PDIA4 (protein disulfide isomerase family A member 4) is an endoplasmic reticulum-localized enzyme that catalyzes disulfide bond formation during protein folding 1. The protein functions as a protein disulfide isomerase with oxidoreductase activity through its active CXXC domains, playing a critical role in endoplasmic reticulum stress responses 2. PDIA4 expression is upregulated during ER stress through transcriptional regulation by XBP1, contributing to cellular survival under stress conditions 2. In cancer contexts, PDIA4 promotes tumor progression through multiple mechanisms: it confers resistance to ferroptosis by inducing the ATF4/SLC7A11 pathway in renal cell carcinoma 3, enhances angiogenesis by regulating VEGF-A secretion in glioblastoma 2, and supports cancer stem cell maintenance 4. The protein also modulates immune responses, with high expression correlating with reduced T cell infiltration and increased regulatory T cell presence 5. In metabolic contexts, PDIA4 contributes to insulin resistance and inflammation in skeletal muscle, with metformin alleviating these effects by modulating PDIA4 expression 6. Clinically, elevated PDIA4 expression is associated with poor prognosis across multiple cancer types and resistance to various therapies, making it a potential therapeutic target 75.