FJX1 (four-jointed box kinase 1) is a serine/threonine kinase involved in multiple cellular processes with emerging roles in disease pathogenesis. FJX1 functions as a component of planar cell polarity (PCP) protein complexes, where it interacts with Fat1 and Dchs proteins to form heterotypic intercellular bridges crucial for organizing microtubule and actin cytoskeletons 1. In testicular tissue, FJX1 supports spermatogenesis by modulating cytoskeletal dynamics between Sertoli cells and spermatids 1. Clinically, FJX1 functions as an oncogene in multiple cancers. It is significantly upregulated in colon adenocarcinoma, nasopharyngeal carcinoma, and other malignancies 234. FJX1 overexpression promotes cell proliferation, migration, and invasion through cell cycle regulation involving Cyclin D1 and E1 3. MicroRNAs miR-532-3p and miR-1306-3p negatively regulate FJX1 expression, and therapeutic modulation via these miRNAs suppresses cancer cell viability 25. Serum FJX1 demonstrates diagnostic and prognostic value in colorectal cancer, with levels decreasing after surgical resection 4. Beyond cancer, FJX1 is dysregulated in endometriosis, where elevated expression correlates with HIF1α stabilization and angiogenesis 6. FJX1 also appears as a shared gene signature between sarcopenia and type 2 diabetes 7, and is involved in endothelial cell senescence induced by hyperhomocysteinemia 8.