SELENOH (selenoprotein H) is a selenocysteine-containing protein that functions primarily in redox regulation and cellular protection mechanisms 1. The protein contains a characteristic CxxU motif (where U is selenocysteine) typical of thioredoxin-like selenoproteins and exhibits nucleus-exclusive localization 1. SELENOH plays critical roles in DNA binding through its conserved PRGRKRK motif, which functions as both an AT-hook DNA-binding domain and nuclear localization signal 2. The selenocysteine residue is essential for maintaining the protein's functionally active conformation and facilitating intramolecular hydrogen bonding networks that stabilize the structure 2. Functionally, SELENOH acts as a tumor suppressor by controlling cell cycle progression and proliferation in colorectal cancer cells, with knockdown studies showing increased proliferation and decreased differentiation 3. The protein demonstrates protective effects against oxidative stress and cellular senescence, with zebrafishes lacking SELENOH showing increased susceptibility to chemical-induced tumorigenesis and DNA damage 1. SELENOH expression is highly sensitive to selenium deficiency and is prioritized for degradation during selenium insufficiency 14. Clinical relevance includes its potential as a prognostic biomarker in breast cancer, where it contributes to a selenium-related risk score that predicts patient outcomes 5.