PCBD2 (pterin-4 alpha-carbinolamine dehydratase 2) is a bifunctional protein that operates as a transcriptional co-factor and exhibits enzymatic activity in pteridine metabolism. Primarily, PCBD2 regulates hepatocyte nuclear factor 1β (HNF1β)-mediated transcription by directly interacting with this essential transcription factor and modulating its activity on target genes involved in renal ion transport and other developmental processes 1. PCBD2 shuttles between cytoplasm and nucleus, with nuclear localization significantly enhanced in the presence of HNF1β 1. As an enzyme, PCBD2 participates in tetrahydrobiopterin (BH4) recycling, a critical cofactor for multiple cellular processes 2. Clinically, PCBD2 dysfunction is implicated in rectal cancer pathogenesis, where miR-3174-mediated suppression of PCBD2 promotes cancer cell proliferation and inhibits apoptosis 3. Additionally, genetic polymorphisms in PCBD2 associated with impaired BH4 recycling correlate with stress hyperphenylalaninemia and increased mortality risk in cardiac ICU patients 2. PCBD2 also participates in host gene regulation of hepatitis B virus transcription in embryonic contexts 45. Its tissue distribution differs from its homolog PCBD1, being abundant in lung, spleen, and adipose tissue alongside kidney and liver 1.