear proteins through interactions with regulatory particle non-ATPase subunits RPN1 and RPN2 2. BIK deficiency leads to increased nuclear p65 levels and spontaneous emphysema in female mice 2. In viral infections, particularly influenza A virus, BIK promotes viral replication through an IAV-BIK-β5 axis, where viral nucleoprotein suppresses proteasome β5 subunit leading to BIK accumulation 3. A genetic polymorphism (rs738276) in the BIK gene influences expression levels and correlates with influenza severity in humans 3. BIK functions as a tumor suppressor in several human tissues, with expression often silenced in cancers through chr22 deletions or epigenetic mechanisms 1. The protein shows clinical relevance as a potential therapeutic target and prognostic marker, particularly in breast cancer where expression correlates with estrogen receptor alpha status 4.