STK35 (serine/threonine kinase 35) is a nuclear-localized serine/threonine kinase with diverse roles in cellular homeostasis and disease pathogenesis. Primary function: STK35 regulates cell proliferation, apoptosis, and cell cycle progression through catalytic kinase activity 1. Mechanistically, STK35 functions within a phosphatase-kinase signaling complex with SCP4 phosphatase and PDIK1L, where it catalytically regulates amino acid biosynthesis and transport while maintaining pathway stability through its catalytic function 2. STK35 expression is transcriptionally regulated by STAT3 in osteosarcoma cells 1 and is downregulated in diabetic hearts under hyperglycemic conditions 3. Disease relevance: STK35 exhibits context-dependent oncogenic roles in osteosarcoma and acute myeloid leukemia, where its knockdown inhibits proliferation and enhances apoptosis 12. Conversely, STK35 downregulation contributes to diabetic cardiomyopathy pathogenesis through endothelial dysfunction and impaired angiogenesis 3. Additionally, STK35 participates in DNA damage response pathways 4 and is critical for germline development and fertility 5. Clinical significance: STK35 gene therapy via AAV9 delivery restores cardiac function in diabetic models 3, while STK35 emerges as a sentinel kinase for predicting kinase inhibitor cardiotoxicity 6, suggesting therapeutic potential in both cardiovascular and hematologic malignancies.