Anterior gradient protein 3 (AGR3) is an 18 kDa member of the AGR family of proteins. It is expressed in the ciliated cells of the airway epithelium, not detected in the mucous cells. Mature human AGR3 shares 92% amino acid sequence identity with mouse AGR3. It is required for calcium-mediated regulation of ciliary beat frequency and mucociliary clearance in the airway. AGR3 might be involved in the regulation of intracellular calcium in tracheal epithelial cells.

Anterior Gradient Protein 2(AG-2) and Anterior Gradient Protein 3 (AG-3) are human homologues of genes involved in differentiation, are associated with oestrogen receptor-positive breast tumours and interact with metastasis gene C4.4a and dystroglycan (hAG-3 protein). AG-3 could serve as a prognostic marker for survival in patients with low grade and high grade serous ovarian carcinomas.

Anterior gradient protein (AGR) 3 is a highly related homologue of pro-oncogenic AGR2 and belongs to the family of protein disulfide isomerases. AGR3 was found in breast, ovary, prostate, and liver cancer, it is associated with the level of differentiation, slowly proliferating tumors, and more favorable prognosis of breast cancer patients. AGR3 is a specialized member of the PDI family that plays an unexpected role in the regulation of CBF and mucociliary clearance in the airway. AGR3 had been characterised as a novel potential biomarker both for breast cancer prognosis and early breast cancer detection from blood.