IK (IK cytokine) is a novel cell mitosis regulator located on chromosome 5 that plays important roles in both viral infection and cancer biology. Primary Function: IK functions as a mitotic cell cycle regulator essential for normal cell division 1. Mechanism: IK works together with SMU1 protein to regulate pre-mRNA splicing of viral transcripts, specifically required for normal splicing of influenza A virus NS1 pre-mRNA to enable production of the viral NS2 exportin protein and subsequent viral particle assembly [UniProt Function]. At the cellular level, IK localizes to nuclear structures including the nucleoplasm, nuclear speckles, and kinetochore regions, functioning in mRNA splicing via the spliceosome and mitotic spindle assembly checkpoint signaling [GO Annotations]. Disease Relevance: Loss of IK expression results in mitotic arrest and cell death, suggesting its dysregulation contributes to carcinogenesis 1. Additionally, IK inhibits interferon gamma-induced HLA class II antigen expression, thereby modulating the tumor immune microenvironment 1. Clinical Significance: IK represents an emerging therapeutic target for cancer treatment given its regulatory role in aberrant cell growth and immune evasion mechanisms. Further research is needed to establish IK's clinical utility in oncology and viral infection contexts.