IBTK (inhibitor of Bruton tyrosine kinase) is a regulatory protein encoded at chr6 locus 6q14.1 that functions as a negative regulator of BTK tyrosine kinase activity in B-cell development 1. The gene produces three protein isoforms (IBTKα, IBTKβ, and IBTKγ) through alternative splicing and transcription start sites 1. IBTK operates through multiple mechanisms: it binds the PH domain of BTK to suppress kinase activity and downstream calcium mobilization 1, and functions as a substrate receptor for the CRL3 E3 ubiquitin ligase complex, promoting proteasomal degradation of the translation inhibitor Pdcd4 2. Recently, IBTK was shown to non-degradatively ubiquitinate eIF4A1 via CRL3IBTK, enhancing cap-dependent translation and oncogenic protein synthesis in a phosphorylation-dependent manner regulated by mTORC1/S6K1 3. Beyond BTK inhibition, IBTK modulates gene expression and RNA splicing in cell-type-specific patterns affecting chr6 organization and cellular migration 4. The IBTK locus encodes a conserved miRNA that regulates B-lymphocyte differentiation 5. Clinically, IBTK is implicated in B-cell lymphomagenesis; loss of IBTK increases apoptosis and delays lymphoma onset in Eμ-myc mice through Myc-dependent mechanisms 6, suggesting IBTK inhibitors may sensitize tumor cells to apoptosis.